Characterizing surface finish and fatigue behavior in binder-jet 3D-printed nickel-based superalloy 625
Characterizing surface finish and fatigue behavior in binder-jet 3D-printed nickel-based superalloy 625
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DOI：
10.1016/j.addma.2018.09.012
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发表时间：
2018-12-01
影响因子：
11
通讯作者：
Chmielus, Markus
中科院分区：
文献类型：
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作者：
Mostafaei, Amir;Neelapu, S. Harsha Vardhan R.;Chmielus, Markus
本文对粘结剂喷射3D打印镍基高温合金625的疲劳性能进行了评价。将标准疲劳试件打印并烧结，然后对一半的试件进行机械研磨，而另一半的试件则保持其烧结状态。然后使用微型计算机x射线断层摄影术、金相样品检查以及用于表面形貌的光学和触针轮廓术对它们进行表征。显微CT观察表明，印刷样品的密度接近50%，而烧结样品在1285℃真空气氛中烧结4h后接近完全致密化(98.9+/-0.3%)。金相检查显示等轴晶。在5 mm的线扫描下，烧结态样品的RMS粗糙度为R-Q=1.39+/-0.20微米，而机械研磨后的RQ=0.47+/-0.02微米。所有的试件都在完全可逆的拉压条件下进行了疲劳破坏试验。虽然与先前关于铸件和球磨零件的报道相比，烧结样品的疲劳性能较差，但研磨样品表现出更好的性能。对断口进行了扫描电子显微镜观察，结果表明，试样经历了穿晶裂纹萌生、沿晶裂纹扩展和最终失效的过程。在机械研磨样品中，硬度增加了近两倍，达到样品表面以下75微米，X射线衍射表明机械研磨样品上存在面内压应力、晶粒细化和微应变。降低的粗糙度、表面硬化和压应力导致了喷射粘结剂的625合金的疲劳寿命增加。
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 similar to 50%, while the sintered sample neared full densification (98.9 +/- 0.3%) upon sintering at 1285 degrees C for 4 h in a vacuum atmosphere. The metallographic examination showed equiaxed grains. The roughness of the as-sintered samples was significant with an RMS roughness of R-q = 1.39 +/- 0.20 mu m as measured over a line-scan of 5 mm, but this was reduced to R-q = 0.47 +/- 0.02 mu m 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 75 mu m 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.