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

Selective Electron Beam Melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. However without post-manufacture HIPing the fatigue life of SEBM parts is currently dominated by the presence of porosity. In this study, the size, volume fraction, 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 (< 0.2%) was measured to be lower than that usually observed in competing processes, such as selective laser melting, but a strong relationship was found with the different beam strategies used to contour, and infill by hatching, a part section. The majority of pores were found to be small spherical gas pores, concentrated in the infill hatched region; this was attributed to the lower energy density and less focused beam used in the infill strategy allowing less opportunity for gas bubbles to escape the melt pool. Overall, increasing the energy density or focus of the beam was 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 beenmore » attributed to a lack of fusion between powder particles. - Graphical abstract: Display Omitted - Highlights: • Vast majority of defects detected were small spherical gas pores. • Gas bubbles trapped in the powder granules expand and coalesce in the melt pool. • Pores have been shown not to be randomly distributed. • Larger and deeper melt pools give more opportunity for gas to escape. • Minor changes to melt strategy result in significant reductions in pore population.« less
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [1] ; ;  [3] ;  [1]
  1. School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom)
  2. (United Kingdom)
  3. Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom)
Publication Date:
OSTI Identifier:
22476069
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 102; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ADDITIVES; ALUMINIUM COMPOUNDS; BEAMS; COMPUTERIZED TOMOGRAPHY; DEFECTS; ELECTRON BEAM MELTING; ENERGY DENSITY; LASER RADIATION; POROSITY; POWDERS; RANDOMNESS; REDUCTION; SPATIAL DISTRIBUTION; TERNARY ALLOY SYSTEMS; TITANIUM; TITANIUM COMPOUNDS; TRAPPING; VANADIUM COMPOUNDS; X RADIATION