Laminated ceramics with weak interface layers have been proven to be effective in toughening ceramics. The energy absorption ability of laminated ceramics may also benefit their ballistic performance. However, the effect of the layer structure on the ballistic performance of laminated ceramics has not been studied. Focusing on the application for body armor, this paper studied the effect of the different layer structures on the ballistic performance of laminated SiC ceramics. The laminated SiC ceramics with different layered structures were designed and prepared by tape-casting and hot-pressing. When used for the ‘in conjunction with’ armor system, the laminated SiC ceramics with a gradual-layered structure had the backface signature depth of 30% less than the laminated SiC with no interface structure and 50% less than the commercial solid-state sintered SiC. However, when used stand-alone, the laminated SiC had a similar ballistic performance regardless of the layer structure, which was likely due to the weak back support. In conclusion, the ballistic performance of the laminated ceramics was related to the back support of the armor system. When used for the ‘in conjunction with’ armor system, the laminated SiC had a better ballistic performance than that of the solid-state sintered SiC.

Dry friction between seal faces, caused by unstable or extreme operating conditions, significantly affects the running stability and service life of mechanical seals. Therefore, in this work, nanocrystalline diamond (NCD) coatings were prepared on the surface of silicon carbide (SiC) seal rings by hot filament chemical vapor deposition (HFCVD). The friction test results under dry environment reveals that the coefficient of friction (COF) of SiC–NCD seal pairs is about 0.07–0.09, which were reduced by 83–86% compared to SiC–SiC seal pairs. The wear rate of SiC–NCD seal pairs is relatively low, ranging from 1.13 × 10⁻⁷ mm³/N·m to 3.26 × 10⁻⁷ mm³/N·m under different test conditions, which is due to the fact that the NCD coatings prevent adhesive and abrasive wear between the SiC seal rings. The analysis and observation of the wear tracks illustrate that the excellent tribological performance of the SiC–NCD seal pairs is due to a self-lubricating amorphous layer formed on the worn surface. In conclusion, this work highlights a pathway to enable mechanical seals to satisfy the high application requirements under highly parametric working conditions.

Silicon carbide (SiC) ceramic is an ideal material for mechanical seal because of its super hardness, high strength, low friction coefficient, good thermal conductivity, and resistance to friction and wear. However, due to relatively high resistivity of SiC ceramic, the triboelectric charge caused by rubbing of mechanical seal end-faces could not be released. It is terrible that the accumulation of triboelectric charge could cause electrochemical corrosion, which would accelerate wear. To decrease the resistivity of SiC ceramic is a desire for improving the performance of mechanical seal. In this research, decreasing resistivity of pressureless sintered SiC ceramic was investigated by conductive pathways through semiconductive grains in a body by incorporation of graphene, which has an extremely low resistivity. With the increasing of graphene from 0 to 2 wt.%, the volume resistivity of SiC ceramics sintered with graphene decreased logarithmically from >10⁶ to around 200 Ω·cm, and the bulk density decreased gradually, from 3.132 to 3.039 g/cm³. In order to meet the requirements of mechanical seal, SiC ceramic sintered with 1 wt.% of graphene, for which the volume resistivity is of 397 Ω·cm, the bulk density is of 3.076 g/cm³, and the flexural strength is of 364 MPa, was optimized when all properties were taken into consideration. It is possible to fabricate low-resistivity SiC ceramic as a useful friction pair material for mechanical seal in a special condition, without excessive loss of their excellent mechanical properties by the introduction of partially connected graphene as conductive pathway into semiconducting ceramic.

Polycrystalline diamond (PCD)-coated mechanical seal rings were prepared by hot filament chemical vapor deposition (HFCVD) on graphite-loaded silicon carbide (GSiC) substrates. From the initial deposition process, the diamond first nucleated and then grew into a dense coating with grain size of 4 μm and thickness of 12.3 μm. The well-grown PCD coating, as confirmed by Raman spectroscopy and X-ray diffractometry, significantly improves the pressure–velocity limit of the mechanical seal applied in harsh operating conditions, no matter whether for a hard-to-soft mating combination or a hard-to-hard mating combination. Comparing GSiC against sintered silicon carbide (SSiC) combination (GSiC/SSiC), GSiC against graphite combination (GSiC/graphite) and PCD against graphite combination (PCD/graphite), PCD against SSiC combination (PCD/SSiC) shows the highest pressure velocity (PV) limit of 42.31 MPa·m/s with 4 kN loading at 4500 rpm rotation speed. An extremely low and stable friction coefficient and super mechanical properties under harsh conditions can be approved as the source of the high PV limit of PCD coating. A mechanical seal with PCD coating can be used for more demanding applications.