Influence of Ultrasonic Surface Rolling Process and Shot Peening on Fretting Fatigue Performance of Ti-6Al-4V

At present,there are many studies on the residual stress field and plastic strain field introduced by surface strengthening,which can well hinder the initiation of early fatigue cracks and delay the propagation of fatigue cracks.However,there are few studies on the effects of these key factors on fretting wear.In the paper,shot-peening(SP)and ultrasonic surface rolling process(USRP)were performed on Ti-6Al-4V plate specimens.The surface hardness and residual stresses of the material were tested by vickers indenter and X-ray diffraction residual stress analyzer.Microhardness were measured by HXD-1000MC/CD micro Vickers hardness tester.The effects of different surface strengthening on its fretting fatigue properties were verified by fretting fatigue experiments.The fretting fatigue fracture surface and wear morphology of the specimens were studied and analyzed by means of microscopic observation,and the mechanism of improving fretting fatigue life by surface strengthening process was further explained.After USRP treatment,the surface roughness of Ti-6Al-4V is significantly improved.In addition,the microhardness of the specimen after SP reaches the maximum at 80μm from the surface,which is about 123%higher than that of the AsR specimen.After USRP,it reaches the maximum at 150μm from the surface,which is about 128%higher than that of AsR specimen.It is also found that the residual compressive stress of the specimens treated by USRP and SP increases first and then decreases with the depth direction,and the residual stress reaches the maximum on the sub surface.The USRP specimen reaches the maximum value at 0.18 mm,about−550 MPa,while the SP specimen reaches the maximum value at 0.1 mm,about−380 MPa.The fretting fatigue life of Ti-6Al-4V effectively improved after USRP and SP.The surface integrity of specimens after USRP is the best,which has deeper residual compressive stress layer and more refined grain.In this paper,a fretting wear device is designed to carry out fretting fatigue experiments on specimens with different surface strengthening.

Mechanical and corrosion fatigue behaviors of gradient structured 7B50-T7751 aluminum alloy processed via ultrasonic surface rolling

In this work,ultrasonic surface rolling process(USRP)was utilized to produce a gradient structured layer on 7 B50-T7751 aluminum alloy,and the mechanical properties and corrosion fatigue behavior of treated samples were studied.These results reveal that underwent USRP,a 425~m thick gradient structure and a 700~m deep compressive residual stress field are created,aluminum grain size become fine(~67 nm),and the corrosion rate of treated surface reduces by 60.08%owing to the combined effect of compressive residual stress and surface nanocrystallization.The corrosion fatigue strength is enhanced to 117%of that of 7 B50 Al alloys by means of USRP due to the introduced compressive residual stress,which is considered as the major favorable factor in suppressing the initiation and early propagation of corrosion fatigue cracks.Besides,the gradient structure is an important factor in providing a significant synergistic contribution to the improvement of corrosion fatigue performance.

Improving fatigue performance of Ti-6Al-4V alloy via ultrasonic surface rolling process

The effect of a gradient nanostructured(GNS) surface layer obtained by ultrasonic surface rolling process(USRP) on the fatigue behavior of Ti-6Al-4V alloy has been studied in this paper. Microstructure, surface topography, surface roughness and residual stress measurements were performed to characterize the surface under different conditions. Rotating bending fatigue tests were carried out to evaluate the fatigue behavior of different treatments. The results present a remarkable fatigue performance enhancement for the Ti-6Al-4V alloy with a GNS surface layer obtained by application of USRP with respect to the untreated condition, notwithstanding its considerable surface roughness due to severe ultrasonic impacts and extrusions. Mechanical surface polishing treatment further enhances the beneficial effects of USRP on the fatigue performance. The significantly improved fatigue performance can mainly be ascribed to the compressive residual stress. Simultaneously, the GNS surface layer and surface work hardening have a synergistic effect that accompanies the effect of compressive residual stress.

Contribution of ultrasonic surface rolling process to the fatigue properties of TB8 alloy with body-centered cubic structure

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.

