Thermomechanical Behavior of Ti-6Al-4V Alloy

Ti-6Al-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6Ak-4V alloy has beeninvestigated by the uniaxial hot isothermal compression tests and a series of dilatometric experiments were also carried out todetermine the transformation temperatures at different cooling rates. Specimens for hot compression tests were homogenizedat 1050℃ for 10 min and then quickly cooled to different straining temperatures from 1050 to 850℃. Cooling rates were chosenfast enough to prevent high temperature transformation during cooling. Compression tests were conducted at temperaturesfrom 1050 to 850℃ in steps of 50℃ at constant true strain rates of 10~(-3) or 10~(-2) s~(-1). The apparent activation energy forcompression in two-phase region was calculated 420 kJ·mol~(-1). Partial globularization of cr phase was observed in the specimendeformed at low strain rates and at temperatures near the transformation zone and annealed after deformation.     

氢对Ti-6Al-4V合金室温压缩性能的影响

为了研究氢对Ti-6Al-4V合金室温压缩性能的影响,采用Zwick/Z100型材料试验机对置氢Ti-6Al-4V合金进行了压缩试验,并利用OM、XRD和TEM等材料分析方法对合金的微观组织进行了观察.研究表明:置氢前,Ti-6Al-4V合金由等轴的α相和β相组成,置氢后,出现马氏体组织和氢化物;随氢含量增加,马氏体和剩余β相数量增多;氢提高了Ti-6Al-4V合金的抗压强度和塑性等室温压缩性能,最大增幅分别为33.9%和56.3%;置氢Ti-6Al-4V合金抗压强度的提高主要归因于氢的固溶强化、马氏体相变强化和氢化物强化;塑性指标的提高主要是置氢合金中塑性β相数量的增多所致.     

Ti-6Al-4V合金的蠕变行为及影响因素

通过T6热处理、蠕变性能测试和SEM,TEM组织观察,研究了T6处理对Ti-6Al-4V合金组织结构与蠕变性能的影响.结果表明,锻造态Ti-6Al-4V合金在400℃/575MPa条件下具有较好的塑性和较低的蠕变寿命,并具有明显的温度敏感性.T6处理可明显提高合金的蠕变激活能和蠕变抗力,与锻造态合金相比,T6处理态合金在蠕变稳态期间具有较低的应变速率,并使蠕变寿命由66h提高到548h.锻造态合金的组织结构由a β相组成,T6处理后,合金的组织结构由a相与"网篮"相组成,其中"网篮"中大量针状β相沿不同取向析出是提高合金蠕变寿命的主要原因.蠕变期间,合金的蠕变机制是双取向的位错和位错在a相内发生柱面滑移和锥面滑移.     

TI-6Al-4V合金置氢-除氢组织与力学性能

为研究除氢处理对置氢钛合金组织与性能的影响,对Ti-6Al-4V合金在不同参数条件下进行了置氢与除氢处理,采用光学显微镜分析了置氢-除氢处理过程中Ti-6Al-4V合金微观组织的演化规律,通过室温拉伸试验研究了置氢-除氢处理后Ti-6Al-4V合金的力学性能,探讨了Ti-6Al-4V合金置氢-除氢组织与力学性能之间的相...     

增材制造Ti-6Al-4V合金组织调控研究现状

增材制造技术可实现复杂钛合金零件的快速成形,制造的Ti-6Al-4V合金具有较高的强度以及优异的高温性能,被广泛应用于航空、医疗等各大领域。综述了金属增材制造的典型工艺,分析了Ti-6Al-4V合金的相变特征,总结了选区激光熔化制造Ti-6Al-4V的力学性能和组织调控方法,着重分析了热处理温度、冷却速率、变质处理以及超声冲击等对合金组织的影响;展望了增材制造Ti-6Al-4V合金的主要发展方向。     

Ti-6Al-4V合金高温变形热加工图的建立与分析

本文根据已有理论建立了Ti-6Al-4V合金的高温变形热加工图,分析了功率耗散效率,为保证该合金加工质量提供依据.     

