Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods

Nanocrystalline bulk high-purity titanium samples were obtained by combined severe plastic deformation SPD, thermal treatment and quasi-hydrostatic extrusion QHE at liquid nitrogen LNT and room RT temperatures. Texture and microstructural evolution of Ti have been investigated by XRD methods. The ef...

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Datum:	2015
Hauptverfasser:	Boklag, E.E., Kolodiy, І.V., Tikhonovsky, M.A., Kislyak, I.F., Khaimovich, P.A., Efimov, A.A.
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Sprache:	English
Veröffentlicht:	Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2015
Schriftenreihe:	Вопросы атомной науки и техники
Schlagworte:	Материалы реакторов на тепловых нейтронах
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spelling	nasplib_isofts_kiev_ua-123456789-824482025-02-09T17:34:40Z Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods Исследование структурного состояния высокочистого титана после интенсивной пластической деформации и криогенной квазигидроэкструзии методами рентгеновской дифракции Дослідження структурного стану високочистого титану після інтенсивної пластичної деформації і криогенної квазігідроекструзії методами рентгенівської дифракції Boklag, E.E. Kolodiy, І.V. Tikhonovsky, M.A. Kislyak, I.F. Khaimovich, P.A. Efimov, A.A. Материалы реакторов на тепловых нейтронах Nanocrystalline bulk high-purity titanium samples were obtained by combined severe plastic deformation SPD, thermal treatment and quasi-hydrostatic extrusion QHE at liquid nitrogen LNT and room RT temperatures. Texture and microstructural evolution of Ti have been investigated by XRD methods. The effect of initial structural state on deformation behavior of Ti after QHE was established. QHE of ultrafine-grained samples leads to structure formation, which parameters are independent on temperature of QHE. Significant differences in QHE process are observed for pre-annealed coarse-grained samples. These differences are related to deformation mechanisms, activated during the QHE process at LNT and RT. Методами комбинированной интенсивной пластической деформации, термообработок и квазигидроэкструзии (КГЭ) при азотной и комнатной температурах получены объемные нанокристаллические образцы высокочистого титана. Исследования текстуры и микроструктурных параметров титана проводились методами рентгеновской дифрактометрии. Установлено влияние исходного структурного состояния образцов на деформационное поведение титана при КГЭ. КГЭ ультрамелкозернистых образцов приводит к формированию структуры, параметры которой практически не зависят от температуры КГЭ. Значительные отличия наблюдаются в случае предварительно отожженных крупнозернистых образцов. Это связано с различными механизмами деформации (скольжением дислокаций и двойникованием), которые активируются в процессе КГЭ при комнатной и азотной температурах. Методами комбінованої інтенсивної пластичної деформації, термообробок та квазігідроекструзії (КГЕ) при азотній та кімнатній температурах отримано нанокристалічні об’ємні зразки високочистого титану. Дослідження текстури та мікроструктури титану проводилися методами рентгенівської дифракції. Встановлено вплив початкового структурного стану зразків на деформаційну поведінку титану при КГЕ. КГЕ ультрадрібнозернистих зразків призводить до формування структури з параметрами, незалежними від температури КГЕ. Значні відмінності спостерігаються у випадку попередньо відпалених крупнозернистих зразків. Це пов’язано з різними механізмами деформації (ковзанням дислокацій та двійнікуванням), що активуються під час КГЕ при кімнатній та азотній температурах. 2015 Article Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods / E.E. Boklag, І.V. Kolodiy, M.A. Tikhonovsky, I.F. Kislyak, P.А. Khaimovich, A.A. Efimov // Вопросы атомной науки и техники. — 2015. — № 2. — С. 95-99. — Бібліогр.: 23 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/82448 621.039:543.442.3 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection	DSpace DC
language	English
topic	Материалы реакторов на тепловых нейтронах Материалы реакторов на тепловых нейтронах
spellingShingle	Материалы реакторов на тепловых нейтронах Материалы реакторов на тепловых нейтронах Boklag, E.E. Kolodiy, І.V. Tikhonovsky, M.A. Kislyak, I.F. Khaimovich, P.A. Efimov, A.A. Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods Вопросы атомной науки и техники
description	Nanocrystalline bulk high-purity titanium samples were obtained by combined severe plastic deformation SPD, thermal treatment and quasi-hydrostatic extrusion QHE at liquid nitrogen LNT and room RT temperatures. Texture and microstructural evolution of Ti have been investigated by XRD methods. The effect of initial structural state on deformation behavior of Ti after QHE was established. QHE of ultrafine-grained samples leads to structure formation, which parameters are independent on temperature of QHE. Significant differences in QHE process are observed for pre-annealed coarse-grained samples. These differences are related to deformation mechanisms, activated during the QHE process at LNT and RT.
