Abstract:
Martensitic transformation in Heusler alloys can be accompanied by various functional effects promising for practical application. However, this is hampered by high thermocycle brittleness in the as-cast state. This paper presents the results of a comparison of the dilation properties in the martensitic transformation region of a Ni-Mn-Ga-Si alloy in a coarse-grained state and with a bimodal structure possessing reduced thermocycle brittleness. It is shown that the formation of a bimodal structure by hot deformation by forging (700$^\circ$C, e = 3.2) results in the development of internal stresses (microstresses) of a preferred orientation, leading to the formation of martensite twins’ transverse to the compression axis of the final forging stage. A rod-shaped specimen cut along this direction is abruptly compressed, while one cut across it, on the contrary, is elongated during the direct martensitic transformation. Thus, using hot forging deformation, it is possible to control the dilation anisotropy in the process of martensitic transformation of the Heusler Ni-Mn-Ga-Si alloys.
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