Effect of graphite addition on impregnated diamond bit properties
Graphite was used as a solid lubricant to reduce thermal damage in diamond bit when drilling without coolant. Graphite was added to the bit matrix material to reduce friction coefficient and heat. The influence of content, granularity, and surface metallization of graphite on the mechanical property...
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Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України
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nasplib_isofts_kiev_ua-123456789-1673172025-02-23T20:23:32Z Effect of graphite addition on impregnated diamond bit properties Lanlan Xie Liyi Chen Xiaolin Huang Одержання, структура, властивості Graphite was used as a solid lubricant to reduce thermal damage in diamond bit when drilling without coolant. Graphite was added to the bit matrix material to reduce friction coefficient and heat. The influence of content, granularity, and surface metallization of graphite on the mechanical property and dry friction properties of the matrix, as well as the effect of diamond lifetime in the working layer were studied. Results showed that the hardness, bending strength, and friction coefficient of matrix gradually decreased with the increase in graphite concentration. Для зменшення термічного пошкодження алмазного інструмента при бурінні без охолоджуючої рідини в якості твердого мастила використовували графіт, його додавали до матеріалу матриці інструмента для зменшення коефіцієнта тертя і виділення тепла. Досліджено вплив вмісту, зернистості і металізації поверхні графіту на механічні властивості та умови сухого тертя матриці, а також часу утримання алмазу в робочому шарі. Результати показали, що твердість, міцність на вигин і коефіцієнт тертя матриці поступово зменшуються зі збільшенням концентрації графіту. Для уменьшения термического повреждения алмазного инструмента при бурении без охлаждающей жидкости в качестве твердой смазки использовали графит, его добавляли к материалу матрицы инструмента для уменьшения коэффициента трения и выделение тепла. Исследовано влияние содержания, зернистости и металлизации поверхности графита на механические свойства и условия сухого трения матрицы, а также времени удержания алмаза в рабочем слое. Результаты показали, что твердость, прочность на изгиб и коэффициент трения матрицы постепенно уменьшаются с увеличением концентрации графита. 2019 Article Effect of graphite addition on impregnated diamond bit properties / Lanlan Xie, Liyi Chen, Xiaolin Huang // Надтверді матеріали. — 2019. — № 4 (240). — С. 33-45. — Бібліогр.: 41 назв. — англ. 0203-3119 https://nasplib.isofts.kiev.ua/handle/123456789/167317 621.892.7:622.24.05 en Сверхтвердые материалы application/pdf Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України |
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Одержання, структура, властивості Одержання, структура, властивості |
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Одержання, структура, властивості Одержання, структура, властивості Lanlan Xie Liyi Chen Xiaolin Huang Effect of graphite addition on impregnated diamond bit properties Сверхтвердые материалы |
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Graphite was used as a solid lubricant to reduce thermal damage in diamond bit when drilling without coolant. Graphite was added to the bit matrix material to reduce friction coefficient and heat. The influence of content, granularity, and surface metallization of graphite on the mechanical property and dry friction properties of the matrix, as well as the effect of diamond lifetime in the working layer were studied. Results showed that the hardness, bending strength, and friction coefficient of matrix gradually decreased with the increase in graphite concentration. |
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Lanlan Xie Liyi Chen Xiaolin Huang |
| author_facet |
Lanlan Xie Liyi Chen Xiaolin Huang |
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Lanlan Xie |
| title |
Effect of graphite addition on impregnated diamond bit properties |
| title_short |
Effect of graphite addition on impregnated diamond bit properties |
| title_full |
Effect of graphite addition on impregnated diamond bit properties |
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Effect of graphite addition on impregnated diamond bit properties |
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Effect of graphite addition on impregnated diamond bit properties |
| title_sort |
effect of graphite addition on impregnated diamond bit properties |
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Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України |
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Одержання, структура, властивості |
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Effect of graphite addition on impregnated diamond bit properties / Lanlan Xie, Liyi Chen, Xiaolin Huang // Надтверді матеріали. — 2019. — № 4 (240). — С. 33-45. — Бібліогр.: 41 назв. — англ. |
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Сверхтвердые материалы |
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AT lanlanxie effectofgraphiteadditiononimpregnateddiamondbitproperties AT liyichen effectofgraphiteadditiononimpregnateddiamondbitproperties AT xiaolinhuang effectofgraphiteadditiononimpregnateddiamondbitproperties |
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2025-11-25T04:47:47Z |
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2025-11-25T04:47:47Z |
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1849736371921485824 |
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ISSN 0203-3119. Надтверді матеріали, 2019, № 4 33
UCD 621.892.7:622.24.05
Lanlan Xie 1, *, Liyi Chen 1, Xiaolin Huang 2
1State Key Laboratory of Geohazard Prevention and Geoenvironment
Protection, College of Environment and Civil Engineering,
Chengdu University of Technology, Chengdu, China
2Institute of Exploration Technology, Chinese Academy
of Geological Sciences, Chengdu, China
*xllcdut@foxmail.com
Effect of graphite addition on impregnated
diamond bit properties
Graphite was used as a solid lubricant to reduce thermal damage in
diamond bit when drilling without coolant. Graphite was added to the bit matrix
material to reduce friction coefficient and heat. The influence of content, granularity,
and surface metallization of graphite on the mechanical property and dry friction
properties of the matrix, as well as the effect of diamond lifetime in the working layer
were studied. Results showed that the hardness, bending strength, and friction
coefficient of matrix gradually decreased with the increase in graphite concentration.
