Origin of Surface Irregularities on Ti–10V–2Fe–3Al Beta Titanium Alloy

We studied the origin of different characteristics and properties of a Ti–10V–2Fe–3Al beta (β) titanium alloy with surface height irregularities that occurred during machining. The height differences were observed in two different regions, labeled as “soft region” and “hard region.” The present study showed a higher Fe and a lower Al content in the hard region, which resulted in higher β-phase stability to resist primary alpha (α_p) phase precipitation caused by a failure of the solution treatment process. In contrast, the soft region contained a higher volume fraction of α_p phase and a lower volume fraction of the matrix, which consisted of a combination of β and secondary alpha (α_s) phase. A high number of α_s/β interface in the matrix with a predicted hardness of 520 HV generated an improvement of hardness in the hard region. Therefore, the hard and the soft regions had different abilities to resist wear during machining process, resulting in surface height irregularities.     

Effect of Heat Treatment on the Wear Properties of Selective Laser Melted Ti–6Al–4V Alloy Under Different Loads

As is well known, titanium alloy precipitates when subjected to aging treatment, which poses great influence on its mechanical properties. Thus, solution and solution-aging treatments were conducted in this work, and the wear performance was investigated under diff erent normal loads. The results showed that acicular α ′ martensite in the original selective laser melted Ti–6 Al–4 V was decomposed into α + β phases after the solution treatment, and then Ti₃Al nanoparticles clusters wer...     

Cyclic Oxidation Behavior of the Ti–6Al–4V Alloy

The cyclic oxidation behavior of the Ti–6Al–4V alloy has been studied under heating and cooling conditions within a temperature range from 550 to 850 °C in air for up to 12 cycles. The mass changes, phase, surface morphologies, cross-sectional morphologies and element distribution of the oxide scales after cyclic oxidation were investigated using electronic microbalance, X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy. The results show that the rate of oxidation was close to zero at 550 °C, obeyed parabolic and linear law at 650 and 850 °C, respectively, while at 750 °C, parabolic—linear law dominated. The double oxide scales formed on surface of the Ti–6Al–4V alloy consisted of an inner layer of TiO₂ and an outer layer of Al₂O₃, and the thickness of oxide scales increased with an increasing oxidation temperature. At 750 and 850 °C, the cyclic oxidation resistance deteriorated owing to the formation of voids, cracks and the spallation of the oxide scales.     

Effect of Heat Input on Microstructure and Mechanical Properties of Joints Made by Bypass-Current MIG Welding–Brazing of Magnesium Alloy to Galvanized Steel

Experiments were carried out with bypass-current MIG welding–brazing of magnesium alloy to galvanized steel to investigate the effect of heat input on the microstructure and mechanical properties of lap joints. Experimental results indicated that the joint efficiency tended to increase at first and then to reduce with the increase of heat input. The joint efficiency reached its maximum of about 70% when the heat input was 155 J/mm. The metallurgical bonding between magnesium alloy and steel was a thin continuous reaction layer, and the intermetallic compound layer consisted of Mg–Zn and slight Fe–Al phases. It is concluded that bypass-current MIG welding–brazing is a stable welding process, which can be used to achieve defect-free joining of magnesium alloy to steel with good weld appearances.     

High-Temperature Oxidation Kinetics and Behavior of Ti–6Al–4V Alloy

Owing to the high-temperature reactivity of titanium, the oxidation and alloying of titanium during hot working processes is an important variable. The oxidation behavior of Ti–6Al–4V alloy in air was investigated at various temperatures between 850 and 1100 °C for different times. The oxidation kinetics were determined by isothermal oxidation weight gain experiments. The results showed that the oxidation kinetics approximately obeyed a parabolic law. The activation energy of oxidation was estimated to be 199 and 281 kJ mol^?1 when temperature was above and below the beta transformation temperature (T _β), respectively. A model to predict oxidation extent was established based on experimental observations. The oxide scales mainly consisted of TiO₂ with a small amount of Al₂O₃ and TiVO₄. The alpha case was defined as solid solution formed because of oxygen diffusion into the substrate. The difference in the morphology and the formation mechanism of the alpha case at different temperature ranges was mainly owing to the participation of the grain boundary and grain orientation of the nucleation site.     

Effect of Surface Polishing Treatment on the Fatigue Performance of Shot-Peened Ti–6Al–4V Alloy

In this study, shot peening is applied to the titanium alloy Ti–6Al–4V, and the surface treatment effect on fatigue life of shot-peened specimens under high cycle loading is investigated. The induced residual stress is measured by using the orbital hole-drilling method. Surface profilometer and optical microscopy are employed to characterize the surface roughness and morphology. The deformed microstructure layers of the shot-peened specimens are investigated by using scanning electron microscopy. Experiments reveal that the fatigue life of Ti–6Al–4V is improved by the shot peening process, and the surface pre-peening polishing. The combination of pre-and post-peening polishing treatments further improves fatigue life of Ti–6Al–4V specimens. The present work provides useful guidelines for developing more efficient shot peening strategies.     

