钛合金超声滚压梯度纳米结构与残余压应力协同抗微动疲劳的机理

The challenge of improving fretting fatigue (FF) resistance of metals is to resolve the contradiction between anti-wear and anti-fatigue. Gradient nanostructured materials could have superior wear resistance and fatigue resistance. Ultrasonic surface rolling process (USRP) has the advantage of achieving good surface integrity, improving fatigue resistance and manufacturing gradient nanostructured materials. Therefore, taking the control of FF as the background, the titanium alloys with high FF sensitivity will be selected as the research substrate. Based on the demand of surface strength, toughness and integrity for anti-FF, the gradient nanostructured layer will be manufactured on titanium alloy surface by using USRP according to the microstructure design and the reasonable regulation of the residual compressive stress field. The new progress of the FF resistance improvement should be obtained by the synergistical action of the gradient nanostructure and residual compressive stress induced by USRP. In this project, the relationship between the USRP process and gradient nanostructure as well as the mechanism will be investigated, the control factors of determining the strength and toughness of modified layer will be revealed, which would guide the design and preparation of the gradient layer. The titanium alloy’s FF behavior and mechanism will be analyzed when its surface microstructure transforms from the original coarse crystal to submicron and then further to nanometer scale gradient stage. The variation and mechanism of the microstructure and residual compressive stress in the modified layer with the change in FF condition and its progression, together with their predominant roles and synergistic mechanism in controlling FF crack initiation and propagation behavior will be studied. Furthermore, the FF theoretical model will be established. The research results would have reference value for controlling various coupling failure involving both wear and fatigue.

提高金属微动疲劳（FF）抗力的难点是要协调解决好抗磨和抗疲劳的矛盾。梯度纳米结构材料可拥有良好的耐磨和抗疲劳性能；超声滚压（USRP）在获得良好表面完整性、提高疲劳抗力和制备梯度纳米结构材料方面优势突出。故本项目以FF控制为背景，根据抗FF对表层强韧性能与表面完整性的需求，选择FF敏感性高的钛合金为基材，以USRP为技术手段，基于微结构设计和残余压应力场的合理调控对钛合金进行形变纳米化处理，取得梯度纳米结构与残余压应力协同提高FF抗力的新进展。研究USRP工艺与梯度纳米结构的关联和机制，揭示改性层强韧性能的控制因素，指导其设计与制备。研究钛合金表层由原始粗晶依次向亚微米、纳米级梯度细晶结构转变时FF行为和机理；改性层结构与残余压应力随FF工况及进程的变化规律和机制，及其在控制FF裂纹萌生和扩展行为中的主导作用与协同机理；建立FF理论模型。研究成果对控制各类磨损与疲劳的耦合失效均有参考价值。

微动疲劳（FF）是承受循环载荷的构件表面同时存在微小位移幅度运动造成的磨损作用，导致构件疲劳抗力显著降低的现象。梯度纳米结构材料可拥有良好的耐磨和抗疲劳性能，超声表面滚压（USRP）在获得良好表面完整性、提高疲劳抗力和制备梯度纳米结构材料方面优势突出。为此，本项目以FF控制为背景，根据抗FF对表层强韧性能与表面完整性的需求，选择FF敏感性高的钛合金为基材，基于微结构设计和残余压应力场的合理调控对钛合金进行USRP纳米化处理，改善钛合金表面耐磨和抗疲劳性能，由此解决了FF控制中抗磨和抗疲劳的矛盾，在梯度纳米结构与残余压应力协同提高钛合金FF抗力上取得了新进展。揭示了USRP工艺与表层梯度纳米结构的关联和机制，澄清了USRP改性层强韧性能的控制因素，并用以指导其设计与制备。揭示了USRP处理钛合金表层微观组织结构对基材FF行为的影响规律和机理，改性层微结构与残余压应力随FF进程的变化规律，及其在控制钛合金FF行为中的主导作用与协同机理。研究发现USRP梯度纳米化机制随金属基材原始组织不同而有所改变，但位错滑移和分割通常起主导作用；同时发现USRP处理使双相钛合金出现了hcp-Ti相转变为fcc-Ti，继之通过孪生进一步细化组织的现象。USRP梯度纳米化对钛合金FF行为和常规疲劳（PF）行为的影响规律及机理既有内在关联，又有所不同，此归于FF抗力的提高需要协调改善抗疲劳和耐磨损性能。同时发现金属基材微结构不同，USRP梯度纳米化改性处理对其FF及PF行为的影响规律及机理也会有所不同。此外，研究表明在特定条件下USRP纳米化处理会使体心立方相钛合金的FF抗力高于其PF抗力。建立了USRP改性层的强韧性能评价方法，并用于指导了抗FF改性层的设计。同时建立了USRP表面改性钛合金FF数值模型，用该模型预测的USRP处理钛合金FF寿命、裂纹萌生位置及取向与试验结果一致性良好。研究成果达到了申请书的预期目标，不仅对FF损伤控制有指导意义，而且对控制各类磨损与疲劳耦合失效均有参考价值。