Compressive response of high-strength [001]-oriented single crystals of a Co35Ni35Al30 shape memory alloy

摘要

The effects of stress-free and stress-assisted aging at 673 K on microstructures, thermoelastic stress-induced B2-L1(0) martensitic transformation and superelasticity were investigated in [001](B2)-oriented Co35Ni35Al30 (at. %) single crystals in compression. The aging of quenched crystals results in the formation of high-strength nanostructured composites containing spherical nanosized particles and elongated epsilon-Co (HCP structure) particles, which do not undergo martensitic transformation. The stress-free and stress-assisted aged at 673 K for 0.5 h Co35Ni35Al30 crystals, oriented along [001](B2)-direction, demonstrate high-yield stress levels for the B2-phase of 1360 divided by 1630 MPa and a wide superelasticity temperature range from 193 K to 563 K with good cyclic stability and narrow stress hysteresis of Delta sigma = 50-60 MPa. It has been shown experimentally that a difference in the effective Young's modulus of austenite and martensite determinates a decrease in the reversible strain with a test temperature in both quenched and aged crystals. The tensile two-way shape memory effect with a reversible strain of epsilon(TWSME) = +2.2% along the [001](B2)-direction is induced due to the oriented growth of elongated epsilon-Co-particles in stress-assisted aged crystals. These results provide a clear demonstration of the potential of aged CoNiAl single crystals for applications involving high stresses and temperatures. (C) 2019 Elsevier B.V. All rights reserved.