采用图像分析技术对球形Ti-6Al-4V粉末粒形的定量分析

采用图像分析技术对4种不同方法制备的球形Ti-6Al-4V粉末进行粒形的定量分析,分别测量了粉末的球形度、椭圆率、赘生物指数及粗糙度。结果表明:4种方法制备的粉末平均球形度均在90%以上。等离子旋转电极雾化法(PREP)、等离子火炬雾化法(PA)、等离子惰性气体雾化法(PIGA)、电极感应熔炼气雾化法(EIGA)制得粉末球形度依次降低,粗糙度依次增加。PREP、PA、EIGA、PIGA法制得粉末的表面卫星球粘附依次增加。对于PREP法制得粉末,粉末粒径范围越细,球形度越高,平均粗糙度越小。粉末粒形指标的差异与其制备方法的原理有关。采用图像分析技术可以实现对金属粉末粒形指标的科学定量分析。     

Effect of Argon-Induced Porosity on Mechanical Properties of Powder Metallurgy Titanium Alloy Components using Hot Isostatic Pressing

This work reported the Ar-induced porosity in powder metallurgy Ti-5Al-2.5Sn alloy prepared by hot isostatic pressing(HIPing).The obtained microstructures of powder compacts were studied through optical and scanning electron micro-scopes,X-ray tomography,and the mechanical properties evaluated through tensile and impact tests.The results showed that the Ar-induced porosity is related to the hollow powder with gas bubble and the Ar leakage of sealed container during the powder densification.The hollow powder with gas bubble shows no obvious effects on mechanical properties of as-HIPed powder compacts.The Ar content decreases with the increasing shrinkage of encapsulated powder.0.7％ Ar-induced porosity degrades the impact toughness,but no reductions of tensile properties were obtained.Ar content test is an effective method to detect the powder compacts with Ar concentration.     

PRODUCTION METHODS AND APPLICATIONS FOR HIGH-QUALITY METAL POWDERS AND SPRAYFORMED PRODUCTS

Metal powders of superlative quality, i.e. high cleanliness, rapidly solidified and spherical shape, have seen an increasing demand in the market. The leading technology for the production of such powders is the inert gas atomization of metal alloy melts. To fulfill these requirements, the metal alloy is usually produced in a vacuum induction melting furnace (VIGA = vacuum induction melting/gas atomization) and poured by means of a preheated tundish system into a gas nozzle where the metal stream is disintegrated by a high kinetic energy inert gas jet. The produced micro-droplets solidify in a free fall inside the atomization tower. For special applications, super-clean and ceramic-free metal powders can be produced by using the EIGA (electrode induction melting/gas atomization) melting- and atomizing system.As an alternative to the metal powder route, the sprayforming technology allows to produce semi-finished products in one step. In this case, the metal droplets produced by the highenergy inert gas nozzle system are directly solidified on a substrate, allowing to form billets,rolls and tubes.     

高温合金差示扫描量热分析(DSC)的影响因素研究III：合金状态和升降温速率

摘 要：对固溶强化型镍基高温合金625进行升、降温差示扫描量热分析（DSC）试验,研究了同一合金不同状态（粉末态、粉末+热等静压态和铸态）以及升/降温速率（5-10℃/min）对相变温度的影响。采用场发射扫描电镜（FESEM）、电子探针（EPMA）对不同状态625合金的微观组织和元素分布进行表征。结果表明：（1）铸态比粉末态合金的枝晶间距大2个数量级,而热等静压态合金为无枝晶偏析的细等轴晶结构。（2）升、降温速率对DSC曲线中加热时基体开始熔化（等于固溶强化型合金的初熔温度）和冷却时开始凝固温度（偏离基线的拐点）无影响,但对合金加热熔化结束、冷却时大量凝固析出温度（峰位）和终凝温度（拐点）有明显影响。采用加热、冷却曲线相应相变温度平均值的方法可减少DSC试验和样品条件的影响,获得相对固定且更具可比性的合金相变温度。（3）合金状态对初熔温度和DSC升温曲线固相线温度附近的圆弧段有明显影响。根据DSC加热曲线固相线温度附近的圆弧大小可以判断合金的偏析倾向,弱偏析倾向的粉末态和热等静压态PM625合金DSC加热曲线固相线附近区域拐点尖锐,表现为合金开始熔化温度（偏离基线的拐点）与名义固相线温度（切线交点）差异很小,分别仅为5℃和6℃;偏析倾向较大的铸态IN625合金的DSC加热曲线中固相线温度附近区域为较大圆弧,开始熔化温度与名义固相线温度差异可达52℃。铸态625合金的初熔温度比热等静压态和粉末态分别低45℃和40℃,在实际热处理和热等静压等热工艺参数选择时应注意圆弧段较大的合金降低初熔温度的影响。在所有DSC冷却曲线中,由于完全熔化重新凝固消除了合金原始显微组织特征,不同状态625合金固相线温度区域附近曲线形态相似,均为较大的圆弧。     

