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29 results on '"You, Qifan"'

11. Effect of Y2O3on microstructure and mechanical properties of 34CrNiMo6 steel fabricated by laser-directed energy deposition

Author

Qiu, Cheng, Liu, Fenggang, Huang, Chunping, Liu, Fencheng, Shu, Zongfu, You, Qifan, Zheng, Haizhong, Wang, Lianbo, and Yu, Dawei

Abstract

Due to the extremely unbalanced temperature gradient at different heights along the deposition direction during additive manufacturing, the microstructure of different areas of the formed components is quite different, which limits the part's service life to a large extent. In this paper, microstructure of the laser-directed energy deposition (LDED) 34CrNiMo6 steel is homogenized by adding Y2O3, and excellent mechanical properties are obtained. The results showed that the homogenization of microstructure at different heights of the as-deposited samples was realized due to addition of Y2O3. The microstructure of the as-deposited samples at different heights contains lath martensite and lower bainite, only retained austenite is present at the top. With the increase of Y2O3content, the size of the austenite grain of the as-deposited LDED 34CrNiMo6 steel showed a tendency of decreasing and then increasing. The austenite grain size and martensite domain size were minimized when the Y2O3content was 2 wt%. The average microhardness showed an increasing and then decreasing trend with the increase of Y2O3content. When the content of Y2O3was 2 wt%, it had the highest average microhardness, which was 597 HV and 640 HV, respectively. The elongation and percentage reduction of area showed a trend of decreasing and then increasing, and tensile strength showed a trend of increasing and then decreasing. When the Y2O3content was 2 wt%, reached the maximum tensile strength of 1501 MPa, an increase of about 56 %, and its elongation and percentage reduction of area was the lowest in the rare-earth-containing samples, and the fracture mechanism is quasi-dissociative fracture.

Published
2024
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29. The Precipitation Behavior and Hot Deformation Characteristics of Electron Beam Smelted Inconel 740 Superalloy.

Author

Tan, Yi, You, Qifan, Zhao, Longhai, Li, Jiayan, You, Xiaogang, and Wu, Chang

Subjects
INCONEL, PRECIPITATION (Chemistry), DEFORMATIONS (Mechanics), ELECTRON beams, SMELTING
Abstract

The Inconel 740 superalloy was prepared by the electron beam smelting (EBS) technology, the precipitation behavior and strengthening mechanism were studied, and the hot deformation characteristics of EBS 740 superalloy were investigated. The results indicate that the EBS 740 superalloy is mainly strengthened by the mechanism of weakly coupled dislocation shearing, and the resulting critical shear stress is calculated to be 234.6 MPa. The deformation parameters show a great influence on the flow behavior of EBS 740 superalloy. The strain rate sensitivity exponent increases with the increasing of deformation temperature, and the strain hardening exponent shows a decreasing trend with the increasing of strain. The activation energy of EBS 740 above 800 °C is measured to be 408.43 kJ/mol, which is higher than the 740H superalloy. A hyperbolic-sine-type relationship can be observed between the peak stress and Zener-Hollomon parameter. Nevertheless, the influence of deformation parameters is found to be considerably different at temperatures below and above 800 °C. The size of dynamic recrystallization (DRX) grains decreases with the increasing of strain rate when the strain rate is lower than 1/s, and reverse law can be found at higher strain rate. As a result, a piecewise function is established between the DRX grain size and hot working parameters. [ABSTRACT FROM AUTHOR]

Published
2018
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