Design of hard surfaces with metal (Hf/V) nitride multinanolayers
Physical properties as mechanical and tribological evolution on 4140 steel surfaces coated with hafnium nitride/vanadium nitride [HfN/VN]n multinanolayered systems deposited in various bilayer periods via magnetron sputtering has been exhaustively studied in this work. The coatings have been charact...
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Escobar, C. Caicedo, J.C. Caicedo, H.H. Mozafari, M. 2017-11-15T17:52:16Z 2017-11-15T17:52:16Z 2014 Design of hard surfaces with metal (Hf/V) nitride multinanolayers / C. Escobar, J.C. Caicedo, H.H. Caicedo, M. Mozafari // Сверхтвердые материалы. — 2014. — № 6. — С. 10-28. — Бібліогр.: 28 назв. — англ. 0203-3119 https://nasplib.isofts.kiev.ua/handle/123456789/126126 621.793:620.179.1/.186 Physical properties as mechanical and tribological evolution on 4140 steel surfaces coated with hafnium nitride/vanadium nitride [HfN/VN]n multinanolayered systems deposited in various bilayer periods via magnetron sputtering has been exhaustively studied in this work. The coatings have been characterized in terms of structural, chemical, morphological, mechanical, and tribological properties by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning and transmission electron microscopies, nanoindentation, pin-on-disc and scratch tests. Moreover, the failure mode mechanisms were observed via scanning electron microscopy. The preferential growth in the face-centered cubic (111) crystal structure for [HfN/VN]n multilayered coatings have been shown by X-ray diffraction results. The best enhancement of the mechanical behavior has been obtained when the bilayer period was 15 nm (n = 80), yielding the highest hardness (37 GPa) and elastic modulus was (351 GPa). The values of the hardness and elastic modulus were 1.48 and 1.32 times higher than the coating with n = 1, respectively, as well as the lowest friction coefficient (~ 0.15) and the highest critical load (72 N). These results indicated significant enhancements in mechanical, tribological, and adhesion properties, compared to HfN/VN multilayered systems with bilayer period of 1200 nm (n = 1). The hardness and toughness enhancement in the multilayered coatings could be attributed to the different mechanisms that produce the layer formation with nanometric thickness due to the number of interfaces acting as obstacles for crack deflection and dissipation of crack energy. Due to the emergent characteristics of the synthesized multinanolayered material, the developed adaptive coating could be considered as higher ordered tool machining systems, capable of sustaining extreme operating conditions for industrial applications. Фізичні властивості як механічні і трибологічні зміни на поверхні сталі марки 4140 з покриттям із нанобагатошарових систем нітриду гафнію/нітриду ванадію [HfN/VN]n, нанесених магнетронним розпиленням з різними проміжками між двома шарами, були ретельно вивчені в цій роботі. Структурні, хімічні, морфологічні і трибологічні властивості покриттів визначали дифракцією рентгенівських променів, фотоелектронною рентгенівською спектроскопією, атомно-силовою мікроскопією, растровою та просвічувальною електронною мікроскопією, наноіндентуванням, методом “штифт на крузі” і випробуванням дряпанням. Крім того, механізми відмов спостерігали за допомогою растрової електронної мікроскопії. Результати дифракції рентгенівських променів показали краще зростання (111) граніцентрованої кристалічної структури для багатошарових покриттів [HfN/VN]n. Максимальне підвищення механічних характеристик було досягнуто при товщині бішару HfN/VN, що дорівнював 15 нм (число шарів 80), твердість складала 37 ГПа, а модуль пружності – 351 ГПа. Ці значення твердості і модуля пружності були вище, ніж у покриття з n = 1 (в 1,48 і 1,32 рази відповідно), також це багатошарове покриття мало найнижчий (~ 0,15) коефіцієнт тертя і найвище (72 Н) критичне навантаження. Ці результати показали значне поліпшення механічних, трибологічних і адгезійних властивостей порівняно з HfN/VN багатошарової системою з товщиною бішару 1200 нм (n = 1). Підвищення твердості і в’язкості руйнування багатошарових покриттів може бути пояснено різними механізмами утворювання шарів нанометричної товщини, зумовлених кількістю меж розділу, що діють як перешкоди для відхилення тріщини і розсіювання її енергії. Завдяки покращеним характеристикам синтезованого багатошарового матеріалу, розроблене адаптивне покриття можна розглядати як більш високо впорядковану інструментальну систему обробки, здатну підтримувати екстремальні робочі умови при використанні в промисловості. Физические свойства как механические и трибологические изменения на поверхности стали марки 4140 с покрытием из наномногослойных систем нитрида гафния/нитрида ванадия [HfN/VN]n, нанесенных магнетронным распылением с различными промежутками между двумя слоями, были тщательно изучены в этой работе. Структурные, химические, морфологические и трибологические свойства покрытий определяли дифракцией рентгеновских лучей, фотоэлектронной рентгеновской спектроскопией, атомно-силовой микроскопией, растровой и просвечивающей электронной микроскопией, наноиндентированием, методом “штифт на круге” и испытания царапаньем. Кроме того, механизмы отказов наблюдали посредством растровой электронной микроскопии. Результаты дифракции рентгеновских лучей показали предпочтительный рост (111) гранецентрированной кристаллической структуры для многослойных покрытий [HfN/VN]n. Максимальное повышение механических характеристик было достигнуто при толщине бислоя HfN/VN равной 15 нм (число слоев 80), твердость была равна 37 ГПа, а модуль упругости – 351 ГПа. Эти значения твердости и модуля упругости были выше, чем у покрытия с n = 1 (в 1,48 и 1,32 раза соответственно), также у этого многослойного покрытия был самый низкий (~ 0,15) коэффициент трения и самая высокая (72 Н) критическая нагрузка. Эти результаты показали значительное улучшение механических, трибологических и адгезионных свойств по сравнению с HfN/VN многослойной системой с толщиной бислоя 1200 нм (n = 1). Повышение твердости и вязкости разрушения многослойных покрытий может быть объяснено различными механизмами образования слоев нанометрической толщины, обусловленных количеством границ раздела, действующих как препятствия для отклонения трещины и рассеяния ее энергии. Благодаря улучшенным характеристикам синтезированного многонанослойного материала, разработанное адаптивное покрытие можно рассматривать как более высоко упорядоченную инструментальную обрабатывающую систему, способную поддерживать экстремальные рабочие условия при использовании в промышленности. This research was supported by “El patrimonio Autónomo Fondo Nacional de Financiamiento para la Ciencia, la Tecnología y la Innovación Francisco José de Caldas” under contract RC-No. 275–2011 and the program “Jóvenes Investigadores e Innovadores Virginia Gutiérrez de Pineda No. 525–2011”. Moreover, the authors acknowledge the Center of Excellence for Novel Materials (CENM) and, CINVESTAV, Mexico. Moreover, the authors acknowledge the Serveis Científico-Técnics of the Universitat de Barcelona for XRD, XPS, and TEM analysis. en Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України Сверхтвердые материалы Получение, структура, свойства Design of hard surfaces with metal (Hf/V) nitride multinanolayers Article published earlier |
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Design of hard surfaces with metal (Hf/V) nitride multinanolayers |
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Design of hard surfaces with metal (Hf/V) nitride multinanolayers Escobar, C. Caicedo, J.C. Caicedo, H.H. Mozafari, M. Получение, структура, свойства |
| title_short |
Design of hard surfaces with metal (Hf/V) nitride multinanolayers |
| title_full |
Design of hard surfaces with metal (Hf/V) nitride multinanolayers |
| title_fullStr |
Design of hard surfaces with metal (Hf/V) nitride multinanolayers |
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Design of hard surfaces with metal (Hf/V) nitride multinanolayers |
| title_sort |
design of hard surfaces with metal (hf/v) nitride multinanolayers |
| author |
Escobar, C. Caicedo, J.C. Caicedo, H.H. Mozafari, M. |
| author_facet |
Escobar, C. Caicedo, J.C. Caicedo, H.H. Mozafari, M. |
| topic |
Получение, структура, свойства |
| topic_facet |
Получение, структура, свойства |
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2014 |
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English |
| container_title |
Сверхтвердые материалы |
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Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України |
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Article |
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Physical properties as mechanical and tribological evolution on 4140 steel surfaces coated with hafnium nitride/vanadium nitride [HfN/VN]n multinanolayered systems deposited in various bilayer periods via magnetron sputtering has been exhaustively studied in this work. The coatings have been characterized in terms of structural, chemical, morphological, mechanical, and tribological properties by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning and transmission electron microscopies, nanoindentation, pin-on-disc and scratch tests. Moreover, the failure mode mechanisms were observed via scanning electron microscopy. The preferential growth in the face-centered cubic (111) crystal structure for [HfN/VN]n multilayered coatings have been shown by X-ray diffraction results. The best enhancement of the mechanical behavior has been obtained when the bilayer period was 15 nm (n = 80), yielding the highest hardness (37 GPa) and elastic modulus was (351 GPa). The values of the hardness and elastic modulus were 1.48 and 1.32 times higher than the coating with n = 1, respectively, as well as the lowest friction coefficient (~ 0.15) and the highest critical load (72 N). These results indicated significant enhancements in mechanical, tribological, and adhesion properties, compared to HfN/VN multilayered systems with bilayer period of 1200 nm (n = 1). The hardness and toughness enhancement in the multilayered coatings could be attributed to the different mechanisms that produce the layer formation with nanometric thickness due to the number of interfaces acting as obstacles for crack deflection and dissipation of crack energy. Due to the emergent characteristics of the synthesized multinanolayered material, the developed adaptive coating could be considered as higher ordered tool machining systems, capable of sustaining extreme operating conditions for industrial applications.
