Increasing magnetoplasticity in polycrystalline Ni-Mn-Ga by reducing internal constraints through porosity.
Foams with 55% and 76% open porosity were produced from a Ni-Mn-Ga magnetic shape-memory alloy by replication casting. These polycrystalline martensitic foams display a fully reversible magnetic-field-induced strain of up to 0.115% without bias stress, which is about 50 times larger than nonporous, fine-grained Ni-Mn-Ga. This very large improvement is attributed to the bamboolike structure of grains in the foam struts which, due to reduced internal constraints, deform by magnetic-field-induced twinning more easily than equiaxed grains in nonporous Ni-Mn-Ga.
Boonyongmaneerat
Yuttanant
Y
Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
Chmielus
Markus
M
Dunand
David C
DC
Müllner
Peter
P