Vacuum tribological properties and impact toughness of polycrystalline diamond based on titanium-coated diamond particle

Vacuum tribological properties and impact toughness of polycrystalline diamond based on titanium-coated diamond particle

Journal Pre-proof Vacuum tribological properties and impact toughness of polycrystalline diamond based on titanium-coated diamond particle Haichao Zh...

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Journal Pre-proof Vacuum tribological properties and impact toughness of polycrystalline diamond based on titanium-coated diamond particle

Haichao Zhang, Wen Yue, Xiaohua Sha, Wenbo Qin, Chengbiao Wang PII:

S0925-9635(19)30919-7

DOI:

https://doi.org/10.1016/j.diamond.2020.107712

Reference:

DIAMAT 107712

To appear in:

Diamond & Related Materials

Received date:

27 November 2019

Revised date:

12 January 2020

Accepted date:

13 January 2020

Please cite this article as: H. Zhang, W. Yue, X. Sha, et al., Vacuum tribological properties and impact toughness of polycrystalline diamond based on titanium-coated diamond particle, Diamond & Related Materials (2020), https://doi.org/10.1016/ j.diamond.2020.107712

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© 2020 Published by Elsevier.

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Vacuum

tribological

properties

and

impact

toughness

of

polycrystalline diamond based on titanium-coated diamond particle Haichao Zhang 1, Wen Yue 1, 2*, Xiaohua Sha1, 4, Wenbo Qin 1, Chengbiao Wang 1, 3* (1. School of Engineering and Technology, China University of Geosciences (Beijing), Beijing100083, China;

451283, China;

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2. Zhengzhou Institute, China University of Geosciences (Beijing), Zhengzhou

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3. Zhengzhou Institute of Multipurpose Utilization of Mineral Resources, Chinese

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Academy of Geological Sciences, Zhengzhou, 450006, China;

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4. Ningxia Vocational Technical College of Industry and Commerce, Ningxia 750021,

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China)

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Corresponding Author: *W. Yue, E-mail: [email protected], [email protected];

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*C. B. Wang, E-mail: [email protected]

Abstract: In this work, the diamond particles were deposited with titanium (Ti) by the magnetron sputtering, and the polycrystalline diamond compact synthesized by the Ti-coated diamond particles (Ti-PDC) was prepared by high temperature and high pressure (HTHP) sintering method. The scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) results show that the Ti coating uniformly distributes on the surface of diamond particles. The results of X-ray diffraction (XRD) indicate that the TiC phase has been produced during the sintering process. The impact toughness of the Ti-PDC is higher than that of the pristine polycrystalline

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diamond compact (P-PDC). In addition, the friction coefficients of Ti-PDC under different vacuum conditions reveal lower values than those of the P-PDC. A less number of exfoliated pits can be observed on the worn Ti-PDC surface. The improved impact toughness and vacuum friction performance of Ti-PDC may be attributed to the enhanced bonding strength between diamond particles, which is induced by the

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TiC phase. In brief, the Ti-coated diamond particles can improve the bonding strength between diamond grains and thus yield to an enhanced service performance of the

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PDC.

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Key words: Polycrystalline diamond compact; Ti-coated diamond particle; Vacuum

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tribological properties; Impact toughness; Bonding strength

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1. Introduction

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The polycrystalline diamond compact (PDC) is a kind of diamond composite sintered under high temperature and high pressure (HTHP) by diamond particles and

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metal or metal alloy, which acts as a bonding material [1-4]. Generally, the PDC tools are used in the geological drilling areas, high-speed cutting and wire drawing dies due to their high hardness and wear resistance, great thermal stability and distinguished toughness [5-8]. However, the high speed, high temperature and high load situations usually accompany by the remove of the surface metallic inclusions and a drop of diamond grains due to poor bonding, which leads to the substantial failure of PDC tools [9-10]. For the sintered PDC, the cobalt is usually used as a binder. The carbon preferentially grows at the grain contact surface under the catalytic action of cobalt

