On the role of B4C on hardness and toughness of TiCN - SiC - TiN -Cr3C2 - Co cermet

This paper reports the development of TiCN - SiC- TiN - Cr₃C₂ - Co cermet modified with B₄C for cutting tool applications. Cermets of three different composition with varying B₄C in TiCN - SiC - TiN - Cr₃C₂ - Co were fabricated for a study of addition of B₄C on hardness and toughness. The cermet pellets were sintered using Spark Plasma Sintering (SPS) at 50 MPa pressure, 1500 °C temperature at a heating rate of 100 °C/min with 10mins soaking with pulse rate of 12/2 ms. Microstructure examination revealed a typical core-rim structure. Vickers hardness test was done at a load of 30 kg and duration of 10s. Fracture toughness was computed using crack length data measured from the hardness test. The cermet with composition 65% TiCN - 15% SiC - 5% TiN - 5% Cr₃C₂–10% Co showed high hardness of 16.2 GPa and toughness of 10.7 MPa √m and 50% TiCN - 15% SiC - 5% TiN - 5% Cr₃C₂–10% Co - 15% B₄C exhibited high fracture toughness of 16.5 MPa √m with hardness value of 12 GPa. The addition of B₄C greatly enhanced the toughness value and reduced the hardness value slightly.     

Wear and thermal stability of TiCN-WC-Co-Cr3C2 cermets modified by TiN

This work assesses the suitability of TiCN-WC-Co-Cr₃C₂ cermet modified by TiN for cutting tool application. Three cermet compositions containing TiN with 5, 10 and 15 wt% were prepared by Spark Plasma Sintering (SPS). The prepared cermets were subjected to pin-on-disk wear testing using EN31 steel as a disc material. The wear testing was conducted at a constant load of 20 N with different sliding velocities: 0.23 m/s, 0.27 m/s, and 0.35 m/s, which corresponds to 150 rpm, 175 rpm, and 225 rpm respectively. The cermet composition 55TiCN-15WC-10Co-5Cr₃C₂–10TiN (all in wt%) has shown lowest mass loss during wear testing. The thermal stability of the cermets were assessed by conducting annealing studies on the prepared cermets at different temperatures: 600°, 800° and 1000 °C for a constant soaking time of 4 h. The prepared cermets had very good thermal stability up to 800 °C. Beyond this temperature, a drastic reduction in the hardness of the cermets was observed. Among the three cermet compositions, 60TiCN-15WC-10Co-5Cr₃C₂–10 TiN showed better thermal stability. The oxide phases formed in all the cermet compositions during annealing at high temperatures (1000 °C) retard their microstructures. As a result, the hardness was decreased.     

Wear and thermal stability of nano-TiB2 modified TiCN-WC-Co-Cr3C2 cermet

This work discusses the friction, wear and thermal response of TiCN-WC-Co-Cr₃C₂ cermet modified by the addition of TiB₂ nanoparticles. The specimens were prepared by spark plasma sintering by adding different weight percentages (5, 10 and 15) of TiB₂ nanoparticles in TiCN-WC-Co-Cr₃C₂ cermets. The sintered pieces were subjected to sliding wear under an unlubricated condition and a constant load of 20 N at sliding velocities of 0.23 m/s, 0.35 m/s and 0.47 m/s against a steel disc of 48 mm diameter. Friction was the maximum at a sliding velocity of 0.23 m/s. The wear loss decreased with increasing speed of sliding and was between 10⁻⁵ to 10⁻⁶ mm³. The wear rates and coefficient of friction were highly dependent on microstructure and mechanical properties of the cermets. Abrasion and adhesion were the active modes of wear. Heating of the samples was carried out at 600 °C, 800 °C and 1000 °C for 4 h. A substantial mass gain and decrease in hardness were observed in the specimen annealed at 1000 °C, for which Scanning Electron Microscopy revealed considerable grain growth and XRD showed oxide phases. A cermet containing 15% TiB₂ nanoparticles displayed the lowest volumetric wear at room temperature, but had rather low thermal stability. Response surface methodology was used to develop models and regression equations for wear and thermal stability.     

