Polycrystalline Diamond Composites Research Articles

Effect of pressure on sintering behavior of polycrystalline diamond

Polycrystalline diamond composites (PDC) have been used as a cutting material in a multitude of fields, from mechanical processing to oil and gas drilling. In this study, PDC samples were prepared under high pressure and high temperature (HPHT) conditions within a pressure interval of 5.5 to 10.5 GPa by sintering diamond powder (average grain size ~3 μm) with WC-10 wt% Co substrate. Samples obtained with varying sintering pressures and temperatures were characterized using Vickers hardness tester, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that: (1) within a specified material system, each distinct sintering pressure condition corresponds to a unique optimal sintering temperature that yields the pinnacle of consolidation efficiency in samples. This optimal temperature exhibits a linearly increasing trend with rising sintering pressure; (2) at the intersection where the sintering pressure attains its optimal match with temperature, an increase in pressure fosters more intimate contact and stronger inter-grain bonding among diamond particles, thus amplifying the DD bond formation effect, which consequently leads to a linear enhancement in the Vickers hardness values of PDC with increasing sintering pressure; (3) simultaneously, under conditions of optimal temperature matching, elevating the sintering pressure notably decreases the cobalt content within the polycrystalline diamond layer of PDC samples. These findings furnish crucial experimental evidence for optimizing PDC material properties, significantly contributing to the advancement of both theoretical exploration and technological innovation within the field, carrying profound academic value and practical guidance implications.

Diamond seed dependent luminescence properties of CVD diamond composite

Diamond-based X-ray luminescent composites are robust materials to be used in synchrotrons and free-electron lasers to detect and visualize high-intensity X-ray beams. Such composites consist of luminescent rare-earth (RE) particles embedded into an X-ray transparent diamond matrix. In this work, polycrystalline diamond composites with embedded particles of EuF3, SrF2:Eu and YAG:Ce were grown by microwave plasma CVD using diamond seeds with an average particle size difference of two orders of magnitude: from 5 nm up to 500 nm, with positive and negative zeta potentials. The structure, phase composition, and luminescent characteristics of the resulting composite films were investigated and analyzed. We found that various particle types can be better-suited for different composites, and the exact seeding should be selected on the case-by-case basis. The direct comparison of various diamond-based composites, grown in the identical CVD conditions but with various luminescent powders, show that YAG:Ce particles in diamond allow achieving a brighter photoluminescence (PL) in comparison to Eu-based fluorides. However, the set of fluoride powders doped with Eu3+ ions allow obtaining unusually narrow (FWHM = 0.9 nm) and intensive line near 611 nm in PL spectra, which might be better-suited for detection and characterization applications rather than a broad peak of Ce with FWHM ≈ 120 nm.

Heterogeneous diamond–TiC composites with high fracture toughness and electrical conductivity

The concurrent enhancement of toughness, electrical conductivity, and thermal stability in polycrystalline diamond composites represents a formidable challenge. Here, a novel diamond-TiC composites (referred to as DTC) with high fracture toughness and conductivity were synthesized through a high-temperature and high-pressure reaction sintering process utilizing two precursors: diamond mixtures containing TiH2 and Ti-coated diamonds. On the one hand, the inherent bonding and encasing of TiC onto the diamond matrix form a heterogeneous structure, providing high strength and excellent fracture toughness up to 11.6 MPa·m1/2. On the other hand, the established oxygen barrier and current pathway offer a thermal stability of 765 °C and high conductivity up to 837 S·m−1. Remarkably, this rare combination of mechanical, electrical, and thermal properties has been realized within a single material under relatively moderate sintering conditions, thus positioning diamond-TiC composites as a promising ceramic for electrical applications in high-stress environments.

Study on super impact resistant polycrystalline diamond compacts with homogeneous PCD/WC-Co interlayer