The Influence of the Alloy Microstructure on the Oxidation Behavior of Ti–46Al–1Cr–0.2Si Alloy

The influence of microstructure of the two-phase alloyTi–46Al–1Cr–0.2Si on the oxidation behavior in air between600 and 900°C was studied. The oxidation rate, type of scale, and scalespallation resistance were strongly affected by the type of microstructure,i.e., lamellar in as-cast material and duplex after extrusion at1300°C. The oxidation rate was affected by the size and distribution ofthe ₂-Ti₃Al phase, being faster for the extrudedmaterial with coarse ₂-Ti₃Al. The type of oxide scaledetermines the spalling resistance. Cast material developed a uniform scalethat spalled off after short exposure times at 800 and 900°C when a criticalthickness was reached. The extruded material presented a heterogeneous scalewith predominant thick regions formed on -TiAl-₂-Ti₃Algrains and thin scale regions formed on -TiAl grains. Thistype of scale could permit an easier relaxation in the matrix of stressesgenerated by both thermal-expansion mismatch between scale and alloy andoxide growth, resulting in a higher spallation resistance.     

Effect of Ultrasound on Heterogeneous Nucleation in TIG Welding of Al–Li Alloy

The effect of ultrasound on heterogeneous nucleation in a tungsten inert gas(TIG) weld pool of 2195 Al–Li alloy has been investigated by a series of experiments. An ultrasonic vibration was imposed on the surface of base material before turning off the welding arc during the TIG welding implemented at a fixed point. The results suggest that ultrasound could promote heterogeneous nucleation in the TIG weld pool of 2195 Al–Li alloy. The grain around the fusion zone is changed from a column grain to an equiaxed grain after applying the ultrasonic treatment. To study the influencing mechanism of ultrasound on heterogeneous nucleation, further investigations were implemented where the welding arc was turned off after turning off the ultrasonic power. The results show that the equiaxed grain around the fusion zone disappeared gradually with an increase in heat input after turning off the ultrasonic power. It suggests that ultrasound could promote the heterogeneous nucleation particle to nucleate in advance before turning off the welding arc and the crystal nucleus could again be melted with an increase in heat input after turning off the ultrasonic power. Moreover, the effects of the welding current and ultrasonic amplitude on heterogeneous nucleation in the weld pool of 2195 Al–Li alloy were also investigated. Possible influencing mechanism of the welding current and ultrasonic amplitude on heterogeneous nucleation was discussed.     

Electrochemical Polishing of Additively Manufactured Ti–6Al–4V Alloy

Metals and Materials International - In this present paper, the electropolishing behavior of Ti–6Al–4V alloy fabricated by additive manufacturing in chloride-containing ethylene glycol...     

高强Ti-3Al-2.5V合金管材的组织与性能

采用冷方法,通过设计不同的变形率和退火温度,研究了Ti-3Al-2.5V钛合金管材的显微组织和力学性能,探素了该合金的一种高强高韧管材的制备工艺.结果表明,当退火温度低于550℃时.Ti 3Al-2.5V合金管的再结晶程度相当低;当退火温度达700℃时,管材发生完全再结晶.合金管材力学性能的剧烈变化集中在退火温度为550～650℃之间.经工艺优化,当变形率为51.1％且退火制度为550℃X90 min.或者变形率为68.5％～80.2％且退火制度为600℃×90min时,Ti-3Al-2.5V合金管材的抗拉强度≥862 MPa.屈服强度≥724 MPa,伸长率≥12％.     

Ti-3Al-2.5V钛合金管织构演变规律研究

各向异性是钛合金管的一种重要性能,宏观上通常用收缩应变比（CSR）进行描述,而在微观上则可以通过织构演变分析其变化规律。本文通过EBSD方法研究了Ti-3Al-2.5V管轴向拉伸过程中的织构演变,揭示了CSR与织构演变的内在联系。结果表明,随着轴向塑性应变的增加,钛合金管α相晶体的基轴从开始变形时的沿径向分布逐渐朝着周向方向偏转,然后稳定在与径向成45°左右的位置。另外,β相在轴向拉伸过程中也表现出了明显的择优取向。正是因为织构的变化导致了CSR先迅速减小,然后缓慢减小,最后趋于稳定的变化规律。考虑到α相密排六方晶胞的基轴取向在轴向上的分量,改进了简化的CSR- f （织构量化参数）模型。与实验结果的对比表明,改进模型与实验值符合得较好。     

Hot Tensile Behaviors and Microstructure Evolution of Ti-6Al-4V Titanium Alloy Under Electropulsing

The effect of electropulsing on the mechanical behaviors and microstructures of Ti-6Al-4V titanium alloy was investigated by an uniaxial tensile test. Compared to the value measured in cold tensile test, the alloy exhibits lower ultimate tensile strength when the tensile deformation is assisted by electropulsing. The tensile elongation is found to vary non-monotonically with increasing root mean square(RMS) current density. Though decreasing at first, the tensile elongation increases with current density once the value exceeds 8.1 A/mm~2. Through applying current with RMS current density of 12.7 A/mm~2, the tensile elongation at strain rate 0.001 s~(-1) can be improved by 94.1%. In addition, it is observed that more remarkable electroplastic effect is induced by the higher peak current density under similar thermal effect. Microstructure analysis reveals that the low plasticity at 8.1 A/mm~2 is attributed to the micro-void easily formation near the tips of acicular β phases. The enhanced ductility at higher current densities, on the other hand, is attributed to the dynamic recrystallization.     