The fabrication of multi-core structure cermets based on (Ti,W,Ta)CN and TiCN solid-solution powders

A novel multi-core structure cermets consisted of both black-core/rim structure and grey-core/rim structure were obtained by partially replacing TiCN powder with (Ti,20W,15Ta)CN powder via low-pressure sintering process. The toughness and strength of TiCN-based cermets were optimized and its feature of high hardness was maintained simultaneously. Systematically, it was investigated that the influences of various weight ratios of both (Ti,20W,15Ta)CN/TiCN and Co/Ni on the microstructure and mechanical properties of the multi-core cermets. The results showed that the addition of (Ti,20W,15Ta)CN powder could cause the refinement of the core size and the occurrence of the secondary phase (W,Mo,Ti)_3 + x(Co,Ni)_3 − xC (0 < x ≤ 1), both of which are responsible for the significant improvement of the mechanical properties. The appearance of the secondary phase was found under two circumstances, one was when the weight ratio of (Ti,20W,15Ta)CN/TiCN was 6:4 while that of Co/Ni was 5:5(cermet M60) and the other was when that of (Ti,20W,15Ta)CN/TiCN was 5:5 with pure Co binder (cermet C50). And there is a monotonous escalation of the fracture toughness (K_IC) of the cermets while increasing the (Ti,20W,15Ta)CN content. The optimal comprehensive mechanical performance was found in cermet M60 with transverse rupture strength (TRS) of 1903.32 MPa, Vickers hardness (HV₃₀) of 16.33 GPa and fracture toughness of 12.19 MPa·m^1/2.     

Effect of Al addition on SiC–B4C cermet prepared by pressureless sintering and spark plasma sintering methods

SiC–B₄C–Al cermets containing 5, 10 and 20 wt.% of Al were fabricated by high-energy planetary milling followed by conventional sintering and spark plasma sintering (SPS) techniques separately. The average particle size reduced to ~ 3 μm from an initial size of 45 μm after 10 h of milling. The as-milled powders were conventionally sintered at 1950 °C for 30 min under argon atmosphere and SPS was carried out at 1300 °C for 5 min under 50 MPa applied pressure. The formation of Al₈B₄C₇ and AlB₁₂ phases during conventional sintering and SPS were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The formation of Al₈B₄C₇ at 700 °C and AlB₁₂ at 1000 °C was well supported by XRD and differential scanning calorimetry (DSC). The maximum relative density, microhardness and indentation fracture resistance of SiC–B₄C–10Al consolidated by SPS are 97%, 23.80 GPa and 3.28 MPa·m^1/2, respectively.     

Sintering and sliding wear studies of B4C-SiC composites

Dense boron carbide (B₄C) – silicon carbide (SiC) composites were obtained by spark plasma sintering technique at 1800°C with 3 wt% and 6 wt% aluminium oxide (Al₂O₃) additives. Addition of sintering additives results in formation of aluminium silicate (Al₂SiO₅) liquid phase which accelerates sintering kinetics and helps in obtaining high density ~ 99%. Microstructures reveal uniformly distributed SiC particles in B₄C matrix. Increase in alumina from 3 wt% to 6 wt% results in decrease in hardness from 35.1 ± 0.8 to 33.7 ± 0.9 GPa, and increase in fracture toughness from 5.9 ± 0.4 to 6.5 ± 0.4 MPam^0.5. Using a ball-on-disk tribo tester under dry unlubricated conditions at 5, 10 or 15 N load, influence of alumina content on friction and wear properties of B₄C-SiC composites was investigated against SiC counterbody with a linear speed of 0.08 m/s for 60 min. The coefficient of friction (COF) increased from 0.25 to 0.65 with load, and the influence of alumina on frictional behaviour appeared to be negligible. With increase in load, wear volume of the composites increased from 7.5 × 10⁻² mm³ to 16.1 × 10⁻² mm³ for B₄C-10 wt% SiC - 3 wt% Al₂O₃ and from 4.7 × 10⁻² mm³ to 14.8 × 10⁻² mm³ for B₄C-10 wt% SiC - 6 wt% Al₂O₃ composites. Microcracking, abrasion and pull-outs contributed as major wear mechanisms of composites in selected wear conditions. The relation between wear behaviour and mechanical properties of sintered composites is discussed.     

