Phase Field Modelling of Abnormal Grain Growth

Ying Liu,Matthias Militzer,Michel Perez

doi:10.3390/ma12244048

Abstract

Heterogeneous grain structures may develop due to abnormal grain growth during processing of polycrystalline materials ranging from metals and alloys to ceramics. The phenomenon must be controlled in practical applications where typically homogeneous grain structures are desired. Recent advances in experimental and computational techniques have, thus, stimulated the need to revisit the underlying growth mechanisms. Here, phase field modelling is used to systematically evaluate conditions for initiation of abnormal grain growth. Grain boundaries are classified into two classes, i.e., high- and low-mobility boundaries. Three different approaches are considered for having high- and low-mobility boundaries: (i) critical threshold angle of grain boundary disorientation above which boundaries are highly mobile, (ii) two grain types A and B with the A–B boundaries being highly mobile, and (iii) three grain types, A, B and C with the A–B boundaries being fast. For these different scenarios, 2D simulations have been performed to quantify the effect of variations in the mobility ratio, threshold angle and fractions of grain types, respectively, on the potential onset of abnormal grain growth and the degree of heterogeneity in the resulting grain structures. The required mobility ratios to observe abnormal grain growth are quantified as a function of the fraction of high-mobility boundaries. The scenario with three grain types (A, B, C) has been identified as one that promotes strongly irregular abnormal grains including island grains, as observed experimentally.

Highlights

Abnormal grain growth (AGG) refers to a subset of grains that will grow excessively at the expense of surrounding normal grains leading to an obvious size advantage of the abnormal grains [1,2]
Multi-phase field modelling (MPFM) is frequently used as a computational method to simulate the microstructure evolution of metallurgical phenomena, including phase transformation [57,58], recrystallization [59,60] and grain growth [61,62,63]
To identify abnormal grain growth conditions, we employ the commercial software MICRESS where for grain growth simulations the multi-phase field modelling (MPFM) formulation according to Eiken et al [64] is used such that the evolution of φi for isotropic grain boundary energies, σ, is governed by μi j σij 2

Summary

Introduction

Abnormal grain growth (AGG) refers to a subset of grains that will grow excessively at the expense of surrounding normal grains leading to an obvious size advantage of the abnormal grains [1,2]. The AGG phenomenon has been observed in many materials, including steels [3,4,5,6,7,8,9,10,11], aluminum alloys [12,13], super alloys [14,15,16], ceramics [17,18,19,20,21], nanocrystalline materials [22,23,24,25] as well as thin films [25,26,27,28]. AGG is of important technological relevance and must be controlled in the thermal processing of polycrystalline materials. It is often undesired since it may lead to heterogeneous microstructures that result in unacceptable material properties. In the context of the present study, AGG will be considered for polycrystalline materials without any external driving pressures or porosity

Methods

Findings

Discussion

Conclusion