Enhanced Surface Mechanical Properties and Microstructure Evolution of Commercial Pure Titanium Under Electropulsing-Assisted Ultrasonic Surface Rolling Process

The effects of electropulsing-assisted ultrasonic surface rolling process on surface mechanical properties andmicrostructure evolution of commercial pure titanium were investigated. It was found that the surface mechanical prop-erties were significantly enhanced compared to traditional ultrasonic surface rolling process （USRP）, leading to smallersurface roughness and smoother morphology with fewer cracks and defects. Moreover, surface strengthened layer wasremarkably enhanced with deeper severe plastic deformation layer and higher surface hardness. Remarkable enhancementsof surface mechanical properties may be related to the gradient refined microstructure, the enhanced severe plasticdeformation layer and the accelerated formation of sub-boundaries and twins induced by coupling effects of USRP andelectropulsing. The primary intrinsic reasons for these improvements may be attributed to the thermal and athermal effectscaused by electropulsing treatment, which would accelerate dislocation mobility and atom diffusion.

Active and passive compliant force control of ultrasonic surface rolling process on a curved surface

Ultrasonic surface rolling process(USRP)is one of the effective mechanical surface enhancement techniques.During the USRP,unstable static force will easily do harm to the surface quality.In order to achieve a higher surface quality on the part with a curved surface,an active and passive compliant USRP system has been developed.The compliant USRP tool can produce the natural obedience deformation along the part surface.Force control based on the fuzzy Proportional-integral-derivative(PID)method is then designed to maintain the static force during the USRP.Experiments have been performed on a real aero-engine blade with curved surface.It is proved that the deigned active and passive compliant USRP system can significantly reduce the force variation from 42.2 N to 4.2 N,and achieve a uniform surface quality after processing.

钛合金材料超声滚压加工的仿真分析与实验研究

采用普通滚压加工工艺对钛合金材料进行加工时,存在因低频冲击造成的工件残余应力分布不均匀和表面硬度低等问题,为此,开展了钛合金材料超声振动滚压工艺仿真及实验研究。首先,从理论层面分析了超声滚压加工的运动学及动力学特性,找出了影响超声滚压加工性能的相关因素;然后,采用ABAQUS有限元软件建立了钛合金材料的仿真模型,分析了超声滚压对残余应力的影响及强化机理;最后,设计了钛合金工件的超声滚压实验,研究了不同参数指标对工件加工质量的影响,并根据实验结果对仿真模型和残余应力结果进行了验证。研究结果表明:随着静载荷和超声振幅的增加,工件表面残余应力分布相对均匀且趋于平稳,表面粗糙度呈现先降低后增加的趋势,表面硬度随强化层深度的增加逐渐降低;在振幅为20μm时,工件表面质量和性能相对较好,此时残余应力均值为849 MPa,表面粗糙度均值为0.1μm。该实验结果与仿真分析结果一致,验证了所建模型的可靠性,可为滚压制造工艺参数的选取提供参考。

超声滚压对DC53钢表面性能的影响

为了改善DC53冷作模具钢的表面性能,使用扫描电子显微镜、激光光谱共聚焦显微镜、显微硬度计、球-盘摩擦磨损试验机等设备分析了超声表面滚压加工工艺(USRP)的静压力、滚压道次、振幅、进给量对DC53冷作模具钢表面粗糙度、显微硬度、摩擦因数和磨损的影响规律。结果表明:与未处理DC53模具钢相比,USRP处理后DC53冷作模具钢表面产生了塑性变形,表面粗糙度由5.570μm最低可降为1.067μm,且在DC53冷作模具钢表面产生了晶粒细化现象,引入了梯度硬化层,表面硬度由基体的720 HV最大可提升为818.6 HV,硬化层深度最大可达300μm。摩擦因数降低,磨痕宽度减小,耐磨性能提高。通过极差分析法获得了对粗糙度、显微硬度、摩擦因数影响最大的工艺参数依次为进给量、滚压道次、静压力。通过灰色关联度分析法获得了工艺参数对表面性能的影响次序为静压力>进给量>滚压道次>振幅,最佳工艺参数组合为静压力400 N,滚压道次4次,振幅12μm,进给量0.05 mm。