Фізичні властивості як механічні і трибологічні зміни на поверхні сталі марки 4140 з покриттям із нанобагатошарових систем нітриду гафнію/нітриду ванадію [HfN/VN]n, нанесених магнетронним розпиленням з різними проміжками між двома шарами, були ретельно вивчені в цій роботі. Структурні, хімічні, морфологічні і трибологічні властивості покриттів визначали дифракцією рентгенівських променів, фотоелектронною рентгенівською спектроскопією, атомно-силовою мікроскопією, растровою та просвічувальною електронною мікроскопією, наноіндентуванням, методом “штифт на крузі” і випробуванням дряпанням. Крім того, механізми відмов спостерігали за допомогою растрової електронної мікроскопії. Результати дифракції рентгенівських променів показали краще зростання (111) граніцентрованої кристалічної структури для багатошарових покриттів [HfN/VN]n. Максимальне підвищення механічних характеристик було досягнуто при товщині бішару HfN/VN, що дорівнював 15 нм (число шарів 80), твердість складала 37 ГПа, а модуль пружності – 351 ГПа. Ці значення твердості і модуля пружності були вище, ніж у покриття з n = 1 (в 1,48 і 1,32 рази відповідно), також це багатошарове покриття мало найнижчий (~ 0,15) коефіцієнт тертя і найвище (72 Н) критичне навантаження. Ці результати показали значне поліпшення механічних, трибологічних і адгезійних властивостей порівняно з HfN/VN багатошарової системою з товщиною бішару 1200 нм (n = 1). Підвищення твердості і в’язкості руйнування багатошарових покриттів може бути пояснено різними механізмами утворювання шарів нанометричної товщини, зумовлених кількістю меж розділу, що діють як перешкоди для відхилення тріщини і розсіювання її енергії. Завдяки покращеним характеристикам синтезованого багатошарового матеріалу, розроблене адаптивне покриття можна розглядати як більш високо впорядковану інструментальну систему обробки, здатну підтримувати екстремальні робочі умови при використанні в промисловості.
Физические свойства как механические и трибологические изменения на поверхности стали марки 4140 с покрытием из наномногослойных систем нитрида гафния/нитрида ванадия [HfN/VN]n, нанесенных магнетронным распылением с различными промежутками между двумя слоями, были тщательно изучены в этой работе. Структурные, химические, морфологические и трибологические свойства покрытий определяли дифракцией рентгеновских лучей, фотоэлектронной рентгеновской спектроскопией, атомно-силовой микроскопией, растровой и просвечивающей электронной микроскопией, наноиндентированием, методом “штифт на круге” и испытания царапаньем. Кроме того, механизмы отказов наблюдали посредством растровой электронной микроскопии. Результаты дифракции рентгеновских лучей показали предпочтительный рост (111) гранецентрированной кристаллической структуры для многослойных покрытий [HfN/VN]n. Максимальное повышение механических характеристик было достигнуто при толщине бислоя HfN/VN равной 15 нм (число слоев 80), твердость была равна 37 ГПа, а модуль упругости – 351 ГПа. Эти значения твердости и модуля упругости были выше, чем у покрытия с n = 1 (в 1,48 и 1,32 раза соответственно), также у этого многослойного покрытия был самый низкий (~ 0,15) коэффициент трения и самая высокая (72 Н) критическая нагрузка. Эти результаты показали значительное улучшение механических, трибологических и адгезионных свойств по сравнению с HfN/VN многослойной системой с толщиной бислоя 1200 нм (n = 1). Повышение твердости и вязкости разрушения многослойных покрытий может быть объяснено различными механизмами образования слоев нанометрической толщины, обусловленных количеством границ раздела, действующих как препятствия для отклонения трещины и рассеяния ее энергии. Благодаря улучшенным характеристикам синтезированного многонанослойного материала, разработанное адаптивное покрытие можно рассматривать как более высоко упорядоченную инструментальную обрабатывающую систему, способную поддерживать экстремальные рабочие условия при использовании в промышленности.
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0203-3119 |
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https://nasplib.isofts.kiev.ua/handle/123456789/126126 |
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Design of hard surfaces with metal (Hf/V) nitride multinanolayers / C. Escobar, J.C. Caicedo, H.H. Caicedo, M. Mozafari // Сверхтвердые материалы. — 2014. — № 6. — С. 10-28. — Бібліогр.: 28 назв. — англ. |
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www.ism.kiev.ua/stm 10
UDC 621.793:620.179.1/.186
C. Escobar, J. C. Caicedo* (Cali, Colombia)
H. H. Caicedo (PA, Chicago, USA)
M. Mozafari (Tehran, Iran)
*jcaicedoangulo1@gmail.com
Design of hard surfaces with metal (Hf/V) nitride
multinanolayers
Physical properties as mechanical and tribological evolution on 4140
steel surfaces coated with hafnium nitride/vanadium nitride [HfN/VN]n multinanolay-
ered systems deposited in various bilayer periods via magnetron sputtering has been
exhaustively studied in this work. The coatings have been characterized in terms of
structural, chemical, morphological, mechanical, and tribological properties by X-ray
diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning and
transmission electron microscopies, nanoindentation, pin-on-disc and scratch tests.
Moreover, the failure mode mechanisms were observed via scanning electron micros-
copy. The preferential growth in the face-centered cubic (111) crystal structure for
[HfN/VN]n multilayered coatings have been shown by X-ray diffraction results. The
best enhancement of the mechanical behavior has been obtained when the bilayer pe-
riod was 15 nm (n = 80), yielding the highest hardness (37 GPa) and elastic modulus
was (351 GPa). The values of the hardness and elastic modulus were 1.48 and 1.32
times higher than the coating with n = 1, respectively, as well as the lowest friction
coefficient (∼ 0.15) and the highest critical load (72 N). These results indicated signifi-
cant enhancements in mechanical, tribological, and adhesion properties, compared to
HfN/VN multilayered systems with bilayer period of 1200 nm (n = 1). The hardness
and toughness enhancement in the multilayered coatings could be attributed to the
different mechanisms that produce the layer formation with nanometric thickness due
to the number of interfaces acting as obstacles for crack deflection and dissipation of
crack energy. Due to the emergent characteristics of the synthesized multinanolayered
material, the developed adaptive coating could be considered as higher ordered tool
machining systems, capable of sustaining extreme operating conditions for industrial
applications.