Comparative studies on corrosion and tribological performance of multilayer hard coatings grown on WC-Co hardmetals

Multilayer TiN/TiCN/TiCN/TiC/TiN and TiN/TiCN/TiCN/TiC/Al₂O₃ hard coatings with total thicknesses of 15.7 μm and 9.3 μm were deposited on WC-10Co substrates using a chemical vapor deposition system. Evaluation of surface, cross-section morphologies, chemical composition and phases of coatings were analyzed by field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analyses respectively. Corrosion properties were evaluated in 3.5 wt% NaCl medium using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Tribological properties of fabricated multilayer hard coatings were evaluated using pin-on-disk tests. Results show that active dissolution of the WC-10Co occurred while the coated samples showed more anodic slopes as well as lower corrosion current densities. The corrosion current densities of 3.3 × 10⁻⁷ A/cm² and 7.5 × 10⁻⁸ A/cm² were obtained for the TiN/TiCN/TiCN/TiC/TiN and TiN/TiCN/TiCN/TiC/Al₂O₃ coated specimens which are much lower than 4 × 10⁻⁶ A/cm² of substrate. EIS analysis confirmed the results of potentiodynamic polarization curves. Delamination of the TiN coating and formation of titanium oxide compounds on the surface of the TiN/TiCN/TiCN/TiC/TiN coating revealed that oxidative wear mechanism is dominant for this sample, while adhesive wear mechanism was dominant for the TiN/TiCN/TiCN/TiC/Al₂O₃ coated sample.     

High-temperature sliding wear,elastic modulus and transverse rupture strength of Ni bonded NbC and WC cermets

The effects of rapid pulse electric current sintering (PECS), substitution of WC by NbC and Co by Ni, and carbide additives (TiC and Mo₂C) on the microstructure, elastic modulus, B3B transverse rupture strength (TRS) and high temperature sliding wear on WC-Co, WC-Ni, NbC-Co and NbC-Ni cermets were studied. Additions of x% Mo₂C and y% TiC (where x and y were <10 wt%), coupled with PECS, significantly refined the NbC-Ni cermet's carbide grain size from ~5.0 μm to <0.8 μm, giving mechanical properties comparable to WC-Co and WC-Ni cermets: >14 GPa hardness and ~10 MPa.m^1/2 fracture toughness (K_IC) and ball-on-three-balls (B3B) TRS > 1600 MPa. The sintering techniques had negligible effect on the samples' elastic and shear modulus, and all WC-based samples had higher elastic modulus than all NbC-based samples (by ~120 GPa). High temperature sliding wear tests were carried out using a ball-on-disk tribometer, with a 10 N force, at a sliding speed of 1.34 m/s for 0.8 km (10 min) and 2.4 km (30 min), using 100Cr6 (AISI 52100) steel balls at 400 °C and 0% humidity. For the 2.4 km sliding distance, all the WC cermets had lower wear volumes than NbC cermets, with LPS WC-0.5Cr₃C₂-10Co having the lowest wear volume. Additions of TiC and Mo₂C to NbC-12Ni improved the sliding wear resistance, with TiC having the greater effect, reducing the sample wear rate by over 30% from 15.1 × 10⁻⁶ mm³/N·m to 9.4 × 10⁻⁶ mm³/N·m after sliding distance of 2.4 km. Generally, the LPS samples had lower wear volumes than the corresponding SPS samples, due to higher K_1c and TRS.     

Effect of SiC nano-whisker addition on TiCN-based cermets prepared by spark plasma sintering

TiCN-based cermets with different amounts of SiC nano-whisker were prepared by spark plasma sintering at 1350 °C with an initial pressure of 30 MPa and a holding time of 8 min. The microstructural and mechanical properties of the as-prepared samples were investigated. The addition of SiC nano-whisker has a significant effect on the cermets, resulting in 6% increase in Vickers hardness and 63% increase in flexural strength, respectively, when 2.5 wt.% of SiC nano-whisker was added, as compared with its counterpart without whisker. X-ray diffraction analysis revealed that no SiC peaks were detected but some peaks of new hard phases due to the reactions of SiC with the cermet matrix. The resultant hard phases were present normally in the grain boundary in the cermets on the basis of observation by transmission electron microscopy, and they are responsible for the hardness increase of the as-obtained cermets. The observation by scanning electron microscopy on the microstructure indicated that the fracture mechanism of the as-obtained cermets was mainly inter-granular of TiCN grains.     

Effect of the Cr content on the sintering behaviour of TiCN–WC–Ni–Cr3C2 powder mixtures

In TiCN–W–Cr–Ni cermets produced by liquid phase sintering melting occurs at lower temperatures as their Cr content increases. For low Cr additions (up to 4 wt.%) eutectic temperatures are close to those found in the TiC–WC–Ni system. For 8 wt.% Cr and above, temperatures are similar to those found in the Cr–Ni–C system. The precipitation of M₇C₃ carbides is observed to start at 8 wt.% Cr in samples sintered at 1425 °C for 1 h. This sets a limit for the Cr solubility in the binder phase of these cermets around 18 wt.%. The dissolution of WC and Cr₃C₂ particles starts at temperatures as low as 1150 °C, but that the homogenization of the binder phase is only achieved after melting. The carbonitride phase exhibits the typical precipitation of inner and outer rims onto Ti(C,N) cores. However, a fine precipitation of Ni-rich particles is found inside Ti(C,N) cores, likely related to coalescence phenomena.     

