Processing maps for hot deformation of α2 aluminide alloy Ti-24Al-11Nb

Using the test data of ₂ titanium aluminide alloy Ti-24Al-11Nb with microstructural observations, studies are made to examine the flow localization concepts as well as the simplified metallurgical stability criterion for delineating the regions of flow instabilities in the processing maps. The optimum hot working conditions for the material are suggested.     

In vivo and in vitro response to electrochemically anodized Ti-6Al-4V alloy

Tissues’ reactions to metals depend on a variety of properties of the metal, most notably surface structure. Anodizing has been shown to alter the surface properties of metal, thus eliciting a change in the biocompatibility of the metal. In order to evaluate the biocompatibility of unoxidized titanium alloy (Ti-6Al-4V) and anodized titanium alloy samples, the samples were implanted in murine abdominal subcutaneous tissues, and maintained for 2 and 4 weeks. The reaction of the abdominal subcutaneous connective tissues to the samples was then assessed. Fibrous connective tissue capsules were observed around the vicinity of the sample, and these capsules were shown to harbor fibroblasts, fibrocytes, and other cells, including neutrophils, macrophages, and giant multinucleated cells. The average thickness of the fibrous capsules observed around the anodized alloy samples was less than that of the capsules seen around samples of the unoxidized titanium alloy. Blood was obtained from the tails of the experimental mice, and blood cell analyses were conducted in order to assess the levels of leukocytes, red blood cells, and thrombocytes. The blood analysis results of the unoxidized control group and treatment group were all within normal ranges. In addition, the biocompatibility of the titanium alloy samples was evaluated using cell culture techniques. The numbers of MG-63 cells cultured on oxidized samples tended to be greater than those in the controls; however, these increases were not statistically significant. The alkaline phosphatase activity of the sample oxidized at 310 V evidenced significantly higher activity than was observed in the control group. These results indicate that the anodized Ti-6Al-4V alloy will be of considerable utility in biomedical applications.     

Types of superplasticm-δ curves of Ti-6Al-4V alloy and their intertransformation

The superplasticm- curves of Ti-6Al-4 alloy have been determined at different temperatures and strain rates; all were of them _L=m _max type, and were of either fundamental, descending or ascending types. The latter two types were transformed from the former through the processes ofm _Lm _O, _LO andm _Lm _F, _LF, respectively. The highest total elongation, _F, was 1150% obtained at 950C and 1.55×10^–3 s^–1. The Chin Liu equation has been applied to all types ofm- curves. The parameters characteristic of all types ofm- curves have been obtained and were found to vary with temperature and strain rate. The total elongation, _F, is determined by the resultant effects of all other parameters, not by a singlem value, theoretically considered to be constant and determined practically by a tensile strain of about 30%–50% (m _30%–50%) as usual.Nomenclature C (=k/k _o ) the normalized slope ofm- curve corresponding to - a material constant corresponding to - m strain-rate sensitivity index corresponding to - m _max maximum on them- curve corresponding to _L - m _min minimum on them- curve corresponding to _L - crosshead speed during the tensile test - the strain of the entire stretching process (has same significance as ordinarily adopted ) - _F total elongation at fracture chosen for the present work - _I intermediate strains including _I1, _I2, _I3, ..., _I(i–1), _Ii , _I(i+1), ..., chosen for the present work - _L limit strain separatingm- curves into sections - _O (=0) starting strain - strain rate - flow stress     

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.     

Influence of alloy element partitioning on strength of primary α phase in Ti-6Al-4V alloy

The partitioning effect of Al(α-phase stabilizer) and V elements(β-phase stabilizer) on strength of the primary α phases in the α/β Ti-6 Al-4 V alloy with the bimodal microstructure was investigated.It was found that partitioning of Al and V elements took place in the Ti-6 Al-4 V alloy during the recrystallization process,leading to the variation of the content of Al and V elements in the primary α phases with changing the volume fraction of the primary α phase.Nanoindentation tests reveal a general trend that the strength of the primary α phases increases with decreasing the volume fraction of the primary α phases,and such trend is independent on the loading direction relative to the c-axis of the α phase.The enhanced strength is attributed to the increase of the content of Al element in the primary α phase,but it is not dominated evidently by the change of the V content.The solid solution strengthening contributed from both the elastic strain introduced by the solute atoms and the variation of the density of states was estimated theoretically.     

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.     

