Three-Dimensional In Situ Texture Development and Plasticity Accumulation in the Cyclic Loading of an alpha-Ti Alloy

TL;DR

This study uses high-energy synchrotron x-rays to observe how grain orientations and internal stresses evolve in a Ti-7Al alloy under cyclic loading below its yield point, revealing gradual plasticity accumulation and texture development.

Contribution

It provides the first in situ 3D analysis of microstructural evolution and plasticity accumulation in a Ti alloy during cyclic loading below yield stress.

Findings

Gradual increase in von Mises stress over cycles

Development of a tension texture despite negligible macroscopic strain

Hard-oriented grains retain more residual stress

Abstract

High-energy synchrotron x-rays are used to track grain rotations and the micromechanical evolution of a hexagonal Ti-7Al microstructure as it is cyclically loaded below its macroscopic yield stress. The evolution of the grains through 200 cycles reveals a continual change in von Mises stress and orientation across the entire specimen indicating a slow accumulation of plasticity even though the sample was cycled below its macroscopic yield. Grain reorientation is consistent with the development of a tension texture despite the negligible magnitude of (macroscopic) plastic strain. It is observed that grains in a "hard" orientation (c-axis close to the loading direction) retain more residual stress on their slip systems upon unloading than the grains in a "soft" orientation.