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[11-12]. During the sintering process, the strong diamond-diamond (D-D) bonds form between the diamond grains due to the process of graphitization dissolution and recrystallization. However, the catalyst cobalt and a large number of defects, such as non-coherent grain boundaries, dislocations, point defects and impurities, etc., discontinuously distribute at the boundaries of diamond grains [13-15]. In this case,

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the interface between diamond and cobalt is always a weak region in PDC, which is prone to crack under the high load and impact force. Studies have shown that the

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boundary of diamond grain is the weak areas of crack propagation [16]. The cracks

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will expand along the boundary of diamond grain or even extend into the grain and

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induce the fracture and spalling of the diamond grains, thereby causing the

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intergranular fractures. A way that the Ti, Mo and Cu are coated on the diamond

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surface, which enhances the interface bonding force by the formation of chemical bonds, has been reported [17-18]. Wang et al. [19] prepared a Ti coating on the

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surface of diamond particles by a vacuum slow vapor deposition method, and found the compression fracture strength of Ti-coated diamond increases by 20% and the oxidation temperature reaches 1024℃. Anne-Kathrin [20] et al. reported that the diamond-silicon nitride composite material, which was prepared with the diamond particles coated by SiC, has a stronger interface force between the diamond grain and substrate. Moreover, the wear rate has been significantly reduced due to the strong interface, which results in a less exfoliation of the diamond grains. Therefore, the deposited coating on the diamond particles is of great benefit to improve their interface bonding. However, most of these studies have focused on the thermal and

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mechanical properties of diamond materials. Research on vacuum tribological properties of diamond particles after sintering is incomplete. In this work, the impact toughness of pristine polycrystalline diamond compact (P-PDC) and Ti-coated polycrystalline diamond compact (Ti-PDC) was compared. The tribological experiments under different vacuum conditions were performed to

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further analysis the bonding state in the PDC.

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2. Experimental details 2.1 Experimental sample preparation

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The diamond particles used in the Ti-PDC was subjected to a vacuum magnetron

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sputtering coating method. A coating with uniform and controllable thickness can be

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obtained. A pure titanium target (99.99%) was used for magnetron sputtering at a

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pressure of 0.4 Pa with a distance of 15 cm between the titanium target and the substrate. The sputtering power and discharging current for the titanium target were

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designed as 150 W and 0.5 A, respectively. In order to ensure the continuous of coating rolling diamond particles, the substrate holder maintains ultrasonic vibration during the sputtering process. Before the deposition, the diamond particles were boiled in NaOH and HNO3 solutions for 30 min, respectively, and rinsed with distilled water for 2-3 times for a surface purification treatment. The P-PDC and Ti-PDC in this work were provided by Zhongnan Diamond Co., Ltd. The sample was constituted by an upper layer of polycrystalline diamond compact and a WC-Co cemented carbide (16wt.% Co)substrate. The diamond particles with a median diameter of 25 μm were used in the sintering process. The

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sintered PDC has a diameter of 45 mm and a thickness of 3.2 mm. Its surface roughness is about 4 nm after the polishing process. 2.2 Impact toughness tests In order to measure the impact toughness of test samples, the Ti-PDC and P-PDC were subjected to the impact tests using a pendulum impact tester (PTM1200-A1).

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The experiments were performed at room temperature (25℃) with a sample size of 42×3×3.2 mm and an impact span of 40 mm. The sample was cut by the wire

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electrical discharge machining and the cutting areas were polished before the impact

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tests. The impact absorbing energy was measured to evaluate the ability of PDC to

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resist impact fracture.

