Fretting behavior of shot peened Ti-6Al-4V under slip controlled mode

Fretting tests of shot peened Ti-6Al-4V were conducted under slip controlled mode using a dual actuator test setup which could apply an independent pad displacement at a given applied bulk stress. Fretting regime was identified based on the hysteresis loop of tangential force versus relative slip range and the evolution of tangential force. Fretting regime changed from partial slip to mixed slip and then to gross slip with increasing relative slip range, and the transition from mixed to gross slip occurred at a relative slip range of ∼50 μm regardless of the applied bulk stress magnitude for both shot peened and unpeened specimens. Fretting fatigue life initially decreased as the relative slip range increased and reached to a minimum value, and then increased with an increase of the relative slip range due to the transition in fretting regime from mixed slip to gross slip. Shot peened specimens had longer fatigue life than unpeened specimens at a given relative slip range, but the minimum fatigue life was at the same value of the relative slip range for both shot peened and unpeened specimens. The relationship between relative slip and fatigue life was also found to be independent of the applied bulk stress level. Further, tangential force was directly related to relative slip and this relationship was independent of other fretting variables.     

Fretting fatigue of laser shock peened Ti-6Al-4V

The objective of this paper is to examine fretting fatigue of laser shock peened (LSP) titanium to quantify the influence of LSP on fretting fatigue life. Contact conditions such as loads and pad geometry are chosen to generate fretting fatigue stresses similar to those occurring in blade/disk contacts in gas turbine engines. LSP treated specimens attained 5-, 10- and 25-fold increase in lives compared to untreated specimens. Metallography of the contact area and fractographic analysis of worn pads detail the fretting behavior of LSP treated specimens.     

The effects of laser peening and shot peening on fretting fatigue in Ti-6Al-4V coupons

This paper describes testing of Ti-6Al-4V coupons in fretting fatigue and compares the effects of mechanical surface treatments on performance. Fretting fatigue tests were performed using a proving ring for fretting load, bridge-type fretting pads, and applied tension-tension cyclic fatigue stress. As-machined (AM), shot peened (SP), and laser peened (LP) coupons were evaluated, and data generated to compare residual stress, surface condition, lifetime, and fractographic detail encountered for each. Near-surface residual stress in SP and LP coupons was similar. The layer of compressive residual stress was far deeper in LP coupons than in SP coupons and, consequently, subsurface tensile residual stress was significantly greater in LP coupons than in SP coupons. SP coupons exhibited a rough surface and had the greatest volume of fretting-induced wear. LP coupons exhibited a wavy surface and had a small volume of wear localized at wave peaks. SP coupons had the greatest fretting fatigue lifetime, with significant improvement over AM coupons. Lifetimes of LP coupons were similar to those for SP coupons at high fatigue stress, but fell between AM and SP coupons at lower fatigue stress. Fractographic evaluation showed that fractures of AM samples were preceded by initiation of fretting-induced cracks, transition of a lead fretting crack to mode-I fatigue crack growth, and crack growth to failure. SP and LP samples exhibited behavior similar to AM samples at high fatigue stress, but in coupons tested at low stress the lead crack initiated subsurface, near the measured depth of maximum tensile residual stress, despite the presence of fretting-induced cracks. The level of fatigue stress above which lead cracks were initiated by fretting was higher for LP than for SP, and was predicted with good accuracy using an analysis based on linear elastic fracture mechanics, the fatigue crack growth threshold stress intensity factor range, and superposition of measured residual stress and applied fatigue stress.     

固态渗碳化硼对Ti-6Al-4V显微组织和性能的影响

研究了Ti-6Al-4V在800℃和1000C下固态渗碳化硼20h后的渗层显微组织以及对硬度等的影响。结果表明：渗层在表面为致密分布的化合物层,其成分主要为TiC、TiB以及TiB2等硬质相,而在基体内部则形成沿晶界分布的板条状或等轴状的颗粒扩散层;表面碳化硼处理可以显著提高Ti-6Al-4V的表面硬度,由359HV提高到了664HV,并且可以得到良好的表面硬、芯部软的硬度梯度;断口形貌分析发现材料由韧性断裂转变成脆性断裂。     

Fretting Wear Behavior of Laser Peened Ti-6Al-4V

This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples.     

