机械合金化制备纳米晶Ti-6Al-4V合金

采用机械合金化制备Ti-6Al-4V粉末。结果表明:采用机械合金化可以制备纳米晶Ti-6Al-4V合金粉,其反应机理以扩散为主,该固态反应是缺陷能和碰撞能共同作用的结果;随球磨时间延长,部分V固溶于Ti中形成置换固溶体Ti(V),球磨过程中没有中间相生成。球磨40 h后都能获得纳米晶,60 h的粉末为纳米晶和非晶的混合物,晶粒尺寸小于60 nm;60 h后晶粒尺寸变化缓慢。球磨后Ti、Al、V的原子比近似为90:6:4,与Ti-6Al-4V元素成分一致。     

Laser Powder Deposition Parametric Optimization and Property Development for Ti-6Al-4V Alloy

In this study, Ti6Al4V alloy was produced via laser powder deposition (LPD). To obtain Ti6Al4V alloy with maximum density, LPD parameters for preparing Ti6Al4V samples were optimized using the Taguchi method. Results were analyzed on the basis of the signal-to-noise (S/N) ratios and analyses of variance. A high energy density should be used to achieve higher levels of densification. The optimal combination of parameters for density was a scanning speed of 550 mm/min, laser power of 160 W, powder feeding rate of 0.99 g/min, and shield gas flow of 8 L/min. An almost fully dense Ti6Al4V sample was prepared using the optimized LPD process, and the relative density was greater than 99%. In addition, the microstructure and properties of Ti6Al4V samples prepared by optimized LPD process were investigated. The microstructure investigation revealed that the LPD-prepared Ti6Al4V sample was predominantly composed of fine acicular α phase and lath-type α phase. Tensile and microhardness tests indicated that the LPD sample had higher mechanical properties than the traditional cast Ti6Al4V alloy because of the acicular martensitic phase and smaller grain size.     

Oxygen effects on the mechanical properties and lattice strain of Ti and Ti-6Al-4V

The effects of oxygen on the mechanical properties and the lattice strain of commercial pure CP) Ti and Ti-6Al-4V alloys are discussed here in terms of the Vickers hardness, tensile strength and elongation. The Vickers hardness and tensile strength of the CP Ti and the Ti-6Al-4V alloys increased with an increase in the oxygen concentration. On the other hand, the elongation of the CP Ti decreased considerably as the oxygen concentration increased, while that of the Ti-6Al-4V alloys gradually decreased as the oxygen concentration increased. Thus, the oxygen concentration has a greater effect on the mechanical properties of CP Ti compared to its effects on the Ti-6Al-4V alloy. This can be explained in terms of the difference in the solid solution effect of oxygen between the CP Ti and the Ti-6Al-4V alloy. Where, the mechanical properties of Ti-6Al-4V alloy were previously affected by an earlier lattice expansion caused by an increment in the c/a ratio of the Ti-6Al-4V during the Al and V alloying process.     

粉末冶金Nb-35Ti-6Al-5Cr-8V合金组织演变及其力学行为

采用粉末冶金法对不同球磨时间的Nb-35Ti-6Al-5Cr-8V合金机械合金化粉末塑变行为,热压烧结材料的微观组织结构和力学行为进行了研究。研究结果表明：塑性良好的Nb-35Ti-6Al-5Cr-8V粉末随着球磨时间增加首先变形为大尺寸的片状、后经持续的加工硬化破碎成絮状;热压烧结能够制备微观组织可控晶粒细化的Nb-35Ti-6Al-5Cr-8V合金,合金由单一的Nbss相构成,Ti、Al、Cr、V元素固溶引起Nb晶格尺寸减小0.0685 ?;随着球磨时间增加合金晶粒明显细化进而显著提高了合金的维氏硬度和室温压缩强度,其变化符合材料硬度和强度的Hall-Petch规律。粉末冶金制备Nb-35Ti-6Al-5Cr-8V合金的各项力学性能明显优于熔铸法制备合金。     

The thermomechanical processing of titanium and Ti-6Al-4V thin gage sheet and plate

