Martensitic transformation and shape memory effect in Pd₅₀Mn_50−xGa_x alloys

Martensitic transformation behaviors, microstructures, magnetic properties, and the shape memory effect (SME) were investigated for Pd₅₀Mn_50−xGa_x (0≦x≦25) alloys. Samples were prepared by arc melting, and they were found to have a single phase after solution heat treatments at 1473 K for 3 days followed by quenching. Though the martensitic transformation temperature for equiatomic Pd₅₀Mn₅₀ binary alloy being as high as about 1000 K, it drastically decreases upon doping with Ga, which is similar to Ni₅₀Mn_50−xGa_x alloys. The Pd₅₀Mn₂₅Ga₂₅ alloy with B2 structure was found to be antiferromagnetic with Néel temperature of 198 K. A magnetic phase diagram was constructed and compared with those for Ni–Mn–Ga, Pd–Mn–Sn, and Ni–Mn–Sn alloys. The crystal structures of the martensite phase were investigated using an X-ray diffractometer and a transmission electron microscope. From these investigations, one of the long-period stacking-ordered structures, 14 M, was found at room temperature in the Pd₅₀Mn₃₅Ga₁₅ alloy. SMEs were investigated for polycrystalline Pd₅₀Mn₃₅Ga₁₅ and Pd₅₀Mn₄₀Ga₁₀ samples by compression tests, and an SME up to 3.47% was observed for the Pd₅₀Mn₃₅Ga₁₅ sample. This is the first observation of SME for Pd–Mn-based alloys.