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Experimental study of Ni-based single-crystal superalloy: Microstructure evolution and work hardening of ground subsurface

Xu Yunchao, Gong Yadong, Wang Zhongxu, Wen Xuelong, Yin Guoqiang, Zhang Huan, Qi Yang

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 2

74--84

In the present study, the grinding experiment of second-generation nickel-based single-crystal superalloy DD5 was carried out under different grinding parameters. The grinding force was recorded during the grinding process, and it was found that it decreased with increasing grinding speed and increased with feed speed. The microstructure evolution of ground subsurface was obtained by optical microscope (OM) and scanning electron microscope (SEM), and the elemental distribution of γ/γ' phases was investigated by energy dispersion spectrum (EDS). The results show that there are two layers different from the bulk material beneath the ground surface: (i) a white layer (WL) with no obvious structural features under limited observation scale and (ii) a severe deformed layer (SDL) with the elongated and rotated γ' phase and the narrowed γ channel. Elements segregation behavior exists in both the white layer and severe deformed layer. The grinding parameters have a great influence on the thickness of the white layer, which is due to the elemental diffusion behavior caused by intensive thermo-mechanical load. There is work hardening in the white layer, and the hardening degree aggravates with the increase in cutting speed and feed speed.

Inconel-steel functionally bimetal materials by hybrid directed energy deposition and thermal milling: Microstructure and mechanical properties

Li Pengfei, Gong Yadong, Xu Yunchao, Qi Yang, Sun Yao, Zhang Huan

Archives of Civil and Mechanical Engineering

2019

Vol. 19, no. 3

820--831

Many engineering applications, particularly those in extreme environments, require com-ponents with properties that vary with location in the part. Functionally bimetal materials (FBM) that combine dissimilar materials, such as those with different density and thermal properties, provide a potential solution to this need. Directed energy deposition (DED) is convenient to fabricate all kinds of complicated parts and to clad different materials at specific locations. Milling can improve the surface quality and dimensional accuracy after DED. Hybrid DED and thermal milling manufacturing can fabricate FBMs and be applied to laser repair. This study used this new method to fabricate Inconel-steel FBM. Inconel 718 powder and 316L stainless steel powder were deposited on the thermal milling surface of parts prepared with DED. The interfacial characteristics of different cladding materials were compared. Microstructure, chemistry, phase composition, element segregation and micro-hardness varied with position and were characterized by energy dispersive spectroscopy, X-ray diffraction, scanning electron microscopy and microhardness testing. Finally, the tensile properties of the FBM were compared to other materials, and the fracture location and morphology were analyzed. The results showed that the yield strength (YS) reached 368 MPa, and the ultimate tensile strength (UTS) reached 516 MPa. The Vickers microhard-ness of the diffusion layer was approximately 250 HV.