Comparative study of martensitic transformation behavior of NiAlMn and NiAlMnFe high temperature shape memory alloys

A comparative study of microstructure and martensitic transformation (MT) behavior of Ni59Al11Mn30 and Ni60Al19Mn16Fe5 high temperature shape memory alloys (SMAs) has been performed by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), optical microscopy, and micro-hardness testing. The MT temperature (MTT) of Ni59Al11Mn30 alloy is higher than that of Ni60Al19Mn16Fe5 alloy, and both alloys’ MTT increases with increasing annealing temperature. The temperature hysteresis and hardness of Ni59Al11Mn30 alloy are smaller than that of Ni60Al19Mn16Fe5 alloy. The MT behavior of Ni60Al19Mn16Fe5 is sensitive to aging temperature and its MTT and hysteresis decrease with increasing aging temperature. However, the MT behavior of Ni59Al11Mn30 alloy is not sensitive to aging temperature. The MT stabilization effects appear in both alloys during thermal cycles. This stabilization effect vanishes from the second thermal cycle. The quenched microstructure of Ni59Al11Mn30 and Ni60Al19Mn16Fe5 alloys is M plus gamma phase, in which the volume fraction of gamma phase is about 40 and 20%, respectively, and the microhardness of M is higher than that of gamma phase. No aging effects were found in both alloys after aging at 400 °C.