Brazing of Ti-6Al-4V and niobium using three silver-base braze alloys

Evaluations of the (infrared)-brazed Ti-6Al-4V and niobium joints using three silver-base braze alloys have been extensively studied. According to the dynamic wetting angle measurement results, the niobium substrate cannot be effectively wetted by all three braze alloys. Because the dissolution of Ti-6Al-4V substrate causes transport of Ti into the molten braze, the molten braze dissolved with Ti can effectively wet the niobium substrate during brazing. For infrared-brazed Ti-6Al-4V/Ag/Nb joint, it is mainly comprised of the Ag-rich matrix. The TiAg reaction layer is observed at the interface between the braze and Ti-6Al-4V substrate. In contrast, Ti-rich, Ag-rich, and interfacial TiAg phases are found in the furnace-brazed specimen. The dominated Ti-rich phase in the joint is caused by enhanced dissolution between the molten braze and Ti-6Al-4V substrate. The infrared-brazed Ti-6Al-4V/72Ag-28Cu/Nb joint is mainly comprised of the Ag-rich matrix and Ag-Cu eutectic. With increasing the brazing temperature or time, the amount of Ag-Cu eutectic is decreased, and the interfacial Cu-Ti reaction layer(s) is increased. The infrared brazed joint has the highest average shear strength of 224.1 MPa. The averaged shear strength of the brazed joint is decreased with increasing brazing temperature or time, and its fracture location changes from the braze alloy into the interfacial reaction layer(s) due to excessive growth of the Cu-Ti intermetallics. The infrared-brazed Ti-6Al-4V/95Ag-5Al/Nb joint is composed of Ag-rich matrix and TiAl interfacial reaction layer. With increasing the brazing time, the amount of Ag-rich phase is greatly decreased, and the interfacial reaction layer becomes Ti₃Al due to enhanced dissolution of Ti-6Al-4V substrate into the molten braze. The average shear strength of the infrared-brazed joint is 172.8 MPa. Additionally, the existence of an interfacial Ti₃Al reaction layer significantly deteriorates the shear strength of the furnace-brazed specimen.     

Bonding Interface Formation between Mg Alloy and Steel by Liquid-phase Bonding using the Ag Interlayer

Liquid-phase bonding between a Mg alloy (AZ31) and low-carbon steel was attempted at 773 K (500 °C) using Ag as an interlayer that forms a eutectic melt with the Mg alloy at this temperature. On the AZ31 side, eutectic melting and subsequent isothermal solidification were observed, and it was confirmed that the solidification of the eutectic liquid was promoted by the diffusion of Ag into the AZ31 base metal. On the steel side, Al was transported from AZ31 during the eutectic melting and isothermal solidification. This transported Al was enriched at the steel surface and reacted with steel to form a uniform, thin Fe-Al intermetallic compound layer. After the isothermal solidification, strong bonding was achieved via the thin intermetallic compound layer between AZ31 and steel, and no Ag remained at the bonding interface. The strength of the joint was found to be higher than the yield strength of AZ31.     

High-Productivity Forge Welding of AZ80 Magnesium Alloy to A2024 Aluminum Alloy Using an AC Servo Press

We have developed a high-productivity dissimilar bonding technology intended for the automobile sector, which is increasingly becoming multimaterial oriented. The forge-welding process, which involves diffusion bonding with plastic deformation in the open air, was used to bond AZ80 magnesium (Mg) alloy with A2024 aluminum (Al) alloy with a pure titanium (Ti) sheet interlayer using a high-speed, high-precision AC servo press. The influences of the preheat temperature, Ti sheet thickness, and the pressure holding time on the tensile strength were surveyed. In addition, the influence of the polishing of the bonding surfaces was examined. A pressure holding time of 0.1 seconds with a cycle time of less than 2 seconds provided high-strength bonding. Furthermore, a high-strength bond could be achieved with a Ti sheet thickness of only 0.3 mm and without needing polishing before bonding or heat treatment after bonding. Cross-sectional textures of the macro- and micro-fracture surfaces and elemental analyses of the bonded interface were examined. The fracture side of the bonded interface, the Ti-Mg alloy side, had a thin (ca. 5 nm) Ti-Al reaction layer (RL), which confirmed a diffusion bonding mechanism between the Ti and Al elements present in the Mg alloy. Despite processing in air with an extremely short processing time, this impacting press method provided good plastic deformability and sufficient elemental diffusion to result in high-strength bonding with a tensile strength ranging from 130 to 150 MPa.

