Phase transformation and indentation response in the surface of MoSi_2 exposed to vacuum at high temperature

摘要

A MoSi_2 sample contains a small amount of Mo_5Si_3C phase was exposed to vacuum at 1300℃ for 100h. The surface of the sample was examined by XRD, SEM and indention test. Two layers were revealed in the surface of the MoSi_2 sample. The outer layer consists of (002) textured Mo_5Si_3 phase and porosities. The Mo_5Si_3 phase is formed through the decomposition of the MoSi_2 phase. The Mo_5Si_3C phase, which is a constituent phase in the matrix, disappears in the inner layer. The phase transformation process was analyzed in the light of assuming that silicon is the predominant diffuser. Indentation test on the surface revealed that the fracture mode of Mo_5Si_3 is completely transgranular.