研究目的
To predict the LSP-induced residual stress superposition on additive manufactured parts and evaluate its effects on microstructural features and mechanical characteristics.
研究成果
The numerical model built in this article successfully predicted the LSP-induced residual stress on laser additive manufactured sample. The simulations results agreed well with the XRD measured results. The thermal-induced tensile residual stress in laser-deposited sample can affect the laser peening results in both horizontal and longitudinal directions. The tensile initial stress can reduce the compressive stress induced by LSP. In laser-deposited sample, the area of the surface compressive stress induced by LSP was a little larger, but the affected depth is relatively lower when compared with the stress-free sample. After LSP there is no obvious phase change and grain refinement in OM and SEM and EBSD observation. A large number of dislocations and twins were spotted in TEM results of LSP-treated sample. The LSP-induced surface deformation can be the accumulative effects of the microdisplacement of the atoms driven by LSP-induced shock wave at high strain rate. Some mechanical properties of the LAMed sample were changed after LSP treatment. The hardness on the surface and 1-mm depth have been increased by 7% and 22%, respectively, and the yield strength was increased by 16%, while there is no significant change in the tensile strength and elongation rate.
研究不足
The slight mismatch between the experimental and simulation results could be caused by the manufacturing error, the final shape of the deposited material is hard to be a strictly 'cuboid' as modeled in FEM program, and the surface quality and grain defects can affect the results of XRD test.
1：Experimental Design and Method Selection:
A finite element model (FEM) model was built to predict the stress distribution on laser-deposited sample, and its changed state is affected by laser peening. The microstructure and mechanical properties were also characterized experimentally.
2：Sample Selection and Data Sources:
The powder used in this article is 1236F/FE-271(Praxair USA), and its composition is close to that of AISI 316 L stainless steel. For different analysis purposes, two kinds of samples were printed.
3：List of Experimental Equipment and Materials:
TruDiode 3006 laser, Q-switched Nd: YAG laser system, HXD-1000TMSC/LCD Vickers hardness test machine, X-ray diffraction (XRD), optical and scanning electron microscopy (OM, SEM), transmission electron microscopy (TEM), CMT5105 electronic universal testing machine.
4：Experimental Procedures and Operational Workflow:
Laser deposition was performed with TruDiode 3006 laser. The laser power applied in the experiment was 800 W, with 2-mm laser diameter. The scan speed was 600 mm/min. LSP experiment was carried out on laser-deposited sample by a Q-switched Nd: YAG laser system. The microstructure of laser-deposited samples before and after laser peening was evaluated through OM and SEM. Microhardness measurements were conducted using HXD-1000TMSC/LCD Vickers hardness test machine. The residual stresses of laser-deposited samples before and after laser peening were measured by using X-ray diffraction (XRD) with sin2ψ method. The uniaxial tension test was carried out on a CMT5105 electronic universal testing machine.
5：Data Analysis Methods:
The residual stress, microstructure, hardness, and tensile strength were investigated by X-ray diffraction measurements (XRD), optical and scanning electron microscopy (OM, SEM), microhardness tester, and electronic universal testing machine.
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