Inelasticity of nanocomposite based on ferromagnetic Fe–Ni–Co–Ti alloy after thermomechanical treatment

Abstract

This paper presents the results of mechanical tests under a uniaxial tension of a nanocomposite obtained as a result precipitation hardening in the process of ageing of quenched ferromagnetic Fe-27.2%Ni-17.4%Co-5.2%Ti (wt%) alloy, having the martensitic, austenitic, or mixed structure of matrix after cooling and/or applied stress. To obtain the nanocomposite, the alloy samples were subjected to a preliminary thermomechanical treatment (TMT), which consisted of multiple drawing operations followed by quenching in water from 1373 K and ageing at 923 K for 5, 10, and 20 min. As a result of such TMT, a sufficiently high level of superelastic deformation and shape memory effect were achieved. It was experimentally established that the preliminary TMT, consisting of drawing with compression degree 22.5% followed by quenching and ageing at 923 K for 5–10 min, favors the deformation of the nanocomposite along the channels of phase and twinning plasticity in the range of testing temperature Ms < Tt < Af, and corresponds to the optimal combination of maximum superelastic strain and shape memory effect. A further increase in the degree of deformation results in inhibition of martensitic transformation and reducing of superelastic deformation by decreasing the austenite grain size and increasing the density of crystal defects.