Microstructural Evolution and Magnetic Properties of Aged CoNiGaAl Shape Memory Alloy

A study on the influence of aging heat treatment conditions at 823 K for 3 h, 24 h, and 120 h, on microstructure, martensitic transformation, and magnetic and mechanical properties of Co50Ni23Ga27−X Al X alloys (X = 0 and 1 at.%) was performed by using x-ray diffraction (XRD) analysis, optical microscopy (OM), energy-dispersive spectrometer (EDS), differential scanning calorimeter (DSC), and vibrating sample magnetometer (VSM). The results show that the microstructure of both aged alloys consists of martensite and fcc second γ phase in addition to ordered cubic gamma prime (γ′) phase precipitates in martensite. The martensitic transformation temperature peak (M p) elevates with prolonging aging time and decreasing valence electron concentration (e v/a). Saturation magnetization (M s) decreases, whereas both remanence magnetization (M r) and coercivity (H c) increase with aging time. Meanwhile, the aging time enhances the hardness property (H v) of the investigated alloys.