超声滚压工艺对镍基单晶高温合金DD6表面完整性和疲劳寿命的影响

目的 改善长期服役于高温高压环境的镍基单晶高温合金DD6材料的表面完整性,提高其使用寿命。方法 采用超声滚压表面强化工艺(UltrasonicRollingProcess,USRP)对镍基单晶高温合金DD6试样进行表面强化,用正交试验法对三因素三水平的试样组进行试验,使用三维形貌仪、显微硬度仪、XRD射线衍射仪和MTS万能疲劳试验机探究静压力、进给速度和加工遍数等超声滚压参数对镍基单晶合金表面完整性和疲劳寿命的影响规律。结果 对于镍基单晶材料,超声滚压强化工艺能有效降低其表面粗糙度,提高表面显微硬度,并在材料内部引入一定的残余应力,并提升疲劳寿命。经USRP处理后,不同晶体取向的材料能够取得的最佳表面增益效果为,表面硬度从465HV提高到679.2HV,表面粗糙度从0.703μm降低至0.253μm,表面引入了约为782 MPa的残余压应力。不同晶向材料的疲劳寿命提升表现为,应力水平为742.4 MPa时,疲劳寿命提升1.3倍;应力水平为649.6MPa时,疲劳寿命提升1.5倍。结论 超声滚压工艺能够有效降低DD6材料的表面粗糙度、提高表面显微硬度,并在表面引入一定的残余应力,疲劳断裂模式主要为沿{110}面的滑移断裂。在低于742.4 MPa的应力加载时,超声滚压强化可以明显提高DD6材料在高温下的疲劳寿命。

超声滚压工艺参数对45钢表面完整性与冲击性能的影响

设计了以静压力(400,800,1200 N)、振幅(3,5,7μm)、滚压道次(1,2,3)等超声滚压工艺参数为变量,表面粗糙度、残余应力、显微硬度和冲击吸收功为响应的的正交试验,研究了超声滚压参数对45钢表面完整性与冲击性能的影响。结果表明:随着静压力和振幅增加,试样的表面粗糙度增大,滚压道次影响较小;随静压力、振幅、滚压道次增加,试样的表面残余压应力略有增大;随着静压力与振幅增加,硬化层深度增大,随着滚压道次增加,硬化层深度先减小后增大;随着静压力和振幅增加,冲击吸收功先减小后增大,随滚压道次增加,冲击吸收功增大;对表面粗糙度、表面残余应力、硬化层深度和冲击吸收功影响最大的因素分别为振幅、静压力、静压力和滚压道次;最佳超声滚压工艺参数为静压力400 N、振幅7μm、滚压3次,此时试样灰色关联度最大,表面完整性和冲击性能较好。

超声表面滚压对氢化钛烧结纯钛显微组织及性能的影响

采用超声表面滚压技术对氢化钛烧结纯钛进行表面强化,并借助X射线衍射、电子背散射衍射、扫描电镜和透射电镜分析滚压后纯钛的微观组织演化及性能影响。结果表明,滚压后组织呈梯度变化,最外表面晶粒为等轴纳米晶,尺寸约100 nm;随距表面距离增大,晶体组织依次为块状晶、层片状组织及等轴粗晶,塑性变形层厚度可达400μm。滚压后表面硬度提高了36%,表面粗糙度显著降低,滚压后引发的晶粒细化和残余应力有助于产生致密的钝化膜,提高了耐腐蚀性能。滚压后抗拉强度和屈服强度为640 MPa、485 MPa,分别提高了32%和27%,但延伸率有所下降,断口形貌总体仍表现为韧性断裂。

