Phase equilibria in the Fe-rich portion of the Fe-Ni-Si system

Investigations relating to the phase equilibria involving the alpha, gamma, sigma and liquid phases and the ordering reactions in the bcc aluminides of the Fe-Ni-Si system in the temperature interval 800 similar to 1100 degrees C have been carried out by energy dispersion X-ray spectroscopic (EDS) analysis and transmission electron microscopy (TEM). The equilibrium compositions of the gamma (Al: fcc-Fe), alpha (A2: bcc-Fe), sigma (sigma phase) and liquid phases and the critical boundaries of the continuous ordering transition in the alpha phase legion have been determined. It is observed that the critical temperatures of the continuous ordering transitions alpha(A2)/alpha'(B2) and alpha'/alpha"(DO3) are mainly functions only of Si content, and not of Ni. It is also found that the tie-line configurations and the partition behavior of the constituents at the alpha/gamma phase equilibrium are strongly affected by the order-disorder transitions in the alpha phase. Results pertaining to these phase equilibria and the stability of the ordered bcc aluminides are presented and discussed. (C) 1998 Elsevier Science S.A.