The two-step reaction sintering method was applied to fabricate SiC ceramics to improve wear resistance using feedstocks of Si, C, and SiC powder, where the powder size of SiC was changed in the wide range from 5 to 150 μm. Various powders were prepared as starting materials by mixing SiC powder of different sizes. The melt infiltration method was also employed using Si and Fe-Si alloy. This study investigated effects of the SiC powder size on the structure and wear properties of sintered SiC ceramics. The microstructure was observed using a laser microscope. Wear properties were evaluated using abrasive and erosive wear tests.
All sintered samples exhibited a constant area fraction of SiC of about 65%, irrespective of the SiC grain size. The SiC grain size only slightly affected the abrasive wear rate, suggesting that the wear rate was not governed by the SiC grain size, but rather by the area fraction of SiC. The erosive wear rate was influenced strongly by the SiC grain size, i. e., the intergranular distance. The wear rate decreased markedly as the SiC grain became finer. The most favorable abrasive and erosive wear rates using steel shots were about 2.2 × 10-6 mm3/Nm in all samples and 0.1 mm3/kg at intergranular distance of the SiC less than 20 μm. Consequently, sintered SiC ceramics with superior wear resistance were obtained using a finer SiC powder feedstock.
Casts of high strength brass containing machining chips of three different shapes were produced using centrifugal casting. The density, microstructure, Vickers hardness, and wear of the casts were analyzed in order to examine the effects of the shape of the machining chips on microstructure and mechanical properties of the casts. It was found that use of machining chips refines the microstructures in the casts and enhances cast hardness as well. However, because some pores were formed on the outer surface of the casts, the cast density decreased, and wear properties deteriorated. For commercial production, it is necessary to decrease the number of pores in order to increase density. The shape of the chips affected the degree of density and microstructural refinement of the precipitated and parent phases, but not the hardness or the amount of the loss of mass.