Термоупругие мартенситные превращения под нагрузкой в [011]-монокристаллах сплава Ni49Fe18Ga27Co6 под действием растягивающих и сжимающих напряжений

Abstract

The effect of the stress state (tension/compression) on the thermoelastic L21 -(14M)L10 martensitic transformations in heating/cooling cycles under the constant stress and in loading/unloading cycles at fixed temperature in [011]-oriented Ni49Fe18Ga27Co6 single crystals was determined. The martensitic transformation at cooling/heating occurs with a maximum reversible strain of 4.1 % at constant tensile stress of 50 MPa, and the value of the thermal hysteresis decreases with the increase of applied stresses. On the contrary, the value of thermal hysteresis in isobaric tests and stress hysteresis in isothermal tests increase with the growth of the external stress level or given strain. An bursting character of the reverse martensitic transformation in compression is observed. The reversible strain reaches 5.5 % in cooling/heating cycles at the compressive stress of 60 MPa. Such asymmetry of the properties in [011]-oriented Ni49Fe18Ga27Co6 single crystals at the stressinduced martensitic transformations is caused both by the detwinning processes of L10-martensite crystals in compression, and by the difficulty of the detwinning processes in tension.