目的研究不同静压力条件下,形变诱导纳米化表层对20CrMnTi局部腐蚀萌生行为的影响。方法采用超声滚压技术(USRP,Ultrasonic surface rolling processing)强化20CrMnTi表层,并运用激光共聚焦显微镜、EBSD与电化学方法进行表征,分别评价...目的研究不同静压力条件下,形变诱导纳米化表层对20CrMnTi局部腐蚀萌生行为的影响。方法采用超声滚压技术(USRP,Ultrasonic surface rolling processing)强化20CrMnTi表层,并运用激光共聚焦显微镜、EBSD与电化学方法进行表征,分别评价形变诱导纳米化表层的腐蚀行为以及局部腐蚀行为对表面应力集中状态以及微裂纹萌生行为的影响。结果在弱碱性腐蚀条件下,20CrMnTi表层经超声滚压处理后,试样的点蚀击穿电位出现显著负移。同时,随着滚压压力升高,20CrMnTi表层钝化出现了显著的滞后,致钝电流与维钝电流同步增长,并伴有钝化区间缩小。借助激光共聚焦显微镜高精度三维重构,观测到在模拟弱腐蚀环境下,20CrMnTi超声滚压表面会显现出沿滚压方向凸出的波纹状局部腐蚀纹理,随滚压压力增长,波纹界面位置局部腐蚀损伤呈现一定的加深与拓宽,具有较高的裂纹萌生风险。通过EBSD表征发现,在超高频冲击作用下,20CrMnTi表层晶粒会转化为晶粒取向随机分布的细化表层,但由于波纹两侧晶粒存在取向差异,在滚压头高频多点的冲击作用下,不同取向晶粒的细化机制存在差别,导致波纹两侧晶粒构成电位差异明显的局部腐蚀微电池,呈现较高溶解选择性。结论在超声滚压过程中,20CrMnTi表层晶粒在局部微区范围内会出现明显的细化程度差异,在电化学作用下,细化晶粒间的微区电位差异会导致表面出现选择性溶解,并在晶粒折叠界面处产生波纹状局部腐蚀坑,且伴随超声滚压压力增大,波纹状腐蚀坑会出现明显的拓宽与加深,具有较高的疲劳裂纹萌生风险。展开更多
The effect of ultrasonic surface rolling process(USRP) as a severe plastic deformation technology was investigated on the evolution of microstructure, residual stress and surface morphology of TB8 alloys with body-cen...The effect of ultrasonic surface rolling process(USRP) as a severe plastic deformation technology was investigated on the evolution of microstructure, residual stress and surface morphology of TB8 alloys with body-centered cubic structure. Stress-controlled rotating-bending fatigue tests indicated increased fatigue strength in USRP samples prepared using different number of passes compared to the base material, which was attributed to the presence of gradient structure surface layers. Five subsequent USRP passes resulted in the highest fatigue strength, due to the optimal surface properties including higher extent of grain refinement, larger compressive residual stresses, "smoother" surface morphology and increased micro-hardness. However, the effect of USRP technology on improving fatigue strength of TB8 alloy was not significant in comparison with that of other titanium alloys(for example, Ti6 Al4 V), which was attributed to the notable surface residual stresses relaxation revealed from measurements on postfatigued USRP samples. Electron backscatter diffraction analysis confirmed that fatigue crack initiation occurred in the larger grains on the surface with high Schmid factor. Small cracks were found to propagate into the core material in a mixed transgranular and intergranular mode. Further analysis indicated that grain growth existed in post-fatigued USRP-treated TB8 samples and that the average geometrically necessary dislocations value reduced after fatigue loading.展开更多
Ultrasonic rolling is an advanced non-cutting surface strengthening method that combines traditional rolling with ultrasonic vibration.In this research,the experiment of orthogonal end milling-ultrasonic rolling compo...Ultrasonic rolling is an advanced non-cutting surface strengthening method that combines traditional rolling with ultrasonic vibration.In this research,the experiment of orthogonal end milling-ultrasonic rolling composite process has been carried out.The surface integrity refactoring changes and its mechanism of Ti-17 titanium alloy during the milling-ultrasonic rolling composite process has been studied and analyzed by the test and analysis of the surface geometric characteristics,residual stress,microhardness and microstructure before and after ultrasonic rolling.The residual stress and microhardness gradient distribution were characterized by cosine decay function and exponential decay function.All indicators of surface integrity were significantly improved after ultrasonic rolling.The study demonstrates that the reduction effect of the surface roughness by ultrasonic rolling process is inversely proportional to the initial surface roughness value.The ultrasonic rolling can only change the distribution form of the surface topography when the initial surface roughness is small.In addition,the improvement effect of ultrasonic rolling on surface compressive residual stress and microhardness decreased with the increase of initial milled surface roughness and surface compressive residual stress due to the factors such as energy absorption efficiency and mechanical properties changes of surface materials.A better ultrasonic rolled surface can be obtained by controlling the roughness and residual compressive stress of the initial milling surface to a small level.展开更多