With ultra-deep wells exceeding 10,000 m, the downhole drilling environment has become increasingly harsh and challenging and poses higher and more urgent requirements for the improvement of mechanical properties of polycrystalline diamond compact (PDC) cutters. In this work, four different types of polycrystalline diamond (PCD) structures were utilized with the purpose of exploiting both the advantages of homogeneous PCD/WC-Co composites in the impact toughness and the advantages of pure PCD composites in the wear resistance. Each PCD layer was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Raman spectroscopy. The indentation hardness, wear resistance and impact resistance of PDC cutters were evaluated using nanoindentation instrument, vertical turret lathe and progressive drop tester, respectively. The field trials of the developed PDC cutters in the ultra-well above 8000 m were also carried out. The experimental results demonstrated that PDC cutters with homogeneous PCD/WC-Co interlayer have excellent impact resistance while the pure PCD top layer ensures the cutter's hardness and wear resistance. Through observing the cracks in the diamond layer after mechanical performance testing, it was discovered that the homogeneous PCD/WC-Co interlayer has the capability of promoting the deflection of cracks on a macroscopic level. In addition, the inclusion of WC-Co alters the fracture mode of the PCD layer from transgranular fracture to mixed-mode fracture, which well explains the toughening mechanism of PCD/WC-Co cutter. This work provides valuable insights for the development of high-quality PDC cutters, and has important significance for the further design of efficient rock-cutting materials and comprehensive improvement of the drilling performance of PDC bits.

Control morphology and properties in additive manufacturing of functional gradient cemented carbides for polycrystalline diamond substrates

Cemented carbide substrates contribute mainly to the strength and impact toughness of polycrystalline diamond composites (PDC). By using a PW-MW-HDPE-EVA-SA mixed polymeric binder and combining Powder Extrusion Printing (PEP) with densification sintering processes, the YG10/YG15 functionally gradient cemented carbides (FGCCs) with different powder loadings were prepared. This study focuses on exploring process feasibility and the integrated regulatory mechanisms for FGCCs morphology and performance. The results showed that the configured cemented carbide feedstocks with different powder loadings exhibited uniform composition and good shear-thinning characteristics, making them suitable for extrusion printing. The FGCC green parts formed by PEP have macro-structurally intact, dense surfaces and uniformly stacked extrusion filaments with a roughness of 12.25 μm. After degreasing and sintering, FGCCs with densities exceeding 99.43% were obtained. The shrinkage and Co gradient distribution of the inner and outer layers were regulated by powder loading design, achieving integrated control of FGCCs morphology and properties. With powder loading increase in YG15, the density of FGCCs remained stable between 14.01 and 14.03 g/cm3, the gradient dimensions difference decreased from 14.34% to 7.9%, and the maximum hardness difference increased from 78 to 121 HV1/15.

Preparation of Ti3Si0.8Al0.2C2 Bonded Diamond Composites and Their Friction Properties Coupled with Different Counterfaces

Polycrystalline diamonds were sintered with the binder of Ti3Si0.8Al0.2C2 to solve the shortcomings of conventional metal binders and ceramic binders. Ti3Si0.8Al0.2C2 bonded polycrystalline diamond composites have been synthesized from a mixture of Ti3Si0.8Al0.2C2 powder (40 wt%) and diamond powder under 4.5–5.5 GPa at 1050–1300°C by high press and high-temperature technology. The characteristic peaks of TiC were observed at 4.5 GPa and above 1100°C. From the microstructure analysis, the diamond particles are equally dispersed throughout the Ti3Si0.8Al0.2C2 matrix and firmly bound to the matrix. The effects of the sintering conditions, test parameters, and counterparts on the friction properties of diamond composites were systematically analyzed. The friction coefficient between diamond composite and glass counterpart is between 0.18 and 0.33 and increases significantly at the speed of 400 rpm/min. SEM and EDS analysis show Ti3Si0.8Al0.2C2 has a strong holding force on the diamond particles. The wear mechanism is mainly abrasive, and there are obvious grooves on the surface of the glass ball. The friction coefficient of diamond composite sintered at 1050°C with POM decreases monotonically with increasing load and reaches the minimum value of 0.42 at 12 N. The higher sintering temperature (1150°C) resulted in lower friction coefficient for diamond/POM pairs. The friction coefficient of diamond/PP pairs decreases first and then increases with increasing load, reaching a minimum value of 0.431 at 10 N. The wear mechanism of PP and POM is a combination of abrasive wear and adhesive wear, while the abrasive chips of POM are small salt-like particles and the abrasive chips of PP are long flocs. The wear track of PP balls has a smoother surface than that of POM balls. For an Al pair, the friction coefficient of diamond composite sintered at 1150°C is higher than that of the composite sintered at 1050°C except for the 10 N load. The friction coefficient of the diamond composites with Cu pairs varies slightly with increasing load, with values ranging from 0.443 to 0.518 and decreases with increasing speed, reaching a minimum value of 0.396 at 600 rpm/min. The wear mechanism of Cu and Al is mainly based on adhesive wear. The presence of the diamond second phase improves the stability of Ti3Si0.8Al0.2C2 compared to the high-pressure treatment of single phase Ti3SiC2. The analysis of friction properties indicates that Ti3Si0.8Al0.2C2 bonded diamond composites are promising candidates for superhard tool materials.

