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...     

Correlation of adiabatic shearing behavior with fracture in Ti-6Al-4V alloys with different microstructures

The correlation of adiabatic shearing behavior with fracture was investigated in Ti-6Al-4V alloys with bimodal and lamellar microstructures by split Hopkinson pressure bar (SHPB) apparatus and ballistic impact test. The experiment results show that the macrographic characteristic of post-critical fracture is closely related with the behavior of adiabatic shear band (ASB) in these titanium alloys under high strain rate conditions. In bimodal microstructure, adiabatic shear bands are self-organized and distributed in somewhat regularly spaced clusters. These adiabatic bands as well as the correlated cracks spread far off along the maximum shear stress plane, which causes the projectiles fracture along the dominant cluster of adiabatic shear bands, and the fracture surfaces make an acute angle with the flat end of the projectile. In case of lamellar microstructure, the adiabatic shear bands branch off and interconnect with one another into a net-like structure. Such adiabatic shearing cracks can't spread deep resulting from the branching off and interaction of adiabatic shear band, but only to split the specimen into small fragments, which leads to the erosion of the projectile and the resulting fracture surfaces almost parallel to the flat end of the projectile.     

Temperature-gradient induced microstructure evolution in heat-affected zone of electron beam welded Ti-6Al-4V titanium alloy

The heat-affected zone (HAZ) of electron beam welded (EBW) joint normally undergoes a unique heat-treating process consisting of rapid temperature rising and dropping stages, resulting in temperature-gradient in HAZ as a function of the distance to fusion zone (FZ). In the current work, microstructure, elements distribution and crystallographic orientation of three parts (near base material (BM) zone, mid-HAZ and near-FZ) in the HAZ of Ti-6Al-4V alloy were systematically investigated. The microstructure observation revealed that the microstructural variation from near-BM to near-FZ included the reduction of primary α (α_p) grains, the increase of transformed β structure (β_t) and the formation of various α structures. The rim-α, dendritic α and abnormal secondary α (α_s) colonies formed in the mid-HAZ, while the “ghost” structures grew in the near-FZ respectively. The electron probe microanalyzer (EPMA) and electron back-scattered diffraction (EBSD) technologies were employed to evaluate the elements diffusion and texture evolution during the unique thermal process of welding. The formation of the various α structures in the HAZ were discussed based on the EPMA and EBSD results. Finally, the nanoindentation hardness of “ghost” structures was presented and compared with nearby β_t regions.     

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.     

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℃.     

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.     

A study on the hot corrosion behavior of Ti-6Al-4V alloy

The titanium alloys are potential materials for high temperature applications in turbine components due to their very high temperature strength and lightweight properties. However, hot corrosion is a life-limiting factor when Ti alloys are exposed to different chemical environments at high temperature. In the present paper, hot corrosion behavior of Ti-6Al-4V (Ti-31) alloy in different salt environments viz. air, Na₂SO₄-60% V₂O₅ and Na₂SO₄-50% NaCl at 750 °C was studied. The parabolic rate constants were calculated for different environments from the thermo-gravimetric data obtained for the samples and they show that corrosion rate is minimum in air when compared to chemical environment. The scale formed on the samples upon hot corrosion was characterized by using X-ray diffraction (XRD), SEM, and EDAX analysis to understand the degradation mechanisms.     

真空感应凝壳熔炼TC4合金的显微组织和力学性能

针对在航空航天等领域有重要应用背景的TC4合金 ,运用水冷铜坩埚真空感应熔炼炉制备了合金铸锭 ,研究了合金在铸态、热处理和热等静压条件下的显微组织和力学性能 .结果表明 ,铸态TC4合金的晶粒粗大 ,基体为大片状α+ β相组织 ,合金的强度较高 ,塑性低 ;合金经热处理 ,尤其经热等静压处理后 ,组织明显细化 ,塑性提高 .     

Preparation method of low-oxygen Ti-6Al-4V alloy by solid state re-deoxidation using calcium

The oxygen concentration in commercial Ti-6Al-4?V alloys was reduced to less than 400?ppm in this study by the method of solid state re-deoxidation, using calcium as a reductant. The concentration of oxygen in the deoxidised Ti-6Al-4?V alloy was 630?ppm at the optimum deoxidation temperature of 1000°C. When the degree of vacuum was increased and re-deoxidation was carried out, the oxygen concentration decreased to 355?ppm. Therefore, it is possible to prepare a Ti-6Al-4?V alloy with an oxygen concentration of less than 400?ppm by using the solid state re-deoxidation method at a high degree of vacuum of 1.5?×?10-6 Torr.     

