粉末冶金制备TiAl合金研究进展

轻质高强耐高温的TiAl合金一直是备受瞩目的先进结构材料,在航空航天、汽车等领域应用潜力巨大。但TiAl合金热加工性差,采用传统方法热成形难度大。而粉末冶金由于近净成形的特点,在制备复杂TiAl合金零部件上具有显著优势。近年来,科研工作者在TiAl合金粉末烧结技术上展开了大量工作,并取得一定进步。本文结合TiAl合金粉末成形技术的国内外发展现状,综述了放电等离子烧结(SPS)、热等静压、热压烧结、喷射成形、金属注射成形等方法制备TiAl合金的工艺、显微组织、力学性能和零部件,论述了上述制备方法的特点以及目前存在的不足,并提出了粉末冶金成形TiAl合金零部件的建议与未来发展方向。     

粉末冶金TiAl基合金及其力学性能的研究进展

综述了粉末冶金法制备TiAl基合金的几种方法，包括预合金粉末法、元素粉末法、自蔓延高温合成、放电等离子烧结等方法，介绍了采用粉末冶金方法制备TiAl基合金的力学性能的研究，指出当前粉末冶金TiAl基合金制备中存在的问题及研究重点。     

TiAl基合金发动机排气门的制备和台架试验

采用真空离心铸造 机加工工艺制备的TiAl基合金排气门在 483Q柴油发动机台架上进行了 48h耐久性试验。结果表明 :TiAl基合金排气门质量轻 ,约为 2 1 4材料排气门质量的 50 % ;TiAl基合金排气门与原气门座组成的摩擦副具有更好的磨合性和耐磨性 ,并且实际接触面积由原来的 30 %提高到 70 % ,相对下沉量由 8.0×1 0 - 3 m降低至 1 .0× 1 0 - 3 m ,说明TiAl基合金排气门可满足高性能发动机的服役要求。     

亚微米晶TiAl合金的机械合金化及其机械性能

最近几年的广泛研究表明,可以通过机械合金化来制备晶粒尺寸范围为10～100nm的纳米晶体材料.由于晶粒边界密度特别高,这些材料显示出极好的机械性能.例如,与粗晶材料相比,硬度提高2～7倍.因此,似乎可以认为,机械合金化是制备能够作为高温结构材料的TiAl合金的颇有竞争力的方法.就粉末冶金工艺而言,除了能够获得近成品形状和避免显微组织不均匀性之外、非常细小的晶粒度还会改善其热加工性.因此,还可以继续通过等温热锻来细比TiAl合金的晶粒,甚至可以利用超塑性成形来达到大约5μm的晶粒尺寸.德国GKSS研究中心材料研究所的M.Ochring及其同事报道了借助机械合金化工艺制取晶粒度为30nm～1μm的TiAl合金及其性能检测结果.     

TiAl合金的制备及应用现状

TiAl合金密度小、高温性能优异,自20世纪50年代以来已发展到第三代。介绍了TiAl合金的性能特点、发展历程,真空感应熔炼、真空自耗电弧熔炼、等离子冷床炉熔炼等熔炼TiAl合金方法的优缺点,以及国内外TiAl合金的制备情况;提出TiAl合金熔炼过程中存在的问题主要是宏观与微观偏析,应从原料加入方式、原料纯度及熔炼工艺等方面进行改进;此外,对TiAl合金在航空航天、汽车工业等领域的应用现状进行了概括,指出TiAl合金近期的研究重点是大尺寸铸锭的均匀化控制。     

放电等离子烧结制备高铌TiAl合金

以Ti-45Al-8．5Nb-0．2B-0．2W-0．1Y合金粉末为原料,采用放电等离子烧结工艺制备了高铌TiAl合金。结果表明,当烧结温度高于1000℃时,可制备出致密度高、组织均匀的高铌TiAl合金;烧结温度对合金的显微组织影响显著,通过改变烧结温度可得到具有近γ（NG）、双态（DP）、近片层（NL）、全片层（FL）4种典型组织的高铌TiAl合金：合金的室温力学性能与显微组织密切相关,当烧结温度为1100℃时,所制备合金显微组织为细小双态组织,其抗拉强度为1024MPa,延伸率为1．16％,显示出较好的室温力学性能。     

TiAl合金叶片铸造成形工艺研究

采用熔模精密铸造工艺制造TiAl合金叶片,通过对浇注系统设计、型壳制备工艺、熔炼浇注工艺的研究,实现了TiAl合金叶片完整成型。结果表明,合理设计浇注系统和型壳制备工艺可以减少集中缩孔、夹杂和气孔。     

增材制造TiAl合金的研究现状及展望

TiAl合金具有高比强度以及优异的抗氧化、高温抗蠕变性能等优点,在航空航天等领域具有广阔的应用前景。然而,TiAl合金室温塑性差、加工成形困难,且传统制备TiAl合金技术效率低、成本高,严重制约了其工程应用。近年来,增材制造技术因其效率高、成本低等优点,在制备TiAl合金方面优势明显。本文首先介绍了TiAl合金的基本特性,然后分别从传统制备工艺、激光增材制造、电子束增材制造以及电弧增材制造几个方面综述了国内外制备TiAl合金技术的研究现状,总结了增材制造TiAl合金力学性能的研究进展及其改善方法,最后分析了增材制造TiAl合金技术的未来研究目标和发展趋势。     

高致密度Fe-Cr合金的粉末冶金制备工艺研究

以单质Fe粉和Cr粉为原料,采用粉末冶金法制备了Fe-25Cr合金。研究了压制压力、烧结温度和烧结时间对合金致密度和显微组织的影响。结果表明,烧结坯体的最终密度在所研究的范围内与压制压力、烧结温度、烧结时间成正比,但当烧结温度为1 300℃,烧结坯体的晶粒明显发生长大。粉末冶金法制备高致密度Fe-25Cr合金的最佳工艺参数为:压制压力800 MPa,烧结温度1 280℃,烧结时间60 min,所得到烧结坯体的相对密度为95.23%,实际密度为7.313 5 g/cm3。     

粉末冶金制备Laves相NbCr2化合物的强韧化研究进展

综述了采用粉末冶金法制备Laves相NbCr2合金的历史及现状,包括粉末冶金工艺以及合金的组织演变及其特征、力学性能及合金化元素的作用,并将粉末冶金Laves相NbCr2合金的力学性能与铸造法制备的合金性能进行对比.发现采用粉末冶金法制备的合金力学性能及抗氧化性显著优于铸造法制备合金的性能.     