粉末冶金Ta合金中的隐性胞状结构

采用Ta-W-Hf预合金化粉末通过冷等静压成型、热等静压和高温退火工艺制备了Ta—W-Hf合金块材，讨论了热等静压和后续的高温退火处理对合金性能的影响。发现在低的热等静压温度下，材料具有较高的强度和硬度，但塑性较低；提高热等静压温度或进行高温退火处理，可以大幅度提高拉伸延伸率和断面收缩率，同时伴随着强度的降低。分析表明，产生这种现象的主要原因是合金中的氧元素在原料颗粒中分布不均匀，并保留在热等静压成形后的块体材料中，形成了一个无相变的隐性硬壳的胞状结构。高温退火处理可以消除这种结构。     

Nitridation of Ti-6Al-4V powder in thermal plasma conditions and sintering of obtained TiN powder

This study is devoted to plasma nitridation of a Ti-6Al-4V powder, and sintering of reaction products so-obtained.Ti-6Al-4V spherical particles (22-45 μm) were injected in a plasma jet using N₂ as plasma gas and collected in two spots: in a cold area located far from the torch and in a hot area submitted to the plasma thermal effect. After plasma nitridation, particles of substoichiometric titanium nitride (TiN_1−x) with no nitrogen gradient were obtained. The reduction of nitrogen concentration in plasma gas improved the massic output of gathered powders. These powders were not exclusively composed by TiN_1−x, since titanium alloy often remained, and a secondary phase β-Ti containing vanadium and aluminium was always present inside the grains. The nitridation rate depended on the collected area. Titanium oxide (rutile) was detected in powders collected in the hot area.Titanium nitride powders in which no rutile was detected were hot pressed up to 1450 °C under flowing nitrogen. In this case, the densification rate did not overload 83% of theoretical value. This fact can be explained by the nitridation of both TiN_1−x and titanium intermetallic phases during the heat treatment. In the case of inert atmosphere (argon), there was only the densification phenomenon which gave a density close to the theoretical value.This work has to be developed on the one hand to improve powder synthesis and its natural sintering, and on the other hand to approach hot pressing sintering mechanism.     

电子封装材料过共晶硅-铝合金的组织特征和热性能(英文)

采用快速凝固制粉技术和粉末热压烧结技术制备55%Si-Al,70%Si-Al和90%Si-Al3种过共晶含量的硅铝合金。结果表明:雾化沉积是制备过共晶硅铝合金的有效的快速凝固工艺,采用该工艺获得的快速凝固硅铝合金粉末的尺寸小于50μm。快速凝固的硅铝合金粉末经过550°C和700MPa热压后,获得3种不同成分合金试样的相对密度分别为99.4%,99.2%和94.4%。作为电子封装材料,3种试样的热导率、热膨胀系数和电导率都可以满足应用要求。55%Si-Al合金的热膨胀系数随温度的变化最剧烈,但是该合金具有较好的热导率。90%Si-Al合金的热膨胀系数较小,但是其热导率最差,小于100W/(m·K)。70%Si-Al合金具备热沉材料所应具备的优良的热导率和热膨胀系数的综合性能。     

Properties of Porous TiNbZr Shape Memory Alloy Fabricated by Mechanical Alloying and Hot Isostatic Pressing

In the past decades, systematic researches have been focused on studying Ti-Nb-based SMAs by adding ternary elements, such as Mo, Sn, Zr, etc. However, only arc melting or induction melting methods, with subsequent hot or cold rolling, were used to fabricate these Ni-free SMAs. There is no work related to powder metallurgy and porous structures. This study focuses on the fabrication and characterization of porous Ti-22Nb-6Zr (at.%) shape memory alloys produced using elemental powders by means of mechanical alloying and hot isostatic pressing. It is found that the porous Ti-22Nb-6Zr alloys prepared by the HIP process exhibit a homogenous pore distribution with spherical pores, while the pores have irregular shape in the specimen prepared by conventional sintering. X-ray diffraction analysis showed that the solid solution-treated Ti-22Nb-6Zr alloy consists of both ?? phase and ???? martensite phase. Morphologies of martensite were observed. Finally, the porous Ti-22Nb-6Zr SMAs produced by both MA and HIP exhibit good mechanical properties, such as superior superelasticity, with maximum recoverable strain of ~3% and high compressive strength.     

