The microstructure and properties of ultra-fine grained Ti-17 powder compact improved through isothermal forging

The microstructure and properties of hot isostatic pressed (HIP-ed) Ti-17 powder compact were improved through isothermal forging with preferable deformation parameters provided by processing map. The processing map was established based on isothermal compression experiments which were conducted at temperatures from 810 °C to 920 °C and strain rates from 0.001 s^?1 to 1 s^?1. The established processing map ascertained the value of the efficiency of power dissipation, the flow stability region and the flow instability region at different deformation conditions. Based on processing map, the isothermal forging was conducted above and below beta transus temperature to fully densify the powder compact and simultaneously improve the microstructure. After isothermal forging in flow stability regions with preferable deformation parameters, the primary coarse grains of HIP-ed Ti-17 powder compact were thoroughly broken. Many ultra-fine dynamic recrystallized grains formed and uniformly distributed in beta matrix. Both experiment data and fracture morphology of tensile sample proved that the microstructure and properties of HIP-ed Ti-17 powder compact were largely improved during isothermal forging. Final properties of prepared ultra-fine grained Ti-17 powder compact even exceeded conventional casting and forging Ti-17 alloy.     

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。     

淬火转移时间对Ti-1023合金组织与力学性能的影响

通过室温拉伸性能测试、断口分析和显微组织分析,研究了淬火转移时间对Ti-1023合金组织演变和力学性能的影响规律和机理。结果表明,随淬火转移时间的增加,淬火转移过程中过饱和β相中析出α相,导致等轴α相含量增加,过饱和β相基体的相对含量降低,时效析出的次生α_s相含量和弥散程度下降,致使合金强度降低、塑性提高。对于厚80 mm的Ti-1023合金板材或锻件,将淬火转移时间控制在120 s之内,合金组织性能不会受到明显的影响。     

Microstructures and mechanical properties of biocompatible Ti-42 wt.%Nb P/M alloy

Ti-42 wt. %Nb powder was prepared by high-energy mechanical milling (HEMM). The particle size distribution (PSD) of the as-milled powder has been investigated using a particle size distribution analyzer. The morphology and microstructure of the as-milled powder have been investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and differential thermal analysis (DTA). Also, the corrosion property and biocompatibility of sintered specimens comprising mixed and milled powders have been investigated. The milled powders were sintered using pulse current activated sintering (PCAS). PCAS was employed in order to provide more refined grain size and full density to Ti-42 %Nb alloy on the basis of short sintering time with pressure. The density of the sintered Ti-42 %Nb specimen fabricated using the milled powder increased with increased milling time due to high free surface area and defect density. The density of the sintered Ti-42 %Nb specimen fabricated using as-mixed powder increased with increased sintering temperature up to 950 °C. The microstructure of the sintered Ti-42 %Nb specimen fabricated using 4h-milled powder was composed of Nb-rich and Nb-poor phases that are more refined and homogeneously distributed. The mechanical properties and biocompatibility of the sintered Ti-42 %Nb specimen fabricated using milled powder were superior to those of a commercial, Ti-6wt.%Al-4wt.%V alloy.     

Ti-6Al-4V合金汽轮机动叶片的热处理工艺

针对Ti-6Al-4V合金汽轮机动叶片出现的组织异常,研究了两种热处理工艺对Ti-6Al-4V合金组织与性能的影响,并对锻造加热温度对该材料显微组织的影响进行了探讨。研究结果表明,Ti-6Al-4V合金汽轮机动叶片的组织异常是由于锻造加热温度过高或加热时间过长引起的,Ti-6Al-4V合金锻后采用固溶+时效或直接时效的热处理的方案都能满足产品毛坯性能要求,且锻后直接时效性能更优异。     

Effect of particle size and manufacturing technique on the properties of the PM Ti-5Fe alloy

In this study the low-cost Ti-5Fe alloy was fabricated by means of the press and sinter powder metallurgy route considering two particle sizes and alternative processing techniques. The primary aim is to reduce the high costs associated with the production of Ti alloys. Thermomechanical processing by means of forging in the β region was also analysed aiming to enhance the mechanical behaviour. The effect of the processing conditions and of the particle size on the microstructure and the mechanical properties was thus investigated. It has been found that the use of larger Fe particles leads to the formation of larger pores due to the dissolution of the Fe powder particles. Consequently, lower mechanical behaviour, tensile properties and Vickers hardness, resulted due to the presence of larger pores. Refinement of the microstructure, texturing, and sealing of the porosity due to forging permits to enhance the mechanical properties with respect to the sintered Ti-5Fe alloy.     

