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SLM成形IN718合金高温持久各向异性影响因素

Study on factors affecting high temperature anisotropic stress rupture properties of SLM-IN718 alloy

  • 摘要: 为研究激光选区熔化(selective laser melting, SLM)成形IN718持久各向异性的影响因素,对其打印态分别进行固溶时效(solution treatment and aging, SA)和直接时效(direct aging, DA)处理,采用X射线衍射、扫描电子显微镜及电子背散射衍射对两种状态试样xOy面及yOz物相、显微组织和织构进行表征,并在690 MPa,650 ℃下对两种状态的横向/纵向试样进行持久性能测试,测试后对断口和截面裂纹进行了表征分析量化研究.研究表明,DA态试样很大程度保持了打印态的显微组织,有明显熔池痕迹. 晶粒尺寸几乎没有变化. 显微组织中有大量偏析,XRD显示有衍射强度微弱的MC相的峰.而SA态试样晶粒尺寸及分布与DA态试样类似,同时存在大范围的δ相析出.横向/纵向试样的高温持久性能的差异随着加载时裂纹萌生点数量差异的减小而减小.垂直于应力加载轴向的熔池结构及晶界结构的差异是影响其高温持久各向异性的关键因素.

     

    Abstract: IN718 components often need to be used in high temperature complex stress environment for a long time. High temperature stress rupture and anisotropy are important performance indexes. In order to study the influence factors on the lasting anisotropy of Selective Laser Melting (SLM) forming IN718, the printing state was treated by solution aging (SA) and direct aging (DA) respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) were used to characterize the phase, microstructure and texture of XY and YZ plane of the samples in two states. The stress rupture of the horizontal/vertical samples in two states was tested at 690 MPa and 650 ℃. After the test, the fracture and section crack were characterized and quantified. The results show that the printed microstructure of DA samples is maintained to a large extent, and there are obvious molten pool traces. The grain size hardly changes. The microstructure shows a large amount of segregation, and XRD shows a slight peak of MC phase. The grain size and distribution of SA samples are similar to that of DA samples, and there is a large range of δ phase precipitation. The difference of high temperature stress rupture between horizontal/vertical specimens decreases with the decrease of the number of crack initiation points. The difference of molten pool structure and grain boundary structure perpendicular to the stress loading axis is the key factor affecting its stress rupture anisotropy at high temperature.

     

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