A new method for producing low-cost titanium powder, the Armstrong Process, has proven to be a scalable process. The process, which reduces TiCl₄ vapor in a molten stream of sodium to produce pure titanium and NaCl, can also be used to in-situ manufacture Ti-6Al-4V alloy powder. Armstrong Process titanium and Ti-6Al-4V powders were used to produce plate by vacuum hot pressing. Also, thin gage sheet was produced by cold rolling solid-phase sintered titanium and Ti-6Al-4V powder compacts. Chemical analysis and mechanical testing revealed that processed Armstrong titanium and Ti-6Al-4V sheet and plate had compositions and properties similar to those of grade 2 titanium and grade 5 Ti-6Al-4V. For more information, contact John D.K. Rivard, Strategic Analysis, 3811 N. Fairfax Drive Suite 700, Arlington VA 22202; e-mail jrivard@sainc.com.     

低成本高性能粉末冶金钛合金

粉末冶金是短流程制备低成本、高性能钛及钛合金的有效方法。低成本氢化脱氢（HDH）钛粉可用于制备粉末冶金钛合金制件,但由于受间隙原子含量高、烧结致密度低和微观组织粗大等因素影响,使粉末冶金钛制品的组织性能优势得不到发挥。实验采用氢化脱氢钛粉—冷等静压—真空烧结的技术路线制备了Ti-6Al-4V烧结坯,间隙原子含量低（O<0.16 wt.%, N<0.05 wt.%, H<0.015 wt.%）,具有均匀细小的近等轴?组织,良好的室温拉伸性能（UTS>930 MPa, YS>870 MPa, El>14%）。实验同时表明了HDH工艺制备低间隙原子含量钛粉的可行性,间隙原子含量的增加主要源于粉末及压坯的操作、转移和储存过程。得益于粉末冶金钛合金的细晶和近终成形特点,它无需通过开坯锻造,并且近成型的烧结坯能够提高材料利用率,减少后续热加工变形量及加工道次。因此,以粉末钛合金烧结坯替代锻坯进行后续的塑性加工能够大幅度降低钛合金构件及型材的成本。     

Effect of high-energy electro-pulses on the compression deformation behavior of Ti-6Al-4V alloy

Compression tests of Ti–6Al–4V alloy were conducted using an electron universal testing machine with discharge voltages that range from 50 V to 70 V and strain rate of 0.01 s^?1. Isothermal compression at equivalent temperatures was also performed on a universal testing machine with furnace, with the same strain rate. Results show that the deformability of Ti–6Al–4V alloy can be significantly improved by high-energy electro-pulses, and the deformation resistance and yield stress were also decreased. Moreover, the effect of high-energy electropulses on compression mechanical properties of Ti–6Al–4V alloy increased with increasing discharge voltage. However, elongation and deformation resistance of compressions with high-energy electro-pulses were higher than isothermal compressions at equivalent temperatures. This result proved that the deformability improvement of Ti–6Al–4V alloy by high-energy electro-pulses results from the joint effects of temperature and electro-plasticity. Fracture modes in different experimental conditions were analyzed by observing the fracture morphologies of specimens by using a scanning electron microscope. Under high-energy electro-pulses, the micro morphology of compression fracture changes from elongated oval to equiaxed dimples, and the fracture modes transfer from intergranular to transgranular fracture.     

Design and characterization of selective laser-melted Ti6Al4V–5Cu alloy for dental implants

Ti6Al4V–5Cu alloys have potential biomedical applications due to their adequate antibacterial properties. However, the wear and corrosion properties of these alloys are also crucial for dental implants. In the present study, Ti6Al4V–5Cu alloys were fabricated by selective laser melting (SLM). The microstructure and composition of Ti6Al4V–5Cu alloys by SLM were evaluated. The wear properties of the alloys in the simulated saliva environment and the atmospheric environment, as well as the electrochemical properties in the simulated saliva environment, were systematically investigated. The results showed that the crystal structure of Ti6Al4V–5Cu alloys was mainly composed of α-Ti and Ti₂Cu. In the SLM process, no preferred texture was observed due to the complex direction of the heat flux. The formation of Ti₂Cu can improve the strength of the material and make the titanium copper alloy have higher microhardness. Ti6Al4V–5Cu alloy showed a satisfactory wear resistance in both wear media. The addition of Cu reduced the second-phase content of the alloy. Meanwhile, the number of microcells was reduced, which was a positive factor to improve the corrosion resistance of the alloys.     