     

Interfacial microstructure and mechanical properties of diffusion-bonded joints of titanium TC4 (Ti-6Al-4V) and Kovar (Fe-29Ni-17Co) alloys

Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature.Titanium alloy TC4(Ti-6 Al-4 V)and 4 J29 Kovar alloy(Fe-29 Ni-17 Co)were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min,under a pressure of 34.66 MPa.Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy,scanning electron microscopy,X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS).The elemental diffusion across the interface was revealed by electron probe microanalysis.Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength.Results of EDS and XRD indicated that(Fe,Co,Ni)-Ti,TiNi,Ti_2Ni,TiNi_2,Fe_2 Ti,Ti_(17) Mn_3 and Al_6 Ti_(19) were formed at the interface.When the bonding temperature was raised from 700 to 850°C,the voids of interface were reduced and intermetallic layers were widened.Maximum tensile strength of joints at 53.5 MPa was recorded by the sintering process at 850°C for 120 min.Fracture surface of the joint indicated brittle nature,and failure took place through interface of intermetallic compounds.Based on the mechanical properties and microstructure of the diffusion-bonded joints,diffusion mechanisms between Ti-6 Al-4 Vtitanium and Fe-29 Ni-17 Co Kovar alloys were analyzed in terms of elemental diffusion,nucleation and growth of grains,plastic deformation and formation of intermetallic compounds near the interface.     

镁合金搅拌摩擦焊接技术

对5mm厚镁合金AZ31B板材的摩擦焊接技术进行了试验研究，结果表明：适合其板材的搅拌摩擦焊接的搅拌头，材料为W6MoSCr4V2高速钢，结构为凹面圆台形，根部直径5．5mm，端部直径为2．5mm，轴肩尺寸为12mm，长度为4．7mm。镁合金搅拌摩擦焊接头的抗拉强度可达母材的90％，延伸率可达母材的50％。搅拌摩擦焊接头焊合区为动态再结晶组织，在接头前进边焊合区与母材有明显的分界线，返回边过渡区有金属微熔的迹象。     

An investigation of the fracture and fatigue crack growth behavior of forged damage-tolerant niobium aluminide intermetallics

The results of a recent study of the effects of ternary alloying with Ti on the fatigue and fracture behavior of a new class of forged damage-tolerant niobium aluminide (Nb₃Al-xTi) intermetallics are presented in this article. The alloys studied have the following nominal compositions: Nb-15Al-10Ti (10Ti alloy), Nb-15Al-25Ti (25Ti alloy), and Nb-15Al-40Ti (40Ti alloy). All compositions are quoted in atomic percentages unless stated otherwise. The 10Ti and 25Ti alloys exhibit fracture toughness levels between 10 and 20 MPa√m at room temperature. Fracture in these alloys occurs by brittle cleavage fracture modes. In contrast, a ductile dimpled fracture mode is observed at room-temperature for the alloy containing 40 at. pct Ti. The 40Ti alloy also exhibits exceptional combinations of room-temperature strength (695 to 904 MPa), ductility (4 to 30 pct), fracture toughness (40 to 100 MPa√m), and fatigue crack growth resistance (comparable to Ti-6Al-4V, monolithic Nb, and inconnel 718). The implications of the results are discussed for potential structural applications of the 40Ti alloy in the intermediate-temperature (∼700 °C to 750 °C) regime.     