Effect of diamond layer thickness on tool wear of polycrystalline diamond composites

Well-sintered polycrystalline diamond composite (PDC) is a hard material obtained from WC–Co substrate and diamond using a high-temperature high-pressure (HPHT) process. PDC has immense potential in aerospace, automobile, oil and gas, and tool manufacturing industries. In this study, PDC was formed by sintering diamond powder (average crystal size = 10 μm) and WC–15 wt% Co substrates at HPHT and the diamond layer thickness is 1.2 mm. The thicknesses of the diamond layer on the PDC cutter were varied, and their effects on the PDC cutter wear were examined. Wear experiments and hardness tests were conducted on samples with varying diamond layer thicknesses. They were characterized using scanning electron microscopy, X-ray diffraction, and Hall effect, and these revealed that (1) hardness of the PDC slightly increased with an increase in the thickness of the diamond layer, and (2) the PDC tool's life could be improved by appropriately increasing the thickness of the diamond layer. The findings of this study provide insights for future studies on designing and optimizing the properties of the PDC.

Nanoengineered Polycrystalline Diamond Composites with Advanced Wear Resistance and Thermal Stability.

Fluorinated grains of micrometer size diamonds overcoated with nanodiamond particles were used as a feedstock for high-pressure, high-temperature synthesis of new polycrystalline diamond composites (PDCs). Such a nanoengineering approach for exploring the interfacial chemistry of diamonds has been implemented in two methods: (i) infiltration of Co from the WC-Co layer into a fluorinated diamond layer with added Al and (ii) sintering of fluorinated micro- and nanosize diamond homogeneous mixtures with added Al and Co. We found that unlike commercial PDCs made with a metallic Co binder for drilling tools, the binding phase in new composites comprises only intermetallic compound AlCo or ternary carbide AlCo3C. As a result, composites made from homogeneous mixtures showed greater promise for improving the thermal stability, while the two-layer experimental composites during granite turning tests have demonstrated >2 times higher wear resistance than leached commercial PDCs.

Study of polycrystalline diamonds produced by infiltration method using natural and synthetic diamond powders

Diamond tooling is used to machine a broad range of materials. Due to their strength, diamond tools can be used to machine extremely hard alloys. At the same time, diamond tooling is also widely used to machine soft nonferrous alloys and polymers. This paper examines polycrystalline diamond (PCD) composites which are used in diamond tooling designed for various applications. A few types of diamond composites are known today, which are produced by different techniques. Such materials can be produced both by sintering diamond powders together with activating agents and by converting graphite into diamond using catalyst alloys. Production of such materials is always associated with the use of high pressures and temperatures. Depending on the production technique applied, the composition, properties and application of the resultant PCD composites can vary greatly. This paper looks at the infiltration method, i.e. when the binding melt infiltrates in pressed diamonds under high pressures and temperatures. Even though the obtained specimens have a lower strength than the ones produced by other methods, this technique proves to be optimum. Unlike it is with the other methods, the sintering operation in this one is not technically difficult (the applied pressure does not exceed 4 GPa), and PCD composites of bigger sizes can be produced. A study was conducted in the framework of this research to better understand the key physical and mechanical properties of PCD composites, which were produced by infiltration method using two binding materials (Ni – Si and Mn – Si alloys) and two diamond powders (the ASM grade of synthetic powder and the AM grade of natural powder). A comparative analysis of their properties was also carried out.This research study was carried out as part of the research initiative 2.2. “Material Qualification and Studies” (“Strategic Areas in the Development of Materials and Processing Technology till 2030”).

Fabrication and evaluation of mechanical properties of polycrystalline diamond reinforced with carbon-nanotubes by HPHT sintering

In this study, carbon nanotubes (CNTs) have been employed as reinforcements for polycrystalline diamond (PCD) to fabricate CNTs/PCD composites at high-pressure and high-temperature (HPHT, 5.5 GPa and 1550 °C) conditions. The microstructure, phase composition, elemental distribution, and the effect of CNTs on mechanical properties of CNTs/PCD composites were systematically investigated. Vickers hardness of the sample with 1.5 wt% CNTs reached to 58.3 GPa, while flexural strength was improved to 650.8 MPa. Fracture toughness was enhanced from 5.4 MPa m1/2 to 9.1 MPa m1/2, which was 68.5% higher compared with that of the monolithic PCD composites. Furthermore, the toughening mechanism was explored, the increase of fracture toughness is attributed to the pull-out and bridging of CNTs during crack deflection. Additionally, it was concluded that sintering time for 90 s in HPHT can effectively ensure the integrity of CNTs and guarantee their toughening effects.

