The Effectiveness of Hot Isostatic Pressing for Closing Porosity in Titanium Parts Manufactured by Selective Electron Beam Melting

Abstract

Ti-6Al-4V parts, produced by selective electron beam melting additive manufacturing, have been studied by X-ray computed tomography (XCT) to track pore closure during a standard hot isostatic pressing (HIPing) cycle. Comparison of repeated XCT scans before and after HIPing, on worst-case samples with different geometries, confirmed that all internal porosity was shrunk to below the resolution limit of the equipment used (~5 µm) following the HIPing cycle, apart from defects with surface connected ligaments.

Porosity regrowth during heat treatment of hot isostatically pressed additively manufactured titanium components

“…To solve this problem, many aerospace companies are considering applying post-build hot isostatic pressing (HIPing) treatments to AM components. It has been reported that HIPIng of AM parts is very effective at closing porosity, which reduces internal stress concentrations, with a consequent increase in fatigue life [2,6].…”

“…1b) to below the detection limit of the equipment used (~5 μm) [6]. Here, we aim to examine the effect of applying a typical β-anneal heat treatment on the porosity closed by HIPing.…”

“…[6]), and following annealing for different times and temperatures, so that individual pores could be tracked at each stage within the sample. The sample comprised a 10 mm high, 1.7 mm diameter, cylinder having an axis aligned with the build direction, machined from the centre edge of the face of a 10 × 10 × 15 mm 3 cuboid sample.…”

“…The cuboid sample was manufactured with argon gas atomised, Ti-6Al-4V powder in an Arcam AB SEBM system using standard operating conditions (see refs. [5,6,8] for details). This consisted of first melting the perimeter of each 2D layer by 'contouring', before consolidating the internal area using a snaking 'hatching' pattern.…”

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

“…X-ray computed micro-tomography (CT) is one of the few techniques able to identify internal features within solid materials over a wide range of compositions. For AM, it has become an important 3D complement to 2D cross-sectional metallography in identifying pore volumes much lower than the particle feedstock [11].…”