An investigation of the fatigue and fracture behavior of a Nb-12Al-44Ti-1.5Mo intermetallic alloy

This article presents the results of a study of the fatigue and fracture behavior of a damage-tolerant Nb-12Al-44Ti-1.5Mo alloy. This partially ordered B2 + orthorhombic intermetallic alloy is shown to have attractive combinations of room-temperature ductility (11 to 14 pct), fracture toughness (60 to 92 MPa√m), and comparable fatigue crack growth resistance to IN718, Ti-6Al-4V, and pure Nb at room temperature. The studies show that tensile deformation in the Nb-12Al-44Ti-1.5Mo alloy involves localized plastic deformation (microplasticity via slip-band formation) which initiates at stress levels that are significantly below the uniaxial yield stress (∼9.6 pct of the 0.2 pct offset yield strength (YS)). The onset of bulk yielding is shown to correspond to the spread of microplasticity completely across the gage sections of the tensile specimen. Fatigue crack initiation is also postulated to occur by the accumulation of microplasticity (coarsening of slip bands). Subsequent fatigue crack growth then occurs by the “unzipping” of cracks along slip bands that form ahead of the dominant crack tip. The proposed mechanism of fatigue crack growth is analogous to the unzipping crack growth mechanism that was suggested originally by Neumann for crack growth in single-crystal copper. Slower near-threshold fatigue crack growth rates at 750 °C are attributed to the shielding effects of oxide-induced crack closure. The fatigue and fracture behavior are also compared to those of pure Nb and emerging high-temperature niobium-based intermetallics.     

Ti-6Al-4V钛合金表面纳米化机制研究

借助X射线衍射仪、透射电镜及显微硬度仪等先进仪器,研究了经超音速微粒轰击( SFPB)形变热处理Ti-6Al-4V合金表面自身纳米化晶粒尺寸演化及纳米化机制.研究结果表明:超音速微粒轰击使Ti-6Al-4V合金表面获得了纳米组织,并发生显著的加工硬化,表面显微硬度比基体硬度提高了1倍多;随着SFPB处理时间的延长,纳米结构层厚度不断增加,晶粒尺寸逐步细化,当SFPB处理30 min后晶粒尺寸趋于稳定,在表层形成了晶粒尺寸约为20 nm具有随机取向的纳米等轴晶.Ti-6Al-4V合金表面自身纳米化是由于位错运动、孪晶的形成及交割共同作用的结果;在多方向载荷的重复作用下,在塑性变形区产生了大量的由位错线和高密度位错缠结分割的位错胞,并在位错寨集处产生应力集中,进而形成孪晶;孪晶自身相互交割和位错的滑移相互协调,形成了细小的孪晶和胞状组织;晶胞组织转变为细小多边形亚晶;当孪晶尺寸细化到亚纳米级时,位错的滑移起主导作用,最终通过位锗的湮灭和重组形成了具有随机取向的等轴状纳米晶粒.     

Friction Stir Lap Welding of Magnesium Alloy to Steel: A Preliminary Investigation

An initial study was made to evaluate the feasibility of joining magnesium alloy AZ31 sheet to galvanized steel sheet in a lap configuration using friction stir welding (FSW). Two different automotive sheet steels were used for comparative evaluation of the dissimilar joining potential: a 0.8 mm thick, electrogalvanized (EG) mild steel, and a 1.5 mm thick hot-dipped galvanized (HDG) high-strength, low-alloy (HSLA) steel. These steels were joined to 2.33 mm thick AZ31B magnesium sheet. A single FSW tool design was used for both dissimilar welds, and the process parameters were kept the same. The average peak load for the AZ31-1.5 mm steel weld joint in lap shear mode was found to be 6.3 ± 1.0 kN. For the AZ31-0.8 mm steel weld, joint strength was 5.1 ± 1.5 kN. Microstructural investigation indicates melting of the Zn coating present on the steel sheets, and subsequent alloying with the Mg sheet resulted in the formation of a solidified Zn-Mg alloy layer.     