Ti-6Al-4V钛合金板与304L不锈钢网的扩散焊

分别在800℃、825℃、850℃焊接温度、30 m in保温时间,3 MPa焊接压力下,进行Ti-6A l-4V钛合金板与304L不锈钢网的真空扩散焊接。对接头组织结构与化学元素扩散进行了扫描电镜与能谱分析,并测试了接头的剪切强度。结果表明:不添加中间过渡层金属,可以成功地实现钛合金板与不锈钢网的扩散焊接,并使接头的剪切强度达到90 MPa以上。不锈钢网中的Fe、N、iCr扩散并固溶到钛合金中,稳定了β相,使钛合金在一定深度上,其组织由原来的α+β双相结构转变为单相的β相。不锈钢中的Cr,由于钛合金中Ti的扩散进入,而在界面发生了上坡扩散现象。这种Cr在不锈钢一定深度内的富集,形成窄长的富Cr区域,冷却后转变为硬脆的σ相。但在焊接接头中没有发现明显其它的金属间化合物或氧化物相的生成,使得接头的机械性能得到了很好的保证。     

置氢对Ti-6Al-4V合金组织和性能的影响

为掌握置氢改善钛合金切削性能的机理,利用光学显微镜与X射线衍射仪分析了置氢Ti-6Al-4V合金的显微组织,采用热膨胀仪与热常数测试仪测定了该合金的热膨胀系数和导热系数,通过高温拉伸试验研究了该合金的力学性能。结果表明:置氢后,随着氢含量的增加,合金中的β相比例提高,并且生成了δ氢化物;与未置氢钛合金相比,在900℃时的热膨胀系数最大降幅为6%,而导热系数在500℃时的增幅最大,为40%;置氮后的钛合金,在800℃时抗拉强度与伸长率的降幅分别为19%和74%。     

Carbon coating of Ti-6Al-4V for reduced wear in combined impact and sliding applications

A range of carbon coatings with different hardness and modulus was compared for wear and frictional behaviours using one-side-carbon-coated Ti-6Al-4V alloy couples tested under conditions of combined impact and sliding contact. Carbon films with hardness over 10 GPa were found to cause far greater volume loss of the uncoated counterpart, and the volume loss was approximately proportional to the extent of hardness deviation above 10 GPa. The coefficient of friction was shown to correlate positively with coating hardness. The tendency of a softer coating to possess a greater sp² or graphite-like content provides more effective solid lubrication in a wet environment, hence minimising both wear and friction. The corresponding low film modulus also provides an optimal structural integrity of the composite system by minimising the elastic modulus mismatch between the film and the underlying substrate.     

钛合金TC4的钻削力试验研究

钛合金TCA属于较难加工材料,其小孔钻削尤为困难。为得到钻头直径、钻削参数（进给量、切削速度）和刀具材料对钻削力的影响规律,采用标准高速钢钻头对TCA与45钢进行了钻削对比试验,并用多元线性回归分析模型分别建立了扭矩和轴向力的经验公式。结果表明,TC4的钻削力比45钢大,钻削参数对钻削力的影响规律与45钢基本相同,即钻头直径对扭矩和轴向力影响最大,进给量次之,切削速度的影响最小。     

Unlubricated gross slip fretting wear of metallic plasma-sprayed coatings for Ti6Al4V surfaces

Plasma-sprayed Al–bronze or CuNiIn coatings are often applied to protect against fretting wear and extend the operational life of Ti-alloy compressor blades in turbine engines. In order to develop a fundamental understanding of how these coating systems perform under gross slip fretting conditions, bench level fretting wear tests were conducted at room temperature to simulate cold engine startup. Alternative coatings such as plasma-sprayed molybdenum and nickel were also evaluated because of their potential for reducing fretting wear under certain simulated engine conditions. The combination of scanning electron microscopy (SEM), surface profilometry, surface chemistry (EDS), and friction analysis were used to study coating performance and evaluate the interfacial wear mechanisms. In this study, it was determined that all coatings caused significant damage to the mating Ti6Al4V surfaces and that the wear mechanisms were all similar to those of the uncoated baseline case.     

