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。     

Ti-6Al-4V真空钎焊研究

针对目前用于Ti合金钎焊的Ti基钎料熔点偏高的现状，设计了Ti-Zr-Cu-Ni钎料，结果 表明，接头强度较高，因钎焊温度较低母材基本上保留了原始组织。同时还证明Ti-Zr-Cu钎料大幅度增加Cu的质量分数易造成钎缝中心区域生成连续分布的Ti2Cu+TiCu，严重影响接头强度。     

马氏体组织Ti-6Al-4V钛合金多向等温锻造组织演变及力学性能强化研究

将铸态Ti-6Al-4V钛合金经过β相区热处理水淬之后获得马氏体组织,经过两步多向等温锻造之后获得了平均晶粒尺寸为1.5 μm的均匀等轴细晶组织,其室温拉伸屈服强度为906 MPa,抗拉强度为954 MPa,伸长率为16.7%,相比铸态Ti-6Al-4V钛合金,其室温力学性能得到了极大提升。研究表明,获得马氏体组织对钛合金晶粒细化有着巨大促进作用。第一步等温锻造之后的钛合金坯料组织并不均匀,存在变形区和“变形死区”,在变形区域内,心部位置应变量最大,组织细化最为明显,从心部到两端应变量逐渐减小,片层组织变形量相应减小;经过90°换向后的第二步等温锻造之后,钛合金坯料组织内的片层组织基本全部细化,形成了均匀的等轴晶组织,从心部到两端,随着应变量的减小,晶粒取向变化相应减小。     

高速铣削钛合金Ti-6Al-4V切屑形态试验研究

对高速铣削的切屑进行了微观组织研究,建立了切削要素、切屑形态、切削力、表面粗糙度等因素之间的关系。研究发现,切削速度越高,热量向外扩散的时间越少,聚集在剪切带内的热量越多,剪切带内发生动态再结晶的可能性也就越高,大量的热量促进了剪切带内的热塑性失稳,进而使绝热剪切带产生的频率大幅度提高,切屑的锯齿化程度也就随之加大;计算了不同切削条件下绝热剪切带中心的温度、热量扩散速度等,发现热量扩散速度远低于其变形速度,进而证明了高速切削钛合金Ti-6Al-4V时,绝热剪切带内发生了动态再结晶现象。考虑到再结晶软化效应对材料本构的影响情况,建立了改进J-C本构模型,该模型用两个表达式表述不同临界应变值区间范围的材料本构特征,理论计算证明了改进J-C本构比J-C本构更准确。     

工件预加载温度对Ti-6Al-4 V车削过程的影响

通过对比仿真和试验的切削力、切屑形态和锯齿化程度验证了仿真模型的可行性,然后用仿真分析的方法研究了工件预加载温度对切屑形貌、切削力和切削温度的影响,获得了锯齿形切屑转变为带状切屑的临界工件预加热温度。结果表明:随着预加载温度的增加,切屑变形减少;在v=50m/min时,锯齿形切屑转变为带状切屑的临界预加载温度为150℃～200℃;切削速度v=110～170m/min时,临界预加载温度为250℃左右。     

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。     

Ti-6Al-4V燕尾榫结构微动疲劳裂纹萌生及扩展行为研究

针对Ti-6Al-4V钛合金燕尾榫连接结构在不同载荷下的微动疲劳现象,采用榫形微动疲劳试验进行研究,并对裂纹萌生扩展、微动磨损及断口进行分析。结果表明,微动疲劳使构件疲劳寿命显著降低约70%;疲劳载荷对微动裂纹扩展的影响比对裂纹萌生的影响更大;微动疲劳裂纹起始于接触面边缘,与接触表面约成45°角,裂纹扩展到60~150μm后转向与接触表面垂直;微动疲劳断口形貌表面在微动磨损区具有多个裂纹源点,但只有一个主裂纹形成。     

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。     

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。     

Wear mechanisms of PVD-coated cutting tools during continuous turning of Ti-6Al-4V alloy

The aim of this study was to investigate the damage of cutting tools coated by physical vapor deposition (PVD) during the continuous turning of a titanium alloy. The investigation utilized scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and transmission electron microscopy (TEM). It was found that a TiN coating on the tool wore faster than an uncoated cemented carbide tool. The damage mode of the coating on the rake face was fracture without plastic deformation. Additionally, there was a pattern to the crystal orientation relationship at some of the interfaces between the adhered workpiece material and the TiN coating. The crystal orientation relationship presumably produced a strong bond between the adhered material and the coating. The coating damage was thus caused by the force exerted by the adhered materials on the grain boundary on the damaged coating surface. A comparison of the tool damages during the machining of Ti-6Al-4V alloy and alloy 718 suggested that the damage of the coating depended on the interfacial strength between the adhered material and the coating, as well as the strength of the adhered material at a high temperature. Hence, to prevent the damage of the tool during the machining of a titanium alloy, it is preferable to use a ductile material (e.g., cemented carbide) rather than a brittle material (e.g., ceramic).     

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.     

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.     

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%。     

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。     

高速车削钛合金时硬质合金刀具和涂层刀具的寿命分析

采用硬质合金刀具和硬质合金TiMN涂层刀具对Ti-6Al-4V钛合金进行高速干车削正交试验,并通过多元线性回归分析得出硬质合金刀具和涂层刀具的寿命经验公式.分析表明:随着所选用的切削参数值的升高,刀具的使用寿命急剧减少,其中速度v对刀具使用寿命的影响最大.涂层刀具在低速切削加工钛合金时其寿命优于未涂层刀具,随着速度的提高,涂层刀具的优势迅速减小.当切削速度低于85 m/min,刀具寿命经验公式可以作为数控机床自动换刀的刀具寿命标准.