Keywords: hard coatings, isostructural systems, multinanolayers,
tool wear.
INTRODUCTION
Superior mechanical properties like extreme hardness and good
wear resistance have been frequently reported [1–3]. Thus, during recent years
transition metal nitride have developed crucial roles in applications where these
properties are required. Control of the microstructural and surface morphological
evolution of polycrystalline transition metal nitride films is essential for the per-
formance and lifetime of coated tools. Many transition metal nitrides such as tita-
nium nitride/vanadium nitride (TiN/VN), titanium nitride/niobium nitride
(TiN/NbN), and tungsten/tungsten nitride (W/WN) with excellent mechanical
properties have been studied [4, 5]. The growth rate of such multilayered structures
with nanometer-scale dimensions has attracted much attention from the scientific
© C. ESCOBAR, J. C. CAICEDO, H. H. CAICEDO, M. MOZAFARI, 2014
ISSN 0203-3119. Сверхтвердые материалы, 2014, № 6 11
and industrial community. These coatings, now called heterostructures, such as
silicon nitride/titanium nitride (a-Si3N4/nc-TiN), or titanium aluminum ni-
tride/silicon nitride (TiAlN/SiNx) coatings, exhibit a relatively-high hardness
(~ 40 GPa) and offer potential advantages for dry milling, drilling, and turning [6,
7]. It has been reported that other bilayer combinations such as chromium ni-
tride/tungsten nitride (CrN/WN) or titanium nitride/niobium nitride (TiN/NbN),
whose maximum hardness values do not exceed 30 GPa, are still interesting for
mechanical applications. Moreover, new tribological and physicochemical proper-
ties like very low friction coefficient and anticorrosive properties are now widely
studied [7–9]. However, very few reports persist in the literature about mechanical
and tribological responses in nanostructured systems based on isostructural assem-
bly from nitride coatings generated by transition metals. Therefore, the benefits of
HfN/VN multilayer system were tested under extreme conditions of corrosion [10],
but have not yet been tested at extreme conditions of mechanical performance.
This work evaluated the influence of hafnium nitride/vanadium nitride
(HfN/VN) multilayered coatings deposited onto silicon (100) and AISI 4140 steel
substrates (most frequently used in the water industry) with different bilayer peri-
ods (Λ) and bilayer numbers (n) on their physical nature compared to uncoated and
coated substrate with HfN, VN single layers. The results indicated that this class of
coating could be effectively used for surface applications in industrial factories
under processes with aggressive environments. For this purpose, silicon and AISI
4140 steel substrates were coated with a set of HfN/VN multilayers with Λ be-
tween 1200 nm and 15 nm and n between 1 and 80, with a total thickness of
1.2 µm.
EXPERIMENTAL
Coating deposition
Metal (Hf/V) nitride multinanolayered coatings were deposited onto silicon
(100) and AISI 4140 steel substrates by using a multi-target rf magnetron sputter-
ing system with an rf source (13.56 MHz) to apply a negative voltage bias on the
substrate and two Hf and V 4-in. diameter targets with 99.9% purity. A 350 W
magnetron power was applied to the hafnium target, while a power of 400 W was
applied to the vanadium target. The deposition chamber was initially pumped down
to less than 5·10−6 mbar by using a turbomolecular pump, and then a mixture of
(80%) for Ar gas and (20%) for N2 gas was introduced into the chamber. An rf
negative bias voltage of −30 V was used; the substrate temperature was around
250 °C and the substrate-to-target distance was 7 cm for both coatings. During the
growth process, the chamber pressure was maintained at 2·10−3 mbar. For multi-
layered depositions, the hafnium and vanadium targets were covered periodically
with a steel shutter. Before deposition, the targets and substrates were sputter-
cleaned during a 20-min period. An exhaustive X-ray diffraction (XRD) study was
carried out by using a PAN analytical X’Pert PRO diffractometer with CuKα ra-
diation (λ = 1.5406 Å) at Bragg-Brentano configuration (θ/2θ) in high-angle range.
Bilayer periods in multilayers were measured by using low-angle XRD θ/2θ scans
and were compared to those obtained from micrographs of transmission electron
microscopy (TEM). Microstructural analysis of the multilayers was mainly per-
formed by TEM, using a Philips CM30 microscope operating at 300 kV. The ratio
between the thicknesses of HfN and VN single layers was obtained by means of a
(Dektak 3030) Profilometer. Morphologic characteristics of the coatings like grain
size and roughness were obtained by using atomic force microscopy (AFM) under
contact mode from Asylum Research MFP-3D® and calculated by a Scanning
www.ism.kiev.ua/stm 12
Probe Image Processor (SPIP®). In this work, SPIP® was used in the grain size
analysis for a quantitative study of the grains and particles, and in the roughness
analysis for an advanced measurement of the surface roughness. Surface character-
istics were determined by scanning electron microscopy (SEM, Phenom FEI) with
a magnification range from 525× to 24.000× and a high-sensibility detector (multi-
mode) for scattering electrons. To determine the chemical composition, an exhaus-
tive X-ray photoelectron spectroscopy (XPS) study was carried out for HfN/VN
multilayered coatings. Thus, XPS was used to analyze the bonding of hafnium,
vanadium, and nitrogen atoms by using ESCAPHI 5500 monochromatic AlKα
radiation and a passing energy of 0.1 eV. As the surface sensitivity of this tech-
nique is so high, any contamination can produce deviations from the real chemical
composition. Therefore, the XPS analysis is typically carried out under ultra-high
vacuum conditions with a sputter cleaning source to remove any undesired con-
taminants. Physical analyses as mechanical were performed by nanoindentations
using an Ubi1-Hysitron device and a diamond Berkovich tip at variable loads.
These results were evaluated using the Oliver-Pharr method. Tribological charac-
terization was performed by means of Microtest, MT 400-98 tribometer, using a 6-
mm diameter 100Cr6 steel ball like pattern slide. The applied load was 0.5 N with
a total running length of 1000 m. Adherence of the layers was studied by using a
Scratch Test Microtest MTR2 system. The parameters were a 6-mm scratch length
and a raising load of 0–90 N. In addition, a SEM was used to identify the different
adherence.
RESULTS AND DISCUSSION
XRD results
The HfN/VN multilayered coatings show a thickness approximately of 1.2 µm.
The individual thicknesses varied in function to the bilayer number from n = 1 to
n = 80, producing layers with thicknesses from 1200 nm to 15 nm, respectively.
Figure 1 shows the high-angle XRD patterns corresponding to the HfN/VN multi-
layered coating. A clear evolution of the patterns is noted in this set of multilayers
as bilayer period is increased. As can be seen in Fig. 1, at large bilayer periods,
there is a clear face-centered cubic (fcc) lattice with (111) preferred orientation for
HfN layer and fcc (200) preferred orientation for VN layers (isostructured multi-
layer). These preferential orientations agree with JCPDS 00-033-0592 (HfN) and
JCPDS 00-035-0768 (VN) from ICCD cards. The texture of the HfN layer remains
constant in the preferential orientation (111) from 1200 nm thick films to multilay-
ers with 15 nm thickness. This behavior suggests the possibility of a quasi cube-on-
cube epitaxial growth. In the thinnest bilayer pattern (Λ ≤ 15 nm), there are still
some small contributions of HfN (311) and (222) reflections, but they disappear for
a large range of bilayer periods till the thickest period multilayer (Λ ≤ 1200 nm),
where a great HfN (111) and a small VN (200) peak appear. On the other hand, the
shift of diffraction patterns towards high angles is in relation to the compressive
residual stress characteristic for those multilayered systems. Therefore, it is ob-
served that the HfN (111) peak position suffers deviation from the bulk value, indi-
cating possible stress evolution of HfN/VN layers with the bilayer period (see Fig.
