Correlating work hardening with co-activation of stacking fault strengthening and transformation in a high entropy alloy using in-situ neutron diffraction

M Frank,B Gwalani,S S Nene,K An,R S Mishra,A Devaraj,E J Kautz,Y Chen

doi:10.1038/s41598-020-79492-8

Abstract

Transformation induced plasticity (TRIP) leads to enhancements in ductility in low stacking fault energy (SFE) alloys, however to achieve an unconventional increase in strength simultaneously, there must be barriers to dislocation motion. While stacking faults (SFs) contribute to strengthening by impeding dislocation motion, the contribution of SF strengthening to work hardening during deformation is not well understood; as compared to dislocation slip, twinning induced plasticity (TWIP) and TRIP. Thus, we used in-situ neutron diffraction to correlate SF strengthening to work hardening behavior in a low SFE Fe40Mn20Cr15Co20Si5 (at%) high entropy alloy, SFE ~ 6.31 mJ m−2. Cooperative activation of multiple mechanisms was indicated by increases in SF strengthening and γ-f.c.c. → ε-h.c.p. transformation leading to a simultaneous increase in strength and ductility. The present study demonstrates the application of in-situ, neutron or X-ray, diffraction techniques to correlating SF strengthening to work hardening.

Highlights

Transformation induced plasticity (TRIP) leads to enhancements in ductility in low stacking fault energy (SFE) alloys, to achieve an unconventional increase in strength simultaneously, there must be barriers to dislocation motion
To investigate the Si content, energy dispersive X-ray spectroscopy (EDS) maps for as-cast condition (AC) and AC + friction stir processing (FSP) are shown in the supplementary document, Figs
The measured Si content was observed to be lower than the nominal value in the AC condition, upon FSP the Si content in the matrix increased suggesting dissolution of the Si-rich phase occurred during FSP

Summary

Introduction

Transformation induced plasticity (TRIP) leads to enhancements in ductility in low stacking fault energy (SFE) alloys, to achieve an unconventional increase in strength simultaneously, there must be barriers to dislocation motion. While stacking faults (SFs) contribute to strengthening by impeding dislocation motion, the contribution of SF strengthening to work hardening during deformation is not well understood; as compared to dislocation slip, twinning induced plasticity (TWIP) and TRIP. Stacking fault strengthening (σSF) was studied in hexagonal close-packed (HCP) M g14,15 alloys, FCC Cu-Al a lloys[16] and FCC Co a lloys[13] using TEM and XRD These studies showed that the decrease in LSF corresponded to an increase in yield strength due to SF-dislocation interactions.

Methods

Results

Conclusion