超塑性合金

摘自《日經力》5(1989),1,92～94. 为了显示超塑性现象一般要求合金具备三个条件:(1)形成粒径约数微米的等轴晶粒组织,并且在变形过程中晶粒组织必须不因热作用而粗化;(2)变形速度在10~(-3)～10~(-5)/s范围以内,超出此范围就会使得延伸率减小;(3)超塑性加工温度高于其熔点绝对温度的1/2,即处于其超塑性温度范围以内,超出此范围则不利于超塑性变形。另外还有在合金加热或冷却过程中相变时显示超塑性的“相变超塑性”。超塑性成型特別有利于在难加工材料的复杂形状成型加工。铝合金、钛合金和镍合金的超塑性加工件,已     

超塑性强化复合材料

日本名古屋工业技术试验所采用粉末冶金法将2124铝粉与强化材料β型氮化硅晶须制成一种新的超塑性强化复合材料。 该种超塑性强化复合材料的表征易于成形加工的变形量(总延伸)为实用水平的250％,表征超     

Ti679合金晶粒度对其超塑性的影响

一、引言众所周知,金属材料产生超塑性一般都要求符合以下条件:材料具有等轴细晶组织;变形温度必须在0.4～0.7绝对熔化温度之间;在10~(-6)至10~(-3)秒~(-1)的应变速率范围内变形;应力对应变速率敏感性指数 m 应大于0.3,最好超过0.5。Ti679合金超塑性研究一文,仅研究了α相粒度为2.02微米的等轴超细晶组织对     

超塑性合金

1920年法国人罗森汉(W.Rosenhain)首先发现合金具有一种异常大的延伸率。1945年,苏联人包赤瓦尔(Bockvar)等人正式把这种现象命名为“超塑性”。但是,直到1968年超塑性合金才在汽车上获得首次应用,自此以后更加广泛的引起人们的注意和研究。所谓塑性是指材料在整体不遭受破断的情况下所具有的最大永久变形的能力。通常以材料的最大延伸率“δ”作为塑性指标。在常温下,黑色金属延伸率不大于40%,有色金属最     

Al-Zn-Mg-Zr高强度铝合金超塑性的研究(Ⅰ)——制取工艺、超塑性力学特性及显微组织

已掌握试验合金超塑性板材的制取工艺,获得平均晶粒大小为7.78μm截长的细晶。该板材的超塑性力学特性系统试验表明,于550℃ε_0=(3.3～6.6)×10~(-1)分~(-1)范围拉伸变形,能获得δ=890～1050％、m≥0.4的较佳超塑性。超塑性变形后断裂试样的显微解析揭示,断裂处附近不仅晶粒粗大(>20μm)而且有密集孔洞,孔洞大小相当于一个粗大晶粒,试验合金系孔洞敏感材料。     

新型Al-Zn-Mg-Cu-Zr合金挤压棒材的超塑性行为研究

文章通过电子背散射衍射(EBSD)、宏观织构(Texture)、扫描电镜(SEM)、透射电子显微镜(TEM)等手段研究了一种热挤压Al-Zn-Mg-Cu-Zr棒材的超塑性行为和组织演变。试验结果表明,合金在470～510℃的温度范围和5×10~(-4)～5×10~(-3) s~(-1)的应变速率范围内可以实现合金的超塑性(伸长率≥200%)。在490℃和5×10~(-3) s~(-1)变形条件下,合金的动态软化机制以动态回复为主,但动态软化过程不够充分,随着变形程度的增加,HAGBs占比减小,形变织构强度增加。同时由于Al_3Zr颗粒的存在,可以有效的钉扎晶界和位错,抑制热变形过程中再结晶的发生。此外,通过分析超塑性拉伸数据可知,Al-Zn-Mg-Cu-Zr合金的平均应变速率敏感性指数和平均变形激活能分别为0.2和187.7 kJ/mol。因此,主要的超塑性变形机制是晶格扩散协调的位错攀移。     

新型超塑性双相不锈钢板

双相不锈钢的强度明显比奥氏体不锈钢高,但延性却较低,给变形加工造成一定困难。然而,由于双相不锈钢在一定条件下显示出优越的超塑性,又给加工制造带来很大的效益。往往采取反复高温热处理与变形加工相配合工艺的传统方法来生产超塑性双相不锈钢。此生产工序很复杂,为了简化该生产工艺,采用行星式轧机,以大压下量高速热轧,随后冷轧,但通常是以与热轧方向相同的轧制方向进行冷轧,造成了超塑性各向异性。为消除这一种现象,日本冶金工业公司开发了生产超塑性双相不锈钢的新     

