TiC bonded diamond composites were prepared from a mixture of Ti, graphite, and diamond powders as raw materials, with Si as sintering additives, through high-temperature and high-pressure (HTHP) technology. The reaction between Ti and graphite under 4.5–5 GPa pressure and 1.7–2.3 kW output power can produce TiC as the main phase. The diamond particles are surrounded by TiC, and the interface is firmly bonded. The coefficient of friction (COF) of TiC–diamond composites with POM and PP balls decreases with increasing load for a specific friction velocity. However, the COF of TiC–diamond composites with agate, Cu and Al balls increases with the rising load because of the enhanced adhesive wear effect. The COF of PP, Cu and Al balls slightly increases with the increase in friction velocity at a certain load. SEM results show that the surface of agate balls has rough, pear-shaped grooves and shallow scratches. The scratches on the surface of POM balls are wrinkled. The PP balls have pear-shaped groove scratches on their wear surfaces. The wear mechanism of TiC–diamond composites with Cu ball pairs is primarily adhesive wear. The abrasion of TiC–diamond composites with Cu ball pairs remains almost unchanged as the load increases. However, the depth and width of the pear-shaped grooves on the wear surface of TiC–diamond composites are significantly increased. This phenomenon may be attributed to the high rotational speed, which helps to remove the residual abrasive debris from the friction grooves. As a result, there is a decrease in both the depth and width of the pear-shaped grooves, leading to a smoother overall surface. The wear mechanism of TiC–diamond composites with Al ball pairs is abrasive wear, which increases with an increasing load. When the load is constant, as the speed increases, the wear morphology of TiC–diamond composites with Al ball pairs transitions from rough to smooth and then back to rough again. This phenomenon may be attributed to the wear mechanism at low speeds being groove wear and adhesive wear. As the speed increases, the wear particles are more easily removed from the wear track, leading to a reduction in abrasiveness. As the speed increases, the wear surface becomes roughened by a combination of grooves and dispersed wear debris. This can be attributed to the increased dynamic interaction between surfaces caused by higher speed, resulting in a combination of abrasive and adhesive wear. In addition, Cu and Al ball wear debris appeared as irregular particles that permeated and adhered to the surface of the TiC phase among the diamond particles. The results suggest that TiC–diamond composites are a very promising friction material.

Rare-earth oxysulfides are a class of functional ceramic materials with excellent physico-chemical properties and rich functionality. In this study, La₂O₂S powders were prepared from La₂S₃ and La₂O₃ powders at 1000 °C by pressureless sintering. La₂O₂S compacts were synthesized from La₂S₃ and La₂O₃ powders at 800–1600 °C by spark plasma sintering. The influences of sintering temperature and time on the preparation of La₂O₂S were studied. XRD results indicated that La₂O₂S ceramics were synthesized successfully and that the lattice constants of La₂O₂S were close to the theoretical values. SEM showed that the microstructure of La₂O₂S compacts was homogeneous. The specific heat of La₂O₂S mainly came from lattice contribution, and its Debye temperature was 237 K. The UV–visible absorption spectra showed different absorption levels in the 240–300 nm range. Raman spectroscopy revealed distinct peaks at different temperatures, indicating changes in the covalence band. The relative density of La₂O₂S ceramics was 92% and lower than theoretical values. Hardness of the synthesized La₂O₂S was greater than that of Gd₂O₂S ceramics.