Ti90及其优化合金的组织与力学性能研究

Ti90合金是我国自主研发的一种新型近α型钛合金,具有高比强度、高韧性、耐蚀和加工性能好等优点。本课题组前期对Ti90合金进行了成分优化,得到一种名义成分为Ti-5. 5Al-4. 0Zr-1. 0Sn-0. 3Mo-1. 0Nb的优化合金。利用X射线衍射仪、金相显微镜、电子探针显微分析仪、电子万能试验机和电化学工作站等检测仪器,对Ti90及其优化合金的组织与力学性能进行对比分析。结果表明,优化合金组织为带有网篮特征的魏氏组织,原始β晶界和α集束清晰可见,有少量残留β相分布于α片层之间。与Ti90合金相比,优化合金的压缩屈服强度与断裂韧性得到了显著的提高,极限应变量有所增加,电化学腐蚀性能较好。     

Microstructure and mechanical properties of friction stir welding of AZ31B magnesium alloy added with cerium

The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding(FSW).The microstructures and mechanical properties of the welded joint were investigated.The results showed that the microstructures in the weld nugget zone were uniform and with small equiaxed grains.The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the base metal zone and the weld nugget zone.The ultimate tensile strength of AZ31B magnesium alloy added with 0.5...     

The Effect of Alloying Elements on the Shear Strength of the Lap Joint of AZ31B Magnesium Alloy to Q235 Steel by Hybrid Laser-TIG Welding Technique

Welding between AZ31B Mg alloy and Q235 mild steel was examined in this study. The effects of welding parameters were first investigated on the penetration depth into the steel and the shear strength of the joints. The optimum parameters and the maximum shear strength were obtained. Based on these parameters, alloying elements in the form of interlayers were added into the joints, and the shear strength was improved as high as 98 pct of the AZ31B Mg alloy. Microstructures of the joints were inspected with a scanning electron microscope and an electron probe micro-analyzer. Two bonding modes were proposed, and their effects on the joint shear strength were discussed. It is suggested that the bonding changed from nonmetallurgical to “semimetallurgical” mode with the addition of the interlayers, which contributed to the enhancement of the shear strength. Micro-hardness profiles were measured in the fusion zone of the joints, and their influence on the joint strength was also discussed. Intermediate phases that distributed uniformly in the fusion zone strengthened the microstructures, and thus, the shear strength was elevated. An empirical trend for Cu and Ni interlayer selection was proposed.     

Fracture characteristics of Ti-6Al-4V and Ti-5Al-2.5Fe with refined microstructure using hydrogen

