Microstructures of As-cast and Homogenized Hypereutectic Nb 62 Ti 16 Ni 22 Alloy

The microstructures of hypereutectic Nb 62 Ti 16 Ni 22 alloy after subjecting as-cast and homogenizing treatment were investigated in detail by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The Nb 62 Ti 16 Ni 22 alloy was prepared by vacuum arc melting, and then homogenized at 950 °C for 8 h. The results show that bcc-Nb, fcc-Ni, B2-NiTi, TiNb, Ni carbides (NiC x ) and NbNi 3 phases can be found in the as-cast alloy, but TiNb and NbNi 3 phases dissolved during homogenizing. Following the cross section of ingot, the fine equiaxed grain, the dendritic grain and the coarse equiaxed grain can be distinguished from surface layer to interior of the ingot, respectively. With homogenizing, the white long granular bcc-Nb phase was precipitated, and embedded in the gray B2-NiTi matrix phase. The coexistence of bcc-(Nb,Ti) phase and eutectic NiTi phase was affected by the diffusion of Nb element. The Vicker’s hardness of the homogenized alloy was higher than that of the as-cast alloy.