Measurements of residual stress and microstructural evolution in electron beam welded Ti-6Al-4V using multiple techniques

Rae, William and Lomas, Zak and Jackson, Martin and Rahimi, Salah (2017) Measurements of residual stress and microstructural evolution in electron beam welded Ti-6Al-4V using multiple techniques. Materials Characterization, 132. pp. 10-19. ISSN 1044-5803

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    Abstract

    The evolution of residual stress and microstructure has been investigated in electron-beam welded Ti-6Al-4V alloy rings in order to develop an understanding of how the distribution of through-thickness residual stress correlates with microstructural evolution. A multiple technique approach to residual stress measurement was employed using a combination of different measurement techniques including X-ray diffraction (XRD), hole drilling method based on electronic speckle pattern interferometry (ESPI), and the contour method. It was found that there is a strong correlation between the change in residual stress and alpha phase morphology across the weld. The fusion zone exhibited highly tensile residual stress which was typified by an entirely acicular α′ microstructure formed by a displacive transformation within prior β grains on cooling. The tensile residual stress in the centre of the weld reduced towards the heat affected zone, transitioning to a compressive residual stress upon increasing distance from the weld centre. The transition from tensile to compressive residual stress correlates with a significant decrease in the volume fraction of α′ and an increase in the bimodal morphology of equiaxed primary alpha in a diffusional transformed beta matrix leading to elongated alpha in the base material.