激光选区熔化与传统加工IN718合金的组织与性能比较研究

本文对比研究了选区激光熔化(SLM)和轧制退火IN718合金的显微组织和力学性能。结果表明：由于快速冷凝造成的不平衡凝固使得SLM合金样品具有成分偏析、晶粒细小和晶内存在大量凝固胞的组织特点；且因为外延生长,出现建造方向平行于<100>晶向的强织构；经比较,轧制退火的合金样品组织均匀,晶粒尺寸是SLM样品的3 倍,晶界和晶内分别观察到少量的laves和d相,无成分偏析和亚结构存在,由于大量退火孪晶存在而使晶粒取向分布较随机。两种样品经拉伸性能试验发现,SLM样品的屈服强度和抗拉强度分别是轧制退火态的4.6和1.3倍,而延伸率有所下降,是轧制退火态的34.4%。分析认为SLM样品中晶粒细小和丰富的凝固胞亚结构是强度高的主要原因,延伸率较比传统加工样品的延伸率大幅降低应归结为打印缺陷如孔隙和残余应力的存在。

Comparison of Microstructure and Properties of IN718 Alloy Processed by Selective Laser Melting and Conventional Processing

A comparative study on the IN718 superalloy prepared by selective laser melting (SLM) and conventional processing, namely mill annealing, was conducted in terms of microstructure and tensile mechanical properties. The results showed that chemical segregation, fine-grained microstructure and abundance in solidification cells were found during non-equilibrium solidification due to rapid cooling in SLM samples. In addition, strong texture of <100> parallel to building direction was observed due to epitaxial growth during SLM processing. By comparison, the microstructure of the annealed alloy was uniform and the grain size was 3 times that of the SLM sample, relatively homogeneous and coarse microstructure with an extremely small amount of laves phase along grain boundary and d precipitation inside grains was found whereas no chemical segregation and solidification cells were present in Mill-Anneal samples. The grain orientation becomes random due to mollification of annealing twins. The tensile testing results showed that the yielding and tensile strength in SLM sample were 4.6 and 1.3 times those in Mill-Anneal samples, respectively. But the elongation percentate decreased and was only 34.4 % that in Mill-Anneal samples. Further analysis pointed out that refined microstructure and abundance in solidification cells were primarily responsible for the high strength for SLM samples, and the reduced elongation percentage should be ascribed into the presence of printing defects and residual stress.