Abstract
The oxidation behavior for in situ synthesized MoSi2-SiC composites with different SiC volume fraction at 500℃ was investigated.The results of oxidation for 1000 h indicate that the oxidation resistance for composites is significantly higher than that of monolithic MoSi_2,MoSi2-30%SiC composite in situ synthesized possesses higher oxidation resistance compared with the traditional composite which is fabricated by hot-pressing the mixture of commercial powders of MoSi_2 and SiC.After oxidation for 1000 h,the composites have not been observed to disintegrate(pest).The oxidation kinetics curves are divided into three stages:incubation period,rapid oxidation period and the steady-state. The oxide scale consists of MoO_3,amorphous silica and β-SiC,therefore,the oxidation of the materials is mainly done between MoSi_2 and O_2,and SiC is not oxidized.The surface morphology observations of samples oxidized for 5,10 and 20 h show that the phase boundary is the preferential oxidation site, the oxides formed at the initial stage of oxidation are irregular-shaped,and MoO_3 whisker and oxide cluster mainly composed of amorphous SiO_2 come gradually into being along with the development of oxidization.It is also found that the nucleation and growth of MoO_3 whisker preferentially take place at the concave and convex sites of substrate surfaces.
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