Neutron diffraction measurements of residual stress in additively manufactured stainless steel
Neutron diffraction measurements of residual stress in additively manufactured stainless steel
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DOI：
10.1016/j.msea.2016.09.086
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发表时间：
2016-12-15
期刊：
影响因子：
6.4
通讯作者：
Thompson, J. M.
中科院分区：
文献类型：
--
作者：
Brown, D. W.;Bernardin, J. D.;Thompson, J. M.
在EOS M280直接金属激光烧结(DMLS)机上，采用粉末床激光熔化技术，在一块17-4级不锈钢的单一不锈钢平板上加成(AM)了Charpy试件。由于DMLS工艺会产生大量残余应力，因此对Charpy试验试件的交叉网格支撑结构进行了不同的支撑宽度和密度的参数研究，以研究它们对构建稳定性和精度的影响。为了确定残余应力，用中子衍射法测定了几个AM样品从支撑结构中取出前后的残余应力分布。在本文研究的有限范围内，残余应力与支承结构的性质几乎没有关系。最大应力分量位于每个研究样品的长方向，约为材料屈服应力的2/3。当试件从支撑结构中取出时，应力场发生了很大的变化。在这项研究中注意到，单个Charpy标本在生长板和支撑结构之间发生了明显的撕裂。支撑结构中撕裂的存在强烈影响了观察到的应力场：不对称撕裂导致了显著不对称的应力场，该应力场通过将样品从基板上移除而传播。样品最终残余应力状态的改变以及观察到的最终形状表明，撕裂是在建造过程中开始的，并且没有中断制造过程，这表明需要进行现场监测。
Charpy test specimens were additively manufactured (AM) on a single stainless steel plate from a 17-4 class stainless steel using a powder-bed, laser melting technique on an EOS M280 direct metal laser sintering (DMLS) machine. Cross-hatched mesh support structures for the Charpy test specimens were varied in strut width and density to parametrically study their influence on the build stability and accuracy as the DMLS process has been known to generate parts with large amounts of residual stress. Neutron diffraction was used to profile the residual stresses in several of the AM samples before and after the samples were removed from the support structure for the purpose of determining residual stresses. The residual stresses were found to depend very little on theproperties of the support structure over the limited range studied here. The largest stress component was in the long direction of each of the samples studied and was roughly 2/3 of the yield stress of the material. The stress field was altered considerably when the specimen was removed from the support structure. It was noted in this study that a single Charpy specimen developed a significant tear between the growth plate and support structure. The presence of the tear in the support structure strongly affected the observed stress field: the asymmetric tear resulted in a significantly asymmetric stress field that propagated through removal of the sample from the base plate. The altered final residual stress state of the sample as well as its observed final shape indicates that the tear initiated during the build and developed without disrupting the fabrication process, suggesting a need for in-situ monitoring.