粉末冶金Ti-Al-Mo-V-Ag合金的显微组织与力学性能

通过粉末冶金元素混合法,制备含α及β相的Ti-Al-Mo-V-Ag合金。通过X射线衍射、金相观察、扫描电镜观察及力学性能测试,研究Ag的添加及烧结温度对Ti-5Al-4Mo-4V合金的组织与性能影响。结果表明：Ag的添加能提高粉末冶金Ti-5Al-4Mo-4V合金的的相对密度,改善合金的力学性能;在1250℃下烧结4h后,Ti-5Al-4Mo-4V-5Ag合金的相对密度及抗压缩强度分别达到96.3%和1656MPa。     

Enhanced Homogenization of Vanadium in Spark Plasma Sintering of Ti-10V-2Fe-3Al Alloy from Titanium and V-Fe-Al Master Alloy Powder Blends

Strong and ductile powder metallurgy (PM) Ti-10V-2Fe-3Al alloy has been fabricated by spark plasma sintering (SPS) of titanium and V-Fe-Al master alloy powder blends at 1100°C for 30 min under 30 MPa. The homogenization of vanadium, which dictates the realization of a uniform microstructure of the Ti-10V-2Fe-3Al alloy, was markedly accelerated by SPS. The mechanism is attributed to the intensive Joule heating effect produced by the direct current passing through the electric conducting powder blends, rather than through spark plasma discharge, because homogenization occurred mainly after near full identification had been achieved. The chemical and microstructural homogeneity ensured the achievement of excellent tensile properties of PM Ti-10V-2Fe-3Al in the as-sintered state, with tensile strength >1250 MPa and elongation >10%.     

Microstructural banding in thermally and mechanically processed titanium 6242

Ti-6Al-2Sn-4Zr-2Mo-0.1Si coupons were shaped by repeated cycles of heating (to 954 °) and hammer or press forging followed by a solution anneal that varied from 968 to 998 °. The coupons were originally extracted from billets forged below the beta transus (1009 °) and slow cooled to ambient temperatures. Macroscopic and microstructural banding is observed in some forged and solution annealed coupons. The microstructure consists of elongated “platelets” of primary alpha. More significant banding is observed subsequent to annealing at lower temperatures (968 °), whereas subsequent to higher annealing temperatures (998 °) much less microstructural banding is present. About the same level of banding is observed in hammer forged coupons and press forged coupons. The observation of these bands is significant, because these may lead to inhomogeneous mechanical properties. Specifically, some types of banding are reported to affect the high-temperature creep properties of this alloy. Classically, banding in Ti6242-0.1Si has been regarded as a result of adiabatic shear, chill zone formation, or compositional in homogeneity. High- and low-magnification metallography, electron microprobe analysis, and micro-hardness tests were performed on forged and annealed specimens in this investigation. The bands of this study appear to originate from the microstructure that consists of the forged billet of elongated primary alpha. The deformation of the extracted coupon is neither fully homogeneous nor sufficiently substantial, and the coupon is only partly statically restored after a solution anneal. Areas not fully restored appear as “bands” with elongated primary alpha that are remnant of the starting billet microstructure. Therefore, a source of banding in Ti- 6242- O.1Si alloy additional to the classic sources is evident. This type of banding is likely removed by relatively high solution treatment temperatures and perhaps greater plastic deformation during forging.     

双步球磨与放电等离子烧结制备细晶TiAl合金

采用双步球磨法和放电等离子烧结(SPS)技术制备细晶Ti-47Al(at%)合金,利用扫描电子显微镜(SEM)、X射线衍射(XRD)仪以及透射电子显微镜(TEM)等分析测试手段对球磨后的粉末形貌结构、相组成以及烧结块体的显微组织结构进行观察和分析。结果表明:双步球磨粉末的颗粒形状较规则,其颗粒尺寸在20~40μm之间,内部结构均匀,主要由TiAl和Ti3Al相组成。放电等离子烧结后的块体主要由主相TiAl和少量的Ti3Al相及Ti2Al相组成,随着烧结温度的升高,Ti3Al相含量有所增加。当烧结温度为1000℃时,烧结块体获得的主要是等轴晶组织,等轴晶粒尺寸大多数在100~250nm之间。当烧结温度为1100℃时,烧结块体致密、无孔洞,等轴晶粒有明显长大的现象,显微组织主要由等轴状的TiAl相和片层状的Ti3Al相组成。     

