Creep behaviour of inconel 718 processed by laser powder bed fusion

Abstract

Additive manufacturing lends itself well to the manufacture of aerospace parts due to the high complexity and small volume of many components found in modern aero engines. By exploiting additive manufacturing design freedoms, enhanced part functionality can be achieved and lead time can be reduced. However, the integrity of these parts is a primary concern which often cannot be guaranteed with current generation additive manufacturing methods and materials. Studies on the performance of additively manufactured parts under service conditions are therefore required.In this study, laser powder bed fusion is used to produce specimens for creep testing. To allow this a novel specimen design, i.e. Two Bar Specimen, was applied for creep testing. The performance of these specimens, in the as-build condition, is showed to be largely poor because of surface integrity defects, in-built pores, and unfavourable microstructure formation. These are clearly highlighted and explored. Further specimens, subjected to heat treatments, have also been tested. These showed a marked improvement of the microstructure and hence creep performance. The lifetime of heat-treated samples was enhanced by as much as four times compared to the as-build specimens. However, this lifetime performance remains 33 percent below that of samples machined from the equivalent wrought material. This work then proposes manufacturing strategies to significantly enhance the performance of Inconel 718 when processed via laser powder bed fusion and post-heat-treatments.

Effect of post processing on the creep performance of laser powder bed fused Inconel 718

“…So that the two-bar specimen can be easily machined and provide information on all three creep stages with fewer materials. This is consistent with the authors' previous study in which the creep testing experimental arrangement of LPBF specimens was determined [22]. Figure 2 shows a schematic of the testing strategy for this study.…”

“…The temperature for the testing was 650˚C which is also the phase transformation temperature for the main strengthening particles, i.e. γ'' phase, in Inconel 718 [4], this is also consistent with the previous study [22].…”

“…In the authors' previous study [22], to determine the potential use of Inconel 718 manufactured by LPBF as an aerospace material, a fundamental investigation into the creep performance of LPBF manufactured Inconel 718 specimens was performed. Here, its creep behavior in comparison to a conventionally manufactured part, is assessed.…”

Temperature- and Time-Dependent Mechanical Behavior of Post-Treated IN625 Alloy Processed by Laser Powder Bed Fusion

“…The microstructural analysis was performed on the horizontal (XY) and vertical (ZX) reference faces of the cubic specimens ( Figure 1a). All the specimens were polished LPBF Stress-relief Annealing [29] Temperature, ᵒC Hot isostatic pressing [33] Time For this study, it was decided to carry out both treatments at the same temperature in the 1100-1150 • C range. This decision can be explained by the fact that HIP at this temperature had already been successfully used to reduce processing-induced porosity, and to homogenize and recrystallize LPBF-built microstructures [16,24,34].…”

“…Unlike IN625 alloy, LPBF IN718 alloy, as a precipitation-hardened alloy with a higher mechanical resistance at elevated temperatures [25], has been covered by many studies [26][27][28][29][30]. It was shown that LPBF IN718 alloy manifested a high build-orientation-related anisotropy of its creep properties, caused by preferentially oriented distributions of dendrites and precipitations formed during LPBF processing [26].…”