The deformation behaviour of hard and soft grains in RR1000 nickel-based superalloy

S Birosca

doi:10.1088/1757-899x/82/1/012033

Abstract

In the current study, the Electron Backscatter Diffraction (EBSD) plastic strain measurement is assessed to ascertain the deformation behaviour within individual oriented grains in polycrystalline RR1000 Nickel-based superalloy. Here, the crystallographic orientation correlations with Geometrically Necessary Dislocation (GND) contents, Schmid and Taylor factors as well as strain hardening were investigated. It is demonstrated that grain boundary is the major factor influencing GND accumulation in soft grains, while the orientation is the critical factor in hard grains’ fragmentation. Furthermore, it is concluded that the total GND value for individual grains varies depending on the deformation stage, whereas the locations of high GND density within the grains indicates on strain hardening state. Keywords: GND, Strain Hardening, FCC, Deformation.

Highlights

It is argued that the classical plasticity theory cannot describe crystalline material behaviour at micron level
It is demonstrated that grain boundary is the major factor influencing Geometrically Necessary Dislocation (GND) accumulation in soft grains, while the orientation is the critical factor in hard grains’ fragmentation
It is concluded that the total GND value for individual grains varies depending on the deformation stage, whereas the locations of high GND density within the grains indicates on strain hardening state

Summary

Introduction

It is argued that the classical plasticity theory cannot describe crystalline material behaviour at micron level. Ashby 4 proposed that work hardening reflects the way in which the arrays of stored dislocations obstruct the motion of other moving dislocations He suggested that in polycrystals the plastic strain gradient is produced by the mismatch of slip directions at grain boundaries. Et al, observed that during deformation, the constituent grains of polycrystals developed complex heterogeneous deformation patterns with variations in local strain and crystal orientation occurring over a wide range of length scales 2. They claimed that interfaces can resist the motion of lattice dislocations, or absorb or emit them depending upon the structure of the interface and local mechanical conditions. Raabe, et al, reported that the orientation gradient may proceed from a variation in slip system activation throughout a grain leading to local domains with different orientation 8

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Conclusion