Ti-6Al-4V组织相变研究进展

钛合金因具有密度小、延展性好、疲劳性优异和断裂性能以及比强度高等优点而被广泛应用于航空航天等领域。综述了近年来国内外学者在Ti-6Al-4V固态相变理论和实验研究方面的进展情况,总结了其由β相区在不同冷却速率下所得到的相变组织,得到了hcp-α向bcc-β转变时具有伯格斯取向关系,介绍了包括马氏体相变、块型转变以及扩散相变的转变温度,当冷却速率达到525℃/s时发生马氏体相变,β相将转变为α￠相,当冷却速率为20~410℃/s时发生竞争扩散型相变β→α_m,低于20℃/s发生扩散控制相变,原始β晶粒中出现不规则的αGB、初生α集束和魏氏α组织。最后探究了新技术在Ti-6Al-4V微观相变组织中的应用。     

TEM study of metastable β-phase decomposition in rapidly solidified Ti-6Al-4V alloy

A new rationale is presented for various decomposition products obtained from the metastable -phase found in Ti-6A1-4V alloy produced by hot isostatic pressing comminuted melt-spun fibres and cooled to room temperature by furnace cooling. This alloy has an -matrix with about 8 vol% retained -phase, which is supersaturated with -stabilizers to such an extent that the martensitic transformation has been suppressed. The metastable -phase decomposes by different modes during continuous cooling, depending on the actual composition of individual -grains. Less enrichment of vanadium and iron favours the direct formation of the equilibrium -phase from the -matrix, while greater enrichment of vanadium and iron leads to a spinodal decomposition of the metastable -phase, resulting in a + two-phase structure. During further continuous cooling, the -phase which is lean in -stabilizers will transform into isothermal -phase. In addition, an unknown phase has also been observed in the -phase, which is typified by the appearance of 1/2{112} reflections in the SAD patterns.     

Multiple α sub-variants and anisotropic mechanical properties of an additively-manufactured Ti-6Al-4V alloy

Additive manufacturing(AM)is a promising material processing method which gains significant momen-tum in the aerospace and biomedical industries.However,the anisotropy in the mechanical properties of additively-manufactured materials is still poorly understood.This study was aimed at elucidating crys-tallographic feature-anisotropy-mechanical property relationship for a Ti-6Al-4V alloy manufactured via selective electron beam melting(SEBM).Abundant α lamellae with six variants were present inside the columnar prior-β grains with a<100>fiber texture during β→α phase transformation.The six αvariants followed the Burgers orientation relationship of{110}β//{0001}α and<1-11>β//<11-20>α.Mul-tiple sub-variants in each α variant were observed for the first time.The anisotropy in the mechanical properties was mainly related to the relative amount of six α variants.While the horizontally-oriented samples had a lower yield strength,they exhibited a higher ductility and longer fatigue life than the vertically-oriented samples.Cyclic softening occurred at higher strain amplitudes,and cyclic stabiliza-tion sustained at lower strain amplitudes.Fatigue crack mainly initiated from the specimen surface at lower strain amplitudes,while multiple crack initiation tended to occur at higher strain amplitudes.Crack propagation was characterized by fatigue striations along with some secondary cracks.     

Tribological behaviour of hot extruded Al–Cu–Mg–Ag alloy reinforced by TiB2 particles

In the present investigation, tribological behaviour of the hot extruded Al–Cu–Mg–Ag (matrix) alloy and the effect of Ti and TiB₂ addition in matrix alloy have been studied. Hot extrusion was introduced to eliminate cast defects like porosity, voids and micro cracks. Addition of Ti and TiB₂ particles increased the hardness of the matrix by grain refinement and dispersion hardening, respectively. It has been observed that the increase in hardness had significantly improved the wear resistance of the material. Detail study of the wear surfaces and debris were carried out to understand the wear mechanism of the samples. It revealed a complex mechanism of micro-cutting, plastic deformation, abrasion and delamination of the wear samples.     

Accelerated flow softening and dynamic transformation of Ti-6Al-4V alloy in two-phase region during hot deformation via coarsening αgrain

The flow softening is an important phenomenon during hot deformation of metallic materials.In the present work,a more evident flow softening of Ti-6 Al-4 V alloy when deformed in two-phase region was observed in coarser a grain sample,which was attributed to an accelerated dynamic transformation from harder α phase into β phases.Notably,full β microstructure was observed in coarse grain samples at strain of 1.2,while retained a phase was observed in fine a grain specimens.In the views of thermodynamics and crystallographic analysis,the in-depth mechanisms of dynamic transformation were further investigated.     