热等静压处理对超低温Ti-5Al-2.5SnELI合金铸造组织与性能的影响

研究了热等静压处理对Ti-5Al-2.5SnELI合金铸造组织、抗拉性能、冲击性能的影响.试验结果表明,热等静压处理使铸态的柱状晶粒转变为等轴晶粒,并且使位错发生运动,缠结中的位错重新组合,位错密度下降,内应力得到释放,导致强度下降,塑性提高,冲击性能提高.     

铸造Ti-6Al-4V合金的疲劳性能研究

通过铸造Ti-6Al-4V合金疲劳性能试验,绘制出了铸造Ti-6Al-4V合金在不同应力比下裂纹扩展速率da／dN-△K曲线。根据logda／dN和log△K的拟合曲线方程,计算出Paris公式下材料常数c、n值。经SEM对铸造Ti-6Al-4V疲劳断口进行分析,发现随着应力比R的增大,疲劳条带越宽,裂纹扩展速率越大。     

焙烧气氛对Ti-6Al-4V合金微弧氧化陶瓷膜相组成影响

在铝酸钠体系中,利用微弧氧化脉冲电源在Ti-6Al-4V合金表面制备了以Al2TiO5为主晶相的陶瓷膜层.试样分别在1000℃下空气和氩气2种气氛中进行焙烧,通过XRD,SEM,XRF等技术分析了陶瓷膜层焙烧前后不同层面的相组成、表面形貌和元素含量变化情况.结果表明:在1000℃空气气氛下,Al2TiO5分解较快,完全分解时,陶瓷膜外层α-Al2O3和金红石相二氧化钛相比例为44:55.而在氩气气氛下,Al2TiO5分解较慢,随反应的不断进行,Al2TiO5含量逐渐减少,完全分解时,陶瓷膜外层为α-Al2O3.膜层由表及里Al2O3含量降低并有Ti2O3生成.焙烧前后陶瓷膜层的形貌变化也不相同,氩气中颗粒较空气中的均匀、细化、孔隙小.膜内元素Ti,Al,P,O的含量在反应前后略有变化.     

Ti-6Al-4V线性摩擦焊实验研究

线性摩擦焊接作为一种先进的固态连接技术,凭借其高效、优质的特点正逐渐引起人们的重视。尤其是在高推重比飞机发动机整体叶盘制造与维修领域,它已经成为最经济、实用的加工技术之一。以航空工业中广泛应用的Ti-6Al-4V合金为实验材料,进行了线性摩擦焊的实验。描述了线性摩擦焊接工件飞边的宏观形态,得出了金属挤出物的规律。初步分析了典型工件焊缝区和热影响区的显微组织。结果表明,焊缝区为高度弥散的网状组织,热影响区为拉长的α相晶粒夹杂着破损的β相晶粒。     

47Zr-45Ti-5Al-3V合金的应力诱发马氏体转变行为研究

本文采用Gleeble 3500热模拟试验机和D/MAX-2500/PC型X射线衍射仪研究了亚稳态β相47Zr-45Ti-5Al-3V合金室温压缩变形过程中的应力诱发马氏体转变行为。结果表明,在压缩变形过程中,应力诱发马氏体的数量随应变速率和初始β相晶粒尺寸的降低而增加。随应变速率和初始β相晶粒尺寸的增加,应力诱发马氏体的触发应力逐渐增加,而抗压强度逐渐降低。加工硬化率随真应力的变化曲线可分为三个阶段,第二和第三阶段的加工硬化率随应变速率和初始β相晶粒尺寸的降低而增加。     

Ti-6Al-4V ELI合金板材的显微组织与力学性能研究

研究了Ti-6Al-4V ELI合金板材的显微组织与力学性能。结果表明:双态组织,强度、塑性都比较高;而对于片层组织,随着片层的粗化,强度降低,延伸率先升高后降低,面缩呈下降趋势。片层粗化,抵抗裂纹穿越、迫使裂纹拐弯能力增大,提高了断裂韧性。     

3D打印Ti-6Al-4V钛合金表面纳米孔洞制备技术

目的 通过3D打印技术制得钛合金,并构建出微米级多孔粗糙表面,再通过阳极氧化表面处理技术在微米级多孔粗糙表面构建出纳米级结构.方法 首先,通过高压水处理与酸蚀处理相结合的方法,对3D打印钛合金表面进行前处理,去除不良结合的球形粉末颗粒,降低3D打印钛合金表面的粗糙度及各向异性.然后,通过阳极氧化处理,在3D打印钛合金表...