砂带干式磨削Ti-6Al-4V钛合金的磨削力

对砂带干式磨削Ti-6Al-4V钛合金的的磨削力进行了测试,分析了磨削参数对磨削力的影响;用动态测力仪、三维体式显微镜、粗糙度仪和显微硬度计对磨削试样表面质量进行了分析,提出了砂带磨削工艺参数的优化方案。结果表明:在砂带干式磨削条件下,磨削力随着磨削深度和工作台进给速度的增大而增加,随着砂带线速度的提高而减小;在砂带线速度为15 m.s-1,工作台进给速度为315 mm.min-1,磨削深度为0.025~0.1 mm时,合金表面粗糙度Ra≤0.35μm。     

Al2O3/(Ag72Cu28)97Ti3/Ti-6Al-4V界面反应

在１．８　ｋｓ、１　０７３～１　１７３　Ｋ条件下对Ａｌ２Ｏ３／（Ａｇ７２Ｃｕ２８）９７Ｔｉ３／Ｔｉ－６Ａｌ－４Ｖ进行了钎焊试验。通过扫描电镜、波谱、能谱和Ｘ射线衍射对界面反应产物进行了测试，确定了界面结构，并讨论了这些反应产物形成的可能性。结果表明，温度小于１　１２３　Ｋ的界面结构为Ａｌ２Ｏ３／Ｃｕ２Ｔｉ４Ｏ／Ｃｕ４Ｔｉ３＋Ｃｕ固溶体／Ａｇ－Ｃｕ共晶　＋　富Ａｇ相；温度１　１７３　Ｋ的界面结构为Ａｌ２Ｏ３／Ｃｕ３ＴｉＯ５　＋　ＣｕＡｌ２Ｏ４／Ｃｕ４Ｔｉ３／富Ａｇ相＋　Ｃｕ４Ｔｉ３。     

摩擦速度对Ti-6Al-4V合金腐蚀磨损的影响

采用腐蚀摩擦磨损试验机,进行了Ti合金/Al2O3摩擦副在林格溶液介质中的腐蚀磨损试验。试验在改变摩擦速度时对材料的耐腐蚀性能及钝化膜的再生能力进行了探讨。结果表明:摩擦破坏了Ti合金表面的钝化膜使电流密度上升。电流密度随摩擦速度的增大而增大。但是,钝化膜再生能力随摩擦速度的增大而减小。摩擦速度影响到磨损形态,速度小时主要以磨粒磨损形态为主,随着速度的增大磨损形态将过渡为腐蚀磨损和粘着磨损。     

The effect of ion implantation on the sliding wear behaviour of ultrahigh molecular weight polyethylene against an oxidised titanium alloy Ti-6Al-4V

Pin-on-disk sliding wear studies have been conducted on untreated and ion-implanted UHMWPE against an oxidised Ti-6Al-4V alloy. Under water lubricated conditions no wear was measured. The enhanced mechanical and physical properties of the surface treated materials are responsible for the improved wear performance which may be of great importance to orthopaedic prostheses.     

Adhesion Wear on Tool Rake and Flank Faces in Dry Cutting of Ti-6Al-4V

Titanium alloys are very chemically reactive and,therefore,have a tendency to weld to the cutting tool during machining.The deterioration in the tool life caused by adhesion is a serious problem when titanium alloys are cut using carbide tools.The chemical reactivity of titanium alloys with carbide tool materials and their consequent welding by adhesion onto the cutting tool during dry cutting leads to excessive chipping,premature tool failure,and poor surface finish.In the present study,dry turning and milling tests were carried out on Ti-6Al-4V alloys with WC?Co carbide tools.The adhesion on the tool rake and flank face was explored,the adhesive joint interface between the workpiece materials and tools were observed.SEM observation showed that adhesion can be observed both on the rake and the flank face,and was more pronounced in rake face than in flank face.There was evidence of element diffusion from the tool rake face to the adhering layer(vice versa) through the adhesive joint interface,which leads to the tool element loss and microstructure change.While the adhering materials at the flank face can be easily separated from the joint interface owing to the lower temperature and less pressure at the flank face,the adhesive wear attack results in an abrasive wear in the flank face.Moreover,adhesion is more notable in turning than in milling.The proposed research provides references for studying the adhesion between the workpiece materials and the tools,the adhesion mechanisms and their effect on the tool wear.     