format	Article
author	Boklag, E.E. Kolodiy, І.V. Tikhonovsky, M.A. Kislyak, I.F. Khaimovich, P.A. Efimov, A.A.
author_facet	Boklag, E.E. Kolodiy, І.V. Tikhonovsky, M.A. Kislyak, I.F. Khaimovich, P.A. Efimov, A.A.
author_sort	Boklag, E.E.
title	Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods
title_short	Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods
title_full	Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods
title_fullStr	Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods
title_full_unstemmed	Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods
title_sort	structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by xrd methods
publisher	Національний науковий центр «Харківський фізико-технічний інститут» НАН України
publishDate	2015
topic_facet	Материалы реакторов на тепловых нейтронах
url	https://nasplib.isofts.kiev.ua/handle/123456789/82448
citation_txt	Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods / E.E. Boklag, І.V. Kolodiy, M.A. Tikhonovsky, I.F. Kislyak, P.А. Khaimovich, A.A. Efimov // Вопросы атомной науки и техники. — 2015. — № 2. — С. 95-99. — Бібліогр.: 23 назв. — англ.
series	Вопросы атомной науки и техники
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fulltext	ISSN 1562-6016. ВАНТ. 2015. №2(96) 95 UDC 621.039:543.442.3 STRUCTURAL STATE STUDY OF HIGH-PURITY TITANIUM AFTER SEVERE PLASTIC DEFORMATION AND CRYOGENIC QUASI-HYDROSTATIC EXTRUSION BY XRD METHODS E.E. Boklag, І.V. Kolodiy, M.A. Tikhonovsky, I.F. Kislyak, P.А. Khaimovich, A.A. Efimov National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine E-mail: giao@ukr.net Nanocrystalline bulk high-purity titanium samples were obtained by combined severe plastic deformation SPD, thermal treatment and quasi-hydrostatic extrusion QHE at liquid nitrogen LNT and room RT temperatures. Texture and microstructural evolution of Ti have been investigated by XRD methods. The effect of initial structural state on deformation behavior of Ti after QHE was established. QHE of ultrafine-grained samples leads to structure formation, which parameters are independent on temperature of QHE. Significant differences in QHE process are observed for pre-annealed coarse-grained samples. These differences are related to deformation mechanisms, activated during the QHE process at LNT and RT. 1. INTRODUCTION Titanium and titanium-based alloys are widely used materials for medical implants manufacturing due to its excellent biocompatibility, corrosion resistance and low ion-formation tendency in aqueous environment [1, 2]. Until recently, alloy materials were preferred (for example, Ti-6Al-4V), because of its higher mechanical properties in comparison with pure titanium. But the development level of the modern medicine has considerably higher material requirements. In spite of high biocompatibility and strength, titanium-based alloys usually contain toxic elements, which can provoke allergic reactions during implant healing process. For this reason researchers are taking an interest in pure titanium. Modern methods of severe plastic deformation (SPD) allow to obtain nanostructured and ultrafine-grained UFG titanium (commercially pure and high-purity), which has unique physical and mechanical properties. For this purpose different SPD methods were realized for commercially pure titanium, such as high pressure torsion (HPT) [3], equal channel angular extrusion (ECAE) [4–7], uniaxial compression [8], large-strain machining [9], cryogenic rolling [10]. Large degrees of true strain and heightened temperatures are usually required for production of UFG and nanocrystalline materials by afore-cited methods. But, at the same time, dynamical recovery effect appears. Besides, the combination of SPD methods results in better mechanical behavior of Ti samples [11]. Therefore, the main goal of this work was to study the structural state of high-purity titanium after SPD (compression-extrusion + wire drawing), thermal treatment and following quasi-hydrostatic extrusion at liquid nitrogen and room temperatures (QHE77K and QHE300K series, respectively). 