Characterization of Deformation Behavior of Individual Grains in Polycrystalline Cu-Al-Mn Superelastic Alloy Using White X-ray Microbeam Diffraction

Eui Kwon,Kentaro Kajiwara,Masugu Sato,Ryosuke Kainuma,Shigeo Sato,Kozo Shinoda,Shun Fujieda,Shigeru Suzuki

doi:10.3390/met5041845

Abstract

White X-ray microbeam diffraction was applied to investigate the microscopic deformation behavior of individual grains in a Cu-Al-Mn superelastic alloy. Strain/stresses were measured in situ at different positions in several grains having different orientations during a tensile test. The results indicated inhomogeneous stress distribution, both at the granular and intragranular scale. Strain/stress evolution showed reversible phenomena during the superelastic behavior of the tensile sample, probably because of the reversible martensitic transformation. However, strain recovery of the sample was incomplete due to the residual martensite, which results in the formation of local compressive residual stresses at grain boundary regions.

Highlights

Characterization of the microscopic deformation behavior in individual grains and their interactions are important for understanding the overall deformation behavior and mechanical properties of polycrystalline materials
The streaked Laue pattern indicates that rotation of the crystallographic orientation has occurred in the parent phase, which is attributed to stress-induced martensitic transformation, resulting in the formation of sub-domains in the deformed grains [4]
It is thought that the reverse martensitic transformation and the resulting orientation recovery are the origin of the characteristic reversible Laue pattern change

Summary

Introduction

Characterization of the microscopic deformation behavior in individual grains and their interactions are important for understanding the overall deformation behavior and mechanical properties of polycrystalline materials. Cu-Al-Mn shape memory alloys that undergo a β1 (bcc) ↔ β1ʹ (monoclinic) martensitic transformation exhibit superelasticity Their recoverable strain is significantly improved when microstructural parameters, such as crystallographic orientation, grain size, and constituent phases, are optimized [1,2]. In our previous investigation on an Fe-Mn-Si-Cr shape memory alloy [5], white X-ray microbeam diffraction was employed to examine microscopic stress evolution in individual austenite grains during shape memory behavior. The magnitude of compressive stress depended on the grain orientation, as the martensitic transformation depended strongly on orientation These experimental findings suggest that internal stress is an important factor that determines the shape memory effect. The strain/stress measurements were performed at different positions within a single grain and in several grains having different orientations to investigate the heterogeneous deformation behavior and orientation dependence of stress evolution

Materials

White X-ray Microbeam Diffraction Experiments

Variation of Laue Patterns during Superelastic Behavior

Strain and Stress Evolution during Superelastic Behavior

Conclusions