Influence of solidification rate on microstructure and texture of Ni47Ti44Nb9 cast alloy

Abstract:

The microstructure and texture of the Ni₄₇Ti₄₄Nb₉ ingots under the condition of fast and slowly cooling rate were studied through optical microscope (OM), scanning electronic microscope (SEM) and X-ray diffraction (XRD). And then the effect mechanism of solidification rate on microstructure and texture was discussed. The results indicated that the preferred growth direction of Ni₄₇Ti₄₄Nb₉ cast alloy is <113> and there is an important impact of solidification rate on the microstructure and texture of Ni₄₇Ti₄₄Nb₉ cast alloy. In detail, when the cooling rate is fast, uniform dendrites with texture of {113} can be achieved, while in the case of slowly cooling, columnar dendrites with specific direction can be obtained and the main textures of vertical section are close to {113}<361>, {113}<332> and {113}<141>. In addition, the directional growth of dendrites induced by directional heat conduction during the process of solidification is found the main reason for the formation of cast microstructure and texture.

Key words:shape memory alloy; Ni₄₇Ti₄₄Nb₉; solidification rate; texture; ingot