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2.3 Tribology tests

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Previous studies have shown that the PDC exhibits serious adhesive wear under vacuum conditions [21]. The tribological behavior is closely related to the bond

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strength between diamond grains, which leads to the exfoliation of diamond grains and a failure of PDC. In order to further investigate the bonding strength in the Ti-PDC, the vacuum tribological test was performed on MSTS-1 ball-on-disc vacuum space tribometer. The experimental temperature was room temperature (25℃). The tribology test conditions are shown in Fig.1. Seven different vacuum conditions (7×10-5 Pa, 7×10-4 Pa, 7×10-3 Pa, 7×10-2 Pa, 7×10-1 Pa and 7 Pa, 1×105 Pa) were selected in this vacuum tribology experiment. The PDC sample was used as a disc in the vacuum tribological test, while the Si3N4 ball was chosen as a counterball. The rotational speed and radius were 100 r/min and 5 mm, respectively, corresponding a

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linear velocity of 52.5 mm/s. The applied normal load was 30 N and the contact stress at the friction interface was 1.56 GPa. The vacuum tribology experiment lasted for 30 min. Each set of experiments was repeated three times to ensure the accuracy of data. Before the experiment, the tribopairs and the fixture were ultrasonically cleaned by

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alcohol and acetone for 30 min and placed in a vacuum drying oven for use.

Fig.1 The Schematic of the parameters of tribological tests in vacuum.

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2.4 Surface analysis

The three-dimensional topography of the sample was observed using a NanoMap-D three-dimensional white light interferometer. The wear scars on the Si3N4 balls and the wear tracks on the PDC surfaces were observed using an Olympus BX51 Macromicroscopy. The surface of the sample was analyzed by a CS3400 scanning electron microscope (SEM). The Oxford EDX-450 energy dispersive X-ray spectrum (EDS) and D/max-2550X X-ray diffraction (XRD) (Cu Kα: 40 kV, 200 mA) were utilized to investigate the chemical compositions of the worn PDC surfaces. 3. Results

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3.1 General properties of sample The composition and microstructure of the Ti-coated diamond particles are shown in Fig.2. Compared with the SEM and EDS photograph, it can be observed that in addition to the Ti coating, the surface of the particle also has the presence of oxygen. This may be due to residual oxygen during vacuum pumping process before

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magnetron sputtering. The AES result (Fig.2 (e)) shows that the thickness of the Ti coating is about 500 nm. A transition layer of about 450 nm is located between the Ti

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coating and the diamond particle.

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Fig.2 (a)-(d) The SEM graph and corresponding EDS mapping image of the Ti-coated diamond particles, (e) the AES result of the Ti-coated diamond particles.

The surface images and composition distribution of the Ti-PDC are shown in Fig.3 (a)-(d). It can be clearly seen that there is Ti element and the binder cobalt element, which are mainly distributed along the boundaries of the diamond particles. From the XRD pattern in Fig.3 (e), it can be seen that in addition to the diamond phase, a TiC phase formed during the HTHP sintering.

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Fig.3 The SEM, EDS and XRD analysis of Ti-PDC surface: (a)-(d) the surface image and

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composition distribution of the Ti-PDC, (e) the XRD pattern of the Ti-PDC.

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3.2 Impact roughness analysis

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The P-PDC and Ti-PDC were tested using a pendulum impact tester to

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characterize the impact toughness. For the impact test, the sample edges were not properly aligned during the preparation process, which might cause the data error of

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the impact toughness. In this case, the censored average of the two sets of data is

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selected for comparison to remove the influence of the singular value. Moreover, five sets of experiments for each sample were carried out. The result shows that the impact toughness of the Ti-PDC is 4.6 ± 0.6 J/cm2 on average while that of the P-PDC is 3.4 ± 0.3 J/cm2 on average. The impact toughness of the Ti-PDC is higher than that of the P-PDC. According to the SEM graph of the fracture surface in Fig.4, a few detached and broken diamond grains can be observed on the fracture surfaces of the P-PDC and Ti-PDC. At the fracture of P-PDC, a large crack due to the detachment of diamond grains for the impact test can be observed. There are also some small cracks distributed along the boundaries of diamond grains. On the fracture surface of the

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Ti-PDC diamond, some complete diamond grains can be observed on the section. A fewer micro cracks also distribute along the boundaries of diamond grains. It can be conducted that the fracture of the diamond layer mainly occurs along the boundaries of diamond grains. The boundaries of diamond grain filled by the cobalt phase

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become the weak areas of the PDC material [22-23].