Evaluation of microstructure and phase relations in a powder processed Ti-44AI-12Nb alloy

Titanium aluminides based on the ordered face-centered tetragonal γTiAI phase possess attractive properties, such as low density, high melting point, good elevated temperature strength, modulus retention, and oxidation resistance, making these alloys potential high-temperature structural materials. These alloys can be processed by both ingot metallurgy and powder metallurgy routes. In the present study, three variations of the powder metallurgy route were studied to process a Ti-44Al-12Nb (at. %) alloy: (a) cold pressing followed by reaction sintering (CPprocess); (b) cold pressing, vacuum hot pressing, and then sintering (HP process); and (c) arc melting, hydride-dehydride process to make the alloy powder, cold isostatic pressing, and then sintering (AM process). Microstructural and phase relations were studied by x-ray diffraction (XRD) analysis, optical microscopy, scanning electron microscopy with an energy-dispersive spectrometer (SEM-EDS), and electron probe microanalysis (EPMA). The phases identified were Ti₃AI and TiAl; an additional Nb₂AI phase was observed in the HPsample. The microstructures of CPand HP processed samples are porous and chemically inhomogeneous whereas the AM processed sample revealed fine equiaxed microstructure. This refinement of the microstructure is attributed to the fine, homogeneous powder produced by the hydride-dehydride process and the high compaction pressures.     

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。     

热处理对含有β相锻造钛铝合金组织和性能的影响(英文)

采用包套锻造技术成功制备Ti-45Al-5.4V-3.6Nb-0.3Y合金锻饼,并研究热处理对该合金锻饼组织和性能的影响。通过热处理得到3种不同的组织形态,分别为双态、近层片、和全层片组织,分析热处理过程中合金组织的演变规律,并对不同组织形态的合金进行力学性能测试。结果发现,双态组织的合金具有最好的室温塑性,其值可达1.35%,近层片组织的合金具有较高的室温强度,屈服强度为605.31MPa,断裂强度为665.75MPa。     

烧结温度对快速凝固TiAl合金组织及力学性能的影响(英文)

将快速凝固Ti-46Al-2Cr-4Nb-0.3Y(摩尔分数,%)合金薄带破碎成粉末,然后通过等离子烧结(SPS)制备成块体。研究烧结温度对烧结块体的组织和力学性能的影响。在1200℃烧结时得到完全致密的块体。进一步升高烧结温度对合金密度的影响不大,但是对烧结块体的显微组织及相结构有显著影响。烧结块体主要由γ和α2相组成,随着烧结温度的升高,α2相的体积分数降低,块体合金由近γ组织演变为近层片组织,且组织逐渐粗化,但是长大不明显。1260℃烧结得到的块体组织细小、均匀,没有明显微偏析,具有良好的综合力学性能,室温压缩断裂强度和压缩率分别为2984MPa和41.5%,高温(800℃)拉伸断裂强度和伸长率分别为527.5MPa和5.9%。     

Deformation behavior of isothermally forged Ti–5Al–2Sn–2Zr–4Mo–4Cr powder compact

The isothermal deformation behavior of hot isostatic pressed (HIPed) Ti–5Al–2Sn–2Zr–4Mo–4Cr(Ti-17) powder compact was investigated by compression testing in the temperature range of 810–920 °C and constant strain rate range of 0.001–1 s^?1. The true stress–true strain curves of the powder compact exhibit flow oscillation and flow softening phenomenon in both beta field and beta + alpha field. The flow softening behavior is related to the globularization of the primary acicular microstructure and deformation heating. The apparent activation energy for deformation in beta field is estimated to be 149 kJ mol^?1, indicating that the deformation is controlled by diffusion. The high apparent activation energy of 537 kJ mol^?1 for deformation in beta + alpha field may be related to the dynamic recrystallization of the primary acicular microstructure. Constitutive equations with the form of Arrhenius-type hyperbolic-sine relationship are proposed to delineate the peak flow stress as a function of the strain rate and the temperature for isothermal forging HIPed Ti-17 powder compact.     