Meanwhile, the abrasion loss decreased first and then increased, and the lifetime of
diamond in the working layer gradually increased. With the decrease in graphite
granularity, the bending strength and friction coefficient of matrix gradually
decreased, whereas the hardness, abrasion loss of matrix, and diamond lifetime in the
working layer gradually increased. After surface metallization of graphite, the
hardness, bending strength, friction coefficient, and abrasion loss of matrix increased,
whereas the lifetime of diamond in the working layer decreased. This study lays a
foundation for drilling without water.
Keywords: graphite, diamond bit, mechanical property, dry friction
properties, lifetime of diamond.
INTRODUCTION
A long-term prospecting practice indicated that diamond drilling is
efficient [1]. However, bit burnt accidents frequently occur due to the thermal damage
of diamond, which seriously affects geological exploration. In the drilling process, the
reduction of diamond heat damage is achieved by the cooling action and lubrication
effect of drilling fluid [2]. However, cooling the diamond bit is difficult in areas
without water, such in the dry regions of western China or in the outer space [3].
Graphite is widely applied as a solid lubricant in grinding because of its re-
markable lubrication effect. Whether added to a grinding wheel or composite
material, or used as a coating, graphite could reduce the friction factor of the
friction pairs [4–9]. And the content and granularity of solid lubricant influence the
dry friction properties of composites. The influence on NiCr–Cr2O3–Ag
composites, Cu-based P/M friction composites and graphite – PTFE dry lubrication
system is known [10–12]. When graphite is in the soft phase form in composite
materials, the dry tribological properties of composites are improved; however,
their mechanical properties, such as hardness and bending strength, are reduced
[3]. In the present study, graphite particles were coated with nickel by
© LANLAN XIE, LIYI CHEN, XIAOLIN HUANG, 2019
http://stmj.org.ua 34
electroplating with optimum technology, as described previously [13]. The nickel–
coated graphite particles were then added to the bit matrix to improve the
compatibility of graphite and matrix material.
Then, graphite is added to the working layer of bit to make graphite–diamond
composite material, and its structure and properties are studied. A lot of works
have been devoted to the study of the properties of composite diamond-containing
materials based on metal matrices containing iron, copper, nickel, tin, tungsten
carbide, cobalt, obtained by powder metallurgy methods. The most significant
scientific and practical results on the formation of the structure of such composites
with improved mechanical characteristics were obtained in [14–23]. The positive
influence of chromium diboride (CrB2) [24–27], tungsten carbide (WC) [28] and
vanadium nitride [29] on the structure and properties of composites is known. The
properties of these composites are determined by the composition, structure and
morphology, which, in turn, depend on the properties of their constituents, methods
and modes of sintering. Some important properties of composites vary depending
on the force parameters of rock failure [30], contact temperatures [31–34], stress-
strain state of the matrix [35, 36], as well as placement of composites on the tool
working surface [37]. Nevertheless, in these works the influence of the graphite
addition on the mechanical and tribological properties of the composites under
consideration is not taken into account.
This study mainly investigated the influence of content, granularity, and surface
metallization of graphite on the mechanical properties (i.e., hardness and bending
strength, dry friction and wear properties) of the composite material, and lifetime
of diamond in the working layer.
