热处理对选择性激光熔炼IN718显微组织和力学性能的影响

Rare Metal et al. / Rare Metal Materials and Engineering, 2018, 47(03): 0？？？-0？？？

摘要:

选择性激光熔炼(SLM)建立在激光熔覆/沉积基础上,能够由粉末直接制备或修复近成形高性能部件。选择性激光熔炼部件优异的力学性能是保证其用于航空发动机产品的先决条件。镍基高温合金IN718广泛用于制备航空发动机中的高性能部件。在过去的研究中,利用预合金化IN718合金粉末,通过选择性激光熔炼制备出增材制造部件。通过优化激光沉积过程试验参数,以最大限度地降低气孔率。对沉积态、直接时效态、固溶时效态、均匀化后固溶时效态四种状态激光沉积IN718合金的显微组织和力学性能进行了对比分析。拉伸试验结果显示,直接时效态合金强度最高,均匀化后固溶时效态合金塑性最好。综合考虑三种热处理状态的室温和高温拉伸试验结果,均匀化后固溶时效态试样不仅具有优于锻态AMS标准的强度,而且有很好的塑性。因此,选择均匀化后固溶时效处理作为选择性激光熔炼IN718合金的热处理方式。考察了该种热处理状态合金的650_oC/700MPa和725MPa持久性能和455_oC低周疲劳性能,并与锻态IN718进行了对比。

Abstract:

Selective laser melting (SLM) is a laser cladding/deposition based technology, which can fabricate and repair near-net-shape high-performance components directly from metal powders. Characterizing mechanical properties of the SLM components is prerequisite to the applications of SLM in aircraft engine industrial productions. Nickel-based superalloys such as IN718 are the most commonly used metal materials in aircraft engine high-performance components. In the present study pre-alloyed, rapidly solidified IN718 powder served as a precursor for the production of additive manufactured components using SLM. The laser deposition process is optimized through a set of designed experiments to reduce the porosity. Material microstructure and mechanical properties of laser-deposited IN718 are studied and compared under heat treatment conditions of as deposited, direct aged, solution treatment and aging (STA), and full homogenization followed by STA. Tensile test results showed that the direct age treatment produces the highest tensile strength to the wrought material, while the homogenization treatment followed by STA exhibits good ductility. Failure modes of the tensile samples were analyzed by fractography. Considering the room and high temperature tensile test results of three heat treatment, homogenized STA samples not only have higher strength than the AMS wrought specifications, but also have good plastic. Therefore, homogenized STA is suitable heat treatment method for LSM IN718 alloy. Then, stress rupture properties at 650 _oC/700 and 725 MPa, low cycle fatigue properties at 455 _oC of the homogenized STA samples were investigated, fracture mode was analyzed and compared to wrought IN718 alloy.