Electropulse modification of polycrystalline CuAlNi shape-memory alloy, its macro- and microstructure

Electro-Pulse Modification (EPM) techniques have been used in the fabrication of polycrystalline CuAlNi shape memory alloys. The grain-size of polycrystalline CuAlNi alloys is significantly reduced and the macrostructure is improved distinctly by EPM. The columnar crystal region of unmodified ingot is changed into very fine equiaxed crystal region and a nearly full equiaxed crystal region of ingot is obtained in the modified ingot, the corresponding concentrated shrinkage is greatly reduced. The modification effect is influenced by EPM voltage, frequency, time and cast mold. The microstructure of as-cast of the modified alloy is martensite, while that of unmodified alloy is flower-like NiAl-phase distributed over alpha+gamma(2) eutectoid structure. The EPM treatment reduces greatly the critical quench speed of the alloy. The modified alloy has good shape memory effect in cast state, while the unmodified alloy has almost no obtainable shape memory effect in cast state.