Decreasing the Grain Boundary Diffusivity in Binary Alloys with Increasing Temperature

Xiaomeng Shi,Jian Luo

doi:10.1103/physrevlett.105.236102

Abstract

An interfacial thermodynamic model predicts that the interplay of grain boundary (GB) premelting, prewetting, and retrograde solubility in a binary alloy can lead to a decrease in the GB diffusivity with increasing temperature. This counterintuitive prediction is experimentally confirmed for a single-phase, Mo +0.5 at. % Ni alloy. This study calls for a reappraisal of the classical GB adsorption (segregation) theories to consider the coupling with structural disordering, and it critically supports GB premelting and prewetting theories with broad applications.

Highlights

Surface premelting, which refers to the stabilization of thin liquidlike layers on the free surface of a unary solid below its bulk melting temperature, has been extensively investigated [1,2,3]
Diffuse-interface theories [5,6] suggested that grain boundary (GB) adsorption can promote premeltinglike interfacial disordering, and the coupling between adsorption and structural disordering can produce interfacial ‘‘phase’’ transitions and critical phenomena [5,6,8,9]
Computational thermodynamic methods were combined with statistical interfacial thermodynamic models to forecast GB disordering in binary alloys [17,18]

Summary

Introduction

Surface premelting, which refers to the stabilization of thin liquidlike layers on the free surface of a unary solid below its bulk melting temperature, has been extensively investigated [1,2,3]. We used a premeltingtype interfacial thermodynamic model [12,17,18] to predict that the GBs in a Mo þ0:5 at: % Ni alloy would ‘‘solidify’’ with increasing temperature, leading to a reduction of GB diffusivity.

Results

Conclusion