Cu-20%Co合金雾化液滴的凝固组织特征

对Cu-20%Co合金进行了高压气体雾化快速凝固实验,获得了富Co相以微细球形粒子形式分布于基体的Cu20%Co合金粉末.富Co相粒子的尺寸随着粉末尺寸的增加而增大.在凝固过程中,富Co相液滴受固-液界面推斥;凝固后,Co相粒子主要分布于晶界.由于富Co液相的表面能较高,液-液相变时弥散相液核通常在雾化液滴内部形成,并在温度梯度的作用下向雾化液滴中心迁移,从而导致在粉末表面形成很薄的富Cu基体相层.     

Oxidation and hot corrosion of coated and bare oxide dispersion strengthened superalloy MA-755E

Cyclic hot corrosion and oxidation testing of an experimental oxide dispersion strengthened (ODS) superalloy MA-755E were conducted in a hot gas stream at Mach 0.3. The response of the ODS alloy, bare or with protective coatings, was similar to that of a conventional cast alloy, IN-792, in hot corrosion at 900°C. However, during oxidation at 1100 and 1150°C the ODS alloy differed from the cast alloy by developing a greater amount of subsurface porosity. Compared with a diffused aluminide coating, an electron beam vapor deposited NiCrAlY coating offered superior oxidation protection and decreased porosity formation. In additional testing, the tendency to form porosity was associated with the large grains of recrystallized powder metallurgy alloys but was independent of the presence of an oxide dispersion.     

Laser melting of Ti-15Al-20Nb alloy

Titanium aluminides have become promising materials for high-temperature applications, but the relatively poor oxidation resistance and elevated- temperature strength of these alloys limit their application to temperatures lower than 1000 °C. Niobium addition improves the properties of titanium aluminide. However, the mechanical, metallurgical, and corrosion properties of Ti- Al- Nb may be improved by treatment with a laser beam. Consequently, the present study examines the properties of Ti- 15Al- 20Nb alloy subjected to the Nd:YAG laser melting process. Hardness in the surface region increases to twice the base material hardness, and corrosion resistance improves considerably after laser treatment.     

Microstructure and oxide particle stability in a novel ODS γ-TiAl alloy processed by spark plasma sintering and laser additive manufacturing

In this work, a novel oxide dispersion strengthened titanium aluminide alloy (Ti-45Al-3Nb-<0.2Y₂O₃ at.%) was developed for powder-based processing technologies with a focus on spark plasma sintering and additive manufacturing. Titanium aluminides are promising structural intermetallics for weight reduction and an increased performance of high temperature components. The alloy design and selection process was supported by computational thermodynamics based on the CALPHAD approach, taking into account requirements for processing as well as long term alloy behavior under service conditions. Processing trials using spark plasma sintering, direct metal deposition and selective laser melting were conducted to study the alloy behavior, microstructure formation and introduction as well as stability of the ODS particles. Additionally, thermal annealing on the sintered and laser consolidated material was performed. Conventional dual phase α₂-Ti₃Al and γ-TiAl duplex and near-lamellar microstructures were obtained from the processed material. The ODS particles were homogeneously distributed in the alloy matrix after processing in the liquid state. For the direct metal deposition process, the novel alloy was compared to the established GE48-2-2 alloy (Ti-48Al-2Cr-2Nb) in terms of phases, microstructure and texture after processing. A significantly reduced texture formation was observed with the novel alloy. The hardness of the consolidated material shows superior properties for ODS-containing TiAl compared to ODS-free material. This work provides a first step towards tailored alloys for AM and the production of ODS TiAl alloys.     

气雾化制备Pd-Ag-Cu粉末钎料的研究

研究了惰性气体雾化法制备Pd-Ag-Cu合金粉末。在喷嘴结构不变的情况下,改变过热度、雾化压力、导流管的内径,导流管伸出长度都会影响到Pd-Ag-Cu合金粉末的粒度与粉末收得率。通过调整各项工艺发参数研究发现,提高过热度和雾化压力,减小导流管内径有利于降低粉末粒度,导流管随着伸出长度的增加,粉末粒度先降低后增加。各项参数都有临界值,不能无限制增大或减小,综合调整才能达到最佳制粉效果。     

