Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
11027743 | Additive Manufacturing | 2018 | 25 Pages |
Abstract
In this study, the fatigue properties of binder-jet 3D-printed nickel-base superalloy 625 were evaluated. Standard fatigue specimens were printed and sintered, then half of the samples were mechanically ground, while the other half were left in their as-sintered state. They were then characterized using micro-computed x-ray tomography, metallographic sample examination, and optical and stylus profilometry for surface topography. The micro-computed tomography observations showed that density of the as-printed sample was â¼50%, while the sintered sample neared full densification (98.9â±â0.3%) upon sintering at 1285â°C for 4âh in a vacuum atmosphere. The metallographic examination showed equiaxed grains. The roughness of the as-sintered samples was significant with an RMS roughness of Rqâ=â1.39â±â0.20âμm as measured over a line-scan of 5âmm, but this was reduced to Rqâ=â0.47â±â0.02âμm after mechanical grinding. All samples were tested to failure in fatigue, under fully-reversed tension-compression conditions. While the as-sintered samples showed poor fatigue properties compared to prior reports on cast and milled parts, the ground samples showed superior performance. Scanning electron microscopy observation was conducted on the fractured surfaces and showed that the samples underwent transgranular crack initiation, followed by intergranular crack growth and final failure. In the mechanically ground sample, hardness increased nearly two-fold up to 75âμm beneath the sample's surface, and X-ray diffraction indicated an in-plane compressive stress, grain refinement, and micro-strain on the mechanically ground sample. The reduced roughness, surface hardening, and compressive stress resulted in increased fatigue life of the binder-jetted alloy 625.
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Authors
Amir Mostafaei, S. Harsha Vardhan R. Neelapu, Cameron Kisailus, Lauren M. Nath, Tevis D.B. Jacobs, Markus Chmielus,