Wear characteristics of cemented carbide tool in dry-machining Ti-6Al-4V

In machining titanium alloys, due to the low thermal conductivity and high chemical activity of titanium alloys, tool wear is serious and processing efficiency is very low. To avoid the effects of impurities, which were brought by the cutting fluid, the uncoated cemented carbide tool (WC-Co), which was suitable for cutting titanium alloys, was used for the experiments of dry-turning titanium alloy Ti-6Al-4V. A scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometer (EDS) was used to analyze tool wear mechanism. Based on analyzing the friction characteristic of tool–chip interface, tool wear mechanism was also studied and a physical evolution model of tool wear was established. The results showed that there existed serious adhesion, diffusion and oxidation at tool–chip interface and increasing cutting speed accelerated their occurrence. The physical evolution of tool wear behavior can reflect the loss process of tool material very well.     

Experimental Study on Cutting Forces and Surface Integrity in High-Speed Side Milling of Ti-6Al-4V Titanium Alloy

This article is concerned with the cutting forces and surface integrity in high-speed side milling of Ti-6Al-4V titanium alloy. The experiments were conducted with coated carbide cutting tools under dry cutting conditions. The effects of cutting parameters on the cutting forces, tool wear and surface integrity (including surface roughness, microhardness and microstructure beneath the machined surface) were investigated. The velocity effects are focused on in the present study. The experimental results show that the cutting forces in three directions increase with cutting speed, feed per tooth and depth of cut (DoC). The widths of flank wear VB increases rapidly with the increasing cutting speed. The surface roughness initially decreases and presents a minimum value at the cutting speed 200 m/min, and then increases with the cutting speed. The microstructure beneath the machined surfaces had minimal or no obvious plastic deformation under the present milling conditions. Work hardening leads to an increment in micro-hardness on the top surface. Furthermore, the hardness of machined surface decreases with the increase of cutting speed and feed per tooth due to thermal softening effects. The results indicated that the cutting speed 200 m/min could be considered as a critical value at which both relatively low cutting forces and improved surface quality can be obtained.     

Constitutive modeling for Ti-6Al-4V alloy machining based on the SHPB tests and simulation

A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 10~4–10~6 s~(–1). Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar(SHPB) technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10~(–4)–10~4s~(–1). The Johnson Cook(JC) model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate(approximately 3×10~4 s~(–1)) conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests(10~(–4)–10~4 s~(–1)) and simulation(up to 3×10~4 s~(–1)). The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.     

应力比和残余应力对Ti-6Al-4V高周疲劳断裂模式的影响

对钛合金Ti-6Al-4V进行室温空气环境下的高周疲劳试验,研究消应力和未消应力试样在多个应力比下的疲劳强度,分析和检测表面残余应力在不同应力比和载荷水平下随循环次数而松弛情况,探讨表面残余应力随循环次数而松弛的规律以及残余应力和应力比对Ti-6Al-4V疲劳强度影响的机理。结果表明,随着应力比的提高,残余压应力对Ti-6Al-4V疲劳强度的提升影响逐步减小并消失;与消除残余应力后疲劳破坏源于表面相比,表面残余压应力使得低应力比下疲劳源于内部;当应力比R=-1.0时,疲劳循环导致表面残余压应力松弛且保持稳定,其产生的表面裂纹闭合是疲劳强度提高的主要机制;当R=-0.6~0.1时,未见疲劳循环导致表面残余应力松弛,由于表面层的平均应力减小使得疲劳破坏主要为内部缺陷和局部应力集中控制。     

不同参数对汽车Ti-6Al-4V气门座圈切削刀具磨损的影响

以汽车Ti-6Al-4V气门座圈为研究对象,研究了PCD金刚石刀具在切削加工中的切削力、进给力、刀具寿命及表面粗糙度随着切削速度和冷却压力的变化规律。试验表明:常规冷却下的刀具切削力随着切削速度的增加而增加,在切削速度207m/min、冷却压力20MPa时取得最小切削力;进给力随着冷却压力的增加先增加后减小,且在切削速度为262m/min时进给力最小;刀具寿命随着切削速度的增加而减小,常规冷却下刀具寿命最短,在切削速度150m/min、冷却压力为20MPa时,刀具寿命最大;表面粗糙度随着切削速度和冷却压力的增加先减小后增大,在冷却压力为10MPa和200m/min时,粗糙度最小。