Martensitic transformation and shape memory effect in Pd50Mn50−xGax alloys

Abstract

Martensitic transformation behaviors, microstructures, magnetic properties, and the shape memory effect (SME) were investigated for Pd50Mn50−xGax (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 Ni50Mn50−xGax 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.