XCT analysis of the influence of melt strategies on defect population in Ti–6Al–4V components manufactured by Selective Electron Beam Melting

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Abstract

Selective Electron BeamMelting (SEBM) is a promising powder bed AdditiveManufacturing technique for nearnet- shape manufacture of high-value titanium components. However without post-manufacture HIPing the fatigue life of SEBMparts is currently dominated by the presence of porosity. In this study, the size, volumefraction, and spatial distribution of the pores in model samples have been characterised in 3D, using X-ray Computed Tomography, and correlated to the process variables. The average volume fraction of the pores (b0.2%) was measured to be lower than that usually observed in competing processes, such as selective laser melting, but a strong relationshipwas foundwith the different beamstrategies used to contour, andinfill by hatching, a part section. The majority of pores were found to be small spherical gas pores, concentrated in the infill hatched region; thiswas attributed to the lower energy density and less focused beam used in the infill strategy allowing less opportunity for gas bubbles to escape themelt pool. Overall, increasing the energy density or focus of the beamwas found to correlate strongly to a reduction in the level of gas porosity. Rarer irregular shaped pores were mostly located in the contour region and have been attributed to a lack of fusion between powder particles.

Keyword(s)

Additive Manufacture; Selective Electron Beam Melting; Titanium; X-ray Computed Tomography (XCT)

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