1, b). The quasi-relaxed position observed for thinner bilayer periods was progres-
sively shifted to the higher compressive stress values as the bilayer period in-
creased until the Λ = 1200 nm value. For thinner multilayered periods (n = 80, Λ =
15 nm), a continuous transition of HfN (111) peak position was observed, from
multilayered films with bilayer periods of 120 nm to those with 15 nm bilayer pe-
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riod, presenting a stress relief due to the movement of this peak towards higher
angles compared to other multilayers, but close to the bulk value (34.01°).
20 30 40 50 60 70
H
fN
�1
11
H
fN
�2
00
H
fN
�2
20
H
fN
�3
11
H
fN
�2
22
V
N
�1
11
V
N
�2
00
V
N
�2
20
V
N
�3
11
2θ, deg
In
te
n
si
ty
,
ar
b.
u
. 5
4
3
2
1
a
30 31 32 33 34 35 36
H
fN
�1
11
2θ, deg
In
te
n
si
ty
,
ar
b.
u
.
5
4
3
2
1
b
Fig. 1. (a) XRD patterns of the HfN/VN multilayered coatings deposited on the silicon (100)
substrates with Λ between 1200 and 15 nm and n between 1 and 80 (1 – n = 1, Λ = 1200 nm; 2 –
n = 10, Λ = 120 nm; 3 – n = 30, Λ = 40 nm; 4 – Λ = 24 nm, n = 50; 5 – n = 80, Λ = 14 nm). Dash
lines indicate the position of the peaks obtained from JCPDS files; (b) shows maximum peak
with shift toward high angles in relationship to increasing bilayer number n.
XPS results
The XPS survey spectra for HfN and VN single layers that make up the
HfN/VN multilayered coatings are shown in Fig. 2. For HfN material (see Fig. 2,
a) the peaks at 523.2, 397.6, 224.8, and 18.4 eV correspond to O1s, N1s, Hf4d5,
and Hf4f binding energies, respectively. The change of binding energy compared
to HfN verifies the formation of binary Hf–N compound. Therefore, calculating the
peak area yields an atomic ratio of Hf : N = 1.1 : 0.9, similar to the stoichiometry
of Hf1.1N0.9 [11]. On the other hand, for VN material (see Fig. 2, b), the peaks at
630.4, 532.0, 516.8, and 397.6 eV correspond to V2s, O1s, V2p3/2, and N1s bind-
ing energies, respectively. The change of binding energy compared to VN verifies
the formation of binary V–N compounds. Therefore, calculating the peak area
yields an atomic ratio of V : N = 1.1 : 0.9, similar to the stoichiometry of V1.2N0.8
[12].
According to the XPS literature, regarding HfN and VN materials [11, 12],
when the peaks are fitted from experimental results, it is necessary first to adjust
the N energy band because it is the element that provides greater reliability for
XPS; then, taking this first adjustment as base, the other peaks related to the re-
maining elements are adjusted. The latter is indispensable due to the characteristic
present in these kinds of insulating materials (coatings) with respect to the incident
signal; thus, avoiding the uncertainties caused by charging and shifts of the Fermi
energy. Thereby, the concentration measurements and identification of the specific
bonding configurations for the HfN and VN layers are more reliable. So, the core
electronic spectra carry information of the chemical composition and bonding
characteristics of the HfN and VN films and generate an increase in the reliability
of the results.
www.ism.kiev.ua/stm 14
1100 1000 900 800 700 600 500 400 300 200 100 0
0
2.0 × 10
4
4.0 × 10
4
6.0 × 10
4
8.0 × 10
4
1.0 × 10
5
1.2 × 10
5
1.4 × 10
5
H
f4
f H
f4
d5
H
f4
p3
N
1s
H
f4
p1
O
K
L
L
In
te
ns
it
y,
c
/s
Binding energy, eV
HfN
O
1s
a
1100 1000 900 800 700 600 500 400 300 200 100 0
0
2.0 × 10
4
4.0 × 10
4
6.0 × 10
4
8.0 × 10
4
1.0 × 10
5
V
2p
3/
2
V
L
M
M
1
V
L
M
M
2
O
1s
V
2s
N
1s
V
3s
In
te
ns
it
y,
c
/s
Binding energy, eV
VN
V
3p
b
Fig. 2. XPS survey spectrum (a) HfN coatings and (b) VN coatings deposited on the silicon
surface with an rf negative bias voltage of −30 V.
TEM results
Figure 3 presents the TEM cross-sectional images of an HfN/VN multilayer
with Λ = 15 nm (80 bilayered). The darkest contrast of HfN layers with respect to
those of VN allowed the clear determination of layer structures. These HfN/VN
multilayered coatings presented well-defined and uniform periodicity because the
bilayer period in multilayers was confirmed by the TEM analysis. All the multi-
layer stacks were resolved by TEM and confirmed quite precisely by the previ-
ously designed nominal values of bilayer thickness, as well as the total thickness.
The TEM images show that VN layers are marginally thicker than those of HfN;
they also confirmed that for each multilayer coating there is a different deviation of
0.3 layer thickness ratio. These multilayer modulations were observed when the
periodicity on the HfN/VN multilayer coating remained constant for the smaller
bilayer periods (from Λ = 1200 to 15 nm). Moreover, the TEM bright field micro-
graph in Fig. 3 shows a multilayer with Λ = 14 nm, typical of thick bilayer periods.
It reveals a compact crystalline structure with wide columnar grains extended along
the entire multilayer stack. The selected area electron diffraction (SAED) pattern of
the whole multilayer indicated the (111) preferred orientation for an HfN layer and
(200) preferred orientation for a VN layer, confirming the structural phenomenon
observed by the XRD results. Also, the region shown in Fig. 3 permitted studying
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the structure of a single crystallite, which can be identified as a small dark zone
propagating throughout the multilayer. The SAED pattern was taken form a region
that overlapping several periods of multilayer structure showing an array of regu-
larly distributed spots (see Fig. 3), confirming together with the XRD results the
multilayer structure.
15 nm
3 nm
<111> <200>
a
b
c
Fig. 3. TEM image of HfN/VN multilayer: (a) modulations of HfN/VN coatings with n = 80, Λ =
15 nm, (b) high resolution TEM (HRTEM) showing multilayer interface, and (c) the SAED
pattern taken from a region that overlapping several periods.
AFM results
The AFM was used to quantitatively study the surface morphology of the sam-
ples in relation to decreased bilayer periods or increased bilayer numbers in
HfN/VN multilayered coatings deposited onto silicon (100). Figure 4 shows the
AFM images for multilayered coatings with statistical distribution of grain size that
was analyzed by an area of 1×1 µm (AFM images for (a) n = 1, (b) n = 10, (c) n =
30, (d) n = 50, and (e) n = 80). The correlation between grain size, part (a), and
roughness, part (b), with the bilayer number is shown in Figs. 5, a and 5, b, respec-
tively.
In Table 1 the quantitative values were extracted from the AFM images by
means of statistical analysis scanning probe image processor (SPIP®). The HfN/VN
multilayer coating has the same total thickness, around 1.2 µm. The roughness
value was greater for a coating with n = 1 or high bilayer period Λ = 1200 nm, and
lower for multilayered coatings with a higher bilayer number n = 80 or lower bi-
layer period Λ = 15 nm, indicating that coatings with n = 1 grow more disordered
than do multilayered coatings with n = 80. It has been demonstrated that the grains
of the multilayered coatings are smaller than those of coatings with low bilayer
period because the Ar+ ions bombardment on the coatings stimulates a greater
number of nucleation places, given the reduction of individual thicknesses for each
layer when the bilayer period is reduced and bilayer numbers are increased. This
implicates a decrease in the entire surface roughness [13]. The research took into
account that the grain size is affected by changes in grain size of inner layers
(HfN/VN) as a function of reduced bilayer period Λ or increased bilayer number n.
