Characteristic features of development of thermoelastic transformations in aged single crystals of a CoNiAl ferromagnetic alloy

Abstract

Using Co 35 Ni 35 Al 30 (at. %) single crystals, the effect of temperature and duration of aging on the development of thermoelastic B2-L1 0 -martensitic transformations during heating/cooling is studied. It is found out that at room temperature these single crystals are in the В2-phase and contain a small volume fraction (about 2%) of the plastic γ-phase. In the aged single crystals, in the В2-matrix, Co-rich particles with hcp-and fcc-lattices and metastable Ni 2 Al particles precipitate, whose size is determined by the temperature and duration of aging. It is shown that aging gives rise decreased temperature of martensitic transformations. At the aging temperatures T ≥ 673 K there is a sharp increase in the temperature hysteresis and a total suppression of thermoelastic B2-L1 0 -martensitic transformations during heating/cooling and under loading. A thermodynamic description of the starting temperature of martensitic transformations M s as a function of microstructure of the aged single crystals particle size and interparticle spacing is proposed.