EXPERIMENTAL
The basic formula of the matrix was 18 wt % WC, 9 wt % nickel, 3 wt % cobalt,
5 wt % manganese, 35 wt % bronze (663), and 30 wt % Fe. The basic formula of the
working layer was unchanged, in which 20 vol % (8.6 wt %) diamond was added,
and particle size of the diamond was 50/60 mesh. Samples were prepared by hot
pressing–sintering method under the following conditions: 945 °С sintering tempera-
ture, 15 MPa pressure, and 3 min holding time. The sample design is shown in Table.
Sample design table
Sample
of matrix
Granularity
of graphite
(mesh)
Content
of graphite
(wt %)
Weight gain
of graphite after
metallization (wt %)
Sample
of working layer
(with diamond)
1 0 1′
2 100/120 0.6 0 2′
3 100/120 1.2 0 3′
4 100/120 1.8 0 4′
5 100/120 2.4 0 5′
6 40/60 1.2 0 6′
7 60/80 1.2 0 7′
8 80/100 1.2 0 8′
9 (with nickel-
plated graphite)
80/100 1.2 36.36 9′
10 (with nickel-
plated graphite)
80/100 1.2 45.35 10′
ISSN 0203-3119. Надтверді матеріали, 2019, № 4 35
Three-point bending method was adopted to test the bending strength of the
sample on the WE-30 hydraulic universal material test machine, and the pressure–
velocity was 100 N/s. A sample of every formula was tested for five times, of
which the average was calculated as bending strength. An HR-150A Rockwell
apparatus was used for hardness test, and the sample of every formula was broken
down into three pieces. Every sample was tested at six points, and then the average
value of the 18 test points was obtained as the hardness.
Friction and wear between the sample and granite were analyzed by the MG-
2000A friction and wear test machine, the contact form is plate-on-plate, and the
type of relative motion is circled. The pressure was 2 MPa, the rotation rate was
0.94 m/s, and the time of dry friction was 10 min, the total distance of the relative
motion was 565 m. The wear resistance was measured by the quality loss before
and after the friction and wear test. The sample was washed by distilled water, dry
by oven, and weigh by the electronic scale with accuracy of 0.001g. The friction
coefficient was calculated by using the software of the MG-2000A friction and
wear test machine. There is initial run-in period in the friction coefficient curve,
and then become stability. Friction coefficient of a sample is the average of the
steady-state sliding period. And the calculation formula is as follows:
n
RN
M
=μ , (1)
where μ is friction coefficient; M is friction torque, N⋅m; N is positive pressure, N;
R is radius of rotation, which is 0.03m; and n is sampling number of the steady-
state sliding period.
The sample of every formula was broken down into three pieces, and the value
is the average of the three.
The interface between the graphite particles and matrix on the fracture surface
of the sample after bending strength test and the surface morphology of the sample
after friction and wear test were observed by Quanta 200 type environmental
scanning electron microscope. After friction and wear test, the surface of the
sample was analyzed by energy spectrum.
RESULTS AND DISCUSSION
Binding properties of graphite and matrix
Figure 1 is the SEM image of the interface between graphite and matrix. Fig-
ure 1, a shows the SEM image of sample 8 with pure graphite, while Fig. 1, b
shows the SEM image of sample 10 with nickel-plated graphite. A large space
between graphite and matrix is observed, and the anchoring effect between them is
very weak in sample 8. No reaction, dissolution, or wettability was observed
between graphite and matrix. This finding can be attributed to the relatively stable
chemical properties of graphite and the absence of metallurgical effect on the
matrix material at sintering temperature. In addition, the interface energy of
graphite is relatively low; thus, wetting by matrix materials at high sintering
temperature is difficult. However, no evident gap is observed between the nickel-
plated graphite particles and the matrix material in sample 10, which indicates that
their interface bonding is close.
