Magnetic field-induced rubber-like behavior in Ni-Mn-Ga particles/polymer composite

Abstract

Single crystalline Ni-Mn-Ga is well known as a prototype ferromagnetic shape memory alloy (FSMA) exhibiting a giant magnetic field-induced strain (MFIS), up to 12%, due to the magnetically driven twin boundary rearrangement. The large stroke and fast magnetomechanical response make it important for actuators and sensors. Polycrystalline Ni-Mn-Ga is inexpensive and technologically easy accessible, but constrains from the grain boundaries inhibit the twin boundary motion, whereby a very low MFIS is observed. Here, we have shown for the first time that a polycrystalline Ni-Mn-Ga can be split into the magnetostrain-active single grains which, being specially assembled in a silicone polymer matrix, caused large and fully reversible MFIS of the resulting composite. We termed the unique reversibility of a large MFIS of the composite as the magnetic field-induced rubber-like behavior. The magnetostrain of individual particles was explored by the X-ray μCT 3D imaging. The results suggest novel solutions for development of the low cost magnetic actuators and sensors for haptic applications.

Framework of magnetostrain responsive Ni–Mn–Ga microparticles driving magnetic field induced out-of-plane actuation of laminate composite

“…Fulfilling these conditions in Refs. 21 , 28 enabled the aforementioned breakthrough in the FSMAs research area.…”

“…A recipe to remove grain boundaries in polycrystalline Ni–Mn–Ga alloys was radically advanced in our recent publications, where these alloys were carefully disintegrated, using specially elaborated intergranular fracture technology, into separate single crystalline grains exhibiting a large MFIS 19 – 25 . Such particles subsequently have been used to create bulk magnetostrain active Ni–Mn–Ga/polymer composites 21 – 23 . Here it is worth recalling that FSMAs show large work output, in the order of 10 7 J m −3 , and very favorable scaling behavior as far as this value tends to rise up to 10 8 J m −3 with decreasing a sample size, all of those assure their multifunctional properties being retained on the microscale 26 .…”

“…Recent elaboration of the bulk composite materials consisting of the Ni–Mn–Ga single crystalline (SC) particles embedded in a silicone polymer, which have shown both a 4% of MFIS and a new phenomenon of the magnetic field induced rubber-like behavior, was a breakthrough in the about 20-years-efforts to create such materials 21 , 22 , 29 – 34 . There are several interrelated preconditions for a design of the magnetostrain active Ni-MnGa/polymer composites which were long time ignored.…”

“…The unique magnetostrain properties, low-cost and easy production of the bulk Ni–Mn–Ga SC particles/silicone composites are characteristics which make these materials very attractive for novel actuator, sensing and haptic applications, where the value of stroke is more important than a generated force. If compared to the bulk single crystals, bulk composites contain no more than 30 vol% of particles embedded in a soft silicone polymer 21 , 24 , both factors obviously entail a reduction of the generated force. Another issue of the bulk composites is the problem of elastic interactions between the particles through a solid polymer whereby not all of them exhibit a magnetostrain 21 , 24 .…”

“…If compared to the bulk single crystals, bulk composites contain no more than 30 vol% of particles embedded in a soft silicone polymer 21 , 24 , both factors obviously entail a reduction of the generated force. Another issue of the bulk composites is the problem of elastic interactions between the particles through a solid polymer whereby not all of them exhibit a magnetostrain 21 , 24 . By a simple size decrease of composite to the microscale all the aforementioned issues should become more pronounced which makes very doubtful their use as microactuators.…”