Integrated high-performance and accurate shaping technology of low-cost powder metallurgy titanium alloys: A comprehensive review

The practical engineering applications of powder metallurgy (PM) Ti alloys produced through cold compaction and pressure-less sintering are impeded by poor sintering densification, embrittlement caused by excessive O impurities, and severe sintering deforma-tion resulting from the use of heterogeneous powder mixtures. This review presents a summary of our previous work on addressing the above challenges. Initially, we proposed a novel strategy using reaction-induced liquid phases to enhance sintering densification. Near- complete density (relative density exceeding 99%) was achieved by applying the above strategy and newly developed sintering aids. By focusing on the O-induced embrittlement issue, we determined the onset dissolution temperature of oxide films in the Ti matrix. On the basis of this finding, we established a design criterion for effective O scavengers that require reaction with oxide films before their dissol-ution. Consequently, a ductile PM Ti alloy was successfully obtained by introducing 0.3wt% NdB6 as the O scavenger. Lastly, a powder- coating strategy was adopted to address the sintering deformation issue. The ultrafine size and shell-like distribution characteristics of coating particles ensured rapid dissolution and homogeneity in the Ti matrix, thereby facilitating linear shrinkage during sintering. As a result, geometrically complex Ti alloy parts with high dimensional accuracy were fabricated by using the coated powder. Our fundament-al findings and related technical achievements enabled the development of an integrated production technology for the high-performance and accurate shaping of low-cost PM Ti alloys. Additionally, the primary engineering applications and progress in the industrialization practice of our developed technology are introduced in this review.

Comparison of Cu−Al−Ni−Mn−Zr shape memory alloy prepared by selective laser melting and conventional powder metallurgy

This work aimed to investigate and critically analyze the differences in microstructural features and thermal stability of Cu−11.3Al−3.2Ni−3.0Mn−0.5Zr shape memory alloy processed by selective laser melting(SLM)and conventional powder metallurgy.PM specimens were produced by sintering 106−180μm pre-alloyed powders under an argon atmosphere at 1060°C without secondary operations.SLM specimens were consolidated through melting 32−106μm pre-alloyed powders on a Cu−10Sn substrate.Mechanical properties were measured through Vickers hardness testing.Differential scanning calorimetry was conducted to assess the martensitic transformation temperatures.X-ray diffraction patterns were collected to identify the metallurgical phases.Optical and scanning electron microscopy was used to analyze the microstructural features.b′1 martensite was found,irrespective of the processing route,although coarser martensitic variants were present in PM-specimens.In conventional powder metallurgy samples,intergranular eutectoid constituents and stabilized austenite also formed at room temperature.PM-specimens showed similar average hardness values to the SLM-specimens,albeit with high standard deviation linked to the porosity.The specimens processed by SLM showed reversible martensitic transformation(T0=171°C).PM-processed specimens did not show shape memory effects.

Properties and forming process of prealloyed powder metallurgy Ti-6Al-4V alloy

The properties and forming process of prealloyed powder metallurgy(PM) Ti-6Al-4V alloy were researched for application of high performance of titanium parts. Hot isostatic press(HIP) technology and two kinds of powders were used in the prealloyed processing to get full density material. Tensile properties,impact toughness and fracture toughness of PM Ti-6Al-4V alloy were studied and discussed. The microstructures were examined with optical microscope and the morphologies of powders were observed by SEM. Forming processes were performed to fabricate PM titanium parts. The experiment results show that the prealloyed PM Ti-6Al-4V alloy has same good properties as wrought material and the complex shape PM parts can be near-net-shaped. Some of the parts have been commercially used. This indicates that the prealloyed process should have bright prospects in making high-performance,complex shape and low-cost titanium alloy parts.

Ti_(2)AlNb合金粉末热等静压成形的组织和性能

分别采用等离子旋转电极雾化法(Plasma rotating electrode process,PREP)和无坩埚感应熔炼超声气体雾化法(Electrode induction melting gas atomization,EIGA)制备了Ti_(2)AlNb洁净预合金粉末,并对预合金粉末进行了表征。通过热等静压(Hot isostatic pressing,HIP)工艺制备了Ti_(2)AlNb合金,研究了制粉工艺对Ti_(2)AlNb合金显微组织与力学性能的影响。试验结果表明,与PREP法相比,EIGA法制备的Ti_(2)AlNb粉末振实密度更高;基于粉末热等静压近净成形技术,在1030℃/140 MPa/3 h的条件下开展了Ti_(2)AlNb叶轮的成形研究,有限元模拟结果显示,粉末振实密度越高,部件热等静压后变形程度越小,综合考虑构件成形,优选振实密度更高的EIGA制粉工艺制备Ti_(2)AlNb粉末合金复杂部件。

