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; Chmielus, Markus; Dunand, David C.; and Müllner, Peter. (2007). "Increasing Magnetoplasticity in Polycrystalline Ni-Mn-Ga by Reducing Internal Constraints Through Porosity". Physical Review Letters, 99(24), 247201-1 - 247201-4. http://dx.doi.org/10.1103/PhysRevLett.99.247201