激光冲击2Cr13不锈钢抗腐蚀疲劳机理研究

发布时间：2019-06-10 23:53

【摘要】：在现如今的工业生产实践中,许多关键位置的零部件受限于其复杂的腐蚀性服役环境,并同时受到循环交变载荷的交互作用,这些零部件往往会产生腐蚀疲劳断裂而导致破坏性的事故。现代机械构件再制造工程核心科学问题之一就是如何选用先进的表面处理技术来强化关键零部件,延长服役寿命的同时提高其使用的可靠性。激光冲击强化作为一种表面形变强化的新方法,其原理是运用激光高能脉冲诱导产生的高幅冲击波压力,在极短的时间内作用于金属靶材表面并使之发生超高应变速率的塑性变形,有效地改善金属材料的应力分布状态并优化微观组织结构,达到抑制腐蚀疲劳断裂过程并提升零部件有效服役寿命的目的。针对上述所存在的问题,本文以2Cr13马氏体不锈钢为探究对象,通过对激光冲击强化不锈钢抗腐蚀疲劳特性进行理论探讨,分析研究了不同层数激光冲击强化对腐蚀疲劳性能的影响。将宏观机械性能和微观断口形貌相结合,详尽地阐明了激光冲击强化的延寿作用,进一步建立了对应残余应力场数值的仿真模拟。获得了如下的结论和进展:(1)完成了以ABAQUS软件为基础的数字化分析,可视化地获得了激光冲击强化仿真应力场的分布,结合模拟来研究应力对裂纹的抑制性。同时仿真分析的结果也可以用来进行不锈钢腐蚀疲劳裂纹扩展特性的预测。经过激光冲击强化,模型表面应力状态发生了明显改变,并产生了塑性变形,冲击强化诱导产生了表面残余压应力,同时也造成了内部拉应力,经过双面激光冲击强化,模型截面的残余应力场呈现对称式分布。(2)通过试验具体分析了不同激光冲击层数、腐蚀介质浓度对腐蚀疲劳寿命的影响,探索了腐蚀疲劳裂纹扩展的变化。通过对数据进行分析处理,获得了裂纹扩展曲线a-N、扩展速率曲线da/dN-ΔK等,定性揭示了裂纹扩展规律。激光冲击强化处理以后,腐蚀疲劳寿命增幅达到了30%~50%;裂纹的扩展速率随着激光冲击层数的增加而减小。而腐蚀介质浓度提高会增大材料的断裂脆性并导致材料寿命的缩短;依据Paris公式求取了激光冲击强化不锈钢材料常数的改变规律,得到了激光冲击对不锈钢腐蚀疲劳寿命的增益机制。(3)深入探讨了不锈钢腐蚀疲劳断口形貌特性,系统地分析了断口宏微观特征以及强化改善机理。根据局部塑性变形的差异,重建了从裂纹开始到最终断裂的微观顺序。未冲击基体断裂面比较平滑,激光冲击强化后的断面变得粗糙不平坦,产生了加倍弯曲转折的裂纹扩展路径,同时出现了疲劳台阶、微观变形及撕裂棱等现象,并损耗了应变能,降低了裂纹扩展速率,起到了阻滞作用。对比了断口主要元素含量的变化,经过激光冲击强化后材料的腐蚀程度降低了,增加冲击层数可以进一步降低腐蚀程度。(4)研究了激光冲击强化不锈钢的机械性能及表面完整性。分析了表面形貌和粗糙度变化:材料表面的塑性变形量随激光冲击强化层数的增加而增大,抗塑性变形能力也得到了显著强化,可以更好地承受外加载荷。探究了激光冲击强化后残余压应力场的分布:残余压应力值随激光冲击层数的增加而增大并趋于饱和,残余压应力有效地抑制了表面裂纹萌生并降低了裂纹扩展速率,形成了扩展抗力并以此改善了抗腐蚀疲劳性能。综上所述,本文研究为实际应用中如何改善关键零部件的抗腐蚀疲劳性能提供了一种新思路,为深入了解激光冲击强化2Cr13不锈钢的表面机械性能改善提供了参考,为系统揭示激光冲击强化对2Cr13不锈钢表面塑性变形和强化机制,提供了可供参考的理论与试验依据。
[Abstract]:In today's industrial production practices, many of the key locations are limited to their complex corrosive service environments and are subject to cyclic and alternating loads that often result in destructive accidents due to corrosion fatigue fracture. One of the core scientific problems in the re-manufacturing of modern mechanical components is how to use advanced surface treatment technology to strengthen the key parts, prolong the service life and improve the reliability of its use. The invention relates to a new method for strengthening surface deformation by laser shock strengthening, which is characterized in that the high-amplitude shock wave pressure generated by laser high-energy pulse induction is applied to the surface of the metal target material in a very short time and the high strain rate is plastically deformed, The stress distribution state of the metal material is effectively improved and the microstructure of the microstructure is optimized, and the purpose of inhibiting the corrosion fatigue fracture process and improving the effective service life of the component is achieved. In the light of the above problems, this paper makes a theoretical study on the corrosion fatigue characteristics of laser shock-reinforced stainless steel by using 2Cr13 Martensitic stainless steel as the research object, and analyzes the effect of laser shock strengthening on the corrosion fatigue property of different layers. In this paper, the macro-mechanical property and the micro-fracture morphology are combined, the life-prolonging effect of the laser shock strengthening is explained in detail, and the simulation of the corresponding residual stress field is further established. The following conclusions and progress have been obtained: (1) The digital analysis based on the ABAQUS software is completed, and the distribution of the laser shock-enhanced simulated stress field is obtained and the suppression of the stress on the crack is studied in combination with the simulation. At the same time, the results of the simulation analysis can also be used to predict the corrosion fatigue crack growth of the stainless steel. Through the laser shock strengthening, the stress state of the model surface is obviously changed, the plastic deformation