Many authors have reported a correlation between AFM and XRD results [13]
www.ism.kiev.ua/stm 16
because AFM analysis delivers surface information (with lateral resolution), and
XRD analysis collects information from the space around the normal vector on the
surface (from a cross-section). If this is taken into account, it is possible to consider
that physical vapor deposition (PVD) coating columns can grow “vertically” from
the substrate to the “top” and can change their cross-section when bilayer thickness
is modified; therefore, significant changes in the grain size and surface roughness
are evident.
a b
c d e
Fig. 4. AFM images for an HfN/VN multilayer grown at rf negative bias voltage of −30 V: (a)
n = 1, (b) n = 10, (c) n = 30, (d) n = 50, Λ = 24 nm, and (e) n = 80, Λ = 15 nm.
Table 1. Surface measurements obtained via AFM and SPIP® analysis
for HfN/VN multilayers with a total thickness of 1.2 µm and bilayer period
from Λ = 1200 to 15 nm with correlation between bilayer number, grain
size, and roughness
Bilayer number Grain size, nm Roughness, nm
n = 1 78 3.9
n = 10 58 2.5
n = 30 70 1.9
n = 50 56 1.3
n = 80 48 1
The error in values of grain size and roughness is ±0.1 nm.
Mechanical properties
Hardness and elastic modulus. It has been frequently reported that the thickness
period for many multilayered systems is between 5 and 20 nm, which is relevant
for mechanical properties [14]; however, in industrial applications, as mentioned in
the introduction, it is necessary to obtain coatings with thicknesses above ∼ 1.0 µm.
Therefore, the multilayer coatings deposited with bilayer period under 20 nm for a
ISSN 0203-3119. Сверхтвердые материалы, 2014, № 6 17
total thickness around ∼1.2 µm imply a complex and extended number of multilay-
ers. Consequently, this study carried out a minimum bilayer period of 15 nm. The
typical load-displacement indentation curves of multilayer coatings was conducted
by using the standard Berkovich indenter and indentation matrix image by AFM, as
shown in Figs. 5, a and 5, b. The values of elasticity modulus (E) and hardness (H)
were obtained by using the Oliver-Pharr method [15]. The experimental results
associated with the mechanical properties correspond to the mixed hardness of the
coated systems as a function of the relative indentation depth. As mentioned be-
fore, to compare the hardness response of the coatings, the work of indentation
models described by Korsunsky et al. [16] was used to analyze the nanoindentation
data. This model uses the following equation (Eq. 1) to describe the composite
hardness, which is based on the total work done by the indentation load to produce
an indentation of depth (h):
21 β+
−
+=
K
HH
HH sf
sc . (1)
20 40 60 80 100 120 140 1600
2
4
6
8
10 542 3
L
oa
d,
m
N
Displacement, nm
1
a
b
Fig. 5. Nanoindentation results with (a) load-displacement indentation curves for all coatings
(n = 1, Λ = 1200 nm (1), n = 10, Λ = 120 nm (2), n = 30, Λ = 40 nm (3), n = 50, Λ = 24 nm (4),
and n = 80, Λ = 15 nm (5)), and (b) the typical indentation track image via AFM for a multilayer
with Λ = 24 nm and n = 50.
In this model Hc is the apparent composite hardness, Hf is the intrinsic film
hardness, Hs is the substrate hardness, k is a dimensionless parameter related to the
composite response mode to indentation and β = h/t, which denotes the relative
indentation depth with respect to the coating thickness, where h is the maximum
indentation depth and t is the coating thickness. The fitting results by applying the
work of the indentation model to the experimental data of the HfN/VN multilayer
coatings are shown in Fig. 6. The reduced elastic modulus here was determined
from nanoindentation measurements, considering the values related to 10% of the
thickness of the coatings.
Normalized relative indentation depth (β = h/t) against hardness measured for
the HfN/VN multilayered coatings, prepared with different bilayer periods is
shown in Fig. 6. All the curves presented in Fig. 6 show a decrease in the compos-
ite hardness when increasing the penetration depth, which is not surprising because
the hardness of AISI 4140 steel in all cases is lower (∼ 5 GPa) than the coated sub-
strates. The hardness value of the HfN/VN sample with n = 80 is clearly higher
than that of HfN/VN multilayered coatings with n at 1, 10, 30, and 50. The greatest
www.ism.kiev.ua/stm 18
hardness of the multilayer set, 37 GPa, was obtained for the thinnest bilayer period
(Λ = 15 nm). Therefore, it was 48 and 43% greater than the values for the HfN and
VN single-layer coatings, respectively. This effect is probable and attributed to
many interfaces that blocking dislocations at the interfaces between HfN and VN
layers due to the differences in the shear module of the individual layer materials,
as well as by coherency strains causing periodical strain–stress fields for lattice-
mismatched multilayered coatings [17]. According to Ipaz et al. [18], another con-
dition to enhance the hardness of multilayered coatings with respect to the single
layer coating can be associated with the discrete nature of the multilayers and the
increased number of interfaces, which is also shown in this study by TEM analyses
(see Fig. 3). The enhancement of mechanical properties for HfN/VN multilayers
results from the increment of hardness values, as shown in multilayer-type coatings
for diverse material systems (e.g., TiN/VN, TiCN/TiNbCN, and TiC/TiB2) [7, 13,
19].
0.2 0.4 0.6 0.8 1.00
5
10
15
20
25
30
35
40
H
ar
dn
es
s,
G
P
a
Relative indentation depth β, (h
c
/t)
Hf Hc Hs
1
2
3
4
5
Fig. 6. Relative indentation depths against hardness measured for HfN/VN multilayered coatings,
as a function of the bilayer number n. Continuous lines correspond to the fitting of Eq. (1): n = 1,
Λ = 1200 nm (1), n = 10, Λ = 120 nm (2), n = 30, Λ = 40 nm (3), n = 50, Λ = 24 nm (4), and n =
80, Λ = 15 nm (5).
The H values of the HfN/VN multilayered coatings measured by nanoinden-
tation results (see Figs. 5 and 6) are presented in the Table 2 as functions of bilayer
period Λ and bilayer number n. The E values of the multilayered coatings are also
presented in Fig. 6, showing the relevant differences in their values. The H and E
in these multilayered coatings varied from 25 to 37 GPa and from 265 to 352 GPa,
respectively. The highest hardness of the multilayer set, 37 GPa, was obtained by
the thinnest bilayer period Λ = 15 nm and it was 76 and 94% greater than the ex-
pected reference value from the rule-of-mixtures applied to VN and HfN single-
layer films, respectively. This increase in the mechanical properties is related to the
remarkable heterostructure effects when a perfect assembly occurs for HfN and VN
coatings deposited over an industrial AISI 4140 steel substrate. The mechanical
properties enhancement can be associated with the improved hardness by using
HfN/VN nanometric multilayered materials. Many authors have used the Hall-
Petch effect to explain the material hardening [2, 13, 20]. Therefore, it is possible
to apply the Hall-Petch effect when the ceramic materials, as hard multilayered
coatings with Λ > 5.2 nm, are obtained. Since the multilayered coatings with lower
ISSN 0203-3119. Сверхтвердые материалы, 2014, № 6 19
Λ are within the nanoscale regime, the dislocations should not occur in nanoscale
structures below certain grain size values [21].
Table 2. Mechanical properties for HfN/VN multilayered coatings
with Λ = from 1200 nm to 15 nm, showing the values of hardness
and elastic modulus as a function of bilayer number n
Bilayer number Hardness, GPa Elastic modulus, GPa
HfN single layer 19 205
VN single layer 21 223
n = 1 25 265
n = 10 29 289
n = 30 32 311
n = 50 35 334
n = 80 37 352
The error in values of hardness and elastic modulus is ±2 GPa.
