Superplastic behavior of iron carbide

A ceramic-base material containing a matrix of 80% fine-grained iron carbide with 20 wt.% Fe, prepared from rapidly solidified powders, exhibited superplastic behaviour at elevated temperatures. High strain-rate-sensitivity exponents, m, of 0.5-0.7, were observed from 675-1000 deg C and at strain rates as high as 10 exp --2 s exp --1 . The fine-grained (3-4 mu m) material remained equiaxed, and exhibited no significant grain growth, after superplastic deformation. The ductility in the high m region was shown to be a strong function of temperature and strain rate, and to increase as the product epsilon exp(Qc/RT) decreased. This trend is associated with the increasing contribution of superplastic flow during grain boundary separation.