2. MATERIALS AND METHODS Iodide purity titanium after double electron-beam melting at a pressure (P = 1.3∙10 -4 Pa) was taken as an initial material. Combined severe plastic deformation was carried out in a few stages. At the first step preliminary compression-extrusion of the initial ingot was performed. The true strain aggregated a value of e = 3.54, after the deformation final billet was Ø10mm. At the second stage, the extruded rod was drawn to diameter 5 mm at room temperature (total true strain after wire drawing was e = 4.93). The foregoing SPD methods are described in more detail in the article [12]. After this, the obtained bar was cut into the set of specimens. Some of them were annealed (1.3∙10 -1 Pa) at temperatures 150, 250, 300, 350, 450, 550 ºC for 1 h to study an effect of the initial structural state on deformation behavior of Ti. Then samples after SPD and annealing were extruded by quasi-hydrostatic extrusion at liquid nitrogen LNT and room temperature RT. True strain after quasi-hydrostatic extrusion was e ≈ 0.86. Quasi-hydrostatic extrusion method was developed in NSC KIPT and described by authors in the articles [13, 14], and its usage, applied to high-purity titanium deformation,  in the article [12]. Texture and structure parameters of samples were studied by XRD methods. Integral intensity, peak position, line profile shape and integral breadth were analyzed. X-ray diffraction patterns were collected in Cu-Kα radiation with DRON-4-07 diffractometer, equipped with scintillation detector and nickel filter. Texture analysis of the specimens was carried out by Rietveld refinement. Degree of preferred orientation determination (percentage of crystal grains, oriented with predetermined crystallographic plane {hkl} normal to deformation direction) was performed by integral intensity analysis combined with March-Dollase approach [15]:    M i iihkl r rP 1 2/322 )sin1cos(  , (1) where Phkl – normalization factor for (hkl) peak intensity correction; M – multiplicity factor (hkl) plane; φ – angle between the reference direction and the normal of the individual lattice plane; r – refined parameter (part of grains, randomly oriented in the sample). Microstructural effect study was performed by integral breadth analysis method. Separated values of coherent-scattering domains (CSD) size and microstrains were obtained using Williamson-Hall plot. The main operational formula of this method is: , cos    tg D    (2) mailto:giao@ukr.net 96 ISSN 1562-6016. ВАНТ. 2015. №2(96) β – physical peak broadening (experimentally observed broadening corrected for instrumental broadening); λ – radiation wavelength; D – crystallite size (volume weighted); η – residual mean square value of microstrains; θ – diffraction angle. Coarse-grained silicon powder (grain size ~ 30 μm) was used as an instrumental-standard specimen. 3. RESULTS 3.1. SPD BY COMPRESSION-EXTRUSION – WIRE DRAWING WITH FOLLOWING ANNEALING After the SPD by compression-extrusion and wire- drawing at room temperature the sample’s structure has practically equiaxed crystallites (CSD size is 70.4 nm along the bar axis and 92.8 nm in a cross-section, value of microstrains is 0.4%). Analysing intensity distribution of the diffraction lines in the sample, it can be concluded an [10.0] axial texture presence in non- annealed deformed sample (e.g. grains are oriented with [10.0] crystallographic directions along rod axis). This is typical crystallographic texture for titanium at uniaxial deformation. During the annealing temperature increasing it is observed crystallite size exponential growth and microstrains reducing depending on temperature (Figs. 1, 2; Table 1). It should be noted, that microstrains decrease weakly on annealing, and just