热轧Ti-6Al-4V的织构分析

Ti-6Al-4V是航空航天等领域广泛使用的高强钛合金之一.由于这种合金在热轧加工过程中形成强烈的形变织构,所以使金属材料的强度、韧性以及疲劳性能等产生明显的各向异性.对此,人们曾用极图方法进行过研究,但是,由于传统方法固有的不足,其结果不是十分准确.近年来,日本现代技术研究中心和NKK的H. Inagaki等人用Bung和Roe提出的ODF方法,结合金相观察,准确地研究了Ti-6Al-4V热轧织构及织构形成机制.试样用真空熔炼成40kg,φ200mm,长250mm的Ti-6Al-4V铸锭,在1050℃下加工成80mm和16mm厚板,然后在1050℃退火1h再水冷.     

Ti-6Al-4V的激光辅助制造

激光辅助制造(LAM)是一种可望应用于钛航空部件的低成本制备技术.美国学者首次研究了沉积态的Ti-6Al-4V显微组织与LAM加工参数之间的关系.因为显微组织在机械性能控制方面起着根本的作用,所以研究组织演化规律对过程控制及工艺设计就显得至关重要.LAM的操作过程是:用激光束扫描基材金属,同时向熔池中添加所需的合金粉末,粉末熔化后冷凝在基材表面.通过有选择地多层扫描熔敷,可以自由成型固态金属零件.     

Ti-6Al-4V合金的风冷切削

不用切削油的切削有风冷切削、吹氮切削等,此外还有只使用微量切削油的MQL(超微量润滑)切削.但风冷加工用于切削加工的实例几乎没有.     

Laser Surface Modification of Ti-6Al-4V with Addition of Pr

The behaviour of oxidation at elevated tem-peratures and fretting in the laser-alloyed layer ofTi-6Al-4V with the addition of Pr was studied.The results show that the addition of Pr changes thestructure of oxide scale of Ti-6Al-4V,controls theshort-range diffusion of oxygen to thescale/substrate interface and increases the adhe-sion and ductility of the scale,thus changing theoxidation kinetics and considerably reducingoxidation rate.The analysis of fretting test showsthat the existence of high hardness layer in the al-loyed zone,fine dendrites perpendicular to the sur-face of the high hardness layer and the oxide scaleproduced during fretting at elevated temperaturesare all beneficial to the improvement of wear resist-ance.     

Surface modification of Ti-6Al-4 V alloy for biomineralization and specific biological response: part II,alkaline phosphatase grafting

Titanium and its alloys are the most widespread materials for the realization of orthopaedic and dental implants due to their good mechanical properties and biocompatibility. Surface functionalization of biomaterials aimed to improve and quicken implant integration and tissue regeneration is an active research field. The opportunity to confer biological activity (ability to directly stimulate cells with proper biological signals) to the Ti6Al4 V alloy, previously modified to be bioactive from the inorganic point of view (apatite precipitation), was explored in this research work. The alkaline phosphatase (ALP) enzyme was grafted to metal surface via tresyl chloride activation, maintaining its activity. A synergistic effect between biological functionalization and inorganic bioactivity was observed.     

Ti-6Al-4V合金的蠕变性能

本文利用现有数据,对Ti-6Al-4V合金的高温、室温蠕变性能及蠕变断裂性能进行了综合分析。分析结果表明,该合金长时间使用的极限温度为300℃或稍高于300℃;在300℃以下,退火状态的合金,同一温度的蠕变强度σ_(0.1)/100与屈服强度σ_(0.1)大致可用σ_(0.1)/100=1.355+0.836σ_(0.1)表示。200～400℃之间,σ_(100)与σ_b之比约为0.92～0.96。该合金存在着明显的室温蠕变现象,某些零部件不宜在高于90％屈服强度的应力下长期使用。显微组织对该合金的蠕变性能具有明显影响,β-加工或处理、淬火时效等可以提高其蠕变性能。     

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...     

Interfacial microstructure and strengthening mechanism in Ti–6Al–4V reinforced Al-7075 alloy

In the present study, an Al-7075 alloy reinforced with 15?wt-% TC4 (Ti–6Al–4V) was synthesised by hot pressing. The results of transmission electron microscopy suggest that a well-bonded multilayer interface was created, and that the multilayer has the ability to limit crack initiation at the interface. Sintering at 913?K for 0.5?h proved to be the most effective procedure for limiting the sources of cracking inside the multilayer interface, resulting in an enhanced tensile strength and a compressive strength for the composite of 454 and 873?MPa, respectively. The desired multilayer structure and the strengthening mechanism are discussed in detail. This structure provides guidance for the development of new methods for fabricating composites with excellent mechanical properties.     

短时双重热处理强化Ti-6Al-4V合金

Ti-6Al-4V合金是典型的两相钛合金,由于它不仅质量轻、耐腐蚀性能好,而且具有优异的强度和塑性匹配性能,因而得到了广泛应用.