The hydrogenation behavior of Ti-6Al-4V, with the starting microstructures of coarse equiaxed α and coarse Widmanstätten α, respectively, was investigated under a hydrogen pressure of 0.1 MPa at temperatures between 843 and 1123 K. The hydrogen content was determined as a function of hydrogenation time, hydrogenation temperature, and hydrogen flow rate. The phases presented in the alloy of after hydrogenation were determined with X-ray and electron diffraction analysis in order to define the effect of Thermochemical Processing (TCP) on the microstructure of the alloy. Mechanical properties and fracture toughness of Ti-6Al-4V and Ti-5Al-2.5Fe subjected to the various TCP were then investigated. Hydrogenation of Ti-6Al-4V with the starting microstructure of coarse equiaxed α at 1023 K, just below hydrogen saturated β (denoted β″ (H)) transus temperature, produces a microstructure of a, orthohombic martensite (denoted α″ (H)) and β (H). Hydrogenation at 1123 K, above β (H) transus, results in a microstructure of α″ (H) and β (H). Microstructure refinement during TCP results mainly from decomposition of α″ (H) and ;β (H) into a fine mixture of α + β during dehydrogenation. An alternative TCP method is below β (H) transus hydrogenation (BTH), consisting of hydrogenation of the alloy below the hydrogenated β (H) transus temperature, air cooling to room temperature, and dehydrogenation at a lower temperature, which is found to improve mechanical properties significantly over a conventional TCP treatment. Compared with the untreated material, the BTH treatment increases the yield strength and increases the ultimate tensile strength significantly without decreasing the tensile elongation in the starting microstructure of coarse equiaxed α or with a little decrease in the tensile elongation in the starting microstructure of coarse Widmanstätten α, although the conventional TCP treatment results in a large decrease in elongation over the unprocessed material in Ti-6Al-4V. In Ti-5Al-2.5 Fe, both conventional TCP and BTH result in a increase in yield strength, ultimate tensile strength, and elongation; however, the BTH gives the best balance between strength and elongation. The TCP-treated Ti-6Al-4V shows smaller fracture toughness compared with the unprocessed material, while TCP-treated Ti-5Al-2.5Fe shows greater fracture toughness compared with the unprocessed material. The BTH treatment results in a improvement in fatigue strength in both Ti-6Al-4V and Ti-5Al-2.5Fe.     

Ti-5553合金车削加工性能研究

Ti-5553(Ti-5Al-5V-5Mo-3Cr-0.5Fe)合金具有优异的综合力学性能,正逐步替代TC4(Ti-6Al-4V)钛合金成为高强度航空用工件的制备材料。然而,由于Ti-5553合金机械加工效率低,一定程度上制约了其在航空领域的大规模应用。为此,对Ti-5553合金与TC4钛合金的车削加工性能参数进行了探索,发现在相同的切削速度下,Ti-5553合金的主切削力和吃刀抗力均高于TC4钛合金,且最高切削速度仅为50 m/min。此外,两种合金在切削过程中均会与车刀发生扩散反应,而Ti-5553合金对刀具的磨损更为严重。相信本研究将为后期优化Ti-5553合金的车削加工参数、提高其加工效率提供有利的实验数据支持。     

Ti-6A14V合金表面改性技术

Ti-6Al4V合金作为一种重要的钛合金,其使用量占到了钛合金总使用量的75％～85％,但其耐磨性差、阻燃性差、疏水疏冰性能差、生物相容性不理想等性能缺陷在一定程度上限制了其在某些领域中的应用。首先对Ti-6Al4V合金在各个领域应用时,其性能缺陷的表现形式及危害进行了概述,然后介绍了目前改善Ti-6Al4V合金性能缺陷所普遍采用的以及具有创新性的表面改性技术,评述了部分表面改性技术的优缺点,最后提出了需对Ti-6Al4V合金表面改性技术进一步研究的方向。     

Mechanical Properties of Gradient Structure Mg Alloy

In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.     

Involvement of tachykinins in endotoxin-induced airway hyperresponsiveness

Three new titanium alloys with Zr, Nb, Ta, Pd and In as alloying elements were developed and compared with currently used implant metals, namely, pure Ti and Ti-6Al-4V alloy, in terms of mechanical and corrosion properties, and cytotoxicity. New alloys showed comparable mechanical properties with that of the Ti-6Al-4V alloy, but increased corrosion potential, somewhat decreased breakdown potential and increased corrosion rate. There were no significant differences in cell growth on the surface of the various metal specimens, indicating that the cells cannot differentiate between the passivated surfaces of the various Ti metals.     

