后处理对激光重熔Inconel 718合金组织及性能的影响

Effect of post treatment on microstructure and property of Inconel 718 superalloy fabricated by laser remelting

采用扫描电镜和电子背散射衍射等研究了激光重熔Inconel 718合金微观组织和显微硬度在不同热处理工艺与超声冲击强化(UIT)作用下的演化规律。结果表明:原始态重熔区(FZ)组织主要由γ枝晶干和Laves相组成;经固溶处理(SHT)后,Laves相大量溶解,元素偏析减弱,显微硬度降低;固溶+双时效处理(SDA)后,γ′和γ″强化相大量析出,显微硬度显著提升;而直接进行双时效处理(DA)时,由于时效温度不足以溶解Laves相,FZ形貌与原始态非常类似,但强化相γ′和γ″充分析出,使FZ显微硬度明显升高。之后,对原始态(AR)试样及热处理态试样表面进行UIT处理后,试样表层均出现严重塑性变形和压应力,位错密度显著增加,并产生了不同深度的硬化层。相比于AR和SHT样品,UIT处理对SDA和DA样品产生的强化效果减弱,这与γ′和γ″强化相的位错强烈交互作用有关。

The effect of heat treatment and ultrasonic impact treatment(UIT)on the evolution of microstructure and microhardness of laser remelted Inconel 718 superalloy was studied by optical microscopy,scanning electron microscopy and electron backscatter diffraction techniques.The results show that the fusion zone(FZ)of as-received(AR)sample is mainly composed ofγdendrite core and interdendritic Laves phase.After solution heat treatment(SHT),the majority of Laves phase dissolves and the element segregation weakens,the microhardness reduce.After the solution+double aging treatment(SDA),a large number ofγ′andγ″strengthening phases precipitate,significantly improve the microhardness.In addition,the direct double aging treatment(DA)sample are similar with the SDA sample in microstructural morphology,which is associated with the undissolved Laves phases due to the relatively low aging temperature.Simultaneously,theγ′andγ″strengthening phases are completely precipitated after aging,resulting in a significant microhardness increment comparable to that of SDA sample.After UIT treatment,severe plastic deformation together with compressive stress and high-density dislocations is produced near the surface of the four samples but the obtained hardening layers ranged indistinct depths.The strengthening effect of UIT on the SDA and DA samples is not as significant as the AR and SHT samples,which is mainly due to the strong interaction betweenγ′/γ″strengthening phases and dislocations.