Highly porous spark plasma sintered Ni-Mn-Ga structures

A new approach for the processing of porous crystalline Ni-Mn-Ga compacts by spark plasma sintering (SPS) from a mixture of gas atomized Ni-Mn-Ga and NaCI powders (25/75 vol%) is reported. The NaCI was removed to reveal a highly porous skeleton of Ni-Mn-Ga. Solid skeletons were heat-treated in vacuum to grow the grains to a size of 22-23 mu m, from the 1.7 mu m found in the powder. The sample with the highest porosity showed a magnetic-field-induced strain of 1.24%. The MFIS is attributed to magnetically induced twinning due to the reduction of grain boundary constraints and the formation of preferred orientation. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.