Shi Xuezhi, Ma Shuyuan, Liu Changmeng, Chen Cheng, Wu Qianru, Chen Xianping, Lu Jiping
School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China.
Beijing Institute of Astronautical Systems Engineering, Beijing 100076, China.
Materials (Basel). 2016 Dec 1;9(12):975. doi: 10.3390/ma9120975.
To increase building rate and save cost, the selective laser melting (SLM) of Ti6Al4V with a high layer thickness (200 μm) and low cost coarse powders (53 μm-106 μm) at a laser power of 400 W is investigated in this preliminary study. A relatively large laser beam with a diameter of 200 μm is utilized to produce a stable melt pool at high layer thickness, and the appropriate scanning track, which has a smooth surface with a shallow contact angle, can be obtained at the scanning speeds from 40 mm/s to 80 mm/s. By adjusting the hatch spacings, the density of multi-layer samples can be up to 99.99%, which is much higher than that achieved in previous studies about high layer thickness selective laser melting. Meanwhile, the building rate can be up to 7.2 mm³/s, which is about 2 times-9 times that of the commercial equipment. Besides, two kinds of defects are observed: the large un-melted defects and the small spherical micropores. The formation of the un-melted defects is mainly attributed to the inappropriate overlap rates and the unstable scanning tracks, which can be eliminated by adjusting the processing parameters. Nevertheless, the micropores cannot be completely eliminated. It is worth noting that the high layer thickness plays a key role on surface roughness rather than tensile properties during the SLM process. Although a sample with a relatively coarse surface is generated, the average values of yield strength, ultimate tensile strength, and elongation are 1050 MPa, 1140 MPa, and 7.03%, respectively, which are not obviously different than those with the thin layer thickness used in previous research; this is due to the similar metallurgical bonding and microstructure.
在这项初步研究中，研究了在400W激光功率下，使用高层厚（200μm）和低成本粗粉末（53μm - 106μm）对Ti6Al4V进行选择性激光熔化（SLM），以提高构建速率并节省成本。利用直径为200μm的相对较大激光束在高层厚下产生稳定的熔池，并且在40mm/s至80mm/s的扫描速度下，可以获得具有浅接触角的光滑表面的合适扫描轨迹。通过调整扫描间距，多层样品的密度可高达99.99%，这比先前关于高层厚选择性激光熔化的研究中所达到的密度要高得多。同时，构建速率可达7.2mm³/s，约为商业设备的2倍至9倍。此外，观察到两种缺陷：大的未熔化缺陷和小的球形微孔。未熔化缺陷的形成主要归因于不适当的重叠率和不稳定的扫描轨迹，通过调整加工参数可以消除这些缺陷。然而，微孔无法完全消除。值得注意的是，在SLM过程中，高层厚对表面粗糙度起关键作用，而不是对拉伸性能起关键作用。尽管生成了表面相对粗糙的样品，但其屈服强度、极限抗拉强度和伸长率的平均值分别为1050MPa、1140MPa和7.03%，与先前研究中使用的薄层厚样品相比没有明显差异；这是由于冶金结合和微观结构相似。