Ti-6Al-4V合金表面超声振动滚压强化研究

采用超声振动滚压加工技术对Ti-6Al-4V合金表面进行处理,探究该项技术对Ti-6Al-4V合金表面质量的影响。通过对该工艺加工前后的Ti-6Al-4V合金进行表面粗糙度参数、XRD图谱、截面微观形貌、表层残余应力及显微硬度的对比分析,结果表明:经该工艺处理后的合金表面各项粗糙度参数皆有明显降低;加工后的合金表面XRD图谱的衍射峰减弱且宽化,衍射角向高角度方向偏移;加工后的合金表层β相组织相较加工前明显细化,且随着深度增加β相组织逐渐增大;在距离表面约50μm位置的残余应力值最大可达到-967 MPa;加工后的合金表面显微硬度可达到421HV,且在0~140μm的深度范围内,显微硬度随着深度的增加逐渐减小至与基体硬度一致。经超声振动滚压加工后的Ti-6Al-4V合金表面质量显著提高,有利于提高其零部件的使用性能。     

The effect of angle on dovetail fretting experiments in Ti-6Al-4V

The objective of this work was to compare the fretting fatigue performance of Ti‐6Al‐4V dovetail specimens on Ti‐6Al‐4V pads having various contact angles typical of engine hardware; 35°, 45° and 55° dovetail angles were considered. The dovetail fixtures were instrumented with strain gages so that the local normal and shear contact forces could be calculated. The contact force hysteresis loops were recorded showing the stick‐slip history. At R= 0.1, gross slip was observed for several thousand cycles followed by partial slip after the average coefficient of friction increased. At R= 0.5, gross slip was present only during the first half cycle. During partial slip, the slope of the shear versus normal force was a function of the dovetail angle. The local contact loads, therefore, differed for the same remotely applied force. Despite this, the fretting fatigue life depended primarily on the remotely applied load not dovetail angle.     

Microstructure developed in the surface layer of Ti-6Al-4V alloy after sliding wear in vacuum

Microstructural changes in the surface layer of Ti-6Al-4V alloy after sliding wear in vacuum have been studied by means of scanning and transmission electron microscopy (SEM and TEM). The wear rates of Ti-6Al-4V alloy in vacuum were measured under different sliding velocities and loads. The experimental results showed that a severely deformed layer with a grain size of 50–100 nm and thickness about 70 μm was formed underneath the worn surface. Under the slower sliding velocities, the substructure of the layer had a high dislocation density, while under higher sliding velocities, twins were found to exist in the substructure. A process by which the deformed layer formed has been proposed and the deformation of materials at the contacting spots of the Ti-6Al-4V sample is discussed.     

Fractographic and microstructural analysis of fatigue crack growth in a Ti-6Al-4V fan disc forging

The constant amplitude fatigue crack growth behaviour of a conventionally (+β) solution treated and aged Ti-6Al-4V fan disc forging was examined by fractographic and microstructural analysis. The crack growth process was complex with many interrelated fracture features. A transition in the fatigue crack growth curve correlated with a change from structure-sensitive to continuum-mode crack growth, primarily in the transformed and aged β grains, and a decrease in fracture surface roughness. The transition was probably caused by the cyclic plastic zone size becoming equal to and exceeding the average platelet packet size. The significance of such transitions for prediction of fatigue crack growth and service failure analysis is discussed.     

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.     

Effects of microstructure on mixed-mode, high-cycle fatigue crack-growth thresholds in Ti-6Al-4V alloy

