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

Abstract

a b s t r a c tAn Mg-7Sn-1Al-1Zn alloy known to have excellent extrudability and superior strength was subjected to artificial cooling during indirect extrusion by directly spraying water onto the extruded rod at the die exit. The results obtained revealed that this artificial cooling dramatically reduces the temperature of the deformation zone during extrusion, thereby creating a finer grain size, an intensified texture and a greater amount of precipitates when compared to extrusion without artificial cooling. The yield and tensile strength of the extruded alloy is also significantly improved, which is attributed to the effects of grain refinement in combination with an enhanced texture and precipitate hardening.

X-ray Tomography Characterisation of Lattice Structures Processed by Selective Electron Beam Melting

“…The probability of any particular particle having a pore however was found to be 0.018% (377 pores in a total of 20,078 scanned particles). Details of such porosity have been reported elsewhere [6], finding that it is delimited by the powder particles, as would be expected, and is close to spherical in shape. The findings here indicate the amount of porosity introduced into SEBM components by the raw materials.…”

“…However, parts are far from being defect free, as internal porosity (i.e., unwanted porosity within the solid trusses of material) is present, among other defects. A significant fraction of these internal pores is considered to arise from gas entrapped in the atomised powder particle feedstock [6]. Such pores are mobile in the melt pool created when powders are molten, and are then re-arranged onto patterns in the resulting solid that appear to correlate to the beam path [7].…”

“…The retention of porosity allowing such formations is reportedly due to the liquid metal forces that restrict the escape of gas bubbles. This is not the Metals 2017, 7, 300 2 of 12 only source of porosity however; for example, non-optimum beam energy densities can also generate defects due to lack of fusion [6]. Contrary to defects originating from trapped gas in the feedstock, these tend to be larger than the particle size and have an irregular shape, and traces of poor adhesion of new particles can sometimes be seen.…”

Powder bed generation in integrated modelling of additive layer manufacturing of orthopaedic implants

“…By using XCT systems with different resolutions, it has been possible to quantify the positions of the particle centres within the deposited powder bed and also to measure their true sizes and morphologies. The applied experimental technique has been described in details elsewhere [46]. Ti6Al4V powder was chosen for the model verification because of the spherical shape of the particles (Fig.…”

Neutron Imaging of Laser Melted SS316 Test Objects with Spatially Resolved Small Angle Neutron Scattering

“…The methods evaluated included simple mass/volume, Archimedes, and direct observation of pores with X-ray tomography, all leading to an observed correlation between speed of sound and porosity [2]. X-ray tomography has also been used to evaluate pore structure shape and size distributions in titanium alloy (Ti6Al4V) objects produced with electron beam melting [3,4], detecting pores down to 5.2 µm diameter. The as yet untouched domain, and the subject of this work, is imaging the spatial variation of sub-micron pores within metal additive manufacturing objects.…”