TY - JOUR
T1 - Giant Magnetic-Field-Induced Strains in Polycrystalline Ni–Mn–Ga Foams
AU - Chmielus, M.
AU - Zhang, X. X.
AU - Witherspoon, C.
AU - Dunand, D. C.
AU - Müllner, P.
PY - 2009/11
Y1 - 2009/11
N2 - The magnetic shape-memory alloy Ni-Mn-Ga shows, in monocrystalline form, a reversible magnetic-field-induced strain (MFIS) up to 10%. This strain, which is produced by twin boundaries moving solely by internal stresses generated by magnetic anisotropy energy, can be used in actuators, sensors and energy-harvesting devices. Compared with monocrystalline Ni-Mn-Ga, fine-grained Ni-Mn-Ga is much easier to process but shows near-zero MFIS because twin boundary motion is inhibited by constraints imposed by grain boundaries. Recently, we showed that partial removal of these constraints, by introducing pores with sizes similar to grains, resulted in MFIS values of 0.12% in polycrystalline Ni-Mn-Ga foams, close to those of the best commercial magnetostrictive materials. Here, we demonstrate that introducing pores smaller than the grain size further reduces constraints and markedly increases MFIS to 2.0-8.7%. These strains, which remain stable over 200,000 cycles, are much larger than those of any polycrystalline, active material.
AB - The magnetic shape-memory alloy Ni-Mn-Ga shows, in monocrystalline form, a reversible magnetic-field-induced strain (MFIS) up to 10%. This strain, which is produced by twin boundaries moving solely by internal stresses generated by magnetic anisotropy energy, can be used in actuators, sensors and energy-harvesting devices. Compared with monocrystalline Ni-Mn-Ga, fine-grained Ni-Mn-Ga is much easier to process but shows near-zero MFIS because twin boundary motion is inhibited by constraints imposed by grain boundaries. Recently, we showed that partial removal of these constraints, by introducing pores with sizes similar to grains, resulted in MFIS values of 0.12% in polycrystalline Ni-Mn-Ga foams, close to those of the best commercial magnetostrictive materials. Here, we demonstrate that introducing pores smaller than the grain size further reduces constraints and markedly increases MFIS to 2.0-8.7%. These strains, which remain stable over 200,000 cycles, are much larger than those of any polycrystalline, active material.
UR - http://www.scopus.com/inward/record.url?scp=70350481466&partnerID=8YFLogxK
UR - https://scholarworks.boisestate.edu/mse_facpubs/42
U2 - 10.1038/nmat2527
DO - 10.1038/nmat2527
M3 - Article
SN - 1476-1122
VL - 8
SP - 863
EP - 866
JO - Nature Materials
JF - Nature Materials
IS - 11
ER -