Structure Evolution and Residual Elastic Stresses in a Ti-Ni-Cu-Co Glassy/Crystalline Phase Alloy

Recently, nanocrystalline Ti-Ni-Cu-Co system alloys were found to have excellent stability of superelastic behaviour for elastocaloric applications. One of the factors limiting implementation of TiNi-based alloys in microelectromechanical systems is residual elastic stresses. In this work, the structure formation and stress evolution in the Ti₅₀Ni₂₂Cu₂₂Co₆ glassy/crystalline ribbon are studied on heating. The as-cast alloy has a glassy structure in the middle part of the ribbon while the surface crystals of textured B2 phase are found. However, due to the sharp [100] texture and B2 phase stabilizing effect, the only partial recrystallization takes place on subsequent heating. The x-ray diffraction studies indicated that the elastic stresses in the B2 phase reach a value of ~750 MPa near the surface plane. After isothermal annealing at crystallization temperature, the level of residual stresses reduced by a factor of 2. The origin of elastic stresses induced in the glassy/crystalline matrix is discussed.