After plating, nickel can be evenly distributed over the entire surface of the
graphite particles, even in the dent on the surface of graphite particles. The
mechanical interlock function between the nickel plating layer and graphite is
http://stmj.org.ua 36
strong [13]. Furthermore, after hot pressing sintering process, graphite particles can
be partly dissolved in the crystal lattice of nickel in the form of elements due to the
high temperature. This process turns the simple mechanical interlock between
nickel and graphite into a solid solution bond with gradient variation, and the
interface between the two is strong [38]. The nickel layer and the copper in the
matrix are mutually illimitably soluble and form a solid solution with face-centered
cubic structure. A two-layer interface model is formed between graphite and matrix
materials, namely, graphite–nickel matrix. Each layer of the interface is relatively
solid, and the graphite is tightly bound to the matrix by nickel.
a
b
Fig. 1. SEM images of the interface between graphite and matrix: sample 8 (a), 10 (b); ×500.
Effect of graphite on the physical properties of the matrix
The values for samples 1–5 in Fig. 2 show that the Rockwell hardness and
bending strength of the matrix continuously decreased with the increase in graphite
content. Figure 1, a shows that the binding force between graphite powder and the
matrix is very weak. In addition, the graphite particles have low strength and are in
the soft phase form in the matrix which can lead to cracks or pores, thus reducing
the hardness and strength of the matrix [39].
84
88
92
96
100
104
0
200
400
600
800
1000
1200
1 2 3 4 5 6 7 8 9 10
H
ar
dn
es
s,
H
R
B
B
en
di
n
g
st
re
n
gt
h,
M
P
a
Sample number
1
2
Fig. 2. Hardness (1) and bending strength (2) of matrix.
The values for samples 3 and 6–8 shown in Fig. 2 demonstrate that with the de-
crease in graphite granularity, the Rockwell hardness of the sample gradually in-
creases, whereas the bending strength gradually decreases. The Rockwell hardness
ISSN 0203-3119. Надтверді матеріали, 2019, № 4 37
is obtained according to the indentation depth in the surface of the sample.
Research shows that the indentation range is approximately 10 times more than the
indentation depth [39]. If a soft phase exists in the indentation range, then the
indentation depth will increase, that is, the hardness decreases. Large graphite
particles in the indentation range lead to large indentation depth and low Rockwell
hardness. Therefore, with the decrease in graphite granularity, the hardness of the
sample is increased. Graphite brings pores or cracks into the matrix, which not only
cause stress concentration but also reduce the effective force area of sample
resistance to external force, thus reducing the stress that the sample can bear. When
the graphite content is certain, a small granularity leads to additional cracks and
pores; a small effective force area of the sample resistance to external force results
in low bending strength.
The values for samples 8–10 in Fig. 2 show that the hardness and bending
strength of the sample increase after graphite surface metallization. Graphite is
added to the diamond bit matrix to create self-lubricating composite materials, the
overall performance of which is affected by the poor physical and chemical
compatibility between graphite and matrix materials. In the process of sintering
pure graphite with matrix material, the matrix particles are only softened and
partially melted. Therefore, completely covering the graphite particles with low
surface energy is difficult. The interface structure of the two is loose, and the
interfacial bonding strength is low; hence, the interface can be easily cracked and
expanded by external forces, which leads to the decrease in sample strength. After
surface metallization, physical and chemical compatibility between graphite and
matrix improved, and interfacial bonding strength increased; thus, the overall
performance of the self-lubricating composite material improved. That is, the
surface metallization of graphite improved the bending strength of the composite
material. Increasing the interfacial bonding strength between graphite and matrix
barely affected composite hardness but reduced the gap between nickel-plated
graphite and matrix; that is, pore volume in the matrix decreased and hardness
increased.
Self-lubricating mechanism of graphite and matrix composites
After friction and wear test of samples 2–10 and granite, a ring of black circle is
observed on the granite surface. This black circle is the running track of the
sample, and the tactile feeling is greasy, thereby indicating the presence of graphite
coating. A considerable amount of friction heat is produced when the composite
material and granite wears and tears each other, and the coefficient of thermal
expansion of graphite and matrix are very different. Consequently, graphite is
extruded by thermal stress and coats the friction surface. In addition, during the
friction, graphite encounters friction and extrusion, which can make graphite fall
off from the composite material and coats on the friction surface. When a
considerable amount of graphite is coated on the friction surface, a layer of
lubricating film with a low shear modulus is formed [40].
From the energy spectrum analysis of the friction surface of sample 5 in Fig. 3,
a small amount of graphite is present on the sample friction surface, approximately
13–15 %. This finding indicates that the combination of graphite lubricating film
and matrix material is poor, but graphite combination with granite is excellent.
