Growth of large crystallites of Co 37Ni 34Al 29 ferromagnetic shape memory alloys under super-high temperature gradient directional solidification

Abstract

Large crystallites of Co 37Ni 34Al 29 ferromagnetic shape memory alloys were prepared by zone melting liquid metal cooling (ZMLMC) directional solidification; the effect of solidification rate and temperature gradient on the crystal microstructure and orientation was studied. Results show that at the solidification rate of 15 μm/s the alloy morphology exhibits coarse columnar crystal that is several millimeters in size and with worm-like γ′ precipitate, while at 150 μm/s it presents coarse dendrite surrounded by β+γ interdendritic eutectic. At the temperature gradient of 800 K/cm, a strong 〈1 1 0〉 oriented austenite crystal can be obtained at 15 μm/s and the preferred orientation turns into 〈1 0 0〉 direction as the solidification rate increases to 150 μm/s. The change of preferred orientation with solidification rate becomes more remarkable when the temperature gradient reaches 1200 K/cm.