Effects of sintering processes on the mechanical properties and microstructure of Ti(C,N)-based cermet cutting tool materials

In this study, two types of Ti(C_0.7,N_0.3)-based cermet cutting tool materials (Ti(C,N)–Mo–Ni–Co, named as TMNC, and Ti(C,N)–WC–Mo–Ni–Co–TaC–HfC, named as TWMNCTH) were fabricated by the hot pressed sintering process at different temperatures (from 1380 °C to 1500 °C) for different holding times (from 30 min to 60 min) in a vacuum atmosphere and at a compressive stress of 32 MPa. The polished surface and the fracture surface of the two types of cermets were observed by a scanning electron microscope (BSE/SEM) and energy dispersive spectrometry (EDS), and the relationships among sintering processes, mechanical properties and microstructure were discussed. The experimental results showed that the sintering temperature and holding time both had a great influence on the flexural strength and a small effect on the hardness and the fracture toughness of the two types of cermets. The two cermets both had the optimal comprehensive mechanical properties when they were sintered at 1400 °C for 30 min. The sintering temperature and holding time also had a great influence on the microstructure of the two cermets, and the grain sizes increased when the sintering temperature varied from 1400 °C to 1500 °C and the holding time varied from 30 min to 60 min. The properties and microstructure of the two cermets were also compared. The results indicated that the cermet TWMNCTH had a lower flexural strength, a similar value of fracture toughness, a higher hardness and a thicker rim in the microstructure.     

烧结温度对(Ti, W, Mo, Nb)(C, N)-(Co, Ni)金属陶瓷组织结构和性能的影响

本文以(Ti,W,Mo,Nb)(C,N)-(Co,Ni)基金属陶瓷材料为研究对象,研究烧结温度对金属陶瓷的成分、微观组织和力学性能的影响,初步探讨成分、微观组织与材料强度的关系。研究结果表明：烧结温度对(Ti,W,Mo,Nb)(C,N)-(Co,Ni)基金属陶瓷组织特征有显著的影响;合金的总碳(Ct%)随着烧结温度的提高而降低,当烧结温度达到1490℃时,合金总碳的急剧降低,导致合金组织中出现脱碳相(η相),从而使得合金的硬度(HV₃₀) 、断裂韧性(KIC)和抗弯强度(TRS)降低;1470℃烧结温度下,(Ti,W,Mo,Nb)(C,N)-(Co,Ni)基金属陶瓷合金的硬度(HV₃₀) 、断裂韧性(KIC)和抗弯强度(TRS)的匹配最佳,表现为在实际应用工况下的综合切削性能最优。     

Effects of Cr3C2 addition on the corrosion behavior of Ti(C,N)-based cermets

The Ti(C, N)-based cermets with different Cr₃C₂ addition were prepared and the effects of Cr₃C₂ addition on the microstructure and properties of cermets were discussed. The corrosion behavior of the cermets with different Cr₃C₂ addition was investigated emphatically in 2 mol/L HNO₃ solution. The results indicate that there is no obvious effect of Cr₃C₂ addition on the densification of the cermets, and all cermets are almost fully densified during sintering. The thickness of rim phase is reduced and the core size is increased remarkably in the cermets with 1 wt.% and 3 wt.% Cr₃C₂ addition; the grains are refined significantly in the cermets with the increase of Cr₃C₂ addition to 5 wt.%. The hardness and transverse rapture strength of the cermets are improved with Cr₃C₂ added properly. In HNO₃ solution, the corrosion resistance of cermets is improved remarkably by Cr₃C₂ addition. The corrosion of binder phase is predominant in the cermets in which the Ni binder phase without Cr has lower corrosion resistance than the rim phase; whereas the corrosion resistance of binder phase with high Cr content is better compared to the rim phase, so that the degradation of rim phase is predominant and a reticulate binder phase forms. With the increase of Cr₃C₂ addition, the Mo content in rim increases, and it is bad for the corrosion resistance of rim phase. Additionally, the inner rim phase has lower corrosion resistance than the outer rim phase owing to the higher Mo content.     