Therefore, when the lubricating film is formed on the granite surface, only a slight
graphite abrasion exists on the matrix surface. When a complete graphite lubricant
film is formed on the granite surface, the contact state of the friction pair turns
immediate contact between local minor region of matrix and granite into contact
http://stmj.org.ua 38
between matrix and soft and thin graphite lubricant film. The actual contact area of
the friction pair increases and the pressure decreases; hence, the matrix and the
granite only demonstrate elastic deformation, but no abrasive or adhesive wear is
present. Graphite has a lamellar structure, and its intermolecular bonding force is
very small. The shear strength of graphite is very low; therefore, slipping easily
occurs. Consequently, the graphite can slip between the friction pair, and the
sliding deformation occurs nearly exclusively within the graphite lubrication film;
hence, the deformation of the matrix material is very small. At this point, the wear
of matrix and granite is very slight; thus, graphite is anti-friction. When the
graphite content is small, it can only form an incomplete lubricating film or a small
graphite grinding dust on the friction surface, which also possesses anti-wear
performance.
0 1 2 3 4 5 6 7 8 9 10 11 12
0.4
0.8
1.1
1.5
KCnt
Element wt % at %
C K 13.44 29
O K 20.42 33.08
Si K 16.87 15.56
K K 1.88 1.24
Ca K 0.68 0.44
Mn K 2.97 1.4
Fe K 22.5 10.44
Ni K 4.96 2.19
Cu K 16.29 6.64
Fig. 3. Energy spectrum analysis of the friction surface of sample 5.
When friction and wear test of the sample are worn, the graphite in the sample
is extruded by thermal and mechanical stresses and is then coated on the friction
surface. Consequently, graphite lubricating film is formed, and the friction
coefficient of the friction pair is reduced. When the lubrication film is destroyed,
the friction coefficient rises again, and the sample continues to be worn; therefore,
the new graphite is extruded to form a new lubricating film. During the entire
process of the friction and wear test, the formation, breakage, shedding, and
regeneration of the graphite lubrication film are continuously circulated.
Effect of graphite on the dry tribological properties of the matrix
The values for samples 1–5 in Fig. 4 show that the friction coefficient of
friction pairs decreases with increase in graphite in the matrix, whereas the
abrasion loss of the sample decreases first and then increases. When the graphite
content in the sample is low, the lubrication film formed on the friction surface is
incomplete, and the newly formed lubrication film cannot catch up with the
shedding of the old one. Friction and wear still occur between the sample and
granite; hence, the friction coefficient average of the entire process and the
abrasion loss of the sample are large. When the graphite content in the sample is
moderate, the lubrication film formed on the friction surface is complete, and the
newly formed lubrication film catches up with the shedding of the old one. The
entire friction and wear process always occurs within the graphite lubricant film;
hence, the friction coefficient average and the abrasion loss of the sample decrease.
ISSN 0203-3119. Надтверді матеріали, 2019, № 4 39
When the graphite content in the sample is extremely large, the friction and wear
also occur within the graphite lubricant film; hence, the friction coefficient average
is slightly reduced. However, the holes due to graphite loss increase; therefore, the
actual contact area between granite and matrix decreases, and the intensity of
pressure increases, thereby consequently increasing the abrasion loss of the sample.
0
0.04
0.08
0.12
0.16
0.20
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5 6 7 8 9 10
A
br
as
io
n
lo
ss
, g
F
ri
ct
io
n
co
ef
fi
ci
en
t
Sample number
1
2
Fig. 4. Friction coefficient (1) and abrasion loss (2) of the matrix.
The values for samples 6–8 and 3 in Fig. 4 show that with the decrease in
graphite granularity, the friction coefficient of friction pair gradually decreases,
whereas the abrasion loss of matrix increases. This finding can be attributed to the
smaller density graphite than that of matrix, thereby making it difficult to realize
uniform material mixing. When the graphite content in the matrix is certain, the
small graphite particle leads to uniform graphite distribution in the matrix; forming
a complete lubrication film is easy when the friction coefficient is small. However,
when the graphite particles are extremely small, many holes due to graphite loss
uniformly distribute on the matrix surface, and the intensity of pressure increases,
thus increasing the abrasion loss of the sample.
