Soft impingement informed modeling framework for precipitation kinetics of T1 in Al-Cu-Li alloy with experimental verification

In the present work, a modeling framework is developed to simulate the precipitation kinetics of $T_1$ in Al-Cu-Li alloy. The effect of soft impingement of diffusion fields around neighboring precipitates on the growth rate is incorporated in the model. An analytical expression of time-varying concentration field assuming 2-D diffusion of solutes around precipitates is derived. The simulation is performed at an ageing temperature of $150℃$ for three different levels of pre-strain, 5%, 10% and 20%. Temporal evolution of the phase transformation parameters of $T_1$ such as volume fraction, average diameter, number density and matrix solute concentration is obtained from the model. These parameters are validated against the experimental data obtained in this work using TEM, XRD and DSC characterization. Model prediction of parameters are found to be in close agreement with the experimental values. Furthermore, the model captures the effect of pre-strain on aging kinetics precisely, i.e. with increasing deformation amount ageing kinetics enhances. Consideration of soft impingement, spatial arrangement of $T_1$ precipitates and their morphological evolution are found to be critical factors in the model to produce results consistent with experiment. Present model is found to be significantly more accurate than the widely popular software Thermo-Calc (TC-PRISMA module) for predicting $T_1$ growth kinetics.