Fig.4 The SEM graph of Ti-PDC and P-PDC fracture surface.

Fig.5 (a) shows the enlarged graph of impact fracture surface on the Ti-PDC. A whole diamond grain can be observed at the fracture surface. As shown in the EDS line scanning (Fig.5 (b)), the content of Ti element at the boundary of diamond grains significantly increases. This indicates that a TiC phase was formed around the

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diamond grains during the sintering process. It was reported that the D-D bonding in PDC is not less strong than the diamond crystal itself, so that the area filled with cobalt binder has weak bonding force [24-26]. Therefore, most of the diamond grains

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exfoliate along the grain boundaries due to the weak bonding.

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3.3 Tribological behaviors

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Fig.5 (a)The enlarged SEM graph of the Ti-PDC fracture surface and (b) the element distribution

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Fig.6 (a) shows the coefficient of friction (COF) curves of Ti-PDC/Si3N4 under different vacuum conditions. It can be seen that the COFs are divided into two regions. The high COF region corresponds to higher vacuum conditions. Under the conditions of 7×10-5 Pa, 7×10-4 Pa and 7×10-3 Pa, the average COF in the stable stage are 0.46, 0.43 and 0.42, respectively. Moreover, the curves under high vacuum conditions show great fluctuation. When the vacuum condition drops to 7×10-2 Pa, the friction coefficient suddenly decreases and the curve tends in a stable level. The average friction coefficient reveals a minimum value of 0.04 at 7 Pa. In order to further evaluate vacuum tribological properties of Ti-PDC, the COFs of Ti-PDC and P-PDC are compared in Fig.6 (b). It can be observed that COFs of Ti-PDC in different high

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the mechanism of friction has been changed.

under different vacuum pressures.

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Fig.6 (a) The variation of the friction coefficient and (b) stable friction coefficient of the PDCs

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Fig.7 shows the two-dimensional images of the Ti-PDC under different vacuum

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conditions. The wear tracks on the Ti-PDC are more widely under 7×10-5 Pa, 7×10-4 Pa and 7×10-3 Pa, and some black substances can be observed on the worn surface. It has been proved in previous work that the black substances are mainly caused by the adhesion of Si3N4during the sliding operation, in which some diamond grains were pulled up due to the high adhesive force [21]. Meanwhile, less adhesively bonded material was observed for the ones obtained under 7×10-2 Pa, 7×10-1 Pa, 7 Pa and 1×105 Pa.

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Fig.7 The wear tracks of Ti-PDC under different vacuum conditions: (a) 7×10-5, (b) 7×10-4 Pa, (c) 7×10-3 Pa, (d) 7×10-2 Pa, (e) 7×10-1 Pa, (f) 7 Pa and (g) 1×105 Pa.

Previous studies reported that the wear mechanism of PDC material under high and low vacuum condition are different [27-29]. In high vacuum conditions, the diamond particle will be pulled up from PDC surface because of high adhesive force during sliding. This mechanism relates to bonding force between diamond particles closely so that in this case, the samples tested in high vacuum conditions were selected to further analysis the bonding conditions in the Ti-PDC. The SEM was performed to observe the wear tracks formed on the Ti-PDC surface after sliding

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operation under high vacuum conditions. Fig.8 shows the worn surface image of Ti-PDC tested under 7×10-3 Pa, 7×10-4 Pa and 7×10-5 Pa conditions and the corresponded EDS mapping images. It can be observed that some light gray matters adhere on the surface of the worn Ti-PDC. By comparison of the SEM images with EDS maps, the distribution of these light gray

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matters is basically the same as that of the silicon elements. Therefore, it can be inferred that the light grey area on the worn Ti-PDC surface is the adhesive Si3N4. In

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order to obtain a clearer feature image of the adhesive area, the adhesion region on the

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wear track formed under 7×10-5 Pa was amplified.