Laser finishing of polycrystalline diamond as strengthening mechanism

Abstract Polycrystalline diamonds are widely used in the cutting tool industry for machining of aluminium alloy and metal matrix composites as they exhibit superior wear resistance. However, their wear characteristics are dependent on their microstructural features (i.e. percentage of binder phase and size of grains) which are defined during the sintering process. Low-energy fibre laser process of polycrystalline diamond composites with different grain dimensions is proposed to promote microstructural changes, enhance their hardness, and retain surface finish. Specimens were processed with a nanosecond pulsed fibre laser (ytterbium-doped) at a wavelength of 1064 nm. Samples treated at various fluences, beam speeds and pulse durations were characterised via 3D interferometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and micro-indentation hardness test. At a fluence below the composite’s ablation threshold (i.e. 20 J cm2), the investigated finishing/polishing process for a coarse grain polycrystalline diamond resulted in a change of diamond grain size, a surface integrity of 140 nm and increased micro hardness (i.e. 240 GPa). The laser treatment caused plastic deformation of the grains, changing the intergranular boundaries area therefore impeding dislocation movements and enhancing hardness.

Strength and plastic deformation of polycrystalline diamond composites

ABSTRACTThe use of nanopolycrystalline diamond has allowed a systematic study on deformation of polycrystalline diamond composites (PCDCs). Bulk PCDCs samples containing either Co or SiC as a binding agent were deformed under high pressure and temperature to strains up to 18% at strain rates ∼10−5 s−1. All samples exhibit strong work hardening. The strength of PCDCs depends on the amount and type of binding agents and is consistently weaker than that of diamond single crystals. The weakening may be due to the binder materials, which play an important role in affecting grain boundary structures. In SiC-based PCDC, significant grain fragmentation occurs. Nearly all grain boundaries are wetted by SiC after large deformation, resulting in lower strength. In Co-based PCDC, the microstructure is dominated by dislocations, deformation twins, and separated grain boundaries. The density of deformation twins increases significantly with strain, with the twin domain width reaching as low as 10–20 nm at 14% strain.

Microhardness and wear behaviour of polycrystalline diamond after warm laser shock processing with and without coating

Cutting tools made of ultra-hard materials such as polycrystalline diamonds offer superior wear resistance in precision machining of Aluminium alloys. However, the wear properties of these materials are dependent on their microstructural characteristics such as grain size and binder percentage. In this context, the present paper evaluates the effects of two low-energy fibre laser processes (nanosecond pulse duration) on microstructural changes of polycrystalline diamond composites and consequently investigates wear and friction characteristics and micro hardness properties. Pockets were first achieved using a single mode SPI pulsed fibre laser (1064 nm wavelength) inducing both laser shock processing (LSP) and laser peening without coating (LPwC) and characterised using a combination of scanning electron microscopy (SEM), white light interferometry, energy dispersive X-Ray (EDX) and micro hardness analyses. The as-received and processed materials were tested on a pin-on-disc for the evaluation of their wear performance. An analytical model based on the asperities of pin and disc after wear test is proposed to predict the trend of wear performance of different laser-processed materials. LSP with vinyl and quartz at a scanning speed of 500 mm s−1 achieved a micro-hardness of 110 GPa at a depth of 632 nm. LPwC at 0.8 GW cm−2 produced hybrid microstructures which share characteristics of laser shock processing and selective laser melted structures. For laser feed speed in the region of 1000 mm s−1, micro-indentation tests revealed an improvement of hardness from 70 GPa to 95 GPa at a depth of 670 nm for LPwC. Tribotest revealed enhanced wear performance for all laser-processed pins and reduced coefficient of friction also validated by increased material removal rate when compared to the as-received material. To the best of authors' knowledge, it is reported for the first time that an improvement of wear performance can be achieved on polycrystalline diamond through LSP and LPwC.