at T = 450 ºC stress relaxation occurs in specimens. More interesting results are observed for CSD size. The crystallite size increases weakly along the bar axis and just at T = 550 ºC it reaches values comparable to standard’s one. Fig. 1. CSD size dependence on annealing temperature in the samples after SPD More intensive growth of crystallite size is observed in a cross-section of the bar depending on annealing temperature and at T = 350 ºC CSD size already reaches standard’s level. Thus, crystallites have oblong shape, oriented normally to bar axis, up to 550 ºC. It should be noted, that annealing at 150 ºC leads to slight CSD size decreasing in comparison with non-annealed deformed sample. This effect may be caused by anisotropy of coefficients of thermal expansion. Peak (10.0) relative intensities are significantly higher in samples, annealed at temperatures from 150 to 350 ºC, then in non-annealed deformed sample. This indicates that the annealing samples are more textured than non-annealed deformed sample. At higher annealing temperatures (450, 550 ºC) texture randomization occurs and, at the same time, axial texture component [11.0] appears (typical annealing texture for titanium). Fig. 2. Microstrains dependence on annealing temperature in the samples after SPD Table 1 Dependence of Ti sub-structural parameters on annealing temperature after the SPD Tanneal, °С Cross-section Longitudinal section D, nm <ε> D, nm <ε> 20 70.4 3.03·10 -3 92.8 4.96·10 -3 150   91.7 4.59·10 -3 250 77.2 3.25·10 -3 202.1 3.77·10 -3 300 86.6 3.15·10 -3 442.9 2.81·10 -3 350 67.9 3.84·10 -3 * * 450 190.3 1.7·10 -4 * * 550 * * * * *Values of microstructural parameters are comparable to the instrumental-standard specimen’s ones. 3.2. QUASI-HYDROSTATIC EXTRUSION AT ROOM AND NITROGEN TEMPERATURES After the quasi-hydrostatic extrusion at LNT and RT practically the same values of sub-structural parameters are observed in deformed non-annealed samples (Table 2, 20 °C). Thus CSD size is equal to D ≈ 62 nm, and the value of microstrains is a bit higher (<ε> = 3.83∙10 -3 ) in sample extruded at LNT as compared with extruded at RT one (<ε> = 3.65∙10 -3 ). Pre-annealing temperature of SPD titanium has a significant effect on sub-structural parameters of quasi- hydrostatic extruded samples. For the pre-annealed samples after the QHE common tendency to microstrains decreasing is observed at annealing temperature decrease (Fig. 3, Table 2). Whereas the similar values of microstrains were obtained for both specimens’ series (QHE77K and QHE300K). Concerning to CSD, exponential growth of crystallite size is observed in specimens, quasi-hydroextruded at room temperature (Fig. 4, 300 K series), with pre- annealing temperature increasing (crystallite size increased up to 136.2 nm at T = 550 ºC). ISSN 1562-6016. ВАНТ. 2015. №2(96) 97 Fig. 3. Microstrains dependence on annealing temperature in the samples after QHE Fig. 4. CSD size dependence on annealing temperature in the samples after QHE Table 2 Dependence of substructural parameters on pre- annealing temperature after the QHE Tanneal, ºC TQHE LNT RT D, nm <ε> D, nm <ε> 20 62.4 3.83·10 -3 62.0 3.65·10 -3 350 74.7 3.48·10 -3 82.9 3.53·10 -3 450 74.2 2.95·10 -3 88.8 3.08·10 -3 550 54.2 2.98·10 -3 136.2 2.85·10 -3 Another situation is observed in the samples, deformed at nitrogen temperature (see Fig. 4, 77 K). In this case two pre-annealing temperature regions can be marked out, in which different tendencies of crystallite size changes are observed. Inside a temperature region up to 350 ºC crystallite size grows up weakly with annealing temperature increasing (up to value D = 74.7 nm at T = 350 ºC). In this region difference of CSD size is slight for samples, quasi hydroextruded at nitrogen and near-ambient temperatures, but it is visible that at T = 350 ºC crystallites are bit smaller in QHE77K samples than in QHE300K ones. This deference