The influence of high-energy process parameters on the prior beta grain structure of additively manufactured titanium alloys

Title : The influence of high-energy process parameters on the prior beta grain structure of additively manufactured titanium alloys

Abstract:

Titanium alpha-beta alloys fabricated by laser-based powder-bed fusion, an additive manufacturing process, present with an undesired martensitic microstructure, high residual stresses, and columnar prior-beta grains. Post-process heat treatments are recommended as an essential step to improve properties such as ductility and fracture toughness; however, they generally do not alter the columnar prior-beta grain structure, as they are below the beta-transis temperature to prevent excessive grain growth. Columnar prior-beta grains have been suggested to cause mechanical anisotropy; it is understood to cause significant anisotropy in ductility, fracture toughness, and fatigue strength. However, the influence of a columnar prior-beta structure, the underlying alpha-beta microstructure, and its influence on anisotropy are not yet well understood. This study investigates the differences in Ti-6Al-4V microstructure produced by laser-based powder bed fusion using a variation in process parameters, the application of above-beta transis temperature heat treatment, and the way the microstructural features control the behaviour of deformation and failure. Microscopy techniques of scanning electron microscopy imaging and backscatter diffraction are used for microstructure characterisation and deformation mode identification. The results identify key crystallographic and morphological features that control slip, microcrack initiation, and final fracture. These are related to anisotropy in mechanical properties.

What will audience learn from your presentation?

• Key laser-based powder-bed fusion process parameters that control the prior-beta grain structure in titanium alpha-beta alloys.
• The influence of the prior-beta grain structure and underlying alpha-beta structure on anisotropy in mechanical properties of titanium alpha-beta alloys produced using additive manufacturing.
• Improvement capabilities and limitations in reducing anisotropy in additively manufactured titanium alpha-beta alloys.

Biography:

Thorsten Becker is appointed is the director for the Centre of Materials Engineering at the University of Cape Town. His research interest is in structural integrity: fatigue, fracture, and creep. His work aims to use advanced techniques such as digital image and volume correlation, high-resolution microscopy, and finite element modelling to measure and extract engineering parameters for structural integrity assessments. One of his keen interests lies in the additive manufacturing of metals and high temperature applications.