Li Gang, Qu Shengguan, Xie Mingxin, Ren Zhaojun, Li Xiaoqiang
Department of Mechanical and Automotive Engineering, South China University of Technology, No. 381 Wushan Road, Tianhe District, Guangzhou 510640, China.
Materials (Basel). 2017 Feb 6;10(2):133. doi: 10.3390/ma10020133.
The main purpose of this paper was to investigate the effect of a surface plastic deformation layer introduced by multi-pass ultrasonic surface rolling (MUSR) on the mechanical and fatigue properties of HIP Ti-6Al-4V alloys. Some microscopic analysis methods (SEM, TEM and XRD) were used to characterize the modified microstructure in the material surface layer. The results indicated that the material surface layer experienced a certain extent plastic deformation, accompanied by some dense dislocations and twin generation. Moreover, surface microhardness, residual stress and roughness values of samples treated by MUSR were also greatly improved compared with that of untreated samples. Surface microhardness and compressive residual stress were increased to 435 HV and -1173 MPa, respectively. The minimum surface roughness was reduced to 0.13 μm. The maximum depth of the surface hardening layer was about 55 μm. However, the practical influence depth was about 450 μm judging from the tensile and fatigue fracture surfaces. The ultimate tensile strength of the MUSR-treated sample increased to 990 MPa from the initial 963 MPa. The fatigue strength of the MUSR-treated sample was increased by about 25% on the base of 10⁷ cycles, and the lifetime was prolonged from two times to two orders of magnitude at the applied stress amplitudes of 650-560 MPa. The improved mechanical and fatigue properties of MUSR-treated samples should be attributed to the combined effects of the increased microhardness and compressive residual stress, low surface roughness, grain refinement and micro-pore healing in the material surface-modified layer.
本文的主要目的是研究多道次超声表面滚压（MUSR）引入的表面塑性变形层对热等静压Ti-6Al-4V合金力学性能和疲劳性能的影响。采用了一些微观分析方法（扫描电子显微镜、透射电子显微镜和X射线衍射）来表征材料表层改性后的微观结构。结果表明，材料表层经历了一定程度的塑性变形，伴随着一些密集位错和孪晶的产生。此外，与未处理样品相比，经MUSR处理的样品的表面显微硬度、残余应力和粗糙度值也有很大提高。表面显微硬度和压缩残余应力分别提高到435 HV和-1173 MPa。最小表面粗糙度降低到0.13μm。表面硬化层的最大深度约为55μm。然而，从拉伸和疲劳断口判断，实际影响深度约为450μm。经MUSR处理的样品的极限抗拉强度从初始的963 MPa提高到990 MPa。在10⁷次循环的基础上，经MUSR处理的样品的疲劳强度提高了约25%，在650 - 560 MPa的外加应力幅值下，寿命从两倍延长到两个数量级。经MUSR处理的样品力学性能和疲劳性能的改善应归因于材料表面改性层中显微硬度增加、压缩残余应力、低表面粗糙度、晶粒细化和微孔愈合的综合作用。
