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采用液态金属冷却定向凝固方法制备了Ni-44Ti-5Al-2Nb-1Mo(原子分数,%)合金,分析了加热温度为1 550℃,抽拉速率为0.3、1.2、3.0、6.0、18.0mm/min时的定向凝固组织特征。结果表明,定向凝固没有改变合金的相组成,但改变了组成相的形态。定向凝固组织均由初生的NiTi相与晶间析出的Ti2Ni相、富Nb的Ti2Ni相组成,与铸态组织相同。定向凝固后,NiTi相发生了强烈的[100]择优取向。随着抽拉速率的增大,NiTi相沿[100]择优取向趋势增强,固液界面形态由发达的树枝晶变为胞状树枝晶,NiTi枝晶及析出相Ti2Ni、富Nb的Ti2Ni明显细化。定向排列的NiTi枝晶组织和分布在晶间的细小析出相将有益于合金高温强度和室温塑性的提高。
The Ni-44Ti-5Al-2Nb-1Mo (atomic fraction,%) alloy was prepared by liquid metal cooling directional solidification method. The heating temperature was 1 550 ℃, the drawing speed was 0.3,1.2,3.0,6.0,18.0mm / min directional solidification tissue characteristics. The results show that the directional solidification does not change the phase composition of the alloy, but changes the composition phase morphology. Directional solidification microstructure consists of primary NiTi phase precipitated Ti2Ni phase and Nb-rich Ti2Ni phase composition, and as-cast microstructure. After directional solidification, NiTi phase has a strong [100] preferred orientation. With the increase of drawing rate, the preferred orientation of NiTi phase increases along [100], and the morphology of solid-liquid interface changes from developed dendrites to cellular dendrites, NiTi dendrites and precipitates, Ti2Ni, Nb-rich Ti2Ni. The directional arrangement of NiTi dendrites and the fine precipitates distributed in the intergranular phase will be beneficial to the high temperature strength and room temperature plasticity of the alloy.