Cu₂S has wide-ranging applications in the energy field, particularly as electrode materials and components of energy storage devices. However, the migration of copper ions is prone to component segregation and copper precipitation, impairing long-term thermal stability and service performance. Ce₂S₃ not only possesses the unique 4f electron layer structure of Ce but also has high thermal stability and chemical inertness. Here, we report for the first time that the thermal stability and mechanical properties of Cu₂S can be significantly enhanced by introducing the dispersed phase Ce₂S₃. Thermogravimetry—differential scanning calorimetry (TG-DSC) results show that the addition of 6 wt% Ce₂S₃ improves the thermal stability of Cu₂S sintered at 400 °C. X-ray diffraction (XRD) results indicate that the crystal structure of Cu₂S gradually transforms to tetragonal Cu_1.96S and orthorhombic Cu_1.8S phase at 400 °C with the increase of Ce₂S₃ addition. Scanning electron microscopy (SEM) results show that the particle size gradually decreased with the increase of Ce₂S₃ amount, indicating that the Ce₂S₃ addition increased the reactivity. The Ce content in Cu₂S increased gradually with the increase of Ce₂S₃ amount at 400–600 °C. The 7 wt% Ce₂S₃-Cu₂S exhibits paramagnetic behavior with a saturation magnetization of 1.2 µ_B/Ce. UV-Vis analysis indicates that the addition of Ce₂S₃ can reduce the optical energy gap and enrich the band structure of Cu₂S. With increasing addition of Ce₂S₃ and rising sintering temperature, the density of Ce₂S₃-Cu₂S gradually increases, and the hardness of Ce₂S₃-Cu₂S increases by 52.5% at 400 °C and by 34.2% at 600 °C. The friction test results show that an appropriate addition amount of Ce₂S₃ can increase the friction coefficients of Cu₂S. Ce₂S₃ modification offers a novel strategy to simultaneously enhance the structural and service stability of Cu₂S by regulating Cu ion diffusion and suppressing compositional fluctuations.

The Ti₃SiC₂TiSi_x ceramic composite was synthesized in situ from a mixture of 3Ti:1.5Si:1.2C powders under pressures ranging from 2 to 5 GPa and temperatures of 1150 °C to 1400 °C. At medium and high temperatures (4–5 GPa and 1400 °C), Ti₃SiC₂ dissolves into the cubic TiC phase. SEM analysis revealed that the high-pressure-produced multilayer structure of Ti₃SiC₂ remained intact. The friction properties of Ti₃SiC₂-TiSi_x composites combined with copper and aluminum were studied under both dry and lubricated conditions. After the break-in period, the Ti₃SiC₂-TiSi_x/Al combination exhibited the lowest friction coefficient: approximately 0.2. In dry-sliding conditions, the friction coefficient varies between 0.5 and 0.8. The wear mechanisms for Ti₃SiC₂-TiSi_x composites paired with aluminum primarily involve pear groove wear and adhesive wear during dry friction. Irregularly shaped aluminum balls accumulate in the pear grooves and adhere to each other. With increasing sintering pressure, the average friction coefficient of Ti₃SiC₂-TiSi_x composites against Cu ball pairs first increases and then decreases. The wear rate of the samples did not vary significantly as the sintering pressure increased, whereas the wear rate of Cu balls decreased with increasing sintering pressure. The adhesive wear of the Ti₃SiC₂-TiSi_x composite with its Cu counterpart is stronger than that of the Al counterpart. Abrasive chips of Cu balls appeared in flake form and adhered to the contact interface.

MoSi₂ composites containing 5–50 wt.% nominal Ti–Si–TiC precursor (Ti:Si:TiC = 1:1.2:2; TSC) were pressurelessly sintered under an Ar-protected atmosphere at 1300–1500 °C for 120 min. Phase evolution, surface morphology, Raman features, Vickers microhardness, dimensional response, and geometric bulk-density trends were evaluated as functions of precursor fraction and temperature, with auxiliary TG–DSC of unsintered powder mixtures. MoSi₂ remained the dominant crystalline phase across the investigated conditions. Ti₃SiC₂-related reflections were most evident at 1425–1450 °C, whereas Mo₅Si₃-related features became more apparent in selected 5–15 wt.% specimens at 1500 °C. Compared with the 50 wt.% specimens, lower-TSC specimens generally retained more continuous Mo–Si-rich surface regions, while the 50 wt.% specimens exhibited coarse Ti-rich domains, open pores, and pronounced compositional heterogeneity. Raman spectra revealed localized crystalline-Si-rich regions, consistent with a spatially nonuniform Si distribution. TG–DSC of the unsintered mixtures showed apparent net mass increases of 2.36–4.44% at 1300 °C under nominal Ar. The highest Vickers microhardness, 1114.6 ± 98.8 HV_0.2, was obtained for the 50 wt.% specimen at 1400 °C. The maximum direction-averaged linear shrinkage was 15.52% for the 10 wt.% specimen at 1500 °C, whereas the 50 wt.% specimens expanded at 1300–1450 °C. Considering phase constitution, surface continuity, Vickers microhardness, dimensional response, and geometric bulk-density trends, 10–25 wt.% nominal TSC at 1400–1450 °C was identified as a qualitative candidate processing region for subsequent validation rather than as a fully optimized condition.