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.     

TiAl基合金电子束快速成形研究进展

TiAl基合金作为一种新型轻质高温结构材料,在航空航天和汽车工业有着广泛的应用前景.电子束快速成形技术是目前制备TiAl基合金最新颖、前沿的技术.本文主要介绍了电子束快速成形技术制备TiAl基合金的原理、优势、最新研究进展,以及预合金粉末制备的发展现状,对TiA1基合金的电子束快速成形技术的不足进行了分析并提出了展望.     

Reaction mechanism in high Nb containing TiAl alloy by elemental powder metallurgy

1 Introduction High Nb containing TiAl alloys have attracted much attention owing to their low densities and potential applications at high-temperature environments[1,2]. It has been found that Nb is the essential and effective element improving their me…     

Reaction mechanism in high Nb containing TiA1 alloy by elemental powder metallurgy

High Nb containing TiAl alloy was fabricated in argon atmosphere by reactive hot pressing process. Reaction mechanism was investigated by means ofmicrostructural analyses and thermodynamic calculations. The results show that it is feasible to prepare high Nb containing TiAl alloy with fine lamellar colonies by reactive hot pressing process. The reaction between Ti and Al powders is dominant in Ti-Al-Nb system. Nb powders dissolve into the Ti-Al matrix by diffusion. Pore nests are formed in situ after Nb powders diffusion. The hot pressing atmosphere is optimized by thermodynamic calculations. Vacuum or argon protective atmosphere should be adopted.     

Densification laws and properties of sintered powder compacts in rotary forging process

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粉末加工工艺对银钯合金靶材制备的影响

粉末冶金法制备的银钯合金靶材存在孔隙率较高和相对密度较低的缺点。采用不同的粉末工艺制备了银钯合金粉末样品,使用氢氧含量分析、表面形貌分析、XRD线形分析等方法,探究使用各组样品经真空热压烧结制备的靶材的差异及其机理。结果表明,球磨后的合金粉末在烧结前有必要真空煅烧除氧;随着球磨时间和球磨转速的增加,粉末先细化后形成薄片,烧结体的相对密度先上升后下降;100 r/min球磨2 h所得粉末制备的烧结体具有最高的相对密度,为99.264%。     

Research on investment casting of TiAl alloy agitator treated by HIP and HT

Using TiAl alloy to substitute superalloy is a hot topic in aeroengine industry because of its low density, high elevated temperature strength, and anti-oxidization ability. In this research, Ti-47.5AL-2Cr-2Nb-0.2B alloy was used as the test material. By applying a combination process of ceramic shell mold and core making, vacuum arc melting and centrifugal pouring, and heat isostatic pressing (HIP) and heat treatment (HT) etc., the TiAl vortex agitator casting for aeroengine was successfully made. This paper introduced key techniques in making the TiAl vortex agitator with investment casting process, provided some experimental results including mechanical properties and machinability, and explained some concerns that could affect applications of TiAl castings.     

Synthesis of nanocomposites by mechanical alloying

Nanocomposites were synthesized by the solid-state powder processing technique of mechanical alloying in Al–Al₂O₃, TiAl–Ti₅Si₃, and MoSi₂–Si₃N₄ systems. The mechanically alloyed powders were consolidated to full density by techniques such as vacuum hot pressing, hot isostatic pressing, and combinations of them. The as-milled powders as well as the consolidated compacts were characterized for their crystal structure features using X-ray diffraction and for the microstructural features using scanning and transmission electron microscopy techniques. Mechanical properties such as hardness, ductility, and fracture toughness were also measured. It has been shown that it is possible to produce a high volume fraction of the reinforcement of nanometer dimensions and that the properties of the nanocomposites are significantly better than those of the monolithic materials. Superplastic deformation has been demonstrated in TiAl–Ti₅Si₃ composite even when 60 vol.% of the ceramic reinforcement was present.     

Prediction model for surface temperature of roller and densification of iron powder during hot roll pressing

The hot roll pressing of iron powder with several rotating speeds was carried out on a pilot-plant scale. From these experiments, it was confirmed that the surface temperature of roller was increased with increasing its rotating speed. It was also known that the heat transfer coefficient between the iron powder and the roller surface is closely related with the rotating speed of roller. These results were quantitatively described by using a mathematical model which was derived based on the steady-state heat transfer during hot roll pressing. In addition, the densification behavior of iron powder during the hot roll pressing was simulated by a finite element model based on the arbitrary Lagrangian and Eulerian (ALE) method and a yield criterion for metal powder. From these models, the maximum critical rotating speed of roller during the hot roll pressing, in which the roller could hold out against the thermal fracture, could be determined.     

粉末冶金制备TiAl基合金板材的研究现状及趋势

综述了TiAl基合金板材的元素粉法和预合金粉法2种粉末冶金制备工艺，介绍了元素粉末法、金属箔片法、预合金粉热轧法、物理气相沉积法和等离子喷涂法等工艺的制备过程和材料性能，论述了上述方法的特点和发展趋势。