The hardness value for the HfN/VN coatings is in relation to the reduction of
the modulation period (see Fig. 3, a). Therefore, from the nanoindentation results
(see Fig. 6), it is possible to observe that indentation test exhibits low deformation
size, as the mechanical properties enhance as a function of bilayer number. It is
argued that there are some correlations between the hardness of the multilayered
coatings and the modulation period [13]. Hence, the hardness enhancement of
HfN/VN coatings is related to the evidence of a stress relieving according to the
distance decrease of interfaces, as shown in the XRD (see Fig. 1) and TEM results
(see Fig. 3). Moreover, this mechanical effect was attributed to many interfaces
blocking the dislocation movement across the interfaces between the HfN layer and
the VN layer due to the differences in the shear moduli of the individual layer ma-
terials, and to the coherency strain, causing periodical strain–stress fields
(–σHfN + σVN) in the case of lattice mismatched multilayered coatings. Each inter-
face also functions as a grain boundary in a Hall-Petch [2, 20, 21] related mecha-
nism like that of the dislocation pile-up that offers a strong interaction again with
interfaces in general. Therefore, each interface serves as a crack tip deflector,
which improves the mechanical properties of coating [22]. According to Kim et al.
[23], another condition to enhance the hardness of multilayered coatings, with
respect to the single-layer coating, is that a layer in the multilayered system has to
be discrete, which was found in this study via TEM analyses (see Fig. 2). Also, the
enhancement of mechanical properties for an HfN/VN multilayer is related to the
increased hardness, as shown in many multilayered-type coating systems (e.g.,
TiN/VN, TiCN/TiNbCN, and TiC/TiB2) [7, 13, 20]. Yashar et al. [2] used a Hall-
Petch approach to model the mechanical behavior of multilayered materials with
layer thicknesses as low as 1–100 nm, transforming the Hall-Petch approach into
the following equation presented by Caicedo et al., [13]:
2
1
21
−
+ += tIMffm DkHH , (2)
where Hm is the multilayer hardness, Hf1+f2 is the hardness from layer 1 and layer 2,
kIM is a constant measuring the relative hardening contribution of the interface
between layer 1 and layer 2, and Dt is the bilayer period Λ. The model predicts the
overall behavior of the hardness on Λ, observed in most multilayered systems.
Previous work has shown that a maximum hardness would be expected when the
www.ism.kiev.ua/stm 20
individual components of the multilayer have a relative equal thickness, as pre-
sented in this work [24].
Furthermore, it is observed that the elasticity behavior depends on n or Λ, and
the highest bilayer number corresponds to the highest E. Therefore, it is concluded
that the elasticity and elastic recovery (R, %) of the multilayered coatings enhance
by increasing the interface number. Thereby, from the nanoindentation measure-
ment, the typical values of E and H were obtained by using the Oliver-Pharr
method [15]. The R for all HfN/VN multilayered coatings was calculated by the
following equation:
max
max
δ
δ−δ
= pR , (3)
where δmax is the maximum displacement and δp is the residual or plastic displace-
ment. The equation data were taken from the load-penetration depth curves of in-
dentations for each coating, according to Fig. 5. Table 3 shows an increase in the
elastic recovery as a function of bilayer number when δmax and δp values from load
and displacement results (see Fig. 5) are introduced in Eq. (3). Thus, it is possible
to observe an interface effect on the multilayered systems, because by increasing
the bilayer number n the interface number is increased. Therefore, this can generate
an effective hardening characteristic on the multilayered hard coatings, evidenced
by an improved elastic recovery. Also, according to Kim et al. [23], a relationship
exists between E and H, known as the plastic deformation resistance (H3/E2); this
relation was calculated for all the multilayered coatings as a function of bilayer
number or bilayer period. Table 3 shows a considerable increase in the resistance
to plastic deformation H3/E2 as a function of increased bilayer number n, which is
due to the relation between the increase of interface number and increase of the
hardness and the elasticity modulus for all of the multilayered coatings. So, the
enhancement in plastic deformation resistance occurs when multilayer period Λ
decreases, with total thickness constant increasing thus the interface number for
coatings. Therefore, the last effect can produce the crystallite refinement, point
defect formations, and increasing the interface number; this improves the hardness
values of HfN/VN multilayered coatings.
Table 3. Elastoplastic properties with plastic deformation for HfN/VN
multilayered coatings with bilayer period from Λ = 1200 to 15 nm:
showing the values of R, and H3/E2 as functions of n
Bilayer number Elastic recovery R, % Plastic deformation resistance H3/E2
HfN single layer 72 0.16
VN single layer 73 0.19
n = 1 75 0.22
n = 10 77 0.29
n = 30 80 0.33
n = 50 87 0.38
n = 80 91 0.40
As shown in Table 3, the HfN/VN nanometric multilayered coatings increased
the plastic deformation resistance and elastic recovery with respect to coatings
deposited with lower bilayer numbers. The maximum value was reached for n = 80
and Λ = 15 nm, i.e., plastic deformation due to the applied load is more markedly
ISSN 0203-3119. Сверхтвердые материалы, 2014, № 6 21
reduced than that of other multilayered systems with fewer bilayer numbers. This
effect clearly correlates to increasing coating density, hardness, and elastic recov-
ery [15]. In general, the bilayer number n or bilayer period Λ has some effects on
the multilayer shown to exhibit very high hardness in nitride multilayered coatings.
Tribological properties
Pin-on-disk analysis. The friction coefficient values for AISI 4140 steel sub-
strates coated with different multilayered systems (Λ = 1200 mm, n = 1; Λ =
120 nm, n = 10; Λ = 150 nm, n = 30; Λ = 40 nm, n = 50; Λ = 24 nm, n = 50; and
Λ = 15 nm, n = 80) were tested against steel balls and presented in Fig. 7, a. These
curves showed two distinct stages. In the first stage, the friction coefficient (µ)
began at a low level (0.15–0.25) in the first contact; this stage can be attributed to
the running-in period associated with a kind of contact between the steel ball and
the coating, where the formation of wear debris occurs by the cracking of rough-
ness tips on both counterparts. This stage has a short time period, and then the
friction coefficient increases to 0.4–0.5 followed by a decrease to the friction coef-
ficient of the second stage. This stage is defined as the steady-state friction period
and begins after about 30–80 m of sliding distance (m) [19]. Figure 7, b shows the
friction coefficient as a function of bilayer numbers. The tribological properties of
the homogeneous HfN and VN single-layer coatings were provided in Fig. 7 for
comparison in relation to multilayered systems. These tribological results showed
the reduction of the friction coefficient, while the bilayer number increased and the
bilayer period decreased. The friction coefficient of HfN/VN multilayer coatings
ranged from approximately 0.33 to 0.15, being the lowest value reported for the
multilayer growth with Λ = 15 nm, and n = 80. The friction coefficient value repre-
sented a decrease at approximately 75 and 65% of the friction coefficient with
respect to the HfN and VN single layers, respectively. The last behavior can be
related to the friction mechanical model proposed by Archard [25], which relates
the contribution of the contact surface roughness and the elastic–plastic properties
of the coating in the following equation:
),(
),(
EHt
asRC
F
F
k
n
f
σ
==μ , (4)
where µ is the friction coefficient, Ck is a constant that depends on the parameter of
the test, R(s, a) is the coating roughness, and σt is a variable that takes into account
the elastic–plastic properties (H or E), obtained by mechanical measures [25]. In
agreement with the model presented by Archard, when the surface coating has low
roughness and high hardness, the friction coefficient will tend to decrease and will
be stable for long sliding distances, specifically if the counterpart of the test is
softer than the coating. On the other hand, although hardness has long been re-
garded as a primary material property that defines wear resistance, strong evi-
dences suggest that the elastic modulus can also have an important influence on the
wear behavior. In particular, the elastic strain to failure, related to the ratio of H
and E, which has been shown by a number of authors to be a more suitable parame-
ter to predict wear resistance than the hardness alone. Until now, scientific re-
searches have been mainly aimed at achieving ultrahigh hardness associated with
high elastic modulus, the latter of which, conventional fracture mechanics theory
would suggest, is also desirable for wear improvement (by preventing crack propa-
gation). This study discusses the concept of multilayered coatings with relatively
high hardness and high elastic modulus, which can exhibit improved toughness and
are, therefore, better suited to optimize the wear resistance of ‘real’ industrial sub-
www.ism.kiev.ua/stm 22
strate materials (i.e., steels and light alloys with low moduli). Recent advances in
the development of ceramic–ceramic (HfN/VN) multilayer coatings are summa-
rized and discussed in terms of their relevance to practical applications. This paper
observed that the elastic strain to failure (which is related to H3/E2, see Table 3)
affects the tribological behavior of HfN/VN multilayered coatings that, although
not necessarily exhibiting extreme hardness, provide superior wear resistance when
deposited on the substrate materials for industrial applications [26]. Therefore, this
behavior suggests that improving plastic deformation resistance when the bilayer
number is increased, exerts more wear resistance due to enhanced mechanical
properties (see Table 3) associated with the perfect modulation assembly (previ-
ously observed in XRD and TEM), thus, generating a
0 200 400 600 800 1000
0.1
0.2
0.3
0.4
0.5
Sliding distance, m
F
ri
cc
io
n
co
ef
fc
ie
nt
1
2
3
5
4
II
I
a
0 10 20 30 40 50 60 70 80
0.1
0.2
0.3
0.4
0.5
0.6
0.7
F
ri
ct
io
n
co
ef
fi
ci
en
t
Bilayer number
HfN
VN
HfN/VN
4
5
3
2
1
Single layers Λ = 1200 nm, n = 1
Λ = 15 nm, n = 80
b
Fig. 7. Tribological results of 4140 steel substrates coated with HfN/VN multilayered systems:
(a) friction coefficient as a function of sliding distance and (b) friction coefficient as a function
of the bilayer numbers n or bilayer periods Λ with wear track observed by SEM: n = 1, Λ =
1200 nm (1), n = 10, Λ = 120 nm (2), n = 30, Λ = 40 nm (3), n = 50, Λ = 24 nm (4), and n = 80,
Λ = 15 nm (5).