Microstructure and tribological performance of NbC-Ni cermets modified by VC and Mo2C

The current study reports on the influence of the addition of 5–15 vol% VC or/and Mo₂C carbide on the microstructure and mechanical properties of nickel bonded NbC cermets, which are compared to cobalt bonded NbC cermets. The NbC, Ni and secondary carbides powder mixtures were liquid phase sintered for 1 h at 1420 °C in vacuum. The fully densified cermets are composed of a cubic NbC grains matrix and an evenly distributed fcc Ni binder. NbC grain growth was significantly inhibited and a homogeneous NbC grain size distribution was obtained in the cermets with VC/Mo₂C additions. The mechanical properties of the NbC-Ni matrix cermets are strongly dependent on the carbide and Ni binder content and are directly compared to their NbC-Co equivalents. The liquid phase sintered NbC-12 vol% Ni cermet had a modest Vickers hardness (HV₃₀) of 1077 ± 22 kg/mm² and an indentation toughness of 9.1 ± 0.5 MPa·m^1/2. With the addition of 10–15 vol% VC, the hardness increased to 1359 ± 15 kg/mm², whereas the toughness increased to 11.3 ± 0.1 MPa·m^1/2. Addition of 5 and 10 vol% Mo₂C into a NbC-12 vol% Ni mixtures generated the same values in HV₃₀ and K_IC when compared to VC additions. A maximum flexural strength of 1899 ± 77 MPa was obtained in the cermet with 20 vol% Ni binder and 4 vol% VC + 4 vol% Mo₂C addition, exhibiting a high fracture toughness of 15.0 ± 0.5 MPa·m^1/2, but associated with a loss in hardness due to the high Ni content. The dry sliding wear behaviour was established at room temperature and 400 °C from 0.1 to 10 m/s.     

Ti (C,N)-based cermets sintered under high pressure

In this study, high pressure and high temperature sintering (HPHT) is adopted in the cermet fabrication process, and the microstructure and mechanical properties of cermets with TiC_0.5N_0.5–15WC–10Mo₂C–5TaC–10Ni–10Co (wt%) sintered under 5 GPa and different temperatures (900–1600 °C) using 6 × 14 MN cubic press are investigated. Results show that the densities of samples can reach up to 7.00 g/cm³. Vickers hardness and fracture toughness of the products are over 1727 HV30 and 7.2 MPa m^1/2 respectively. In addition, the sintering results are compared with the data that obtained from commercial samples which produced via conventional sintering technique. The conclusion is that high density and high hardness cermets can be obtained through HPHT sintering.     

High-temperature oxidation and hot corrosion of Cr2AlC

High-temperature oxidation and hot corrosion behaviors of Cr₂AlC were investigated at 800–1300 °C in air. Thermogravimetric–differential scanning calorimetric test revealed that the starting oxidation temperature for Cr₂AlC is about 800 °C, which is 400 °C higher than other ternary transition metal aluminum carbides. Thermogravimetric analyses demonstrated that Cr₂AlC displayed excellent high-temperature oxidation resistance with parabolic rate constants of 1.08 × 10⁻¹² and 2.96 × 10⁻⁹ kg² m⁻⁴ s⁻¹ at 800 and 1300 °C, respectively. Moreover, Cr₂AlC exhibited exceptionally good hot corrosion resistance against molten Na₂SO₄ salt. The mechanism of the excellent high-temperature corrosion resistance for Cr₂AlC can be attributed to the formation of a protective Al₂O₃-rich scale during both the high-temperature oxidation and hot corrosion processes.     

金属陶瓷nc-Ti(C,N)复合自润滑碳介质涂层的制备及性能EI北大核心CSCD

金属陶瓷涂层与类金刚石涂层的性能不同,在实际应用中两种涂层不能够互换使用,对于涂层的应用来说是一个缺陷。为了克服上述缺陷,将金属陶瓷涂层与类金刚石涂层的优异性能相结合,提出一种金属陶瓷复合自润滑碳涂层,并以三元TiCN涂层为对象,采用SEM、EDAX、XRD、Raman、XPS及维氏硬度计、压痕试验、摩擦磨损试验,研究具有自润滑特性的碳相对含量对涂层微观组织结构、力学及摩擦磨损性能的影响。结果表明:随着碳含量的增加,涂层表面更为致密光滑,涂层的主要组成相为TiN、TiC、TiC_(0.3)N_(0.7)及TiC_(0.7)N_(0.3);涂层中Ti-N、Ti-C键随着碳含量的增加呈现先增加后减少趋势,当碳含量为31.24 at%时,涂层中便有多余的非晶碳析出,形成金属陶瓷复合自润滑碳涂层nc-Ti(C,N)/a-C,此时涂层不锈钢的硬度最高为HV_(0.05)1052.2,同时涂层表现出较好的结合力、较低的摩擦因数及磨损率;涂层中碳含量为43.85 at%时,摩擦因数较低,在0.1以下波动,磨损率达最小值3.31×10^(−15) m^(3)/(N·m),但压痕周围有微裂纹产生。解释了自润滑碳对于金属陶瓷涂层性能的影响机制,可为高性能涂层的制备提供理论指导及试验依据。     