ZnAl5-0.03合金超塑性的研究(Ⅰ)——超塑性变形的力学行为

本文研究ZnAl5-0.03合金超塑性拉伸变形的力学行为。实验表明,合金具有极优异的超塑性(δ≥5000％)。其超塑性能参量(δ、m)依温度变化的规律不同于一般的细晶材料,不存在呈现δ和m峰值的温度区间。合金在试验选取的范围内,应力对应变速率具有高的敏感性。合金呈现超塑效应的温度和应变速率范围均较宽广。轧制状态下,合金具有变形纤维组织,其对超塑变形有利,轧态合金可直接作为超塑态用于成形加工而不需进行特殊的超塑性处理,有利于工业应用。     

置氢Ti-6Al-4V钛合金超塑性研究

通过采用Gleeble-1500D热模拟试验机进行超塑性变形试验,研究变形温度和应变速率对置氢TC4合金超塑变形性能的影响,利用XRD,SEM和TEM分析热氢处理改善钛合金超塑性能的机制.结果表明:置氢可降低超塑成形流变应力、变形温度,提高应变速率和m值;但只有适量的氢才有利于改善钛合金超塑性,即存在一个最佳置氢量;置氢0.35%H(质量分数)的TC4合金在800℃和3×10-3 s-1条件下仍有一定超塑性.分析表明,置氢钛合金超塑变形过程除晶粒转动和滑动机制外,位错滑移和孪生也作为辅助超塑变形机制.     

18Cr2Ni4WA钢的临界点超塑性的研究

本文对18Cr2Ni4WA钢的临界点超塑性及其影响因素进行了研究，结果表明，在临界点(Ac1)温度变形时，由于发生相变，钢的塑性大幅度提高。临界点超塑性具有对应变速率及晶粒尺寸的敏感性。通过对变形过程中组织变化的观察与分析，探讨了临界点超塑性的微观机制。     

Superplastic Al-Cu-Li-Mg-Zr alloys

Superplastic properties have been developed in Al-Cu-Li-Mg-Zr alloys. The alloys have low Zr levels (≤0.2 wt pct) and are experimental compositions that were originally designed as low-density, highmodulus, and high strength alloys for room temperature, aerospace structural applications. The alloys have been manufactured both by an ingot metallurgy (IM) route and a powder metallurgy (PM) route involving rapid solidification processing. After conventional manufacturing, the alloys are not superplastic but require further thermomechanical processing. The microstructural changes that occur during this processing are described. Superplastic properties have been evaluated as a function of temperature, strain rate, and processing history. Prior to thermomechanical processing, the alloys have elevated-temperature ductilities of 100 to 200 pct, strain rate sensitivities of about 0.25, and activation energies corresponding to lattice diffusion. After thermomechanical processing, the alloys have ductilities of 500 to 1000 pct, strain rate sensitivities of about 0.4, and activation energies corresponding to grain boundary diffusion. In addition, room temperature properties have been measured in the solution-treated and peak aged (T6) condition for all the alloys and comparison is made with other commercial, non-Li containing, superplastic alloys. Particular emphasis is placed on properties of interest in aerospace applications such as specific modulus, specific strength, and a buckling failure criterion.     

Superplastic forging of Zn-Al-Cu alloys

Abstract

Superplastic forging of non-ferrous alloys offers the advantages of very low forging loads, inexpensive die materials, and the ability to forge precision complex-shaped parts in a single step. The main disadvantages of the process are the required low forging rates and the necessity of temperature controlled dies. Upset forging and closed die forging have been performed on Zn-22% Al and Zn-20% Al - 2% Cu alloys. Cylinders 1.4 in (35.6 mm) in diameter by 2.5 in (63.5 mm) high have been upset to a reduction in height of 97% and also have been forged into a complex part with thin web sections. The optimum forging conditions are discussed for these materials.

Résumé

Le forgeage superplastique des alliages non-ferreux offre les avantages suivants: très faibles charges, matériaux de matrices peu dispendieux, possibilité de former en une opération des pièces de précision de forme complexe. Les principaux désavantages du procédé sont les faibles taux de forgeage qu'on doit utiliser et la nécessité d'avoir des matrices à température contrôlée. Les alliages Zn-22%Al et Zn-20% Al-20%Cu ont été formés par refoulement et en matrice fermée. Des cylindres de 1.4 po (35.6 mm) de diamètre et de 2.5 po (63.5 mm) de hauteur ont été refoulés jusqu'à une réduction de hauteur de 97% et forgés en une pièce complexe comportant des nervures fines. Les conditions optimales pour forger les deux alliages sont discutées.     