ISSN 0203-3119. Сверхтвердые материалы, 2014, № 6 23
reduction in the friction coefficient (see Fig. 7). As can be seen in Fig. 7, b (SEM
micrographs), it is possible to find different wear mechanisms, such as abrasion,
adhesion, oxidation, and diffusion. In this sense, the abrasion mechanism is a pre-
dominant phenomenon at multilayers with low bilayer number (low mechanical
properties). The values for multilayer period, at which the maximum wear values
occur, will depend on different factors like the combination of high roughness,
small grain size, and low elastic modulus, among others.
Adhesion behavior. The scratch test was used to characterize the coating adher-
ence strength. The adhesion properties of single-layer coatings and multilayered
coatings can be characterized by the following two terms: Lc1, the lower critical
load, which is defined as the load where cracks first occurred (cohesive failure);
and Lc2, the upper critical load, which is the load where the first delaminating at the
edge of the scratch track occurred (adhesive failure) [25]. The values of critical
load (Lc1 and Lc2) for the different coatings are shown in Fig. 8. The Lc1 was shown
for the different coatings in the range of 27–58 N, in which the lowest value was
attributed to the multilayered coating deposited with n = 1 and the highest value
was attributed to the HfN/VN multilayered coating growth with Λ = 15 nm and n =
80.
10 30 50 70 90 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
10 30 50 70 90 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Load, N
F
ri
ct
io
n
co
ef
fi
ci
en
t
F
ri
ct
io
n
co
ef
fi
ci
en
t
Load, N
L
c2
L
c1
L
c2
L
c1
L
c1
L
c2
L
c1
L
c2
L
c1
L
c2
a b
Fig. 8. Tribological results for friction coefficient curves versus load for HfN/VN multilayered
coatings, showing the adhesion failure (Lc2): (a) n = 1, Λ = 1200 nm (1), n = 10, Λ = 120 nm (2),
(b) n = 30, Λ = 40 nm (3), n = 50, Λ = 24 nm (4); and n = 80, Λ = 15 nm (5); Lc1 – cohesive
failure, Lc2 – adhesive failure.
The critical loads in Lc2 values for the different coatings are summarized in Ta-
ble 4. This table clearly shows that the adhesion properties of HfN/VN multilay-
www.ism.kiev.ua/stm 24
ered coatings increase as a function of decrease in bilayer period. Due to the quan-
titative adhesion measurements between the layers and substrates, this process is
complex even for single-layer coatings, which is in agreement with some previ-
ously published reports [19]. A qualitative characterization is necessary to evaluate
the adhesion behavior of all multilayered systems, as described before in this sec-
tion, i.e., in terms of Lc1 and Lc2 critical loads. Therefore, for the purpose of ensur-
ing a fair comparison between the different coating systems, it was assumed that
the adhesion between the substrate and the first layer of the multilayered system
remains constant (since the preparation conditions and parameters were the same).
Besides, in all cases, it was verified that the parameters of the scratch test for all
samples were also the same. According to the latter, it was expected that the re-
sponse to the applied load will only depend on the coating properties because of
the effect of each layer and the interfaces that make up the entire multilayered sys-
tem.
From Table 4, it was observed that the values of critical load increased when bi-
layer period Λ was increased and bilayer number n was increased. This improve-
ment is in part due to the increase in the coating/substrate deformation resistance.
In this mechanism, each interface serves as a crack tip deflector that changes the
direction of the initial crack when it penetrates deep into the coating, and strength-
ens the coating performance. Moreover, by decreasing the bilayer period, the dislo-
cations among the layers found a major impediment to moving; therefore, those
will require higher critical shear stress to move and spread throughout the coating
and allow a delaminating of the coating. This means that multilayered coatings fail
in a laminar manner [14] due to the multilayered assembly, as found in the TEM
analysis (see Fig. 3). In consequence, multilayered and multiple structures like
those studied in this research can enhance the resistance of coatings against crack
propagation in relation to the mechanical property evolution presented by the en-
hanced hardness and elastic modulus (see Table 2) with highest elastic recovery
(see Table 4), preserving the integrity of the coatings under punctual and dynamic
loads [27]. In this work, it was observed that an increase of 27% in the Lc2 for
HfN/VN multilayered systems with Λ = 15 nm and n = 80 is in relation to the mul-
tilayers with lowest bilayer number (n = 1).
Table 4. Correlation of critical loads Lc2 with bilayer numbers n or bilayer
periods Λ
Bilayer number Critical loads Lc2
HfN single layer 34
VN single layer 41
n = 1 52
n = 10 57
n = 30 64
n = 50 68
n = 80 72
The error in values of critical loads is ±1 N.
Surface tribological results
Scanning electron microscopies images showing the different behaviors of the
multilayered coatings after scratch tests are shown in Figs. 9, a and 9, b. These
images, revealed that at the beginning of the scratch pronounced deformation ap-
ISSN 0203-3119. Сверхтвердые материалы, 2014, № 6 25
peared due to the substrate plastic deformation and a coating debris removal, asso-
ciated with the adhesive layer/substrate failure mechanism sideward lateral flank-
ing [28]; thus, the SEM images confirm the scratch test results observed in Fig. 9.
I I
I
a b c
II
I
d e
Fig. 9. SEM micrographs of the scratch tracks on (a) n = 1, Λ = 1200 nm; (b) n = 10, Λ =
120 nm; (c) n = 30, Λ = 40 nm; (d) n = 50, Λ = 24 nm; and (e) n = 80, Λ = 15 nm, deposited onto
industrial AISI 4140 steel; I – buckling cracks; II – recovery spallation.