Fig.8 The SEM images of the worn Ti-PDC surfaces after sliding operation under (a) 7×10-5 Pa, (b) 7×10-4 Pa and (c) 7×10-3 Pa and the corresponding EDS mapping images.

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Fig.9 reveals the enlarged SEM photograph of the worn Ti-PDC surface tested under 7×10-5 Pa. It can be observed that there is a large amount of adhesive materials at the wear track. A typical adhesion area and spalling pit can be observed at the wear track of Ti-PDC. According to the comparison of the EDS result, the main element of these adhesions are Si which could come from the wear debris generated during the

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sliding process of the Si3N4 against Ti-PDC and adhered to the wear tracks during the

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repeated extrusion of the sliding process.

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Fig.9 (a) The SEM image of the wear track of Ti-PDC formed under 7×10-5 Pa and (b) the enlarged SEM image with the corresponding EDS mapping images of the spalling piton the wear track in (a). (c) ~ (f) the corresponding EDS mapping images of (b).

In order to further analysis the difference of worn surface between Ti-PDC and P-PDC, three-dimensional topographies of the worn Ti-PDC and P-PDC surfaces tested under high vacuum conditions are shown in Fig.10. At the conditions of 7×10-5 Pa, 7×10-4 Pa and 7×103 Pa, many adhesive material and spalling pits appear on the surfaces of wear tracks. The adhesive Si3N4 on the wear tracks of the Ti-PDC and P-PDC gradually decreases with the decrease of vacuum pressure. Notably, under the

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same high vacuum conditions, the area of spalling pits caused by adhesion on the

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worn Ti-PDC surface are less than that appear on the P-PDC.

Fig.10 Three-dimensional topographies of the worn Ti-PDC and P-PDC surfaces tested under high

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vacuum conditions after sliding operation:(a-c) the worn P-PDC and (d-f) Ti-PDC surfaces tested under 7×10-5 Pa, 7×10-4 Pa and 7×10-3 Pa.

In order to further quantify the area of the spalling pits on the worn PDC surface under high vacuum conditions, the ratio of the area of the spalling pits to that of the view filed was calculated. The area of the spalling pits was averaged by five different detecting positions on a wear track, and the view area was a square with a side length of 4 mm. As shown in Fig.11, the spalling pits ratio of P-PDC and Ti-PDC under high vacuum condition increases with the increase of the vacuum pressure, which corresponds to the variation law of the COF. In addition, it is notable that the spalling

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pit ratios of P-PDC under various vacuum conditions are smaller than those of Ti-PDC, which indicates that the Ti coated-diamond particles on the Ti-PDC surface are hard to be pulled up during the friction process under high vacuum conditions. This may be due to the introduction of Ti element, which enhances the adhesion

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between particles.

Fig.11 The spalling pit area ratio of the P-PDC and Ti-PDC under high vacuum conditions.

4. Discussions

In this work, the impact toughness of the Ti-PDC is demonstrated higher than that of the P-PDC. To further investigate the cohesion state among diamond grains in the PDC, vacuum tribological properties of the Ti-PDC under different vacuum conditions were studied. The results show that the vacuum tribological properties of Ti-PDC have dependence to the vacuum conditions. The area ratio of spalling pits on the worn Ti-PDC surface, which were produced by the adhesion force between the counter pairs, is lower than that of the P-PDC under the same conditions.

