Effect of alloying elements on fcc/hcp martensitic transformation and shape memory properties in Co-Al alloys

Effects of alloying elements (Si, Ti, V, Cr, Mn, Fe, Ni, Nb, Mo, Ta and W) on γ (fcc)/ε (hcp) martensitic transformation, ductility and shape memory (SM) properties of Co ₉₀Al ₁₀ alloy were investigated by means of differential scanning calorimetry, X-ray diffraction method, cold-rolling and an SM test. The addition of Ti, V, Mn, Fe, Ni, Nb, Mo, Ta or W decreased the volume fraction of the ε martensite phase (V _m), resulting in improvement of the ductility due to the stabilization of the γ phase, and the addition of Si or Cr, known as hep stabilizing elements, slightly decreased V _m. The relationship between the martensitic transformation temperatures and V _m was determined in Co-Al and Co-Al-Fe alloys. Co-Al alloys showed behavior different from that of other alloys. The SM effect decreased with decreasing V _m and the Co-Al binary alloys showed the highest SM effect in this study, whereas the transformation temperatures and the ductility could be controlled by the alloying element.