Polishing And Mechanical Property Modulation Of Laser Shock Peened Metallic Glasses Surfaces

Metallic glasses(MGs)exhibit unique mechanical,physical and chemical properties,such as high strength,high hardness and excellent corrosion resistance due to their structural characteristics such as long-range disorder,short-range order,isotropy,lack of dislocations and grain boundaries.However,the low plasticity at room temperature causes MGs to catastrophic fracture when subjected to loads,limiting their use as structural materials.Laser shock peening(LSP)technology can improve the plasticity of MGs,however,it also deteriorates the surface quality and decreases the surface hardness of MGs,which affects the practical application of MGs as engineering materials.To address the above problems,this paper focuses on the polishing and surface hardness improvement of LSPed MGs surfaces,and the main work is as follows:Firstly,LSP tests on Zr-based MGs were carried out to investigate the effects of LSP on the surface morphology,roughness and hardness of MGs under different test conditions were investigated using scanning electron microscopy,laser confocal microscopy and nanoindentation instrument.The results showed that the surface roughness increased and the surface hardness decreased after LSP.The softening layer depth of LSP was determined by characterization and analysis of the cross-sectional hardness change,the load-depth curve and indentation residual morphology showed that the surface microplastic deformation ability was improved after LSP.Then,to address the problems of deterioration of surface quality and reduction of surface hardness caused by LSP,experiments on nanosecond pulsed laser polishing of LSPed surfaces under argon atmosphere were carried out to study the effects of laser parameters on polished surface morphology,roughness and hardness.The results showed that laser polishing in argon can significantly improve the quality of the LSPed surface,and at the same time can improve the surface hardness to some extent.With the preferred laser parameters,the laser polished surface roughness reached an average value of 27.33 nm,which was 87.89%lower compared to the LSPed surface,and the surface hardness increased by 12.06%(from 5.331 GPa to 5.974 GPa).Further,to address the problem that the polishing of LSPed surfaces in argon gas has very limited regulation of surface hardness,experiments on nanosecond pulsed laser polishing of LSPed surfaces under nitrogen atmosphere were carried out to investigate the effects of laser power on polished surface morphology,roughness and hardness,and the surface chemical composition and cross-sectional hardness changes were analyzed.The results show that the roughness of the polished surface tends to decrease and then increase with the increase of laser power.The depth of the hardened layer of nitride phase was 40μm when the laser polishing power was 11.4 W,and the depth of the layer affected by the softening effect of LSP was about 200μm.The results of X-ray diffraction inspection and nanoindentation test showed that the generation of nitride phase increased the hardness of the laser polished surface within the nitrogen atmosphere to 10-15 GPa.At the same time,the surface quality and mechanical properties of Zr-based MG can be effectively regulated by changing the laser parameters.In order to solve the problem that the surface roughness is still high under most laser parameters of nitriding,LSP tests on the nitrided surface of Zr-based MG under argon atmosphere were carried out to investigate the effects of laser parameters on the morphology,roughness and hardness of the nitrided surface,and to compare with the previous test results.The results showed that the impact of LSP on the nitrided surface in argon can make some of the raised nitride particles disappear,and with the increase of laser energy density,the distribution density of nitride particles on the surface became lower and lower,and the surface roughness also became lower.The surface hardness is higher than the original surface lower than the nitrided surface.When the LSP energy density is 178.3 J/cm~2,the surface roughness decreases from 480 nm to183 nm,and the hardness decreases from 9.116 GPa to 7.451 GPa,which is still higher than the original surface hardness.In summary,this paper has achieved the regulation of the surface quality and hardness of Zr-based MG by LSP through nanosecond pulsed laser polishing,which provides a useful reference for the regulation of the surface properties of MG.