Local Stress Analysis in an SMA during Stress-Induced Martensitic Transformation by Kossel Microdiffraction

Denis Bouscaud,Etienne Patoor,Sophie Berveiller,Raphaël Pesci,Adam Morawiec

doi:10.4028/www.scientific.net/amr.996.45

Abstract

The Kossel microdiffraction in a scanning electron microscope allows for local stress determination. This technique has been applied to monitor stress evolution within grains of austenite in the course of martensitic transformation in a shape memory alloy. Kossel diffraction patterns were recorded during in situ tensile straining of Cu-Al-Be alloy. These innovative measurements show large stress heterogeneities between grains, with the stress ratio exceeding two. As martensite variants are stress-induced, shear stress components appear in individual grains of austenite.

Highlights

The distinctive properties of shape memory alloys (SMA) are based on a reversible martensitic transformation induced by an external stress or a temperature variation
In order to explain the mechanism causing the motion of internal interfaces between austenite and martensite, many experimental works have been done on single crystals during uniaxial loading and/or temperature changes
Synchrotron diffraction experiments on a Cu-Al-Be polycrystal with coarse grains [4] showed that individual grains rotate during uniaxial loading and split into subdomains of different orientations during the martensitic transformation

Summary

Introduction

The distinctive properties of shape memory alloys (SMA) are based on a reversible martensitic transformation induced by an external stress or a temperature variation. Such preliminary results highlight the need for developing experimental methods coupling the characterization of the material behavior with observations of micromechanisms occurring during the martensitic transformation and in situ stress determination. Kossel microdiffraction is a suitable technique to study the evolution of the austenite stress state in individual grains.

Results

Conclusion