Carbide morphology in bulk and unidirectionally solidified Fe-C-V eutectics

Abstract

Investigations on the development of eutectic structures in Fe-C-V are of considerable interest as a result of the unique properties exhibited by these alloys. In this work a series of Fe-C-V alloys were prepared in order to investigate the solidification conditions and sequence, eutectic morphology, and the development of in situ eutectics. It was found that near perfect eutectic structures can be achieved by slow cooling of an Fe-C-V alloy. The eutectic obtained consisted of semispherical grains with fibrelike VC_1–x carbides. These fibres were found to develop appreciable ramifications during the solidification process. Assuming a critical area of liquid per fibre at the solidification front, as needed for stable eutectic growth, yielded a parabolic type of expression N_b ∝ t² for the number of branches (N_b) developed as afunction of the solidification time t. A qualitative model is proposed in this work to explain the different stages involved during the solidification of alloys of hypo-, hyper-, and eutectic composition. In addition, unidirectional solidification gave rise to in situ eutectics with aligned fibres. Finally, a solidification constant (u_eλ² = K) of 202 μm³ s⁻¹ for stable eutectic growth was experimentally determined.