Abstract
To better understand the properties of polycrystals at a microscopic scale during cyclic mechanical loading we have measured the relationship between grain orientations, their positions inside the sample and their internal stresses. In this work, in-situ 3DXRD technique was performed on over hundred grains during the stress-induced martensitic transformation in a Cu-Al-Be shape memory alloy. Information about the position, orientation, and stress field was obtained for each austenitic grain. These results have been used to develop a procedure that allows automatic processing for a large number of grains, matching them during loading and leads to a quantitative stress field. A strong heterogeneity of stress state between the grains at the surface and in the volume is evident.
Highlights
The bulk properties of Shape Memory Alloys (SMA), such as the macroscopic stress-strain during the superelasticity effect, have been widely studied at the macroscopic scale
In Cu-based alloys, a factor 3 between the critical shear stresses was observed. These results cannot be extended to the case of polycrystals where the individual grains are embedded in the bulk material as they do not take into account grain interactions
In this paper we describe the development and the methodology to simultaneously track the stress tensors of hundreds of individual grains inside a polycrystalline shape memory alloy during an in-situ tensile test
Summary
The bulk properties of Shape Memory Alloys (SMA), such as the macroscopic stress-strain during the superelasticity effect, have been widely studied at the macroscopic scale. The average behavior of each phase, austenite and martensite, can be measured by X-rays or neutron diffraction: the stress-strain state depends strongly on the crystallographic orientation of the grains [1]. In Cu-based alloys, a factor 3 between the critical shear stresses was observed These results cannot be extended to the case of polycrystals where the individual grains are embedded in the bulk material as they do not take into account grain interactions. To obtain such data it is necessary to validate nondestructive analyzes for accessing surface as well as volume data. It has been used to study lattice rotations of individual grains in aluminium alloys [6] and in Cu-AlBe SMA [7], phase transformation kinetics in steels [8,9]
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