Structure and properties of the metal of rods and stamped preforms for blades of VT6 alloy

In Russia functional blades of low-pressure cylinders (LPC) are produced from single-phase titanium alloys. These blades do not meet the strict requirements currently imposed on their material because the length of the blades has increased. In foreign countries such blades are preferentially produced from a biphase Ti - 6% Al - 4% V alloy. This alloy possesses high adaptability to manufacturing and a good combination of mechanical properties and corrosion resistance. A domestic counterpart of the Ti - 6% Al - 4% V alloy is VT6. The present article is devoted to the possibility of its use for functional blades of LPC.     

Dynamic stress–strain properties of Ti–Al–V titanium alloys with various element contents

A series of Ti–Al–V titanium alloy bars with nominal composition Ti–7Al–5V ELI,Ti–5Al–3V ELI,commercial Ti–6Al–4V ELI and commercial Ti–6Al–4V were prepared.These alloys were then heat treated to obtain bimodal or equiaxed microstructures with various contents of primary a phase.Dynamic compression properties of the alloys above were studied by split Hopkinson pressure bar system at strain rates from 2,000 to 4,000 s-1.The results show that Ti–6Al–4V alloy with equiaxed primary a(ap)volume fraction of 45 vol%or 67 vol%exhibits good dynamic properties with high dynamic strength and absorbed energy,as well as an acceptable dynamic plasticity.However,all the Ti53ELI specimens and Ti64ELI specimens with ap of 65 vol%were not fractured at a strain rate of4,000 s-1.It appears that the undamaged specimens still have load-bearing capability.Dynamic strength of Ti–Al–V alloy can be improved as the contents of elements Al,V,Fe,and O increase,while dynamic strain is not sensitive to the composition in the appropriate range.The effects of primary alpha volume fraction on the dynamic properties are dependent on the compositions of Ti–Al–V alloys.     

YbB6 对Ti-6Al-4V钛合金组织和性能的影响

采用放电等离子烧结（SPS）制备了含YbB₆的Ti-6Al-4V钛合金,并研究了YbB₆对Ti-6Al-4V钛合金显微组织和力学性能的影响。结果表明,随着YbB₆含量的增加,复合材料的显微组织发生转变,晶粒明显细化,原位反应生成的TiB晶须和Yb₂O₃颗粒有利于复合材料力学性能的提高。此外,当添加0.6%（质量分数）YbB₆后,烧结样品的相对密度、显微硬度、屈服强度、极限拉伸强度和延伸率分别为99.43%、4030 MPa、903 MPa、1148 MPa和3.3%。与Ti-6Al-4V试样相比,其数值分别提高了0.37%、13.8%、38.07%和17.14%。强化机制主要是组织转变、晶粒细化和弥散强化。随着YbB₆含量的增加,断裂方式主要为韧性断裂和脆性断裂。     

Tensile properties of gas tungsten arc weldments in commercially pure titanium,Ti–6Al–4V and Ti–15V–3Al–3Sn–3Cr alloys at different strain rates

Abstract

The influence of microstructure and strain rate on the mechanical behaviour of three titanium alloys having applications in aerospace, namely, commercially pure titanium (α phase), Ti–6Al–4V (α + β phases) and Ti– 15V–3Cr–3Sn–3Al (β phase) is investigated for both the parent metals and their gas tungsten arc weldments. The results indicate that the tensile strengths of the three as received titanium alloys and their weldments increase with increasing strain rate. However, their elongations decrease with increasing strain rate. The as received Ti–6Al–4V alloy and its weldment, with a mixed α and β phase microstructure, have the maximum strength and microhardness. Commercial purity titanium metal and its weldment exhibit the minimum strength and microhardness. The tough Ti–15V–3Cr–3Sn–3Al alloy and its weldment, having a fully β phase microstructure, appear to have optimum strength and microhardness. The tensile properties of all three titanium alloy weldments are inferior to those of the as received metals.     

