【作者】 刘博；

【导师】 黄虎；

【作者基本信息】 吉林大学 ， 工程硕士（专业学位）， 2023， 硕士

【摘要】 非晶合金因具有长程无序、短程有序、各向同性、缺少位错和晶界等结构特点,表现出独特的机械、物理和化学性能,如高强度、高硬度和优异的耐腐蚀性。然而,室温下低塑性导致了非晶合金受到载荷时易发生灾难性断裂,限制了其作为结构材料的使用。激光喷丸技术可以改善非晶合金的塑性,但与此同时也会恶化非晶合金表面质量,降低非晶合金表面硬度,进而影响其实际工程应用。针对上述问题,本文聚焦非晶合金激光喷丸表面的抛光及表面硬度提高开展研究,主要工作如下:首先,开展了锆基非晶合金激光喷丸试验,利用扫描电子显微镜、激光共聚焦显微镜和纳米压痕仪,研究了不同试验条件下激光喷丸对锆基非晶合金表面形貌、粗糙度和硬度的影响。结果表明,激光喷丸后表面粗糙度提高,表面硬度降低。通过表征分析横截面硬度变化,确定了激光喷丸软化层深度;载荷-深度曲线和压痕残余形貌表明,激光喷丸后表面微观塑性变形能力得到提高。接着,针对激光喷丸处理引起表面质量变差和表面硬度降低的问题,开展了氩气氛围下纳秒脉冲激光抛光喷丸表面的试验,研究了激光参数对抛光表面形貌、粗糙度和硬度的影响。结果表明,氩气中激光抛光可明显改善激光喷丸表面的质量,同时可一定程度提高表面硬度。在优选的激光参数下,激光抛光表面粗糙度平均值(Ra)达到27.33nm,与激光喷丸表面相比降低了87.89%,表面硬度提高了12.06%(从5.331GPa提高到5.974GPa)。进一步,针对氩气中抛光对激光喷丸表面硬度调控有限这一问题,开展了氮气氛围下激光抛光试验,研究了激光功率对抛光表面形貌、粗糙度和硬度的影响,并对表面化学组成和横截面硬度变化进行了分析。结果表明,抛光表面粗糙度随着激光功率的增加呈现先降低后升高的趋势,当激光抛光功率为11.4W时,氮化相硬化层深度为40μm,激光喷丸软化效果影响层深度约200μm。X射线衍射检测结果和和纳米压痕测试结果表明,氮化相的生成使得氮气内激光抛光表面硬度提高至10-15GPa。与此同时,改变激光参数可有效调控锆基非晶合金表面质量和力学性能。为解决大部分激光参数氮化下,表面粗糙度仍然较高这一问题,开展了氩气氛围下锆基非晶合金氮化表面的激光喷丸试验,研究了激光喷丸参数对氮化表面形貌、粗糙度和硬度的影响,并与前文试验结果进行对比分析。结果表明,在氩气中使用激光喷丸冲击氮化表面,可使部分凸起氮化物颗粒消失,并且随着激光能量密度增加,表面氮化物颗粒的分布密度越来越低,表面粗糙度也随之降低,表面硬度高于原始表面而低于氮化表面。当激光喷丸能量密度为178.3J/cm~2时,表面粗糙度(Ra)从氮化表面的480nm降低到183nm,硬度从氮化表面9.116GPa降低至7.451GPa,但仍高于原始表面硬度。综上,本文通过纳秒脉冲激光抛光,实现了对锆基非晶合金激光喷丸表面质量和硬度的调控,为非晶合金表面特性调控提供了有益参考。更多还原

【Abstract】 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.更多还原