Ti-6Al-4V合金的室温蠕变行为

研究了Ti-6Al-4V钛合金板材的室温蠕变行为及其对合金后续使用性能的影响.结果 表明:合金的宏观织构、应力水平以及预塑性应变都显著影响其室温蠕变行为.在加载方向上合金的<0001>峰值极密度越高,则其加工硬化指数越大、蠕变指数越小、室温蠕变性能越好.足够大的应力,是合金发生室温蠕变的必要条件.只有在蠕变应力不小于0...     

Ti-6Al-4V合金的吸氢行为和氢化过程中的相变

本文研究了 Ti-6Al-4V 合金在氢压为一个大气压下的吸氢行为和氢化过程中的相变,结果发现:合金在570℃有一个吸氢峰;氢化过程中氢固溶于β相,使 d_(200)面间距增大;氢化物(γ)在α相内析出,为 fcc 结构(α=440.1pm),与基体的取向关系为{(?)}_α//{(?)}γ,<(?)>α//<110>γ;充氢使α,β相明暗衬度和充氢前比较正好相反;充氢后合金出现 Ti_3Al 有序结构。     

强迫剪切条件下Ti-6Al-4V合金的绝热剪切失效

采用分离式Hopkinson压杆(SHPB)加载装置,分别用200 mm和150 mm打击杆以28 m/s速度对Ti-6Al-4V合金帽形试样进行强迫剪切实验,利用OM、SEM、TEM等手段分析了强迫剪切条件下Ti-6Al-4V合金的绝热剪切带演化特征和高应变率剪切变形条件下的失效模式。结果表明,在本文所述实验条件下,Ti-6Al-4V合金的绝热剪切带(ASB)表现为"白亮带";ASB的宽度随加载时间的延长而增加;ASB边缘的裂纹是由于ASB的变形与基体的不协调而产生的,ASB中心部位的裂纹是由于非晶形成而后破碎导致的。     

Ti-6Al-4V合金包覆叠轧薄板的轧制工艺对力学性能的影响

主要研究了包覆叠轧加工及热处理工艺对Ti-6Al-4V合金室温拉伸及疲劳性能的影响规律,用金相显微镜和扫描电镜观察分析了疲劳裂纹的扩展路径及断口形貌.结果表明,在交叉轧制状态下,Ti-6Al-4V合金板材的织构较弱,且该状态下的疲劳性能最好,疲劳裂纹尖端有塑性钝化;而在较低轧制温度和单向轧制状态下,合金板材具有强烈的织构,疲劳裂纹呈快速扩展.     

Ti3Al基合金与Ti-6Al-4V合金TLP连接接头的组织转变

采用TiZrNiCu合金作为中间层材料研究了Ti3Al基合金与Ti-6Al-4V合金的瞬间液相(TLP)扩散连接接头成分、组织转变及显微硬度.研究结果表明,连接温度和连接时间对接头成分和组织有较大的影响.随着连接温度的提高和连接时间的延长,接头中元素分布趋于均匀,连接区宽度增大.连接温度为850℃和900℃时,液相的残留使得接头中存在Ti-Cu金属间化合物.当连接温度为950℃,连接时间为30min时,等温凝固的完成使Ti-Cu金属间化合物从接头中消失.随着连接温度的提高和连接时间的延长,接头连接区硬度降低.当连接温度为950℃,连接时间为30min时,接头硬度分布较均匀.     

Hydrogen Treatment of Cast Ti-6Al-4V Alloy

This paper presents the results of an investiga-tion of the effect of hydrogen treatment onmicrostructures and tensile and low cycle fatigueproperties of a Ti-6Al-4V cast alloy.The phasetransformation and the refining mechanism of thecast microstructure during the process of hydrogentreatment were studied.It was found that afterhydrogen treatment,the coarse Widmanstttenstructure of the as-cast Ti alloy was transformedinto a very fine and equiaxed α+β microstructurewithout any GBα phase.The tensile strength andductility and the low cycle fatigue life of thehydrogen treated specimens were significantly im-proved.     