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M.Szutkowska et al. [30] found that the PDC with a Ti3(Si,Ge)C2 binder had a great bonding state, which was attributed to the TiC phase formed around the boundaries of diamond particles. Wang et al. [19] also demonstrated a stable TiC phase in the prepared Ti-diamond. The fracture properties of the PDC are different from those of other diamond related materials. The cracks usually spread along the grain boundaries

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and lead to the exfoliation of diamond grains from the PDC surface, which ultimately yields to a severe failure of the PDC tools [31]. According to EDS and XRD results in

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this work, the Ti-PDC produced a stable TiC phase during the HTHP sintering process.

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The stable TiC phase form a strong bond of C-Ti between the diamond grains, thus an

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enhanced bonding force. The presence of these bonds makes it difficult for the

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diamond grains on the Ti-PDC surface to exfoliate due to the adhesion under vacuum

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conditions. Therefore, the TiC phase enhances the bonding strength between diamond

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grains by the chemical bonding action and thus improve the impact resistance of PDC.

Fig.12 Schematic illustration of tribological behavior under high vacuum conditions and low vacuum conditions.

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Due to the special structure, the wear mechanism of the PDC is significantly different from other diamond related materials. Mehan et al. [32] studied the wear mechanism of PDC through a pin-type tribological tester. The results showed that the spalling of fine diamond particles is the main failure mode of PDC Sha et al. [33] studied the tribological properties of PDC materials when sliding with different

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materials under vacuum conditions. As shown in Fig.12 (I), spalling pits and adhesion appeared on polycrystalline diamond surface under high vacuum conditions due to

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due to σ bonding between pairs which shown in Fig.12 (II). The tribological behavior

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under low vacuum and ambient air condition is different because of absorbed film

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which constituted by water or oxygen molecule, passivation of dangling bonds

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isolates tribological interface so that to make eliminates interface bonding.

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Because of the dangling bonds occurred at the interface, which results in a high COF when the Si3N4 and SiC counter balls are used, the diamond grains are pulled up

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and exfoliate simultaneously. As it presents in Fig.13 (a), due to the influence of particle size and shape, the gaps of diamond particles are filled with cobalt phase in P-PDC, the diamond particles combined to each other by cobalt binder. In the present study under high vacuum conditions, the PDC surface adsorption layer was desorbed and the surface dangling bonds were exposed. During the sliding process, the dangling bonds generated by the Si3N4 counterball are bonded so that resulting in adhesion. Some of the diamond grains are pulled out under the action of strong interface bonding, and are separated from the PDC surface to form a spalling pit. Therefore, the friction and wear properties of the PDC under vacuum conditions have

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a corresponding relationship with the bonding force between the diamond particles. As shows in Fig.13 (b), TiC phase that generated during HTHP sintering process causing a strong chemical bond between the diamond particles to replace the weak combination of cobalt binder. This strong bonding force makes diamond particle hard

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to be pulled out from surface of Ti-PDC.

Fig.13 Schematic illustration of the bonding state of (a) P-PDC and (b) Ti-PDC.

The COF under vacuum condition is much higher than that under ambient air. Under high vacuum conditions, the COF curves of Ti-PDC and P-PDC fluctuate sharply. This kind of fluctuation is related to interface bonding which dangling bonds on both sides of the grinding pair are continuously combined and broken during grinding. Under different high vacuum conditions, the average COFs of Ti-PDC are lower than those of the P-PDC, which may be due to the less exfoliation of diamond

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grains. When the number of exfoliated diamond grains is reduced, the exfoliated fine diamond grains reduce the ploughing action of the Ti-PDC surface and the counterball, resulting in a lower COF. 5. Conclusions (1) The impact toughness of the Ti-PDC (4.6 ± 0.6 J/cm2) is higher than that of

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the P-PDC (3.4 ± 0.3 J/cm2). This may be due to the existence of the TiC phase, which enhances the interface bonding of diamond grains. The weak mechanical force

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chemical bonding of titanium-diamond.

