Microstructural and mechanistic insights into the Tension–Compression asymmetry of rapidly solidified Fe–Cr alloys: A phase field and strain gradient plasticity study

Rapid solidification in Additively Manufactured (AM) metallic materials\nresults in the development of significant microscale internal stresses, which\nare attributed to the printing induced dislocation substructures. The resulting\nbackstress due to the Geometrically Necessary Dislocations (GNDs) is\nresponsible for the observed Tension-Compression (TC) asymmetry. We propose a\ncombined Phase Field (PF)-Strain Gradient $J_2$ Plasticity (SGP) framework to\ninvestigate the TC asymmetry in such microstructures. The proposed PF model is\nan extension of Kobayashi's dendritic growth framework, modified to account for\nthe orientation-based anisotropy and multi-grain interaction effects. The SGP\nmodel has consideration for anisotropic temperature-dependent elasticity,\ndislocation strengthening, solid solution strengthening, along with GND-induced\ndirectional backstress. This model is employed to predict the solute\nsegregation, dislocation substructure and backstress development during\nsolidification and the post-solidification anisotropic mechanical properties in\nterms of the TC asymmetry of rapidly solidified Fe-Cr alloys. It is observed\nthat higher thermal gradients (and hence, cooling rates) lead to higher\nmagnitudes of solute segregation, GND density, and backstress. This also\ncorrelates with a corresponding increase in the predicted TC asymmetry. The\nresults presented in this study point to the microstructural factors, such as\ndislocation substructure and solute segregation, and mechanistic factors, such\nas backstress, which may contribute to the development of TC asymmetry in\nrapidly solidified microstructures.\n