文摘目的研究不同静压力条件下,形变诱导纳米化表层对20CrMnTi局部腐蚀萌生行为的影响。方法采用超声滚压技术(USRP,Ultrasonic surface rolling processing)强化20CrMnTi表层,并运用激光共聚焦显微镜、EBSD与电化学方法进行表征,分别评价形变诱导纳米化表层的腐蚀行为以及局部腐蚀行为对表面应力集中状态以及微裂纹萌生行为的影响。结果在弱碱性腐蚀条件下,20CrMnTi表层经超声滚压处理后,试样的点蚀击穿电位出现显著负移。同时,随着滚压压力升高,20CrMnTi表层钝化出现了显著的滞后,致钝电流与维钝电流同步增长,并伴有钝化区间缩小。借助激光共聚焦显微镜高精度三维重构,观测到在模拟弱腐蚀环境下,20CrMnTi超声滚压表面会显现出沿滚压方向凸出的波纹状局部腐蚀纹理,随滚压压力增长,波纹界面位置局部腐蚀损伤呈现一定的加深与拓宽,具有较高的裂纹萌生风险。通过EBSD表征发现,在超高频冲击作用下,20CrMnTi表层晶粒会转化为晶粒取向随机分布的细化表层,但由于波纹两侧晶粒存在取向差异,在滚压头高频多点的冲击作用下,不同取向晶粒的细化机制存在差别,导致波纹两侧晶粒构成电位差异明显的局部腐蚀微电池,呈现较高溶解选择性。结论在超声滚压过程中,20CrMnTi表层晶粒在局部微区范围内会出现明显的细化程度差异,在电化学作用下,细化晶粒间的微区电位差异会导致表面出现选择性溶解,并在晶粒折叠界面处产生波纹状局部腐蚀坑,且伴随超声滚压压力增大,波纹状腐蚀坑会出现明显的拓宽与加深,具有较高的疲劳裂纹萌生风险。
基金the support of National Natural Science Foundation of China(51771155)National Science and Technology Major Project(2017-VII-0012-0107)Equipment Pre-research Field Fund(61409220202)。
文摘The effect of ultrasonic surface rolling process(USRP) as a severe plastic deformation technology was investigated on the evolution of microstructure, residual stress and surface morphology of TB8 alloys with body-centered cubic structure. Stress-controlled rotating-bending fatigue tests indicated increased fatigue strength in USRP samples prepared using different number of passes compared to the base material, which was attributed to the presence of gradient structure surface layers. Five subsequent USRP passes resulted in the highest fatigue strength, due to the optimal surface properties including higher extent of grain refinement, larger compressive residual stresses, "smoother" surface morphology and increased micro-hardness. However, the effect of USRP technology on improving fatigue strength of TB8 alloy was not significant in comparison with that of other titanium alloys(for example, Ti6 Al4 V), which was attributed to the notable surface residual stresses relaxation revealed from measurements on postfatigued USRP samples. Electron backscatter diffraction analysis confirmed that fatigue crack initiation occurred in the larger grains on the surface with high Schmid factor. Small cracks were found to propagate into the core material in a mixed transgranular and intergranular mode. Further analysis indicated that grain growth existed in post-fatigued USRP-treated TB8 samples and that the average geometrically necessary dislocations value reduced after fatigue loading.
基金supported by the National Natural Science Foundation of China(Grant Nos.51875472,91860206,51905440,and 92160301)the National Science and Technology Major Project(Grant No.2017-VII-0001-0094)the Key Research and Development Program of Shaanxi Province(Grant No.2021ZDLGY10-06).
文摘Ultrasonic rolling is an advanced non-cutting surface strengthening method that combines traditional rolling with ultrasonic vibration.In this research,the experiment of orthogonal end milling-ultrasonic rolling composite process has been carried out.The surface integrity refactoring changes and its mechanism of Ti-17 titanium alloy during the milling-ultrasonic rolling composite process has been studied and analyzed by the test and analysis of the surface geometric characteristics,residual stress,microhardness and microstructure before and after ultrasonic rolling.The residual stress and microhardness gradient distribution were characterized by cosine decay function and exponential decay function.All indicators of surface integrity were significantly improved after ultrasonic rolling.The study demonstrates that the reduction effect of the surface roughness by ultrasonic rolling process is inversely proportional to the initial surface roughness value.The ultrasonic rolling can only change the distribution form of the surface topography when the initial surface roughness is small.In addition,the improvement effect of ultrasonic rolling on surface compressive residual stress and microhardness decreased with the increase of initial milled surface roughness and surface compressive residual stress due to the factors such as energy absorption efficiency and mechanical properties changes of surface materials.A better ultrasonic rolled surface can be obtained by controlling the roughness and residual compressive stress of the initial milling surface to a small level.