is generated, the impact strengthening induction generates the surface residual compressive stress, and the internal tensile stress is also caused, and the double-sided laser shock strengthening is carried out, The residual stress field of the model section presents a symmetric distribution. (2) The effects of different laser shock layers and corrosion medium concentration on the corrosion fatigue life were analyzed, and the change of corrosion fatigue crack propagation was investigated. By analyzing the data, the crack propagation curve a-N, the extension rate curve da/ dN-K and the like are obtained, and the crack propagation rule is revealed. The increase of the corrosion fatigue life is 30% ~ 50% after the laser shock-strengthening treatment, and the crack growth rate decreases with the increase of the number of laser shock layers. The increase of the concentration of the corrosion medium increases the fracture and brittleness of the material and leads to the shortening of the life of the material. The change of the constant of the laser shock-reinforced stainless steel material is obtained according to the Paris formula, and the gain mechanism of the laser shock on the fatigue life of the stainless steel is obtained. (3) The characteristics of the fracture morphology of the corrosion fatigue fracture of the stainless steel are discussed, and the micro-characteristics of the fracture and the strengthening mechanism of the fracture are systematically analyzed. The micro order from the beginning of the crack to the final fracture is re-established according to the difference of the local plastic deformation. the fracture surface of the non-impact substrate is relatively smooth, the cross section after the laser shock strengthening becomes rough and uneven, the crack propagation path of the double bending transition is generated, the phenomena of fatigue steps, micro-deformation and tearing edges and the like are generated, the strain energy is lost, the crack growth rate is reduced, And has a blocking effect. The change of the main element content of the fracture is compared, the corrosion degree of the material after the laser shock strengthening is reduced, and the corrosion degree can be further reduced by increasing the number of the impact layers. (4) The mechanical properties and surface integrity of laser shock-reinforced stainless steel were studied. The change of surface morphology and roughness is analyzed. The plastic deformation of the surface of the material is increased with the increase of the number of the laser shock-enhancing layers, and the anti-plastic deformation capability is greatly enhanced, and the applied load can be better borne. The distribution of residual compressive stress field after laser shock strengthening is explored. The residual compressive stress value increases with the increase of the number of laser shock layers and tends to be saturated. The residual compressive stress effectively inhibits the surface crack initiation and reduces the crack growth rate. The extension resistance is formed and the anti-corrosion fatigue property is improved. To sum up, this paper provides a new idea for how to improve the corrosion fatigue performance of key parts in practical application, and provides a reference for the in-depth understanding of the improvement of the surface mechanical properties of the laser shock-reinforced 2Cr13 stainless steel. The plastic deformation and strengthening mechanism of the surface of the 2Cr13 stainless steel is revealed by laser shock strengthening for the system, and the theoretical and experimental basis for reference is provided.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.71;TG665

【参考文献】