Solidification processing of NbCr2 alloys

Microstructural development in alloys bordering the NbCr2 Laves phase composition has been evaluated following solidification processing. With splat quenching of binary alloys, rapid solidification has yielded supersaturation of both Nb-rich and Cr-rich primary solid solutions as well as some solubility extension of the C15 phase during cooling as compared to as-cast structures. Ternary additions of Ti are soluble in NbCr2 along the pseudobinary NbCr2-TiCr2 section for C15 structures and completely miscible in bcc Nb and Cr solutions. In the rapid freezing of splats, modest Ti additions to NbCr2 enhance the development of an extended bcc solution during freezing and the supersaturation of the C15 phase during solid-state cooling. In the solid state, the C14 →C15 transformation of the Laves phase is suppressed partially in arc-cast ingots and more completely at high cooling rates. Upon heating, thermal analysis has revealed that the retained C14 phase undergoes a decomposition sequence with at least two stages, possibly involving polytypes and associated faulting, to the stable C15 structure. The microstructual options developed by solidification processing, solid state transformations, and alloying have been observed to modify the brittle behavior of the as-cast structures