Effect of microstructure on mixed‐mode (mode I + II), high‐cycle fatigue thresholds in a Ti‐6Al‐4V alloy is reported over a range of crack sizes from tens of micrometers to in excess of several millimeters. Specifically, two microstructural conditions were examined—a fine‐grained equiaxed bimodal structure (grain size ～20 µm) and a coarser lamellar structure (colony size ～500 µm). Studies were conducted over a range of mode‐mixities, from pure mode I (ΔK_II/ΔK_I = 0) to nearly pure mode II (ΔK_II/ΔK_I ～ 7.1), at load ratios (minimum load/maximum load) between 0.1 and 0.8, with thresholds characterized in terms of the strain‐energy release rate (ΔG) incorporating both tensile and shear‐loading components. In the presence of through‐thickness cracks—large (> 4 mm) compared to microstructural dimensions—significant effects of mode‐mixity and load ratio were observed for both microstructures, with the lamellar alloy generally displaying the better resistance. However, these effects were substantially reduced if allowance was made for crack‐tip shielding. Additionally, when thresholds were measured in the presence of cracks comparable to microstructural dimensions, specifically short (～200 µm) through‐thickness cracks and microstructurally small (< 50 µm) surface cracks, where the influence of crack‐tip shielding would be minimal, such effects were similarly markedly reduced. Moreover, small‐crack ΔG_TH thresholds were some 50–90 times smaller than corresponding large crack values. Such effects are discussed in terms of the dominant role of mode I behaviour and the effects of microstructure (in relation to crack size) in promoting crack‐tip shielding that arises from significant changes in the crack path in the two structures.     

真空高温退火对锻态Ti-6Al-4V合金显微组织与超塑性性能的影响

退火处理是改善钛合金显微组织,提高力学性能及超塑成形性能的一种重要工艺。使用真空退火炉在850℃-950℃温度区间内对锻态Ti-6Al-4V合金的进行了高温退火处理,研究了退火态Ti-6Al-4V合金微观组织演变及其在温度为900℃,应变速率为0.01 s^-1时的超塑拉伸性能。结果表明,锻态Ti-6Al-4V合金的初生α晶粒尺寸随真空退火温度的升高而减小,β相比例随真空退火温度升高而增大。当真空退火温度为910℃时,Ti-6Al-4V合金的晶粒尺寸和α相与β相分布较为均匀,其超塑拉伸试验结果表明,该合金表现出最佳的超塑拉伸性能,其拉伸延伸率达到785%,峰值应力仅为26.8 MPa。     

Friction-stir welding and processing of Ti-6Al-4V titanium alloy: A review

In this work, the current understanding and development of friction-stir welding and processing of Ti-6Al-4V alloy are briefly reviewed. The critical issues of these processes are addressed, including welding tool materials and design, tool wear, processing temperature, material flow, processing window and residual stresses. A particular emphasis is given to microstructural aspects and microstructure-properties relationship. Potential engineering applications are highlighted.     

Diffusion kinetics of explosively treated and plasma nitrided Ti-6Al-4V alloy

Ti-6Al-4V alloys, which were exposed to an explosive shock process, were nitrided in nitrogen plasma in the temperature range of 700-900°C for 3-12 h. During the plasma nitriding, the surface layer consisted of TiN (δ), Ti₂N (ε) and nitrogen solid solution layers (α-Ti). The growth rate of nitride and solid solution layers were found to be controlled by the diffusion of nitrogen. An effective nitriding was achieved due to high dislocation density and vacancy concentration. Based on the present layer growth data, an analytical model for multiphase diffusion was used to estimate the effective nitrogen atom diffusion coefficient in the nitride layers. The interface velocity equations were derived from Fick's law and a numerical method has been used to compute the diffusion coefficients of nitrogen in a binary multiphase Ti-TiN system. Depending on temperature and layer thickness, the activation energies of nitrogen in TiN and Ti₂N phases were found to be 18,950 (±2116) and 27,925 (±1105) cal/mole, respectively.     

Nanoscale characterization of anodic oxide films on Ti-6Al-4V alloy

The paper analyses, at nanoscale levels, the chemical composition and mechanical properties of the anodic oxide films formed on Ti-6Al-4V alloy by galvanostatic polarization at maximum final voltages of 12-100 V. For the investigations Auger Electron Spectroscopy, Photoelectron Spectroscopy and nanoindentation measurements have been used. The results have shown that anodizing the Ti-6Al-4V alloy produces an oxide film whose thickness depends on the final voltage. The chemical composition is not significantly dependent on the thickness, the film consists of TiO₂ and Al₂O₃. However, the best insulating properties of the films, determined from the growth parameter nm/V, are achieved with a final voltage between 30 and 65 V. Nanohardness and Young's modulus measurements have shown that the anodic films formed by different voltages exhibit similar mechanical properties which is consistent with the results of the surface analysis.