Room temperature friction and wear of Ti3SiC2-Ag sliding against Inconel 718 with a hemisphere-on-disc configuration were investigated in air. The effects of Ag content and TiAlN coating on Inconel 718 substrate were also included. Ti3SiC2/Inconel 718 tribo-pair showed high friction coefficient (0.6) and severe wear due to pullout of Ti3SiC2 grains was observed at a sliding speed of 1 m/s. Ti3SiC2-Ag composites had better tribological behavior than that of monolithic Ti3SiC2 in sliding against Inconel 718. At a sliding speed of 0.01 m/s, Ti3SiC2-Ag/Inconel 718 tribo-pairs exhibited moderate friction coefficient (0.32-0.4). At a sliding speed of 1 m/s, severe wear was not observed for Ti3SiC2-15vol.%Ag and Ti3SiC2-20vol.%Ag composites although the tribo-layer was not rich in Ag. When Ti3SiC2-Ag composites mated with TiAlN coating on Inconel 718 substrate, moderate friction coefficient (0.29-0.36) and low wear rate (10-6 mm3N-1m-1) were obtained at 0.01 m/s. A transition from mild wear to severe wear of Ti3SiC2-Ag composites at 0.1 m/s can be attributed to the ploughing effect by hard asperities on TiAlN coating.

The ZrB2 powders with different morphology were prepared by pressureless reactions, using ZrO2, B2O3, B4C, and graphite as raw materials. Three kinds of chemical reaction system were employed. The ratio of raw materials and reaction temperature were adjusted to prepare ZrB2 powders of different morphology and particle size. The phase composition and purity of the as-prepared powders were analyzed by XRD, while the morphology and particle size were analyzed by SEM. The ZrB2 powders were purified by removing impurities at 600 °C in a muffle furnace in air atmosphere. The results showed that in the reaction systems of ZrO2-B2O3-C and ZrO2-B4C-C, the ZrB2 could be generated at 1500 °C. The morphology of the as-prepared ZrB2 powders were particles, rod-like or near spherical for ZrO2-B2O3-C system and particles for ZrO2-B4C-C system. In the reaction system of ZrO2, B2O3, B4C, and C with a mole ratio of 3:2:1:8, the ZrB2 powders with high purity could be produced at 1700 °C. The ZrB2 powder was near spherical. After heat treatment, the particle size and morphology changed to some extent.

The surface polishing of Ti3SiC2 disk in fluids (water, ethanol, propanol, glycol, and glycerol) is conducted on a Buehler grinder/polisher and evaluated using surface roughness. Using Buehler automatic grinder/polisher, the Ti3SiC2 disks are grinded and polished in the as-mentioned lubricants by grinding disk of diamond with sizes of 45 μm to 3 μm. The surface roughnesses of Ti3SiC2 disks at each stage are measured by 3D surface profiler. The results show that the lowest surface roughness (Ra) of Ti3SiC2 disk obtained by mechanical polishing is 0.04 μm. The optimum polishing process of Ti3SiC2 disk is as follows: using water as lubricant, at a load of 5 N, for steps 1 to 4, the Ti3SiC2 and grinding disk rotates comparatively and the sizes of diamond particles on the abrasive disk are 45, 15, 9, and 3 μm, respectively. For step 5, the abrasive disk is woven cloth with no diamond particles. The duration of each step is 5 min. Using the same polishing process, the surface roughness of Ti3SiC2 disk by direct hot pressing is lower than that by in situ reactive hot pressing. Using the same polishing process but different lubricants, the surface roughness of the Ti3SiC2 disks increases in the order of water, ethanol, propanol, glycol, and glycerol. In water, the surface roughness of Ti3SiC2 disk decreases with the increasing quantity of water and polishing duration.

Silicon nitride (Si3N4) is one of the most important engineering materials. The developing trend of Si3N4 ceramic should be its composite with reinforce phase. However, due to its low self-diffusion coefficient at high temperature, the Si3N4 is very hard to be densified without sintering aids. In the present work, the Y2O3 and light rare-earth oxides of La series (La2O3, CeO2, Pr2O3, Sm2O3) and AlN, Al2O3, MgO, CaCO3 were chosen to be sintering aids. Their effect on the sintering of Si3N4 composite was studied. The results showed that the Y2O3 was the best sintering aid in all members, and the Y2O3-La2O3-AlN ternary composition was the best formula.