凝固速度对Ni47Ti44Nb9铸态合金组织和织构的影响

对比研究了Ni₄₇Ti₄₄Nb₉合金快冷铸锭和慢冷铸锭的宏、微观组织和织构特点,分析了凝固速度对组织和织构的影响机理。采用光学显微镜(OM)和扫描电子显微镜(SEM)观察了微观组织,采用X射线衍射(XRD)分析了织构。结果表明,铸态Ni₄₇Ti₄₄Nb₉合金具有<113>方向的择优生长取向；凝固速度对Ni₄₇Ti₄₄Nb₉合金铸态组织和织构的形成具有重要影响,快速冷却条件下获得均匀的树枝晶组织,铸锭的横、纵截面均形成{113}织构,慢速冷却条件下形成具有特定方向的柱状树枝晶,纵截面织构以{113}<361>、{113}<332>和{113}<141>为主；凝固过程中热量方向性传导造成的树枝晶定向生长是影响合金铸态组织和织构形成的主要原因。

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

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.