Effect of Heat Treatment on Microstructure and Properties of as-Forged TiAl Alloy with β Phase

采用包套锻造技术成功制备Ti-45Al-5.4V-3.6Nb-0.3Y合金锻饼,并研究热处理对该合金锻饼组织和性能的影响。通过热处理得到3种不同的组织形态,分别为双态、近层片、和全层片组织,分析热处理过程中合金组织的演变规律,并对不同组织形态的合金进行力学性能测试。结果发现,双态组织的合金具有最好的室温塑性,其值可达1.35%,近层片组织的合金具有较高的室温强度,屈服强度为605.31MPa,断裂强度为665.75MPa。     

Low cost synthesis and property evaluation of P/M Ti alloys and ti-based particulate composites

Ti-6A1-4V alloy and Ti-6Al-2Sn-4Zr-2Mo/10TiB particulate composites were synthesized using a hlended elemental powder metallurgy processing route. Microstructures and mechanical properties, such as tensile, creep, Young’s modulus and high-cycle fatigue-strength were evaluated. Special attention was paid to improve the high-cycle fatigue-strength of these two materials by modifying the matrix microstructure or process innovation. The fatiguecrackinitiation mechanism, relationship between α-phase morphology and high-cycle fatigue-strength, and other factors contributing to the increase in fatigue strength were analyzed.     

Effects of processing parameters in P/M steel forging on part properties: A review part II forging of sintered compact

In the last decade, powder metallurgy (P/M) technology has made marked advances in competitive manufacturing. P/M offers design opportunities that are not possible with other methods, as well as significant cost savings. The processing parameters, material characteristics, individual stages of parts production, deformation and densification mechanics and tooling, and preform design influence the properties of the P/M part and related economics. Therefore, a review of the various parameters involved in the different stages of P/M steel forging in net-shape manufacturing and their implications on resulting properties of the P/M parts is presented in a three-part review. Part I discussed the issues of powder preparation, compaction, and sintering in the stages of preparing a sintered compact. This review (Part II) identifies key parameters in forging the sintered compact that influence the properties of the powder forged part. Part III reviews currently available analysis methods for studying the powder forging process.     

不同SPS烧结温度Ti-45Al-5.5(Cr,Nb,B,Ta)合金的显微组织及力学性能(英文)

采用高能球磨和放电等离子烧结(SPS)技术,制备成分为Ti-45Al-5.5(Cr,Nb,B,Ta)的TiAl合金块体,随后对TiAl合金进行热处理。研究在不同SPS烧结温度下制备的TiAl合金经过热处理后的显微组织和力学性能。结果表明:高能球磨后的合金粉末形状不规则,粉末颗粒尺寸大约为几十微米。XRD分析表明,机械球磨后的粉末由TiAl和Ti3Al两相组成;烧结后的Ti-45Al-5.5(Cr,Nb,B,Ta)合金块体主要是TiAl相,以及少量的Ti3Al和TiB2相。当烧结温度为900°C和1000°C时,合金的显微组织为双相结构,并伴随有一些细小的等轴γ晶粒和细小的针状TiB2相。当烧结温度从900°C上升到1000°C时,Ti-45Al-5.5(Cr,Nb,B,Ta)合金的显微硬度变化不大,抗压强度从1812MPa提高到2275MPa,压缩率从22.66%增加到25.59%,合金的断裂方式为穿晶断裂。     

电子束选区熔化技术对钛合金组织和力学性能的影响

利用光学显微镜、扫描电镜和力学万能试验机研究了ELI TA7金属粉末在电子束选区熔化快速成形件的显微组织和力学性能.结果表明:真空度3.0×10-2～5.0×10-2 Pa、工作电流2.0～3.0 mA,Z字型扫描路线可以有效提高烧结件的致密度、室温强度和延伸率.烧结件的相对密度可达97%,抗拉强度740 MPa,延伸率8%,接近锻件的性能.致密度高的原因是电子束高的能量利用率在烧结过程中产生瞬时液相,同时真空下粉末的表面得到净化,提高了烧结活性;而快速的冷凝过程有助于产生细小的晶粒.同时致密度的提高以及晶粒的细化均有助于烧结件力学性能的提高.