Effect of Triple Annealing Treatment on Stress Relaxation of Ti-6Al-4V Alloy

The effect of triple annealing on stress relaxation of Ti-6Al-4V alloy as well as the microstructure after stress relaxation werestudied. The results showed that triple annealing treatment enhanced the resistance of stress relaxation performance, andwhen the temperature was rising, this effect became notable. The stress relaxation deformation mechanism is of dislocationcreep at 400℃ and recovery creep at 600℃.     

Ti-6Al-4V合金包覆叠轧薄板的加工工艺与组织性能研究

研究了包覆叠轧加工及热处理工艺对Ti-6Al-4V合金室温拉伸及疲劳性能的影响规律,观察分析了不同状态下组织形貌的特征及变化情况.结果表明,单向热轧工艺有利于提高合金薄板的延伸率,但对疲劳性能则会产生不利影响,而交叉换向热轧工艺则有利于板材获得较好的综合性能.     

Effect of mean stress on fretting fatigue of Ti-6Al-4V on Ti-6Al-4V

Fretting fatigue tests of Ti‐6Al‐4V on Ti‐6Al‐4V have been conducted to determine the influence of stress amplitude and mean stress on life. The stress ratio was varied from R=−1 to 0.8. Both flat and cylindrical contacts were studied using a bridge‐type fretting fatigue test apparatus operating either in the partial slip or mixed fretting regimes. The fretting fatigue lives were correlated to a Walker equivalent stress relation. The influence of mean stress on fretting fatigue crack initiation, characterized by the value of the Walker exponent, is smaller compared with plain fatigue. The fretting fatigue knockdown factor based on the Walker equivalent stress is 4. Formation of fretting cracks is primarily associated with the tangential force amplitude at the contact interface. A simple fretting fatigue crack initiation metric that is based on the strength of the singular stress field at the edge of contact is evaluated. The metric has the advantage in that it is neither dependent on the coefficient of friction nor the location of the stick/slip boundary, both of which are often difficult to define with certainty a priori.     

Influence of rotational speed on process characteristics in friction surfacing of Ti-6Al-4V

Friction surfacing process is employed to deposit metallic coatings, whereby similar and dissimilar material combinations can be realized. The process can be applied as a local repair technology, or the coating material can locally modify the surfaces. One advantage of this process is that the coatings are deposited in solid state without reaching the melting range of materials, thereby avoiding dilution with the substrate. The involved severe plastic deformation under high temperatures alters the microstructure of the coating material, leaving it fully dynamically recrystallized. The current work focuses on deposition of Ti-6Al-4V coatings. For that material, the process parameter rotational speed plays a major role in the material’s response during processing. Two different regimes with a threshold at 2000?min^?1 exist, upon which the flow behavior of Ti-6Al-4V significantly differs, affecting among others the coating dimensions. Microstructural analysis reveals that the material is deformed in a high temperature β phase, and the high cooling rates (46.4 Ks^?1) lead to martensitic transformation. The β grain size differs in the low and high rotational speed regimes. This study shows that metallurgical processes play an important role in friction surfacing, since they influence all relevant process characteristics, including microstructure, material efficiency and process forces.     

Superplastic Forming and Diffusion Bonding for Sandwich Structure of Ti-6Al-4V Alloy

Superplastic forming and diffusion bonding (SPF/DB) is a well-established process for the manufacture of components almost exclusively from Ti-6AI-4V sheet material. The sandwich structure of Ti-6AI-4V alloy is investigated. The effects of the microstructure on the SPF/DB process were discussed. The microstructure at the interfaces and the distribution of thickness were researched.