定向凝固铁磁形状记忆合金Co-Ni-Ga的择优取向及其组织演化

PREFERRED ORIENTATION AND MICROSTRUCTURAL EVOLUTION OF DIRECTIONALLY SOLIDIFIED Co-Ni-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

采用液态金属冷却定向凝固方法制备出Co-Ni-Ga取向晶体,并研究了不同晶体生长速度下,晶体的轴向择优取向及其定向凝固组织的变化．结果表明:在温度梯度为250 K/cm、晶体生长速度为0．9 mm/min时,柱晶具有完全的〈110〉取向,存在单变体马氏体并有麦穗状γ′相析出;当生长速度提高至9 mm/min时,合金试样为〈111〉+〈001〉+〈110〉混合取向,凝固组织转变为单一的马氏体板条．EDS表明,定向晶体沿稳定生长区轴向成分比较均匀,无明显宏观偏析存在．采用此方法能够获得比较长的稳定的马氏体单变体区,为制备铁磁形状记忆合金取向多晶材料提供了新思路．

The directionally solidified Co-Ni-Ga ferromagnetic shape memory alloys were prepared by liquid metal cooling method. The preferred orientation along axial direction and microstrucrural evolution of the alloys under different growth velocities were investigated. The results indicated that under the condition of the temperature gradient GL=250 K/cm, and the growth velocity of 0.9 mm/min, （110} preferred orientation sample was obtained and the worm-like secondary phase γ′ precipitated in the martensitic matrix; with increasing the growth velocity up to 9 mm/min, 〈111〉＋〈001〉＋〈110〉 mixed orientation sample was obtained, and only martensite was observed. EDS results showed that the composition along the stable solidification zone was homogeneous. The present work proposed a directional solidification method to prepare long and stable solidification zone with single martensite variant in ferromagnetic shape memory polycrystals.