Tension/compression asymmetry of quasi – Static and dynamic mechanical properties in a face centered cubic Ni-W-Co ternary alloy

Abstract

In this paper a typical tension/compression asymmetry (TCA) behavior of a Ni48W35Co17 alloy is found by quai-static and dynamic mechanical tests and then systematically investigated by in-situ tensile and compression tests equipped with SEM, EBSD, TEM, etc. The true stress obtained by compression of this alloy is found increasing to 2500 MPa or even larger with strain over 0.5, which is almost twice of the value of tension. In tension, a little increase of reinforcement coefficient is found with increasing strain rates, from 0.36 to 0.56 max. In compression, reinforcement coefficient is found increased apparently from 0.76 to 1.24 according to the exponential stress-strain relationship. The TCA behavior of this alloy is related to the dislocation nucleation stress asymmetry. The TCA of yield strength is related to the formation of textures on [111] and [110] directions, since a larger nucleation stress is required in uniaxial compression than tension. TCA is also promoted by the formation of twin boundaries or sub-grain boundaries due to the higher average nucleation stress tilt grain boundaries in compression than intension. TCA behavior of this alloy in dynamic deformation is attributed to the high dislocation densities due to the formation of very thin deformation twins.