The preparation of in-situ MoSi2-SiC-MoB three-phase composite completely eliminating the PEST phenomena

Publication date: Available online 11 June 2019Source: Materials Chemistry and PhysicsAuthor(s): Zhang xiaoli, zhang xiaoyi, Duan jiawei, Kathy LuAbstractBecause of high melting point (2300 K), rather low density (6.28g/cm3) and excellent elevated oxidation resistance (above 1600 °C), MoSi2 have been treated to be one of the most attractive high temperature materials. However, thus a MoSi2 materials have their intrinsic limitations, one of the worst things is it suffered from an accelerated oxidation at low temperatures (between 350–550 °C) which was first discovered by Fitzer in 1955 and was named PEST oxidation. The phenomena of PEST extremely hindered the application of MoSi2 in advanced engineering and aerospace, also limited its longevity and safety. In this paper, an in-situ MoSi2-SiC-MoB three-phase composite was prepared by reactive infiltration process which is known as low-cost and net shape method, and after the oxidation process in 500 °C for 3 h, it was found that there is no PEST occurred anymore. And the residual bending strength of this composite will still over 68%. The reasons for overcoming PEST would be the in-situ formed MoB phase will be stiffly covered over the surface of MoSi2 grains, and the volume expansion of SiC phase and volume contraction of MoB phase will be matched in the composite system 9.7%wt MoB/8.6%wt SiC/ MoSi2.
Source: Materials Chemistry and Physics - Category: Materials Science Source Type: research