The values for samples 8–10 in Fig. 4 show that the friction coefficient of
friction pair and the abrasion loss of matrix both increase after surface
metallization of graphite. This result can be attributed to the strong interface force
between matrix and nickel-plated graphite. Moreover, falling off from the matrix is
difficult for graphite. Consequently, the lubricating film formed in the friction pair
surface is incomplete, and the friction coefficient of friction pair and the abrasion
loss of matrix are both large.
Wear morphology analysis of the sample
Figure 5 shows the SEM figure of the wear morphology of samples 1 and 5. In
Fig. 5, the main wear form of sample 1 is adhesive wear, and the main wear form
of sample 5 is abrasive wear. The surface temperature of sample 1 without graphite
sharply increases during the process of friction with the granite, and severe plastic
deformation occurs on the matrix. The matrix is then daubed by the friction force.
Graphite falls off from the matrix when the sample 5 with 10 vol % of graphite rub
and wear with granite, and then become into lubricating film on the surface of the
friction pair. Consequently, the friction coefficient of the friction pair decreases,
and the increase in friction surface temperature is controlled. Therefore, plastic
deformation of the matrix is small, and the main wear formed is abrasive wear due
to hard particle in granite powder.
http://stmj.org.ua 40
a
b
Fig. 5. SEM images of the sample wear morphology: sample 1 (a), 5 (b); ×300.
Effect of graphite on the dry tribological properties of the working layer
Figure 6 is the friction coefficient curve recorded by the software of the testing
machine in the process of friction and wear test. The x-coordinate is the sampling
point, and the y-coordinate is friction coefficient. It shows that the friction
coefficient is large and repeatedly changes at first; the friction coefficient then
stabilizes and become small after certain period. Figure 7 shows the scanning
electron micrograph of the diamond on the friction surface of the working layer
after the friction and wear test. From the figure, numerous grooves and cracks can
be observed on the diamond surface, and the diamond is broken and dull, thereby
indicating that the diamond completely failed. At first, the diamonds appear and
break the granite; hence, the friction coefficient significantly fluctuates.
Simultaneously, the temperature of the friction interface sharply increases, and the
performance of diamond sharply decreases, thereby producing hard particle in
granite-powder groove on the diamond surface. Cracks perpendicular to the friction
direction occur on the diamond surface by tensile stress. The diamonds are then
broken and become dull by normal load and friction, and severe thermal injury
finally occurs. Owing to the low abrasiveness of granite, the abrasion loss of matrix
is small, and the damaged diamond cannot fall off but still remained on the sample
friction surface. In this way, friction and wear only occur between a few diamonds
and granite; therefore, the contact area and friction coefficient are considerably
reduced.
Fig. 6. Friction coefficient curve of working layer sample.
ISSN 0203-3119. Надтверді матеріали, 2019, № 4 41
Fig. 7. SEM image of the failure diamond.
In the initial stage of the friction and wear test, the diamond breaks the granite,
and the resulting granite powder wears the matrix. Consequently, the graphite in
the matrix is extruded by thermal and mechanical stresses. The binding force
between graphite and matrix materials is weak, and the surface of granite is
continuously broken by diamond. Therefore, forming a lubricating film on the
surface of either is difficult for graphite. Moreover, graphite can form a lubricating
film on the diamond surface [41] and convert the contact between diamond and
granite to the contact between lubrication film and granite. When the graphite
lubrication film is damaged, the diamond continues to contact the granite. The
addition of graphite can prolong the time of diamond cutting granite, namely the
life of diamond.
The diamond lifetime of every sample can be calculated by the curve diagram
of its friction coefficient. As shown in Fig. 6, friction coefficient is large and
repeatedly changes from 0 to 600 sampling point, which is the period diamond cut
granite, namely the life of diamond. The calculation formula is as follows:
t =
N
nT
, (2)
where t is the life of diamond, min; n is the number of sampling points during dia-
mond cutting granite; T is the testing time of the friction and wear test, which is 10
min; and N is the total number of sampling points during the friction and wear test.
The experimental results are shown in Fig. 8, with the increase in graphite con-
tent, the graphite lubricant film on the diamond surface is complete, and its
regeneration speed increases. Thus, the chances of wear between diamond lifetime
and granite are reduced, and the lifetime of diamond increases. With the decrease
in graphite granularity, the graphite distribution in the sample is uniform, and the
graphite lubrication film on the diamond surface is complete, thereby improving
the lifetime of diamond. The force between matrix and nickel-plated graphite is
strong, and falling off from the matrix surface is difficult for graphite.
