Effect of Al incorporation for Co on the gamma-beta phase boundary of rapidly solidified CoNiAl ferromagnetic shape memory alloys

The alloys Co64−xNi36Alx(at%, X=23,24,26 and 28) prepared through melt spinning technique revealed β- and γ-phase structure at room temperature. A monotonous increase in β-phase and simultaneous decrease in γ-phase has been observed with increasing Al content. The synergistic competition between β- and γ-phase influence β(B2)→L10 martensitic transformation. Therefore transformation broadening has been observed with Al content. Consequently, martensitic transformation temperature decreases and austenite transformation temperature increases. The γ-rich alloys showed magnetically soft phase, with high initial susceptibility and enhanced saturation magnetization. These alloys also revealed large magneto-strain values which are also supported by micro-structural morphology.