超声滚压GCr15表面性能模型建立及工艺参数优化

目的基于超声滚压后GCr15试样表面粗糙度和表面硬度与工艺参数之间的数学模型,获取超声滚压GCr15的最佳工艺参数。方法首先,通过单因素试验筛选4个工艺参数的取值范围;其次,建立基于响应曲面的超声滚压GCr15表面硬度及表面粗糙度预测模型;再次,基于遗传算法对2个预测模型进行多目标复合优化,得到最佳工艺参数;最后,针对多目标优化结果进行试验验证。结果在超声滚压处理GCr15时,滚压静压力及滚压次数对试样表面硬度及表面粗糙度的影响极显著,转速的影响不显著;进给量对表面硬度有显著影响,对表面粗糙度的影响不显著。粗糙度模型受到静压力和滚压次数双因子交互作用的影响,硬度模型不受交互作用的影响。基于遗传算法进行多目标优化得到的最佳工艺参数如下:转速为207 r/min,进给量为0.34 mm/r,静压力为0.49 MPa,滚压次数为3。在最佳工艺参数下得到试样的最低表面粗糙度为0.34μm、最高硬度为60.5HRC。结论基于响应曲面法的GCr15超声滚压表面性能预测模型准确有效。采用最优工艺参数能够获得最优表面质量。

激光熔覆高熵合金涂层组织和性能研究的进展

高熵合金涂层性能优异,在航空航天等领域得到了广泛应用。综述了激光熔覆高熵合金涂层研究的新进展,包括激光熔覆工艺参数、合金成分、退火、超声表面滚压和超声冲击强化等。研究发现:影响激光熔覆高熵合金涂层组织和性能的工艺参数为激光功率、扫描速率、激光能量密度、送粉电压和氧气流量等;对组织和性能有影响的合金成分为Cu、Nb、Co、Cr、Mo、Ti、W等;退火、超声表面滚压和超声冲击处理也对涂层组织和性能有影响。

电脉冲对9SiCr钢超声滚压表面性能的影响

目的提高9SiCr钢表面硬度、光洁度,获得更好的表面质量。方法对9SiCr钢棒状试样进行车削加工,然后分别进行不同参数下的超声滚压(USRP)和高能电脉冲辅助超声滚压(EP-USRP)加工。通过表面粗糙度测试、微观形貌分析、表层显微维氏硬度测试,分别评价不同加工状态试样的表面粗糙度、表面形貌、表层一定深度内的硬度梯度分布,并通过光学显微镜和扫描电子显微镜对试样表层形貌进行分析。结果车削后试样的表面粗糙度为0.45μm,经施加压力为1000 N的USRP加工后,试样表面粗糙度为0.043μm,对试样进行EP-USRP加工,当均方根电流密度为0.71 A/mm^(2)时,表面粗糙度降至0.032μm,比单纯USRP加工后试样的表面粗糙度降低了25.6%。经车削后,试样的显微维氏硬度约为550HV,经施加压力为800 N的USRP加工后,试样表层硬度为590HV。当对试样施加均方根电流密度为0.71 A/mm^(2)的EP-USRP处理后,其硬度为612HV,比USRP加工后的硬度增加了3.8%。从硬化层深度来看,经USRP加工后试样径向表层到心部大概有300μm得到硬化,而经EP-USRP加工后硬化层的深度可以增至400μm。从微观形貌分析可以看出,试样表层具有一定深度的细晶层,随着加工状态的不同,晶粒大小和细晶层深度也不同。结论采用USRP、EP-USRP加工都可以在一定程度上提高9SiCr钢的表面质量,电脉冲可以提高USRP加工的效果,进一步提高表面质量。

超声表面滚压工艺影响镍基690合金冲-切磨损行为的研究

通过超声表面滚压技术(USRP)改善镍基690合金表面的粗糙度和硬化层,并探究该工艺对其冲-切磨损行为的影响机理.首先,采用USRP对镍基690合金表面进行强化处理,然后,基于可控能量式冲-切磨损试验装置,探究镍基690合金强化前后在不同冲-切变量下其磨损界面的动态响应行为与损伤机理.得出了USRP工艺可有效降低磨损界面的摩擦力和摩擦系数,降低冲切能耗,进而减少材料的磨损程度,此外,冲击或切向滑动速度的增加均会导致磨损界面所受冲击力和摩擦力的增大,并降低动能吸收率.