Formation of the Structure and Phase Composition of Polycrystalline Diamond with Cobalt Infiltration in the System Diamond – Hard Alloy

Polycrystalline diamond composites (PCD) were obtained by cobalt infiltration from a hard-alloy substrate into a porous diamond layer at temperature 1600°C and pressure 6.0 GPa in a cubic hydrostatic-compression press. To improve the thermal stability of the composite the upper layer of the cobalt was etched by hydrofluoric acid to depth 150 μm. Transmission electron microscopy (TEM) was used to analyze the interaction at grain-binder and grain-grain boundaries. After cobalt infiltration a nanodiamond phase and a cubic cobalt-carbide phase CoCx are present on the grain-binder intergrain boundaries while after etching of the cobalt bulbous structures were found in the surface layer of the sintered polycrystalline diamond composite.

Surface engineering of ultra-hard polycrystalline structures using a nanosecond Yb fibre laser: Effect of process parameters on microstructure, hardness and surface finish

The use of lasers for near-net shape manufacturing of cutting tools, made of ultra-hard materials such as polycrystalline diamonds, is recently becoming a standard processing step for cutting tool manufacturers. Due to the different machinability exhibited by microstructurally different composites, the laser processing parameters and their effects need to be investigated systematically when changing the material. In this context, the present paper investigates the effects of a fibre laser milling process (nanosecond pulse duration) on surface topography, roughness, microstructure and microhardness of two microstructurally different polycrystalline diamond composites. Pockets were first milled using a pulsed ytterbium-doped fibre laser (1064 nm wavelength) at different fluences, feed speeds and pulse durations, and finally characterised using a combination of Scanning Electron Microscopy, White Light Interferometry, Energy Dispersive using X-Ray (EDX) and micro hardness analyses. For laser feed speed in the region of 1000 mm/s, micro-indentation tests revealed an improvement of hardness from 75 GPa to 240 GPa at a depth of 350 nm, and to 258 GPa at a depth of 650 nm below which the microstructure is preserved as confirmed by microscopy images of the analysed cross sections. For fluences in the region of 11.34 Jcm−2 a variation of cobalt binder volume between the two composites causes a change in milling mechanism. At fluences below 20 Jcm−2, the proposed milling process for CTM302 resulted in a microstructural change (ultra-hard grain size and Cobalt binder weight), better surface integrity (140 nm) and improvement of micro hardness (up to 258 GPa). The properties achieved through the proposed process achieve better hardness and roughness when compared to laser shock processing. To the best of authors’ knowledge, it is reported for the first time that an increase of hardness accompanied by improved surface roughness can be achieved on polycrystalline diamond through low-energy laser processing.

Thermal damage mechanisms of Si-coated diamond powder based polycrystalline diamond

The polycrystalline diamond (PCD) composites were synthesized from Si-coated diamond or diamond powder mixtures with Si. The characterizations of phase structures, morphologies and thermal stability of PCD were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal gravimetric-differential scanning calorimetry (TG-DSC). The thermal damage mechanisms of PCD were studied under air condition up to 750 ℃ by thermal weight loss, XRD, SEM and wear tester. The results showed that the PCD was successfully synthesized by the Si-coated diamond with a homogeneous structure. The thermal stability and wear resistance of PCD with Si-coated diamond were better than those of PCD with uncoated diamond. It was determined that the chemical thermal damage mechanism with oxidation reaction dominated the damage of the PCD after high temperature annealing and the physical thermal damage mechanism also took effect on the exfoliation of binder and fine diamond grains from PCD.

Contact damage and residual strength in polycrystalline diamond (PCD)

The tolerance to contact damage of polycrystalline diamond (PCD) composites is investigated. Three different PCD grades are considered. Contact damage is extrinsically introduced by spherical indentation techniques, an approach well-established to evaluate damage tolerance issues in other hard materials. Such damage is induced on the surface of polished specimens, under both monotonic and cyclic loading conditions, and is characterized by optical and scanning electron microscopy. Residual strength is used as discriminative parameter for evaluation of damage tolerance. Hence, non-indented (reference) and indented specimens are fractured by means of biaxial ball-on-three-ball flexure testing. Results show that tolerance to contact damage is dependent on the microstructural characteristics of each PCD grade. Hence, although fine PCD grade exhibits the highest reference strength, corresponding indented specimens show pronounced fracture resistance decay for relatively high applied loads or number of cycles. On the other hand, the bimodal and coarse PCD variants are found to be more tolerant to contact damage, i.e. fracture strength shows only slight changes as cracks are introduced. The trends discerned are discussed on the basis of relative discontinuous character and sharpness of the induced damage, as well as effective depth of corresponding cracks, all of them directly dependent on the PCD microstructure assemblage.

