Microstructures and mechanical properties of in-situ fabricated alumina by spark plasma sintering process

Abstract

Alumina $(Al_2O_3)$ is most widely used engineering ceramic materials due to its excellent mechanical performance, high chemical resistance, good electrical properties, and so on. It is generally known that the strength and fracture toughness of $Al_2O_3$ depend on the grain size, The strength and fracture toughness are enhanced by refinement of $Al_2O_3$ grain size. Therefore, there are several researches for refinement of $Al_2O_3$ grain size There are two representative way to obtain fine Al2O3 grain size One is sintering of ultra-fine α- $Al_2O_3$ powder and the other is controlled crystallization of amorphous $Al_2O_3$ so that it shows ultra-fine grain size. Until now, the researches are focused on the sintering of ultra fine of nanocrystalline α-Al2O3 powder, because the simultaneous crystallization and densification is very difficult by conventional sintering process tough its advantages of low cost raw material and simple fabrication process. In this study, to fabricate ultra-fine grained α- $Al_2O_3$A, the amorphous $Al_2O_3$ powder was directly sintered by spark plasma sintering(SPS) process, i. e. in-situ sintering, where the crystallization and sintering process are combined without additional high temperature (>1300℃) calcination step. During the in-situ sintering process, amorphous to α-phase transformation was completed by 1100℃. Relative density of in-situ sintered alumina reached 99% , when it is sintered at 1400℃ under a pressure of 65 MPa without holding time at the sintering temperature. Although initial particle size of amorphous powder was similar to that of crystalline α- $Al_2O_3$ powder, average grain size of in-situ sintered alumina body was much finer(~500nm) than that of Al2O3 sintered from crystalline α- $Al_2O_3$ powder(~1.5μm). This result shows that in-situ sintering of amorphous powder by spark plasma sintering process is very prospective method to fabricate ultra-fine grained ceramics with high density. In in-situ sinter...