Microstructure control in two-phase (B2+Ll(2)) Ni-Al-Fe alloys by addition of carbon

Abstract

Carbon and titanium were added in two-phase (B2+ Ll(2)) Ni-Al-Fe alloys for carbides precipitation, and the additions of 0.2 wt.% C and 3 at.% Ti have been found to produce the most adequate high temperature structural material. Carbon doped alloys showed more refined microstructure than carbon free alloys. The carbides, which were formed in the as-cast microstructure showing equiaxed dendrites, appeared to play a role in suppressing grain growth and coarsening of the second phases. The NAF29-10 alloy, including no carbides, showed the lamellar type microstructure. while the NAF29-10-C alloy. including carbides, showed a much more refined mesh type microstructure. When the carbon free alloys were quenched into water. cracks occurred at the grain boundaries probably due to martensitic transformation, however, these cracks were not observed in the carbon doped alloys. In order to suppress quenching cracks in the carbon free alloys, the solutionizing treatment time was reduced. However, cracks still formed as a severe intergranular mode at an early stage of elastic deformation. The refined microstructure of carbon doped alloys could compensate for elongation loss due to solution hardening and precipitation hardening. As a result, the carbon doped alloys showed good room temperature ductility and also showed much higher yield strength than other alloys including no carbides over the entire temperature range. (C) 2002 Elsevier Science B.V. All rights reserved.