Introduction to Electron Beam Welding on Ti-6Al-4V: 

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Electron beam welding (EBW) is a popular method used for joining titanium alloys such as Ti-6Al-4V (Ti64). This research focuses on understanding the microstructural and mechanical changes in Ti64 after post-weld heat treatments. The effects of solution treatment and aging on the welded samples were investigated.

 

Microstructural Changes Due to Post-Weld Heat Treatments: 

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Post-weld heat treatments significantly affect the microstructure of EBW Ti64 samples. The results revealed that the martensitic 𝛼′ phase coarsened, the size of the heat-affected zone (HAZ) changed, and grain growth occurred in the base material (BM). These transformations influence the material's overall properties and behaviour during mechanical testing.

 

In-Situ Tensile Testing: 

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In-situ tensile testing was conducted, monitored via optical microscopy, to examine the tensile behaviour of the welded samples. This real-time observation of deformation and failure provided valuable insights into the mechanical responses of the EBW Ti64 alloy. Interestingly, failure locations varied depending on the type of post-weld heat treatment applied.

 

Effects of Heat Treatment on Mechanical Properties: 

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The mechanical properties of the EBW Ti64 alloy, such as tensile strength and elongation-to-failure, were negatively impacted by post-weld heat treatments. After aging, both tensile strength and elongation decreased, and these properties further declined following solution treatment and aging. The study thus highlights a clear relationship between heat treatment, microstructural evolution, and mechanical performance.

 

Predictive Modelling and Finite Element Analysis: 

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To better understand the mechanical behaviour just before failure, thermodynamic databases were utilised to predict mechanical properties like yield strength for various grain sizes resulting from different heat treatments. These properties were incorporated into a finite element model, simulating the tensile testing process and providing insights into stress and strain distributions.