Roll bonding behaviour of Ti-6Al-4V sheets during pack rolling

Low density, excellent corrosion resistance, moderate strengths at high temperatures make titanium based alloys candidate materials for advanced aerospace structures. Advanced joining techniques are emulating for fabrication of complex aerospace structures. Roll bonding is one such solid state joining technique where bonding between two rough and clean surfaces is obtained under high temperature and pressure. The work horse dual phase titanium alloy Ti-6Al-4V finds extensive structural application in aerospace and space industries. In the present study, two Ti-6Al-4V sheets are stacked together and encapsulated in a mild steel can followed by evacuation and hot crimping. The pack is extensively deformed to ∼84% reduction in thickness employing conventional hot rolling mill. Partially roll bonded 0.74mm thick sheets were obtained and microstructural evolution was studied using light microscopy and scanning electron microscopy. The incompletely bonded interface was analyzed through elemental mappings by Electron Probe Micro Analyzer and compared with completely bonded region. The partially bonded region revealed the presence of aluminium oxide at the interface which possibly could have hindered complete bonding at that region. The room temperature tensile properties of as- roll bonded Ti-6Al-4V nearly approaches the base material properties.     

On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic Rutile

Mechanical property data of a low-cost titanium alloy derived directly from synthetic rutile is reported. A small-scale testing approach comprising consolidation via field-assisted sintering technology, followed by axisymmetric compression testing, has been designed to yield mechanical property data from small quantities of titanium alloy powder. To validate this approach and provide a benchmark, Ti-6Al-4V powder has been processed using the same methodology and compared with material property data generated from thermo-physical simulation software. Compressive yield strength and strain to failure of the synthetic rutile-derived titanium alloy were revealed to be similar to that of Ti-6Al-4V.     

Fracture characteristics,microstructure, and tissue reaction of Ti-5Al-2.5Fe for orthopedic surgery

The microstructure of Ti-5Al-2.5Fe, which is expected to be used widely as an implant material not only for artificial hip joints but also for instrumentations of scoliosis surgery, was variously changed by heat treatments. The effect of the microstructure on mechanical properties, fracture toughness, and rotating-bending fatigue strength in the air and simulated body environment, that is, Ringer’s solution, was then investigated. Furthermore, the effect of the living body environment on mechanical properties and fracture toughness in Ti-5Al-2.5Fe were investigated on the specimens implanted into rabbit for about 11 months. The data of Ti-5Al-2.5Fe were compared with those of Ti-6Al-4V ELI, which has been used as an implant material mainly for artificial hip joints, and SUS 316L, which has been used as an implant material for many parts, including the instrumentation of scoliosis surgery. The equiaxedα structure, which is formed by annealing at a temperature belowβ transus, gives the best balance of strength and ductility in Ti-5Al-2.5Fe. The coarse Widmanstättenα structure, which is formed by solutionizing overβ transus followed by air cooling and aging, gives the greatest fracture toughness in Ti-5Al-2.5Fe. This trend is similar to that reported in Ti-6Al-4V ELI. The rotating-bending fatigue strength is the greatest in the equiaxedα structure, which is formed by solutionizing belowβ transus followed by air cooling and aging in Ti-5Al-2.5Fe. Ti-5Al-2.5Fe exhibits much greater rotating-bending fatigue strength compared with SUS 316L, and equivalent rotating-bending fatigue strength to that of Ti-6Al-4V ELI in both the air and simulated body environments. The rotating-bending fatigue strength of SUS 316L is degraded in the simulated body environment. The corrosion fatigue, therefore, occurs in SUS 316L in the simulated body environment. Fatigue strength of Ti-5Al-2.5Fe in the simulated body environment is degraded by lowering oxygen content in the simulated body environment because the formability of oxide on the specimen surface is considered to be lowered comparing with that in air. The mechanical property and fracture toughness of Ti-5Al-2.5Fe and Ti-6Al-4V ELI are not changed in the living body environment. The hard-surface corrosion layer is, however, formed on the surface of SUS 316L in the living body environment. The C1 peak is detected from the hard-surface corrosion layer by energy-dispersive X-ray (EDX) analysis. These facts suggests a possibility for corrosion fatigue to occur in the living body environment when SUS 316L is used. The fibrous connective tissue and new bone formation are formed beside all metals. There is, however, no big difference between tissue morphology around each implant material.