颗粒增强铝基复合材料热等静压近净成形有限元模拟

目的建立可靠的模拟方法,以更高效地预测颗粒增强铝基复合材料(PRAMC)粉末热等静压中的形状变化和不同部位致密度的差异,解决传统实验试错方法适用性差且费时费力的问题,满足批量应用的需求。方法以45%(体积分数)SiCp/6092Al复合材料为研究对象,构建了能预测粉末热等静压成形过程的有限元模型。使用Gurson-Tvergard-Needleman(GTN)模型作为粉末本构模型,建立了粉末尺度的代表性体积单元(RVE)对GTN模型进行修正。结果通过对比GTN模型计算结果与实验结果,发现修正后的GTN模型能更准确地预测模型的最终变形尺寸,与修正前相比,相对误差降低了1.6%~2.9%。使用修正后的GTN模型对杯形回转体零件的热等静压成形过程进行预测,最终形状的计算结果与实验结果的相对误差仅为0.2%~3.1%,致密度分布的相对误差在0.5%以内。在探究包套厚度对热等静压过程的影响时发现,随着包套厚度的增大,热等静压过程中的屏蔽作用增强,内部粉体致密度下降。结论为PRAMC热等静压近终形制备的形状和致密度控制问题提供了有限元预测工具,辅助优化了热等静压工艺和包套设计,降低了颗粒增强铝基复合材料热等静压近净成形过程开发的试错成本。

Microstructure and high-temperature mechanical properties of near net shaped Ti−45Al−7Nb−0.3W alloy by hot isostatic pressing process

Near net shaped Ti−45Al−7Nb−0.3W alloy(at.%)parts were manufactured by hot isostatic pressing(HIP).The microstructure and high-temperature mechanical properties of the alloy were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that at a temperature of 700℃,the peak yield stress(YS)and ultimate tensile stress(UTS)of alloy are 534 and 575 MPa,respectively,and the alloy shows satisfactory comprehensive mechanical properties at 850℃.The alloy exhibits superplastic characteristics at 1000℃ with an initial strain rate of 5×10^−5 s^−1.When the tensile temperature is below 750℃,the deformation mechanisms are dislocation movements and mechanical twinning.Increasing the tensile temperature above 800℃,grain boundary sliding and grain rotation occur more frequently due to the accumulation of dislocations at grain boundary.

A Novel near Net-Shape Technique for P/M Parts with Large H/D Ratio

In order to overcome the shortcomings of conventional hot pressing, a novel near net-shape technique, called radial hot pressing, for P/M parts with large height-to-diameter (H/D) ratio was introduced. Effects of processing parameters on the microstructures and density of P/M TiAl base alloy valves were studied. Results show that the radial hot pressing is an effective technique for manufacturing valves with a H/D ratio of about 10:1, and the perfect joint interface between the Mo sheet and the parts is helpful for subsequent HIPing.

Microwave sintering effects on the microstructure and mechanical properties of Ti–51at%Ni shape memory alloys

Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformation temperatures,and mechanical properties were investigated by optical microscopy,field-emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests,and microhardness tests.Varying the microwave temperature and holding time was found to strongly affect the density of porosity,presence of precipitates,transformation temperatures,and mechanical properties.The lowest density and smallest pore size were observed in the Ti–51at%Ni samples sintered at 900°C for 5 min or at 900°C for 30 min.The predominant martensite phases of β2 and β19′ were observed in the microstructure of Ti–51at%Ni,and their existence varied in accordance with the sintering temperature and the holding time.In the DSC thermograms,multi-transformation peaks were observed during heating,whereas a single peak was observed during cooling;these peaks correspond to the presence of the β2,R,and β19′ phases.The maximum strength and strain among the Ti–51at%Ni SMAs were 1376 MPa and 29%,respectively,for the sample sintered at 900°C for 30 min because of this sample's minimal porosity.

