无保护层激光冲级强化提高K24镍基合金疲劳强度试验研究

Experiment study on improving fatigue strength of K24 nickel based alloy by laser shock processing without coating

摘要:

无保护层激光冲击强化是一种可以诱导高数值残余压应力和微观组织变化来达到提高金属材料疲劳性能目的的先进表面强化技术。本文的研究目标是通过采用无保护层激光冲击强化提高K24镍基合金的抗疲劳特性。首先，采用高周振动疲劳试验验证了无保护层激光冲击强化效果，疲劳试验结果表明，强化后K24镍基合金疲劳强度相比于未强化试件的282 MPa提高到328 MPa。其次，本文通过采用扫描电镜（SEM）观察、残余应力和显微硬度测试研究了多次冲击对K24镍基合金机械性能以及断口形貌的影响。残余应力测试结果表明，无保护层激光冲击强化后表面形成了压应力，表面最大达到-595 MPa，且影响深度为150 μm。同样3次冲击后表面显微硬度增加到526 HV0.5，深度约为100μm。断口形貌特征表明强化后裂纹源区更加平坦，同时裂纹扩展速率降低。最后，基于疲劳试验和力学性能测试结果进一步讨论了激光冲击强化提高疲劳强度的影响机制。

Abstract:

Laser shock processing without coating (LSPwC) is a novel surface treatment, which can effectively increase the fatigue strength of metal materials by introducing compressive residual stress and microstructural changes. The objective of this work is to improve the fatigue resistance of K24 nickel based alloy by LSPwC. Firstly, high cycle vibration fatigue experiment was adopted to verify the LSPwC strengthening effect. Compared to the untreated samples, the results of the vibration fatigue experiments showed that the fatigue strength of K24 alloy was enhanced and improved from 282MPa to 328MPa after LSPwC. Secondly, the effects of multiple impacts on mechanical properties and fatigue fracture morphologies were investigated, which were observed and measured by scan electron microscope (SEM), X-ray diffractometer and microhardness tester. The results indicated that residual stress presented compressive state on the superficial layer with about 150μm depth and the maximum value reaches -595MPa. The microhardness is about 526 HV0.5 with about 100 μm depth from the top surface after three impacts. The fracture observation indicated that the flatness area was larger in the FCI after LSPwC, meanwhile, the growth rate of fatigue crack was decreased. Lastly, the strengthening mechanism of LSPwC on the fatigue resistance was discussed based on the experimental results.