Microstructure And Properties Of The Si-B-C-N-Zr Ma-powders And Ceramics

In this paper, Si-B-C-N-Zr powders were prepared by mechanical alloying(MA)with two different methods using c-Si, BN, C, Zr, B as raw materials. The influence ofthe propotion of Zr and B, parameters of ball milling on the microstructure, particlesize, and other properties of the powders were studied. And Si-B-C-N-Zr ceramicswere sintered by hot-pressing (HP). The effect of propotion of Zr and B, temperatureof sinting, parameters of ball milling on the microstructure and properties ofSi-B-C-N-Zr ceramics were also investigated.The result shows that the powders present amorphous after high-energy ballmilling, the degree of amorphous decresed with the increase of propotion of Zr and Bdue to the formation of ZrB2. The powders prepared by two different parameters ofball milling have the same morphology, particle size and chemical bond. The mediansize of the powders less than1μm, and the powders have Si-C,B-N，B-N-C,C-C,Zr-B,Zr-O chemical bondings.With the sinting tempreature increase from1800℃to1900℃, the density ofceramic had no change but the mechanical property improved a little. With the sintingtemperature up to2000℃, the density and mechanical property of ceramic had asignificantly improvement. The sintering temperature, propotion of Zr and B, andparameters of ball milling have no influence on the phase composition ofSi-B-C-N-Zr ceramics that consist of SiC,BN（C）,ZrB2,ZrN, little ZrOxand/or ZrO2and the microstructure of ceramics. The flexure strength and Vickers hardness ofSi-B-C-N-Zr ceramics increased with the propotion of Zr and B, but the elasticmodulus decreased. Si-B-C-N-Zr ceramics have a low fracture toughness about3MPa·m1/2. The ceramics that prepared by two different parameters of ball millingnearly have the same mechanical property.After1h oxidation at1100℃,1200℃,1300℃, the surface of ceramic have thesame phase composition that mainly ZrSiO4with a little ZrO2and SiO2. The surfaceof ceramic were covered with a continuous liquid layer after oxidation at1100℃and1300℃, but discontinuous at1200℃. The oxidation weight gain of ceramic increasedwith time, present tow parabolic laws. The oxidation weight gain of ceramic increasewith the propotion of Zr and B; the oxidation weight gain curves of ceramics with twotwo different parameters of ball milling have no no obvious differences.