Consequently, the lubricating film formed on the surface of the diamond is
incomplete, and the lifetime of diamond is shortened.
CONCLUSIONS
The results of this study reveal that the addition of graphite improved the dry
friction properties of the bit and the lifetime of diamond in the working layer but
http://stmj.org.ua 42
reduced the hardness and bending strength of the matrix. With the increase in
graphite, the hardness, bending strength, and friction coefficient of matrix
gradually decreased, but its abrasion loss decreased first and then increased. By
contrast, the lifetime of diamond in the working layer gradually increased. With the
decrease in graphite granularity, the bending strength and friction coefficient of
matrix gradually decreased, whereas the hardness, abrasion loss of matrix, and the
lifetime of diamond in the working layer gradually increased. After surface
metallization of graphite, the hardness, bending strength, friction coefficient, and
abrasion loss of matrix were increased, whereas the lifetime of diamond in the
working layer was decreased.
0
1
2
3
4
5
6
1 2 3 4 5 6 7 8 9 10
L
if
e
of
d
ia
m
on
d,
m
in
Sample number
Fig. 8. Diamond lifetime of working layer.
The properties of the diamond bit, including hardness, bending strength, abra-
sion resistance, friction coefficient, etc., should be matched with the strata drilled.
In this study, granite was selected as the drilling object. The optimal method was to
add 2.4 wt % nickel-plated graphite with a particle size of 100/120 mesh in dia-
mond bit. With this method, hardness and bending strength of diamond bit reduced
a little, but dry friction properties of the diamond bit improved, and the life of
diamond improved remarkably.
Для зменшення термічного пошкодження алмазного інструмента при
бурінні без охолоджуючої рідини в якості твердого мастила використовували графіт,
його додавали до матеріалу матриці інструмента для зменшення коефіцієнта тертя і
виділення тепла. Досліджено вплив вмісту, зернистості і металізації поверхні графіту на
механічні властивості та умови сухого тертя матриці, а також часу утримання алмазу
в робочому шарі. Результати показали, що твердість, міцність на вигин і коефіцієнт
тертя матриці поступово зменшуються зі збільшенням концентрації графіту. Проте
втрати від дії тертя спочатку зменшувалися, а потім збільшувалися, а час утримання
алмазу в робочому шарі поступово збільшувався. Зі зменшенням гранулярності графіту
міцність на вигин і коефіцієнт тертя матриці поступово зменшувалися, тоді як твер-
дість, втрати від тертя матриці і час утримання алмазу в робочому шарі поступово
збільшувалися. Після металізації поверхні графіту твердість, міцність на вигин, коефіці-
єнт тертя та втрати від тертя матриці зростали, а час утримання алмазу в робочому
шарі зменшувався. Це дослідження закладає основу для буріння без використання води.
Ключові слова: графіт, ромб, механічні властивості, властивості су-
хого тертя, час утримання алмазу.
ISSN 0203-3119. Надтверді матеріали, 2019, № 4 43
Для уменьшения термического повреждения алмазного инструмента
при бурении без охлаждающей жидкости в качестве твердой смазки использовали гра-
фит, его добавляли к материалу матрицы инструмента для уменьшения коэффициента
трения и выделение тепла. Исследовано влияние содержания, зернистости и металлиза-
ции поверхности графита на механические свойства и условия сухого трения матрицы, а
также времени удержания алмаза в рабочем слое. Результаты показали, что твердость,
прочность на изгиб и коэффициент трения матрицы постепенно уменьшаются с увели-
чением концентрации графита. Однако потери от действия трения сначала уменьша-
лись, а затем увеличивались, а время удержания алмаза в рабочем слое постепенно увели-
чивалось. С уменьшением гранулярности графита прочность на изгиб и коэффициент
трения матрицы постепенно уменьшались, тогда как твердость, потери от трения
матрицы и время удержания алмаза в рабочем слое постепенно увеличивались. После
металлизации поверхности графита твердость, прочность на изгиб, коэффициент тре-
ния и потери от трения матрицы росли, а время удержания алмаза в рабочем слое
уменьшался. Это исследование закладывает основу для бурения без использования воды.
Ключевые слова: графит, ромб, механические свойства, свойства сухо-
го трения, время удержания алмаза.
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Received 17.05.18
Revised 25.06.18
Accepted 25.06.18
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