超声表面滚压加工参数对40Cr表面粗糙度的影响

研究了超声表面滚压加工各种加工参数对供货态40Cr轴表面粗糙度的影响.采用表面粗糙度分析仪对初始及加工表面进行测定,并使用显微硬度计测量该技术对40Cr表层沿深度方向的硬化作用.试验结果表明:超声表面滚压加工技术能显著降低车削的加工痕迹,改善金属材料的表面质量;各工艺参数对试样表面粗糙度均有一定影响,并产生不同程度的表层硬化作用;并且给出了各工艺参数的合理范围,试样的表面粗糙度值可降低至0.2.μm以下.

40Cr超声表面滚压加工纳米化

采用超声表面滚压(Ultrasonic surface rolling extrusion,USRE)加工方法对调质态40Cr轴进行处理。通过对处理表层进行微观结构观察发现:该加工方法既可以使表层纳米晶粒细化至3～7nm,还可以使表面粗糙度水平降至0.05μm;USRE样品表面附近区域形成了厚度约为200μm的流变组织,且晶粒尺寸沿厚度方向呈现梯度分布。力学性能测试证明:USRE试件表面显微硬度提高了63%,表面残余应力最高为-846MPa,压缩应力层深度可达1mm以上。摩擦磨损对比试验表明:USRE方法能够降低金属表面摩擦因数,提高其抗磨损性能。

超声表面滚压加工40Cr表层的纳米力学性能

研究了超声表面滚压加工40Cr表层的力学性能.采用纳米压痕实验测定了表层的弹性模量、纳米硬度和残余应力.实验结果表明:经过超声表面滚压后,40Cr表层的弹性模量和硬度都得到显著提高,最大值均位于表面,往复加工3遍的表面弹性模量和硬度分别为217.16,GPa和3.588,GPa,加工6遍的表面弹性模量和硬度分别为224.8,GPa和3.857,GPa;同时表层获得一定数值的残余压应力,最大值位于表面并随着加工遍数的增加而增大.对比实验结果发现往复加工次数对表层的力学性能有重要的影响.

表面超声滚压处理对高速列车车轴钢疲劳性能的影响

对EA4T型高速列车车轴钢棒状旋转弯曲疲劳试样实验段磨削加工后进行了表面超声滚压处理。观察了处理前后试样的表面形貌及表层微观组织,测量了处理前后试样的表面粗糙度、表层硬度及表层残余应力。利用旋转弯曲疲劳实验得到处理前后试样的疲劳极限。结果表明:表面超声滚压处理后,试样的疲劳极限由352MPa提高到401MPa。疲劳极限的提高主要由于表面超声滚压处理后试样表面粗糙度降低、表层强度及残余压应力增加。

超声表面滚压处理铝合金钻杆的高温摩擦学性能

为了提高铝合金钻杆的耐磨性,利用超声表面滚压技术(USRP)对2219铝合金钻杆材料进行表面强化处理。采用透射电子显微镜(TEM)表征了USRP处理后铝合金的晶粒大小,采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和显微硬度计测量了强化层的微观形貌、相组成和显微硬度,并利用高温摩擦磨损试验机评价了试样的摩擦学性能,对磨副为玛瑙球。结果表明,经USRP处理后2219铝合金表面形成了纳米晶和厚度约500μm的塑性强化层,表面硬度由120 HV0.05提高至190 HV0.05。随着摩擦磨损试验温度的升高,未处理试样和USRP试样的平均摩擦因数和磨损率都逐渐增大。在相同试验温度下,USRP试样的平均摩擦因数和磨损率均小于未处理试样的。未处理试样和USRP试样的磨损机制主要是黏着磨损和磨粒磨损。