becomes cardinal at higher pre-annealing temperatures; whereas the reverse trend is observed in samples extruded at nitrogen temperature – growth of pre-annealing temperature causes crystallite size decreasing (see Fig. 4, Table 2). So, minimal CSD size is obtained at T = 550 ºC (D = 54.2 nm), which less than appropriate value even for non-annealed quasi- hydroextruded sample (62 nm). In our opinion, so striking difference in crystallite size behavior can be related to the various mechanisms of titanium deformation at room and liquid nitrogen temperatures, as well as these mechanisms’ dependence on grain size. It is known [16], that in HCP titanium <а>-type slip is a dominant mode of plastic deformation at room temperature (usually slip take place on {10.0} first-order prism planes along the <a> direction). As temperature decreases the twinning mode considerably contributes to plastic deformation due to the limited number of slip systems in HCP metals and it can provide additional slip systems. It should be noted, that strength increases during the deformation twinning process due to the dislocation storage on the twins’ boundaries [17]. Twinning propensity decreases for coarse-grained FCC and HCP metals with the grain size decreasing during deformation [18, 19]. At the same time temperature threshold, from which the twinning contributes essentially to deformation process, declines. So according to authors [20], during the deformation at LNT critical grain size, above which the twinning mechanism activates, is equal approximately 2 μm for titanium. (It should be kept in mind that increase of material purity promotes twinnability). As it shown earlier [21], investigated in this work titanium after SPD (compression-extrusion + wire-drawing) has ultrafine- grained or sub-microcrystalline structure (average grain size is about 150 nm). Annealing at temperatures till 300 ºC practically doesn’t influence the grain size. After the annealing at 350 ºC bimodal structure with average grain sizes of 150 nm and 0.6 μm forms in specimens (individual grains can reach larger size). Annealing at 450 and 550 ºC leads to the recrystallization process, thus microstructure with average grain size of 4 and 9 μm, respectively, is formed. Therefore, during the quasi-hydrostatic extrusion process of these samples at LNT twinning must be activated, especially in Ti, annealed at 550 ºC. Direct conformation of this fact is the effect of QHE temperature on texture of the specimens, pre-annealed at different temperatures (Table 3). It is obvious, that the deformation temperature practically doesn’t influence on the degree of the preferred orientations of sub-microcrystalline samples, obtained by SPD. Difference between r values for QHE77K and QHE300K samples increases with pre-annealing temperature growth. Less degree of texture of the samples after QHE77K is a consequence of twinning activation. During the twinning process grains fragmentation occurs and, therefore, different crystallographic orientations generates, providing specimens’ texture randomization. This process of intensive grain fragmentation is responsible for the crystallite size decreasing in the samples, pre-annealed at 550 ºC (see Fig. 4). From our point of view, observed crystallite size decreasing can explain non-monotonic microhardness and tensile strength dependencies of titanium after QHE77K on pre-annealing temperature, which can be observed in [12]. Based on the obtained results of the QHE temperature influence on CSD size and texture in SPD titanium, we can conclude the following. In HCP Ti twinning effect occurs during the SPD process of coarse-grained samples only and disappears in 98 ISSN 1562-6016. ВАНТ. 2015. №2(96) nanocrystalline and UFG state. This conclusion adjusts with the authors’ results [19], who also didn’t observe twinning effect in nanocrystalline titanium, which is inherent to FCC metals [22, 