Figure 9, a shows a premature adhesion failure due to the accumulation of
stress at the scratch edges to the multilayered system deposited with n = 1
(Λ = 1200 nm). Performing a detailed analysis of failure mechanisms for the
[HfN/VN]80 multilayer (Λ = 15 nm) at the beginning of the scratch mark, there was
a pronounced irregularity due to the plastic deformation of the metal substrates (see
Fig. 9, e). Later (furthest from scratch), conformal cracking of the layer associated
with adhesive failure (Lc2) appears. As other multilayered systems (n = 1, 10, 30
and 50), the systems with 80 bilayers coatings also presented “Recovery Spalla-
tion” type wear mechanisms (see Fig. 9, e). These series of multilayers showed a
failure behavior type “Buckling Cracks” that is characteristic of protective systems
where the substrate is ductile and hard coating have good adhesion between them,
these systems generate compressive efforts that are characteristic of cracks buck-
ling failure mode [26].
CONCLUSIONS
Multilayered structure has been identified as an isostructural multilayer of HfN
and VN phases. The preferential orientation (111) for fcc lattice of HfN and (200)
for fcc lattice of VN single layers has been shown in the XRD patterns. From the
XPS results, it has been possible to identify the chemical composition in both sin-
gle-layer coatings.
www.ism.kiev.ua/stm 26
The TEM analysis confirmed well-defined multilayered structures and showed
slight variations in layer thickness ratio. The morphology and surface quality have
been determined for all coating systems, establishing homogeneous surfaces for all
of them. The grains of the multilayers were smaller than those of the individual
HfN and VN coatings. This fact has been attributed to the ion bombardment of the
coatings, which stimulated a greater number of nucleation sites that together with
grain size reduction by decreased bilayer period led to the decrease of the entire
surface roughness.
It has been found that the highest values of hardness and elastic modulus,
37 GPa and 351 GPa, respectively, were observed for multilayered systems with Λ
= 15 nm and n = 80. The enhancement in the hardness value of the HfN/VN stack
has been attributed to many interfaces blocking the micro-crack movements across
the interfaces between the HfN layer and VN layer due to the differences in the
shear module of the individual layer material, and to the coherency strain causing
periodical strain–stress fields; together with the Hall-Petch models, which gives a
good overall picture of the hardness enhancements.
High tribological performance with critical loads in adhesive failure of 72 N
and friction coefficient of 0.18 have been observed for the multilayered systems
with Λ = 15 nm and n = 80. From the SEM micrographs, it has been determined
that for the multilayered coatings different types of adhesive layer/substrate fail-
ures appear under strong plastic deformation conditions, which is important for the
preparation of wear resistant cutting and forming tools and mechanic devices used
in industrial applications.
This research was supported by “El patrimonio Autónomo Fondo Nacional de
Financiamiento para la Ciencia, la Tecnología y la Innovación Francisco José de
Caldas” under contract RC-No. 275–2011 and the program “Jóvenes Investi-
gadores e Innovadores Virginia Gutiérrez de Pineda No. 525–2011”. Moreover, the
authors acknowledge the Center of Excellence for Novel Materials (CENM) and,
CINVESTAV, Mexico. Moreover, the authors acknowledge the Serveis Científico-
Técnics of the Universitat de Barcelona for XRD, XPS, and TEM analysis.
Фізичні властивості як механічні і трибологічні зміни на поверхні сталі
марки 4140 з покриттям із нанобагатошарових систем нітриду гафнію/нітриду ванадію
[HfN/VN]n, нанесених магнетронним розпиленням з різними проміжками між двома ша-
рами, були ретельно вивчені в цій роботі. Структурні, хімічні, морфологічні і трибо-
логічні властивості покриттів визначали дифракцією рентгенівських променів, фото-
електронною рентгенівською спектроскопією, атомно-силовою мікроскопією, растровою
та просвічувальною електронною мікроскопією, наноіндентуванням, методом “штифт
на крузі” і випробуванням дряпанням. Крім того, механізми відмов спостерігали за допо-
могою растрової електронної мікроскопії. Результати дифракції рентгенівських променів
показали краще зростання (111) граніцентрованої кристалічної структури для багато-
шарових покриттів [HfN/VN]n. Максимальне підвищення механічних характеристик було
досягнуто при товщині бішару HfN/VN, що дорівнював 15 нм (число шарів 80), твердість
складала 37 ГПа, а модуль пружності – 351 ГПа. Ці значення твердості і модуля
пружності були вище, ніж у покриття з n = 1 (в 1,48 і 1,32 рази відповідно), також це
багатошарове покриття мало найнижчий (∼ 0,15) коефіцієнт тертя і найвище (72 Н)
критичне навантаження. Ці результати показали значне поліпшення механічних,
трибологічних і адгезійних властивостей порівняно з HfN/VN багатошарової системою з
товщиною бішару 1200 нм (n = 1). Підвищення твердості і в’язкості руйнування багато-
шарових покриттів може бути пояснено різними механізмами утворювання шарів
нанометричної товщини, зумовлених кількістю меж розділу, що діють як перешкоди для
відхилення тріщини і розсіювання її енергії. Завдяки покращеним характеристикам син-
тезованого багатошарового матеріалу, розроблене адаптивне покриття можна розгля-
дати як більш високо впорядковану інструментальну систему обробки, здатну підтри-
мувати екстремальні робочі умови при використанні в промисловості.
ISSN 0203-3119. Сверхтвердые материалы, 2014, № 6 27
Ключові слова: тверде покриття, ізоструктурні системи, мультінано-
шар, знос інструменту.
Физические свойства как механические и трибологические изменения на
поверхности стали марки 4140 с покрытием из наномногослойных систем нитрида гаф-
ния/нитрида ванадия [HfN/VN]n, нанесенных магнетронным распылением с различными
промежутками между двумя слоями, были тщательно изучены в этой работе. Струк-
турные, химические, морфологические и трибологические свойства покрытий определяли
дифракцией рентгеновских лучей, фотоэлектронной рентгеновской спектроскопией,
атомно-силовой микроскопией, растровой и просвечивающей электронной микроскопией,
наноиндентированием, методом “штифт на круге” и испытания царапаньем. Кроме
того, механизмы отказов наблюдали посредством растровой электронной микроскопии.
Результаты дифракции рентгеновских лучей показали предпочтительный рост (111)
гранецентрированной кристаллической структуры для многослойных покрытий
[HfN/VN]n. Максимальное повышение механических характеристик было достигнуто при
толщине бислоя HfN/VN равной 15 нм (число слоев 80), твердость была равна 37 ГПа, а
модуль упругости – 351 ГПа. Эти значения твердости и модуля упругости были выше,
чем у покрытия с n = 1 (в 1,48 и 1,32 раза соответственно), также у этого многослойно-
го покрытия был самый низкий (∼ 0,15) коэффициент трения и самая высокая (72 Н)
критическая нагрузка. Эти результаты показали значительное улучшение механических,
трибологических и адгезионных свойств по сравнению с HfN/VN многослойной системой с
толщиной бислоя 1200 нм (n = 1). Повышение твердости и вязкости разрушения много-
слойных покрытий может быть объяснено различными механизмами образования слоев
нанометрической толщины, обусловленных количеством границ раздела, действующих
как препятствия для отклонения трещины и рассеяния ее энергии. Благодаря улучшенным
характеристикам синтезированного многонанослойного материала, разработанное
адаптивное покрытие можно рассматривать как более высоко упорядоченную инстру-
ментальную обрабатывающую систему, способную поддерживать экстремальные рабо-
чие условия при использовании в промышленности.
Ключевые слова: твердое покрытие, изоструктурные системы, муль-
тинанослой, износ инструмента.
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Thin-Film Group, Universidad del Valle Cali, Colombia Received 29.11.13
Tribology Polymers, Powder Metallurgy
and Processing of Solid Recycled Research Group
Universidad del ValleCali, Colombia, USA
BiologicsResearch, Biotechnology Center of Excellence,
Janssen R&D, LLC, Pharmaceutical Companies of Johnson & Johnson,
Spring House, PA, USA
National Biotechnology & Pharmaceutical Association, Chicago, USA
Bioengineering Research Group, Nanotechnology
and Advanced Materials Department,
Materials and Energy Research Center (MERC), Tehran, Iran
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