Rolling of Plates and Sheets from As-Cast Ti-6Al-4V-0.1B

Trace boron addition (~0.1 wt.%) to conventional titanium alloys reduces the as-cast prior-beta grain size by an order of magnitude to about 200 μm, a grain size typically observed after ingot breakdown. In this study, the feasibility of producing plate and sheet by hot rolling of as-cast Ti-6Al-4V-0.1B (wt.%) was evaluated. Starting from an initial thickness of 25 mm, as-cast Ti-6Al-4V-0.1B was successfully rolled to 2 mm sheet in a multistep rolling process. As-cast Ti-6Al-4V (without boron addition) rolled under similar conditions exhibited severe cracking. Tensile properties of the sheets and plates made from the boron-containing alloy met or exceeded AMS 4911 specifications for Ti-6Al-4V plates and sheets produced by conventional processing route. The process of making plate and sheet stock from cast titanium alloy ingots, without recourse to expensive ingot breakdown, can significantly reduce the number of expensive and time-consuming processing steps for making titanium alloy components, thereby enhancing the affordability and expanding the range of titanium applications.     

Microstructures and mechanical properties of Ti–Al–V–Nb alloys with cluster formula manufactured by laser additive manufacturing

Ti–Al–V–Nb alloys with the cluster formula, 12[Al–Ti₁₂](AlTi₂)+5[Al–Ti₁₄](V,Nb)₂Ti, were designed by replacing V with Nb based on the Ti–6Al–4V alloy. Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.% were prepared by laser additive manufacturing to examine their formability, microstructure, and mechanical properties. For single-track cladding layers, the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability. The alloy, Ti–5.96Al–1.94V– 3.54Nb (wt.%), exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder. The microstructures of the bulk samples contained similar columnar β-phase grains, regardless of Nb content. These grains grew epitaxially from the Ti substrate along the deposition direction, with basket-weave α-phase laths within the columnar grains. The α-phase size increased with increasing Nb contents, but its uniformity decreased. Along the deposition direction, the Vickers hardness increased from the substrate to the surface. The Ti–5.96Al–1.94V–3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between the α-phase size and its content among the designed alloys.     

Boride coatings obtained by pack cementation deposited on powder metallurgy and wrought Ti and Ti-6Al-4V

Wear resistance of Ti alloys needs to be improved, and an effective way to achieve this is through surface treatment. Boronizing is a surface treatment in which boron diffuses into the surface of Ti leading to the formation of hard and wear-resistant Ti borides. Boronizing of wrought and/or cast Ti alloys by pack cementation has been studied, while similar coatings on Ti alloys produced by powder metallurgy (PM) have not been reported. Also critical process parameters for boronizing Ti alloys, such as pack cementation powder composition and the process temperature have not been systematically studied and analysed. The present work reports on the surface modification of PM Ti and PM Ti-6Al-4V by boronizing, and presents some important thermodynamic aspects of the process comparing it with similar coatings applied to wrought Ti-6Al-4V. The coatings were characterised using scanning electron microscopy and X-ray diffraction. For both Ti and Ti-6Al-4V alloys the use of amorphous B as a B element supplier in the boriding powder pack led to the formation of a uniform external boride layer, while the use of B₄C as a B element supplier in the pack and under the same boronizing conditions, led to the formation of an external TiN layer and an internal layer containing B. The thermodynamic calculations performed proved successful in determining the appropriate conditions for boride coating deposition and estimating the phases likely to be formed. Finally the effect of surface roughness on the coating quality is discussed.     

离心研磨工艺对Ti-6 Al-4 V钛合金表面组织性能的影响

目的改善Ti-6Al-4V钛合金的组织性能。方法使用离心研磨工艺对Ti-6Al-4V钛合金进行表面处理,通过显微硬度计、X射线应力分析仪、金相显微镜,对不同加工时间下试样表层的显微硬度、残余应力、金相组织进行测试。结果离心研磨加工后,Ti-6Al-4V钛合金表面的显微硬度得到提高,试样最表面的显微硬度随加工时间的延长呈现逐渐增大的趋势,加工时间为40 min时,显微硬度达到最大值385HV,比试样基体硬度值提高了55HV;在加工深度方向上,随着深度的增加,显微硬度值逐渐降低,在深度为400μm附近,显微硬度值已与基体硬度值相差不大,并且基本不再下降。加工完成后,试样表面产生了有益的残余压应力,最大残余压应力值为436 MPa。金相组织分析结果表明,试样表层组织形成了剧烈塑性变形层,其深度约40μm,在变形层内,组织的晶粒得到明显细化。结论离心研磨抛光工艺对Ti-6Al-4V钛合金表面组织性能改善效果明显,验证了使用该工艺对Ti-6Al-4V钛合金进行表面强化的可行性。     