Evolution of grain size and grain shape during thermomechanical processing in a powder metallurgical nickel-based superalloy

With a strain rate range of 0.01–10 s^(−1) and a deformation temperature range of 1110–1200℃,the isothermal compression test was performed on one powder metallurgy superalloy which is macroscopic segregation free.Using electron backscatter diffraction,the effect of strain rate and deformation temperature on grain shape and grain size of superalloys during thermal deformation was studied.The results established that exquisite and equiaxed dynamic recrystallization(DRX)grains are procured at supernal deformation temperature and high strain rate because of the high dislocation density.At the same time,the interaction between high DRX nucleation rate and low grain growth rate at high strain rate is favorable in making finer DRX grains.The equivalent medial grain size expanded with lowering strain rate and elevating proof temperature.Moreover,the grain shape was researched by the effective method of aspect ratio.Most aspect ratio of original grains is 0.61,and the aspect ratio has important implications for DRX and grain growth process.The average aspect ratio increases slightly when deformation temperature rises from 1110 to 1140℃,while the average aspect ratio increases memorably as the deformation temperature is higher than 1140℃.

粉末热等静压成形TA7 ELI高承压泵壳体的性能和尺寸控制

基于粉末热等静压近净成形技术,在930℃/120 MPa/3 h的条件下开展了TA7 ELI(超低间隙)高承压泵壳体的成形研究,通过两批次粒度存在差异的粉末(粉末表面为胞晶形貌,D_(50)为67μm、74μm)分析了制粉时的粒度波动对成形材料力学性能的影响,并结合有限元仿真手段开展了高承压泵壳体的粉末收缩规律研究。此外,根据高承压泵在液体火箭发动机中的实际服役情况,对近净成形的高承压泵毛坯进行解剖,分析了特征截面位置的显微组织及硬度分布情况。结果表明,粉末热等静压近净成形技术制备的TA7 ELI合金力学性能达到锻件水平,粉末粒度波动对合金力学性能无显著影响,高承压泵壳体的显微组织均匀,特征截面的硬度值波动小,壳体内部流道关键尺寸实测结果与模拟预测结果的最大偏差为5.37%。

药型罩发展现状与趋势研究

药型罩作为破甲弹的核心部件材料,是形成聚能射流的最核心部分,对聚能射孔效果有着重要的影响。其破甲性能主要受材料密度、声速、晶粒尺寸和组织结构的影响。因此设计高性能的药型罩需要采用既具有高密度、高声速、细晶粒尺寸,又具有良好的高温力学性能、抗氧化性能和良好工艺性能的材料。文章通过对目前国内外新型合金药型罩的发展方向进行了简要研究,为我国合金药型罩的后续发展提供了一定的参考。

粉末钛合金热等静压近净成形技术及发展现状

粉末钛合金热等静压(HIP)近净成形技术作为一种理想的钛合金构件制备工艺之一,可以通过整体近净成形产品来提高材料利用率,降低钛合金产品的生产成本和生产周期,因此越来越受到武器装备等军工领域的关注。自该工艺出现以来,材料学者从原材料粉末的制备、包套设计、近净成形过程到材料的后处理都做了系统的研究,以了解该工艺的技术原理和材料性能影响因素,进而获得更高性能的产品,并进一步降低生产成本。研究表明,原材料粉末和包套设计是影响粉末钛合金近净成形产品质量和成本最重要的两个因素。球形度高、流动性好的钛合金粉末具有好的填充性和高的松装密度,能增加产品的成形精度。与此同时,作为控制粉末冶金制品中组织结构、孔洞和杂质元素的关键因素,高质量钛合金粉末的使用还可以获得力学性能更加优异的产品,但此种粉末的价格较高,增加了粉末冶金的生产成本,所以高质量、低成本钛合金粉末的制备是钛合金粉末冶金未来发展的重要方向之一。包套作为钛合金HIP近净成形技术的主要成本构成之一,合适的材料选择和结构设计既可以提高产品的成形精度又可以改善产品的表面质量,而通过计算机仿真模拟技术来设计包套和模拟近净成形过程,可以进一步提高成形精度和降低构件的研发成本,因此计算机仿真模拟是钛合金HIP近净成形未来发展的重点。通过选择合适的原材料粉末、设计合理的成形包套以及精确控制的成形过程,目前HIP近净成形获得的钛合金构件显示出与锻件相当的力学性能,而成本相对铸锻件节约了1/3以上。近年来,粉末钛合金热等静压近净成形技术在国外的航空航天等军工领域都已经得到了广泛的应用,并显现出理想的减重和降低成本的效果;国内则主要以航天领域的应用为主,而对其疲劳性能的质疑是限制其在国内航空领域广泛应用的主要原因。本文对粉末钛合金HIP近净成形技术进行了全面综述,对工艺过程中的影响因素,粉末致密化过程、力学性能及其影响因素等分别进行了阐述,同时介绍了计算机仿真模拟技术在粉末钛合金HIP近净成形技术上的应用。最后对该技术在国内外的应用情况进行了简要总结,并展望了该技术未来的发展趋势。

