Effect of Cyclic Strain on Microstructure and Properties of Ti₄₉Ni₅₁ Shape Memory Alloy Prepared by Rapid Solidification

Ti₄₉Ni₅₁ alloy rods were prepared by rapid solidification technique, and the as-cast alloy rods were subjected to quasi-static loading and unloading compression tests under different cyclic strains (5.0%, 6.0%, 6.5%) at an ambient temperature of 10℃. The effects of cyclic strains on the microstructure and properties of the alloy were studied, and hyperelastic behavior of the alloys under different cyclic strains was discussed. The results show that the Ti₄₉Ni₅₁ alloy after test was composed of B2-TiNi matrix phase, Ti₃Ni₄ precipitation phase and Ti₂Ni precipitation phase under three cyclic strains. With increasing cyclic strain, the equiaxed B2-TiNi grains were gradually elongated, and the Ti₃Ni₄ phase increased, and part of the Ti₃Ni₄ phase at the grain boundary aggregated and became larger due to extrusion. Martensitic transformation stress platform existed in the stress-strain curves of the alloy under three cyclic strains, and the stress platform was not obvious under 5.0% cyclic strain. Under 6.0% and 6.5% cyclic strains, with increasing number of cycles, the dissipative energy decreased while the recoverable strain energy density increased. Compared with those under 6.0% cyclic strain, the dissipated energy under 6.5% cyclic strain was slightly lower, while the recoverable strain energy density was higher. The Ti₄₉Ni₅₁ alloy had good hyperelasticity. The hardness of the alloy increased with increasing cyclic strain.