Effect of low-angle grain boundaries on morphology and variant selection of grain boundary allotriomorphs and Widmanstätten side-plates

Abstract

Morphology and variant selection (VS) of grain boundary (GB) allotriomorphs and Widmanstätten side-plates of α phase in an α/β titanium alloy, Ti-6Al-4V (wt.%), are investigated using a three-dimensional phase field model. The structures of low-angle GBs (misorientation ≤ 10°)are modeled as discrete dislocation networks using Frank-Bilby theory. It is shown that α allotriomorphs and side-plates compete with each other during precipitation and the final morphology and selected α variants exhibit a strong correlation with the GB dislocation structures.While the side-plate morphology is more preferred by a symmetrical tilt GB with ∼ 10°, it can also be induced by a pure twist GB with ≤ 5°. Quantitative analysis indicates that precipitate morphology and VS are determined by the interplay among (i) elastic interaction between a nucleating α precipitate and the GB dislocation networks, (ii) growth anisotropy determined by the relative inclination of the habit plane with respect to the GB dislocations, (iii) density of nucleation sites for the same variant and coalescence during growth, and (iv) spatial confinement from simultaneously nucleated neighboring α variants of dissimilar types.

Formation of slip bands and microstructure evolution of Ti-5Al-5Mo-5V-3Cr-0.5Fe alloy during warm deformation process

“…-5 -dislocations and slip bands [26,27,28,29]. For instance, dislocations belonging to the {112}<111> slip systems would favor the nucleation and growth of a single a variant whose orientation relationship is described by the components of the specific slip system [26,27].…”

“…D. Qiu et, al. systematically elaborated the effects of low-angle grain boundaries (LAGBs) and dislocations on α phase morphology and variant selection mechanism through three-dimensional phase-field simulations [28,29]. Moreover, the lattice defects introduced by deformation increase the number of nucleation sites and consequently raise the nucleation rate of the product phase.…”

Integrated Simulation Framework for Additively Manufactured Ti-6Al-4V: Melt Pool Dynamics, Microstructure, Solid-State Phase Transformation, and Microelastic Response

“…A three-dimensional multi-phase field model for an elastically and structurally inhomogeneous system 15,16 is employed to simulate microstructural evolution (a precipitation) in a bicrystalline Ti-64. In this approach ( Fig.…”

“…The total free energy of the system, F, is formulated as a functional of these two sets of order parameters. The phase-field model associated with the precipitation process has been employed in our previous works, 15,16 to address the influence of applied stress/ strain and grain boundary dislocation on variant selection of a precipitates upon isothermal aging. The only difference in the methodology is the replacement of Langevin noise terms in the governing equations by the explicit nucleation algorithm to account for the nucleation process under continuous cooling conditions, as described in detail in ''Explicit Nucleation Algorithm'' section.…”

“…As shown in Fig. 2, the modeling framework is developed on the basis of the interaction between (a) an arbitrary Lagrangian-Eulerian (ALE)-based powder-scale model to predict spatiotemporal evolution of thermal history, 12 (b) a cellular automaton (CA) 14 model to Integrated Simulation Framework for Additively Manufactured Ti-6Al-4V: Melt Pool Dynamics, Microstructure, Solid-State Phase Transformation, and Microelastic Response simulate grain structure evolution (size as well as orientation), and (c) a quantitative phase-field (PF) 15,16 model to predict the subgrain/intragranular precipitate microstructure.…”