The Study on the fabrication of self-lubricant ceramics with high-hardness and surface modification of metals by their ceramics.

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We tried to fabricate self-lubricant composite ceramics consisting of transition metal nitride (TiN or ZrN) matrixes and hexagonal boron nitride (h-BN) dispersions. Mixture powders were milled with a planetary ball mill for not more than 180ks. Xray-diffraction patterns for the mixed powder showed that h-BN powder was finely grounded smaller than a submicron level and dispersed by the milling for longer than 36ks. The pulse current pressure sintering (PCPS) method was employed in order to consolidate the mixed powders. Relatively high density consolidation of more than 90% for single ZrN (or TiN) compact was obtained from the sintered compact of ZrN + 5mass % h-BN powders milled for 180ks. The hardness of the sintered compacts decreased with the addition of BN of more than 5 mass%. This result suggests that the sintering of mixed powder could be strongly inhibited by the addition of h-BN.Sliding friction tests between sintered compacts of composite ceramics and SUJ-2 steel ball were performed using a ball-on-disc apparatus, in order to estimate the tribological characteristics of sintered compacts by the friction coefficient evolution. Only a 5% addition of h-BN into the ZrN matrix showed a marked decrease in the friction coefficient to about 0.2, preventing adhesive wear. The sintered compact of ZrN-5 mass% h-BN powders milled for 180ks maintained low friction coefficient for two-times longer compared to the sintered compact of ZrN-5 mass% h-BN mixed powders. However, finer dispersion of h-BN particle under the range of nanometer size is essential to sustain the self-lubricant effect for longer time to be practical.Cr-B, Cr-B-N and Cr-B/Cr-B-N multilayer films were synthesized by reactive sputtering. Cr-B-N films contain Cr2B and h-BN phase with a small amount of other phases. Friction coefficient of Cr-B/Cr-B-N multilayer exhibited an intermediate value of 〜0.45 between those of Cr-B (0.9) and Cr-B-N (0.2).