Deconstructing the high-temperature deformation of phase-separating alloys

Abstract

At high temperatures, a microstructure evolves in order to lower the energy (including interfacial and elastic) of the system. Microstructure evolution can be influenced by applied loads if the elastic constants are anisotropic and/or inhomogeneous. When plastic deformation occurs during microstructure coarsening (e.g., under creep conditions), dislocations modify microstructure evolution (e.g., through relaxing misfit and conversion of interfaces from coherent to semicoherent) and microstructure evolution leads to changes in the plastic deformation behavior. Here, we employ phase field simulations to examine the interplay between plasticity, phase separation and microstructural coarsening. In particular, we separately control microstructure evolution, stress effects and plastic deformation in order to deconstruct the observed deformation behavior. We show that in the absence of an applied stress, the alloy with dislocation sources coarsens more quickly than that without and that the presence of dislocations reorients two-phase interfaces. A comparison of the stress-strain curves for alloys with microstructure that evolves during deformation with those for which the microstructure is static shows that simultaneous microstructure evolution leads to (1) lower effective elastic moduli, (2) a peak in the stress-strain curve (it is monotonic in the absence of microstructural evolution) and (3) lower large-strain flow stresses. The decrease in elastic modulus is the result of the reorientation of the microstructure with time (the two phases have different stiffnesses). We elucidate the microstructural sources of these changes. © 2013 IOP Publishing Ltd.