锌合金粉在KOH溶液中析氢行为的研究

采用气雾法制备Zn-In,Zn-Pb,Zn-Bi,Zn-Al合金粉,利用收集气体的办法测定了各种合金粉在KOH溶液中的腐蚀速度,确定了In,Pb,Bi,Al四种元素与Zn分别形成合金的最佳含量,随后研究了In,Bi,Al三种金属元素与Zn形成的四元合金的析氢行为。     

The effect of native Al2O3 skin disruption on properties of fine Al powder compacts

In the presented study we characterize how various powder metallurgical routes (extrusion, forging, and HIP/sintering) affect the fracture of native Al₂O₃ layer present on the surface of ultra-fine atomized Al powders. It is shown that the different distribution, morphology and interconnectivity of in situ introduced Al₂O₃ dispersoids strongly affect the thermal stability and mechanical and thermal properties of subsequent powder compacts.     

High pressure EIGA preparation and 3D printing capability of Ti—6Al—4V powder

Ti—6Al—4V alloy powder was processed by electrode induction melting gas atomization (EIGA) at high gas pressure (5.5–7.0 MPa). The effects of atomizing gas pressure on the powder characteristics and the microstructure, along with the mechanical properties of the as-fabricated block by laser melting deposition (LMD), were investigated. The results indicate that the diameters of powders are distributed in a wide range of sizes from 1 to 400 μm, and the median powder size (d₅₀) decreases with increasing gas pressure. The powders with a size fraction of 100–150 μm obtained at gas pressures of 6.0 and 6.5 MPa have better flowability. The oxygen content is consistent with the change trend of gas pressure within a low range of 0.06%–0.20%. Specimens fabricated by LMD are mainly composed of α+β grains with a fine lamellar Widmanstatten structures and have the ultimate tensile strength (UTS) and yield strength of approximately 1100 and 1000 MPa, respectively. Furthermore, the atomized powders have a favorable 3D printing capability, and the mechanical properties of Ti—6Al—4V alloys manufactured by LMD typically exceed those of their cast or wrought counterparts.     

基于同步辐射CT技术表征3D打印用气雾化TC4粉末的研究

本研究利用气雾化技术制备球形TC4合金粉末,作者利用SEM、同步辐射CT扫描-三维重建等分析手段对异常颗粒粉体以及不同粒径的TC4合金粉末表面和内部的孔缺陷进行了表征。实验结果表明,本研究制备的TC4合金粉末随着粉末粒径减小,粉体表面由凸凹不平的冷凝收缩痕迹渐变为光滑表面,粉体内部的孔隙逐渐减少,且孔隙尺寸也随之减小;经分析,由于雾化过程中凝固与球化时间的差异及飞行轨迹的不同等原因导致了包裹式、连体式、椭球形、卫星粉等异常粉末颗粒的生成;同步辐射CT扫描-三维重建表明,粉末内部的孔隙率和孔隙尺寸随着粉末粒度的增大而增大;作者认为通过调整雾化工艺,使金属熔滴在未开始冷却凝固前彻底雾化破碎,从而能有效解决粉末内部孔隙缺陷的问题。     

Microstructure and corrosion of Pd-modified Ti alloys produced by powder metallurgy

A method for the fabrication of titanium alloy parts with enhanced corrosion resistance by a powder metallurgy route is presented in this paper. Commercial purity titanium powders modified with Pd have been hot isostatically pressed (HIPped) and the microstructure and distribution of the noble metal characterised by optical and scanning electron microscopy. The electrochemistry of the HIPped alloy has been assessed and the effect of powder size fraction evaluated. Results show that the phase composition and electrochemistry of the HIPped Pd-modified alloy is equivalent to that of wrought grade 7 Ti.     

DEVELOPMENT AND PRODUCTION OF FeAl BASED INTERMETALLIC ALLOYS

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金属液流的气固两相流雾化破碎准则(英文)

介绍了一种自行发明的新的雾化方法。该方法是采用含有固体介质的高速气流即气固两相流对液体金属或合金进行雾化而制备粉末的一种方法,对比研究了同等条件下普通气体雾化与两相流雾化制备粉末的特征,研究了固体雾化过程中主要工艺参数对固体雾化粉末特征的影响规律。结果表明,两相流雾化制得粉末的平均粒度约为普通气体雾化所得粉末的二分之一,而且粒度分布更集中,粉末的冷却速度比普通气体雾化高一个数量级,粉末微观组织更细小;采用液体雾化破碎准则韦伯数以衡量雾化介质的破碎能力,得出两相流雾化介质的韦伯数为气体韦伯数和颗粒流韦伯数之和,建立了两相流雾化破碎的临界方程,并以此讨论了主要工艺规律。