Santamaria Ricardo, Salasi Mobin, Rickard William D A, Pojtanabuntoeng Kod, Leadbeater Garry, Iannuzzi Mariano, Reddy Steven M, Quadir Md Zakaria
Curtin Corrosion Centre, Curtin University, Perth, WA 6102, Australia.
Microscopy and Microanalysis Facility, John de Laeter Centre (JdLC), Perth, WA 6845, Australia.
Materials (Basel). 2023 Jun 9;16(12):4289. doi: 10.3390/ma16124289.
There is a fast-growing interest in the use of selective laser melting (SLM) for metal/alloy additive manufacturing. Our current knowledge of SLM-printed 316 stainless steel (SS316) is limited and sometimes appears sporadic, presumably due to the complex interdependent effects of a large number of process variables of the SLM processing. This is reflected in the discrepant findings in the crystallographic textures and microstructures in this investigation compared to those reported in the literature, which also vary among themselves. The as-printed material is macroscopically asymmetric in terms of both structure and crystallographic texture. The <101> and <111> crystallographic directions align parallel with the SLM scanning direction (SD) and build direction (BD), respectively. Likewise, some characteristic low-angle boundary features have been reported to be crystallographic, while this investigation unequivocally proves them to be non-crystallographic, since they always maintain an identical alignment with the SLM laser scanning direction, irrespective of the matrix material's crystal orientation. There are also 500 ± 200 nm columnar or cellular features, depending on the cross-section, which are generally found all over the sample. These columnar or cellular features are formed with walls made of dense packing of dislocations entangled with Mn-, Si- and O-enriched amorphous inclusions. They remain stable after ASM solution treatments at a temperature of 1050 °C, and therefore, are capable of hindering boundary migration events of recrystallization and grain growth. Thus, the nanoscale structures can be retained at high temperatures. Large 2-4 μm inclusions form during the solution treatment, within which the chemical and phase distribution are heterogeneous.
选择性激光熔化（SLM）用于金属/合金增材制造的应用正迅速受到关注。我们目前对SLM打印的316不锈钢（SS316）的了解有限，而且有时显得零散，这可能是由于SLM加工中大量工艺变量之间复杂的相互依存效应所致。与文献报道相比，本研究中晶体织构和微观结构的差异结果就反映了这一点，文献中的结果彼此之间也各不相同。打印后的材料在结构和晶体织构方面在宏观上是不对称的。<101>和<111>晶体方向分别与SLM扫描方向（SD）和构建方向（BD）平行排列。同样，一些特征性低角度边界特征据报道是晶体学的，但本研究明确证明它们是非晶体学的，因为它们总是与SLM激光扫描方向保持相同的排列，而与基体材料的晶体取向无关。根据横截面不同还存在500±200nm的柱状或胞状特征，通常在整个样品中都能发现。这些柱状或胞状特征由位错紧密堆积形成的壁构成，位错与富含Mn、Si和O的非晶质夹杂物缠结在一起。在1050℃的奥氏体化固溶处理后它们保持稳定，因此能够阻碍再结晶和晶粒生长的边界迁移事件。这样，纳米级结构就能在高温下保留下来。在固溶处理过程中会形成2 - 4μm的大夹杂物，其内部的化学和相分布是不均匀的。