Dissolution behavior of TiN in liquid cobalt

A confocal scanning laser microscope (CSLM) with a hot stage was used to study the dissolution of TiN in liquid cobalt under different gas atmospheres. The dissolution of cubic carbonitrides in cobalt is a key step in the formation of the cobalt enriched zone (CEZ) during cemented carbide production. A model system of cobalt + TiN was used in this work and in-situ observations were made at 1500 °C and 1550 °C in 5%H₂-Ar and 5%H₂-N₂. Dissolution was observed in 5%H₂-Ar but not 5%H₂-N₂. At 1550 °C in 5%H₂-Ar, gas bubbles were observed in the liquid cobalt and rapid dissolution was observed. The dissolution rate of TiN was quantified at 1500 °C in 5%H₂-Ar. The rate-controlling step of TiN dissolution was hypothesized to be mass transfer of nitrogen in the liquid cobalt to the liquid/gas interface. This was tested by using the shrinking core model to calculate the diffusivity of nitrogen based on the measured dissolution rates. The diffusivity was between 6.4 × 10⁻⁵ cm²/s and 5.3 × 10⁻⁴ cm²/s, which was consistent with a previous study (approximately 1 × 10⁻⁴ cm²/s). The findings of this work can be utilized in detailed models of CEZ formation during cemented carbide production.     

Mechanical and tribological properties of electrically conductive SiC based cermets

Three different types of SiC based cermets with various content (30, 40, 50 wt.%) of electrically conductive TiNbC phase have been fabricated by hot-pressing without sintering additives. The effect of TiNbC content on the basic mechanical, electrical and tribological properties of SiC-TiNbC cermets was investigated. Tribological properties have been characterized by the ball-on-disc method at the ambient temperature and dry wear conditions with air humidity 35–40% at the load of 5–30 N, sliding distance of 500 m, with the static partner made from SiC. Corresponding wear rate was calculated and wear mechanisms were identified. Resulting materials were relatively hard, with increasing amount of TiNbC the hardness increased from 19.8 ± 1 GPa for 30 wt.% of TiNbC up to 25.4 ± 0.9 GPa at 50 wt.% of TiNbC. The fracture toughness values were independent on TiNbC phase and varied between 2.7 and 2.9 MPa.m^1/2. Similarly, Young's modulus increased from 354 GPa to 435 GPa. It was found that electrical conductivity of SiC cermets was rapidly improved with increased fraction of metallic phases and was three orders of magnitude higher at 30 wt.% TiNbC addition and around four order of magnitude higher at 50 wt.% of TiNbC metallic phase comparing to conventional semiconductive SiC ceramics with electrical conductivity ~ 10 Sm^− 1. Coefficient of friction (between 0.3 and 0.5) and wear resistance (10^− 6–10^− 7 mm³/Nm) were comparable with the wear resistant SiC materials.     

In situ production of ultra-fine Ti(C,N)–TiB2–Co cermets by reactive hot processing from the Co–Ti–C–BN system

In this paper, ultra-fine Ti(C,N)–TiB₂–Co cermets were prepared by reactive hot processing from the Co–Ti–C–BN system. Microstructure observation indicated that Co and TiB₂ uniformly distributed in the ultra-fine Ti(C,N) matrix. Carbon contents in the reactants had a great influence on the porosity and properties of synthesized cermets. In the range of 11.76–13.79 at.% carbon, dense samples were obtained. With increasing carbon contents, the relative density and hardness decreased due to the existence of residual carbon. The wear resistance of dense Ti(C,N)–TiB₂–Co cermets were better than that of YT15 cemented carbide. In addition, the reaction process in the Co–Ti–C–BN system was explored by differential scanning calorimeter and X-ray diffraction. Results revealed that Ti(C,N) was synthesized through the solid solution of carbon into TiN, and the addition of Co to Ti–C–BN mixtures promoted the production of Ti(C,N) by the formation of Co–Ti liquid.