Casting of Iron Aluminides

Iron aluminides form an interesting class of materials which combine excellent corrosion and oxidation resistance with good mechanical properties at moderate to high temperature (up to 500 °C). These materials, however, suffer from low room-temperature ductility (under 5% elongation in tension), which is mostly due to environmental effects. Casting is a processing route traditionally applied to brittle alloys (e.g., gray cast irons), but to cast a part without defects, several thermochemical properties are needed, as well as information on the tendency of the alloy to form foundry defects (e.g., shrinkage voids, pores). The present work aims to provide this information using parts produced on laboratory scale. In particular, the solidification contraction and the efficiency of TiB₂ as inoculant are investigated. Three alloys with nominal composition (in at.%) Fe28Al, Fe28Al6Cr, and Fe28Al6Cr1Ti (about 1.5 kg for each melt) were melted in an induction furnace under argon flux protection using conventional raw materials (carbon steel, commercial aluminum, metallic chromium, and commercial ferrotitanium). The resulting melts were treated by adding Al-TiB₂ master alloy used in the aluminum industry and poured into “staircase” molds, designed to investigate feeding distance effects in complex parts. Characterization of the microstructure of the alloys revealed that alloys Fe28Al and Fe28Al6Cr showed κ-carbide precipitation, while alloy Fe28Al6Cr additionally showed chromium carbides at dendritic boundaries. Addition of 1 wt.% Ti in alloy Fe28Al6Cr1Ti changed the solidification microstructure, refining the dendrite morphology and forming TiC-containing eutectic in interdendritic spaces.     

Machinability of titanium alloys (Ti6Al4V and Ti555.3)

Near-beta titanium alloys like Ti555.3 are increasingly being used in aeronautics replacing in some critical applications the most common Ti6Al4V. However, these near-beta titanium alloys have a poor machinability rating which needs to be overcome so as to maintain at least the same productivity levels as in Ti6Al4V.This paper presents the machinability results carried out for Ti555.3 compared with the commonly used Ti6Al4V. The aim of this research work is to understand tool wear mechanisms when machining Ti555.3. Analysis of variables such as cutting forces, chip geometry and tool wear shows that: (I) greater difficulty is encounterd when machining Ti555.3 alloy compared with Ti6Al4V alloy which can be machined at higher speeds up to 90 m min^?1; (II) there was a correlation between the mechanical properties of work material, tool wear, and component forces; (III) the occurrence of the diffusion process leads to the formation of a layer of adhered material composed of Ti and TiC on the tool's rake face for both Ti alloys.     

Relation Between the Microstructure and Properties of Commercial Titanium Alloys and the Parameters of Gas Nitriding

Titanium alloys are unique materials with an excellent combination of properties. However, their applications are limited due to low surface hardness. In the present work gas nitriding is performed with the aim of improving the surface properties of commercial titanium alloys. Four widely used titanium alloys, namely, Ti – 6% Al – 4% V, Ti – 6% Al – 2% Sn – 4% Zr – 2% Mo, Ti – 8% Al – 1% Mo – 1% V, and Ti – 10% V – 3% Fe – 3% Al, are studied. The process is performed in a nitrogen atmosphere at 950 and 1050°C for 1, 3, and 5 h. The resulting surface hardness exceeds the normal value for titanium alloys by a factor of 3 – 5 due to the change in the phase composition of the surface layer, yielding a solid solution of nitrogen in an α-Ti phase, a TiN nitride, and TiO₂ dioxide. The influence of the parameters of the treatment process and the chemical composition of the alloys on the phase composition, microstructure, microhardness, and thickness of the surface layer is analyzed. It is shown that nitriding of alloys with α- and (α + β)-structures at 1050°C yields surface layers with inhomogeneous composition and irregular thickness, whereas after nitriding at 950°C the surface layers are homogeneous and have high properties. Practical recommendations are given for choosing nitriding parameters for different alloys and variants of application are discussed.     

Mechanical properties and deformation behavior of Ti-5Al-2.5ZrELI alloy used at cryogenic temperature

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