An Assessment of the Wear Characteristics of Microcutting Arrays Produced From Polycrystalline Diamond and Cubic Boron Nitride Composites

The current methods for manufacturing super-abrasive elements result in a stochastic geometry of abrasives with random three-dimensional abrasive locations. This paper focuses on the evaluation of wear progression/failure characteristics of micro-abrasive arrays made of ultrahard composites (polycrystalline diamond—PCD; polycrystalline cubic boron nitride—PCBN) in cutting/wear tests against silicon dioxide workpiece. Pulsed laser ablation (Nd:YAG laser) has been used to manufacture repeatable patterns of micro-abrasive edges onto microstructurally different PCD/PCBN composites. Opposing to these highly engineered micro-abrasive arrays, conventional electroplated abrasive pads containing diamond and CBN abrasives, respectively, have been chosen as benchmarks and tested under the same conditions. Contact profiling, optical microscopy, and environmental scanning electron microscopy have been employed for the characterization of the abrasive arrays and electroplated tools before/during/after the wear/cutting tests. For the PCD abrasive micro-arrays, the type of grain and binder percentage proved to affect the wear performances due to the different extents of compressive stresses occurring at the grain boundaries. In this respect, the micro-arrays made of PCD with mixed diamond grain sizes have shown slower wear progression when compared to the electroplated diamond pads confirming the combination of the high wear resistance typical of the fine grain and the good shock resistance typical of the coarse grain structures. The micro-arrays made of fine grained diamond abrasives have produced lower contact pressures with the workpiece shaft, confirming a possible application in polishing or grinding. As for the PCBN abrasive micro-arrays, the increase of metallic binder and the presence of metalloids in the medium content-CBN specimens have shown to produce higher contact pressure with the workpiece when compared to the electroplated specimen, causing fracturing as the main wear mechanism; while the PCBN micro-array with purely a metallic binder phase has shown slower wear and lower contact pressure in comparison to the electroplated CBN specimen. Among all of the tested arrays, the mixed grained PCD and the purely metallic binder phase PCBN micro-arrays have shown slower wear when benchmarked to the electroplated pads, giving a possible application of their use in the cutting tool industry.

Laser fabrication of diamond micro-cutting tool-related geometries using a high-numerical aperture micro-scanning system

The machining of micro-geometries requires a corresponding micro-cutting tool. Up to now, industry primarily fabricates such tools by grinding or electrical discharge machining. In this paper, an overview of the direct laser fabrication of micro-cutting tool-related geometries on polycrystalline diamond composites and single crystal diamond is presented. This is made possible using picosecond laser pulses operating at second harmonics and a micro-scanning deflection system exhibiting a high-numerical aperture. The generated geometries are inspected using scanning electron microscopy while quality of the cutting edge radius and graphitisation is investigated. The laser ablation process is further enhanced by demonstrating the feasibility of a sequential roughing and finishing strategy.

Oxidation, graphitization and thermal resistance of PCD materials with the various bonding phases of up to 800 °C

Three types of polycrystalline diamond composites (PCDs) were studied. The first material was sintered using the mixture containing 80wt.% diamond, 15wt.% of Ti–Si–C powder (mixture of 47.1wt.% Ti3SiC2 and TiSi2, TiC and SiC, from self-propagating high-temperature synthesis) and 5wt.% nanometric Ti(CN) powders. The second material was prepared using diamond powder and 10wt.% of titanium diboride. Materials were sintered using a Bridgman-type high-pressure apparatus at 8GPa and at the temperature of 2000°C. The third material was a commercial PCD containing 88wt.% of diamond, 10wt.% of Co and 2wt.% of WC. The coefficients of friction for diamond composites in a sliding contact with an Al2O3 ceramic ball were determined from room temperature of up to 800°C, in air. X-ray diffraction patterns of diamond composites after HP–HT sintering and wear tests are presented. In the studies, due to the use of Raman spectroscopy the strong influence of the bonding phase on the oxidation of diamond composites was confirmed. The most thermally stable material is the diamond composite with TiB2. High temperature bonding phase for diamond composites guarantees higher hardness and low coefficient of friction at elevated temperatures.