23]. Table 3 Quasi-hydrostatic extrusion temperature (RT and LNT) influence on degree of texture (%) of the titanium samples, annealed at different temperatures TQHE Tanneal,ºC 20 °C 350 °C 450 °C 550 °C LNT 72% 69% 58% 41% RT 71% 74% 67% 57% CONCLUSIONS Texture and micro-structural investigations of high- purity Ti, obtained by combination of SPD (compression-extrusion + wire-drawing), thermal treatment and quasi-hydrostatic extrusion at nitrogen (QHE77K) and room temperatures (QHE300K) were made using X-ray diffraction methods. It was established, that in the titanium after the SPD structure is formed, characterized by [10.0] axial texture presence. Crystallite size in this sample was D = 70.4 and 92.8 nm along the bar axis and in the cross-section, respectively. Value of microstrains was slightly higher in longitudinal section (<ε> = 4.96·10 -3 ) than in cross- section (<ε> = 3.03·10 -3 ). In the preliminary deformed non-annealed samples, obtained by QHE at room and nitrogen temperatures, structural state is formed, parameters of which are practically independent on the QHE deformation temperature (degree of texture is r ≈ 0.7 and CSD size is D ≈ 60 nm, value of microstrains is <ε> = 3.6…3.8∙10 -3 ). At the same time, QHE deformation temperature has significant influence on the structural parameters of the samples after SPD and following recrystallization annealing at 450 and 550 ºC. Quasi-hydrostatic extrusion at nitrogen temperature leads to more effective crystallite size grinding than the deformation at room temperature, especially in the coarse-grained samples. This is a consequence of the twinning activation at nitrogen temperature, which is an alternative deformation mechanism to dislocation slip. This assumption is confirmed by significant degree of texture decreasing in samples. REFERENCES 1. C.N. Elias, J.H.C. Lima, R. 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Ефимов Методами комбинированной интенсивной пластической деформации, термообработок и квазигидроэкструзии (КГЭ) при азотной и комнатной температурах получены объемные нанокристаллические образцы высокочистого титана. Исследования текстуры и микроструктурных параметров титана проводились методами рентгеновской дифрактометрии. Установлено влияние исходного структурного состояния образцов на деформационное поведение титана при КГЭ. КГЭ ультрамелкозернистых образцов приводит к формированию структуры, параметры которой практически не зависят от температуры КГЭ. Значительные отличия наблюдаются в случае предварительно отожженных крупнозернистых образцов. Это связано с различными механизмами деформации (скольжением дислокаций и двойникованием), которые активируются в процессе КГЭ при комнатной и азотной температурах. ДОСЛІДЖЕННЯ СТРУКТУРНОГО СТАНУ ВИСОКОЧИСТОГО ТИТАНУ ПІСЛЯ ІНТЕНСИВНОЇ ПЛАСТИЧНОЇ ДЕФОРМАЦІЇ І КРИОГЕННОЇ КВАЗІГІДРОЕКСТРУЗІЇ МЕТОДАМИ РЕНТГЕНІВСЬКОЇ ДИФРАКЦІЇ О.Є. Боклаг, І.В. Колодій, М.А. Тихоновський, І.Ф. Кисляк, П.О. Хаймович, О.А. Єфімов Методами комбінованої інтенсивної пластичної деформації, термообробок та квазігідроекструзії (КГЕ) при азотній та кімнатній температурах отримано нанокристалічні об’ємні зразки високочистого титану. Дослідження текстури та мікроструктури титану проводилися методами рентгенівської дифракції. Встановлено вплив початкового структурного стану зразків на деформаційну поведінку титану при КГЕ. КГЕ ультрадрібнозернистих зразків призводить до формування структури з параметрами, незалежними від температури КГЕ. Значні відмінності спостерігаються у випадку попередньо відпалених крупнозернистих зразків. Це пов’язано з різними механізмами деформації (ковзанням дислокацій та двійнікуванням), що активуються під час КГЕ при кімнатній та азотній температурах.

Structural state study of high-purity titanium after severe plastic deformation and cryogenic quasi-hydrostatic extrusion by XRD methods

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