Precipitations in a Ni Ti-Nb alloy during annealing

The methods of XRD, TEM and energy dispersive X-ray (EDX) were used to investigate the precipitation process in Ni47Ti44Nb9 specimens annealed at 850 degrees C. A diffusional transformation took place when the alloy was subjected to a long time heat treatment, most of beta-Nb particles disappeared and a new precipitate (Ni, Nb)(3)Ti with an h. c. p. structure (a=0.512 2 nm, c=0.837 6 nm, and c/a= 1.63) was found, which was similar to Ni3Ti in structure. The upper critical precipitation temperature of the alloy was above 950 degrees C, it meant that the presence of niobium inhibited the occurance of the precipitation. In addition, the orientation relationship between the remaining beta-Nb precipitate and matrix was observed: [111](beta-Nb)//[111](M), (110)(beta-Nb)//(110)(M).