粉末冶金TiAl基合金排气阀的制备及性能

研究了粉末冶金TiAl基合金柴油机排气阀的近型成形技术 ,其要点为 :采用元素粉末冶金方法 ,以元素Ti,Al粉末为主要原料 ,首先在刚模中冷压成排气阀菌部 ;然后在真空热压炉中 ,通过准等静压工艺 ,同时实现TiAl基合金的反应合成与近型成形 ;最后通过真空扩散联接工艺 ,使粉末冶金TiAl基合金菌部与铸态TiAl基合金杆部联接成完整的排气阀零件。通过发动机台架的初步试验表明 ,所制备的粉末冶金TiAl基合金排气阀表现出良好的服役性能。

粉末挤压成型的进展

阐述了粉末挤压成型技术的发展现状,评述了近年来这一领域国内技术引进开发的状况和存在的主要问题,并讨论了发展挤压成型技术的对策。

V_2O_5对镍铁尖晶石烧结机理及性能的影响

为了提高镍铁尖晶石的性能,以NiO,Fe2O3和微量V2O5为原料,采用粉末冶金法制备了含有过量15%(以质量计,下同)NiO,掺杂V2O5的镍铁尖晶石惰性阳极。原料经混合、成型后,于1200℃烧结6h。研究了添加V2O5的NiFe2O4尖晶石样品的烧结机理、导电性、腐蚀性。结果表明:添加V2O5后样品的烧结为液相烧结;添加剂V2O5提高了惰性阳极样品的密度;尤为重要的是,添加V2O5后样品在冰晶石融盐中的抗腐蚀性明显改善。腐蚀10h后,添加1.5%V2O5的样品基本完好,腐蚀率降为无添加剂样品的1/80。但是添加1.5%V2O5后,样品的电导率有一定的降低。

粉末冶金近型成形技术——陶瓷模工艺

详细介绍了一种粉末冶金近型成形新技术——陶瓷模工艺。分析了影响该工艺的主要因素,如陶瓷模的制备、传压介质的选择、原料粉末的特性等。并展望了该技术在制造复杂形状零件方面的广阔应用前景。

钛镍多孔材料的制备及其显微组织与形状记忆性能

采用粉末烧结法制备了高孔隙率的Ti-50.8 at%Ni形状记忆合金(SMA),并对其显微组织和形状记忆性能进行了研究。结果表明,用该种方法制备的多孔合金样品具有孔隙分布均匀以及开孔率高的特点,其平均孔径在200μm左右。合金组织主要由奥氏体NiTi相(B2)和单斜马氏体NiTi相(B19’)组成。循环加载-卸载实验结果表明,该多孔材料能表现出一定的形状记忆效应,而且形状记忆效应随孔隙率的增加而降低。

铁基粉末凝胶注模成形工艺的研究

本文对凝胶注模成形工艺应用于铁基粉末冶金进行了研究。着重研究了凝胶注模成形工艺中分散剂、固相体积分数对浆料流变性的影响,采用该工艺对铁粉进行了成形与烧结。结果表明,加入分散剂可以使浆料黏度降低,有利于成形为复杂形状;随着固相体积分数的增加,浆料的黏度增加。采用合适的工艺参数,制备了相对密度为90%,抗弯强度为517 MPa,抗拉强度为280 MPa的复杂形状的铁基粉末冶金零件。

金属注射成形中的高技术、新概念及其对产业化进程的影响

比较系统地阐述和分析了金属注射成形(MIM)在粉末冶金学科中的发展过程,特别是近年来这一领域发展起来的高技术、新概念的特点。分析了它们对MIM产业化进程的影响。

聚能装药粉末药型罩材料技术的发展和现状

文章介绍了近年来国内外粉末药型罩材料技术的研究现状,综述了一些国内外优秀研究成果。重点分析了合金粉末药型罩中各成分的优化配比及制造工艺对粉末罩成型和射流质量的影响。最后以含能药型罩为主线,提出了其新的发展方向和应用前景。