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between the cobalt binder and diamond grains has been replaced by the strong

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(2) Under high vacuum conditions, the worn Ti-PDC surface produces a severe

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adhesion wear, and the amount of adhesive Si3N4on the Ti-PDC surface and the COF

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increase as the vacuum pressure increases. The spalling pit area ratios of Ti-PDC are lower than those of P-PDC under same condition, which is due to the enhancement of

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bonding between diamond particles.

(3) The Ti-PDC and P-PDC exhibit a same trend of COF under different vacuum conditions. The Ti-PDC performs a lower average COF than P-PDC under the same vacuum condition. This may be attributed to the less exfoliation of diamond grains, which produces less wear debris during the sliding operation. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51875537, 41572359, 51375466), Beijing Natural Science Foundation (3172026), Beijing Nova program (Z171100001117059) and Fundamental Research

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Figure captions Fig.1 The Schematic of the parameters of tribological tests in vacuum. Fig.2 (a)-(d) The SEM graph and corresponding EDS mapping image of the Ti-coated diamond particles, (e) the AES result of the Ti-coated diamond particles.

Journal Pre-proof Fig.3 The SEM, EDS and XRD analysis of Ti-PDC surface: (a)-(d) the surface image and composition distribution of the Ti-PDC, (e) the XRD pattern of the Ti-PDC. Fig.4 The SEM graph of Ti-PDC and P-PDC fracture surface. Fig.5 (a) The enlarged SEM graph of the Ti-PDC fracture surface and (b) the element distribution along the arrow. Fig.6 (a) The variation of the friction coefficient and (b) stable friction coefficient of the PDCs under different vacuum pressures. Fig.7 The wear tracks of Ti-PDC under different vacuum conditions: (a) 7×10-5, (b)

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7×10-4 Pa, (c) 7×10-3 Pa, (d) 7×10-2 Pa, (e) 7×10-1 Pa, (f) 7 Pa and (g) 1×105 Pa.

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Fig.8 The SEM images of the worn Ti-PDC surfaces after sliding operation under (a) 7×10-5 Pa, (b) 7×10-4 Pa and (c) 7×10-3 Pa and the corresponding EDS mapping

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Fig.9 (a) The SEM image of the wear track of Ti-PDC formed under 7×10-5 Pa and (b)

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the enlarged SEM image with the corresponding EDS mapping images of the spalling piton the wear track in (a). (c) ~ (f) the corresponding EDS mapping images of (b).

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Fig.10 Three-dimensional topographies of the worn Ti-PDC and P-PDC surfaces tested under high vacuum conditions after sliding operation:(a-c) the worn P-PDC and

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(d-f) Ti-PDC surfaces tested under 7×10-5 Pa, 7×10-4 Pa and 7×10-3 Pa. Fig.11 The spalling pit area ratio of the P-PDC and Ti-PDC under high vacuum conditions.

Fig.12 Schematic illustration of tribological behavior under high vacuum conditions and low vacuum conditions.

Fig.13 Schematic illustration of the bonding state of (a) P-PDC and (b) Ti-PDC.

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Declaration of competing interest The authors declare that there is no conflicts of interest regarding the

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Author contributions Haichao Zhang: Conceptualization, Methodology, Investigation, Data Curation , Writing - Original Draft. Wen Yue: Resources, Writing - Review & Editing, Supervision, Data Curation. Xiaohua Sha: Validation, Formal analysis, Visualization. Wenbo Qin: Validation, Formal analysis, Visualization. Chengbiao Wang: Writing - Review & Editing.

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Graphical abstract

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Journal Pre-proof Highlights Titanium-coated diamond particle sintered PDC was prepared.



The vacuum tribological regular of Ti-PDC was summarized.



The wear mechanism of Ti-PDC under vacuum condition was highlighted.



The bonding force of diamond particles in Ti-PDC was enhanced by powder coating.

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