不同气氛对激光熔覆IN718涂层形貌、组织与性能的影响

目的研究不同气氛条件下激光熔覆IN718高温合金涂层的微观偏析。方法利用激光熔覆技术,在不同送粉气和不同保护气条件下制备了IN718高温合金涂层,并对制备的涂层进行双时效热处理。采用光学显微镜观察显微组织结构和特征,采用扫描电镜和能谱仪对涂层组织和相成分进行分析,采用维氏硬度计对涂层热处理前后的硬度进行测定。结果送粉气种类对熔覆层的形貌和组织有一定影响,而保护气种类对熔覆层的形貌和组织影响不明显。与氩气作为送粉气制备的涂层相比,氦气作为送粉气制备的涂层组织更加细密,Laves相的尺寸更小且分布更均匀,Laves相的体积分数由氩气送粉的9.35%减少到氦气送粉的5.25%,并且Laves相中Nb的质量分数由20%下降到16%,涂层硬度由287HV0.2提高到306HV0.2。双时效热处理后,涂层的显微硬度明显提高,氦气作为送粉气制备的涂层硬度为468HV0.2,高于氩气作为送粉气制备的涂层硬度447HV0.2。结论氦气作为送粉气能有效降低激光熔覆IN718涂层的Nb元素偏析,同时细化涂层组织,提高涂层显微硬度。氦气作为保护气对涂层形貌和组织的影响不明显。

Influence of Atmospheres on Morphology, Microstructure and Properties of Laser Cladding IN718 Coatings

The work aims to study micro-segregation of laser clad IN718 superalloy coatings fabricated under different atmosphere conditions. IN718 superalloy coatings were fabricated under different carrier gas and shielding gas conditions, and double-aging heat treatment was applied to the coating. Microstructure and characteristics of the coatings were analyzed using optical microscope (OM), structure and phase composition of the coatings were analyzed using scanning electron microscope (SEM) and energy disperse spectrometer (EDS), and hardness of the coatings before and after heat treatment was analyzed using Vickers hardness tester. Type of carrier gas had certain effects on the morphology and microstructure of the cladding layer, while type of shielding gas had no obvious effect. Compared with the coating prepared with argon (Ar) as carrier gas, the microstructure of the coating prepared with helium gas (He) as carrier gas was finer, the size of Laves phase was smaller and more uniformly distributed, volume fraction of the Laves phase decreased from 9.35% (Ar as carrier gas) to 5.25% (He as carrier gas), and Nb content in the Laves phase decreased from 20% to 16%, and hardness of the coating increased from 287HV0.2 to 306HV0.2. After the double-aging heat treatment, microhardness of the coatings was significantly increased. Hardness of the coating prepared with He as carrier gas was 468HV0.2, which was higher than that of the coating prepared with Ar gas as carrier gas (447HV0.2). Using He gas as carrier gas can effectively reduce segregation of Nb element in laser cladding IN718 coating, refine microstructure and increase microhardness of coating. However, He gas as shielding gas has no obvious effect on morphology and microstructure of coating.