Phase-Field Simulation of Orowan Strengthening by Coherent Precipitate Plates in an Aluminum Alloy

The density-functional theory and phase-field dislocation model have been used to compute and simulate the strength of theta' plates and precipitate-dislocation interactions in an Al-4Cu-0.05Sn (wt pct) alloy that is strengthened exclusively by coherent theta' precipitate plates. The density-functional theory computation indicates that a 1.06 GPa applied stress is required for a dislocation to shear through a theta' plate, which is far larger than the critical resolved shear stress increment (Delta CRSS) of the peak-aged sample of the alloy. The Delta CRSS values of the alloy aged for 0.5, 3, 48, and 168 hours at 473 K (200 A degrees C) are computed by the phase-field dislocation model, and they agree well with experimental data. The phase-field simulations suggest that the Delta CRSS value increases with an increase in plate aspect ratio and number density, and that the change of Delta CRSS is not sensitive to the variation of the distribution of theta' plate diameters when the average diameter of theta' plates is fixed, and that the coherency strain of theta' plates does not contribute much to Delta CRSS of the alloy when the theta' number density and aspect ratio are below certain values. The simulations further suggest that, when the volume fraction of theta' is constant, the Delta CRSS value for a random spatial distribution of the theta' plates is 0.78 times of that for a regular spatial distribution. (C) The Minerals, Metals & Materials Society and ASM International 2015