Maimaitiyili Tuerdi, Woracek Robin, Neikter Magnus, Boin Mirko, Wimpory Robert C, Pederson Robert, Strobl Markus, Drakopoulos Michael, Schäfer Norbert, Bjerkén Christina
Photons for Engineering and Manufacturing Group, Paul Scherrer Institute, 5232 Villigen, Switzerland.
Department of Materials Science and Applied Mathematics, Malmö universitet, 20506 Malmö, Sweden.
Materials (Basel). 2019 Feb 23;12(4):667. doi: 10.3390/ma12040667.
Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform α- and β-Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in α and β phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary β grains. However, no relation was found between measured residual strains in α and β phase. Large primary β grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior β grain size in experimental planning, as well as for mathematical modelling.
增材制造材料中使用的残余应力/应变和微观结构强烈依赖于工艺参数组合。为了更好地理解和关联钛合金Ti-6Al-4V电子束熔炼（EBM）中使用的工艺参数与所得相分布以及残余应力/应变之间的关系，已开展了大量实验工作。使用不同的优化EBM工艺参数组合制备了大量多晶Ti-6Al-4V试样。随后依次使用高能X射线和中子衍射对这些试样进行研究。此外，还进行了可见光显微镜、扫描电子显微镜（SEM）和电子背散射衍射（EBSD）研究，并将其与其他研究结果相关联。结果表明，扫描速度和偏置焦点对全致密样品中所得残余应变的影响并不显著。与一些先前的文献不同，在所有研究的试样中均发现了均匀的α相和β相钛分布。此外，未发现沿构建方向相对于沉积存在强烈的应变变化。α相和β相中的应变大小在构建平面和沿构建方向上均表现出一些变化，这似乎与初生β晶粒的尺寸相关。然而，未发现α相和β相中的实测残余应变之间存在关联。较大的初生β晶粒和织构似乎对基于X射线的应力结果有很大影响，因为光束尺寸相对较小，因此建议使用大光束进行具有代表性的整体测量，并在实验规划以及数学建模中考虑先前的β晶粒尺寸。