Microstructural Effects in Superplastic Deformation

TheresultsofrecentChineseinvestigationsonmicrostructuralaspectsofsuperplasticdeformationarereviewed.Attentionisgiventograingro-wth,precipitate-freezoneformation,grainboundaryslidingandmigration,anddislocation(bothintragranulardislocationandgrainboundarydisloca-tion)activity.Inthefinalpartofthearticle,anewmodelofmicrograinsuperplasticdeformationbasedonthemovementofgrainboundarydisloca-tionsandinvolvingbothgrainboundaryslidinganddiffusionisdescribed.Thepredictionsofthemodelarecomparedwiththedataexperimentallydetermined.     

单相组织金属间化合物的超塑性行为

在一定条件下具有单相微观组织的L12型[Ni3Al,Ni3(Si,Ti),Co3Ti],L10型（TiAl)和B2型（FeAl,Fe3Al,NiAl)金属间化合物均表现出超塑性行为。其中,L12型和L10型金属间化合物的超塑性变形机制为晶界的滑移,而B2型金属间化合物的超塑性变形则来自于变形过程中发生的动态回复及再结晶,超塑性变形机制的多样性是由于金属间化合物在微观组织及位错结构上（如反向畴界能,层错能和化学成分差异,超位错及界面位错等）比普通金属合金要复杂得多。     

Superplastic behavior of the Sn-Pb eutectic in the as-worked state

Superplastic behavior of the Sn-Pb eutectic was studied in the as-worked state by mechanically working the cast material to varying degrees. The flow behavior was explored in the temperature range of 298 to 443 K and metallographic observations of longitudinal and transverse sections were made. The microstructure was inhomogeneous for low degrees of working, while at high reductions the grains were nonequiaxed. There was strain softening or hardening up to some strain depending on the test conditions. The grains became more equiaxed and coarser in size with increasing deformation. Due to these changes in microstructure and the nonunique stress-strain rate relation, the as-worked material is not suitable from the viewpoint of assessing the mechanisms of superplastic flow based on steady state. Strain dependency of flow stress was also observed in specimens specially processed to obtain equiaxed grains in the as-worked state. formerly a graduate student at Indian Institute of Technology, Kanpur, India.     

Superplastic behavior of two-phase titanium aluminides

A two-phase Ti(57 at. pct)-Al(43 at. pct) alloy with an initial lamellar microstructure was thermomechanically processed to form an equiaxed fine-grained structure. The fine-grained (- L = 5 μm) material was superplastic in the temperature range 1000 °C to 1100 °C, exhibiting a stress exponent of about 2 with a tensile ductility of 275 pct. The rate-controlling deformation mechanism is proposed to be grain boundary sliding accommodated by slip controlled by lattice diffusion in TiAl. At room temperature, the lamellar and fine-grained materials exhibit the same compressive yield stress. The compressive strain to failure, however, for the fine-grained material was about 28 pct compared to 6 pct for the lamellar material.     

Superplastic behavior of spray-deposited 5083 Al

A 5083 Al alloy was synthesized using spray deposition processing with N₂ as the atomization gas. It was noted that the grains that were present in as-spray-deposited 5083 Al were equiaxed with an average size of 15.2 μm. The matrix of the material was supersaturated with Mg and Mn. The asspray-deposited microstructure contained irregular pores with porosity in the range of 0.1 to 5.4 vol pct, depending on spatial location in the preform. The spray-deposited alloy was thermomechanically processed using extrusion and multiple-pass warm rolling to reduce grain size and close porosity. It was observed that spray-deposited 5083 Al exhibited superplasticity following thermomechanical processing by extrusion followed by rolling. Superplasticity was observed in the 500 °C to 550 °C temperature range and 3 × 10⁻⁵ to 3 × 10⁻³ s⁻¹ strain rate range. The corresponding strain-rate-sensitivity factors were in the 0.25 to 0.5 range and increased with decreasing strain rate. A maximum elongation of 465 pct was noted at 550 °C and 3 × 10⁻⁵ s⁻¹. The spray-deposited 5083 Al, thermomechanically processed by direct rolling, exhibited superplasticity in the same temperature and strain rate ranges as those for the extruded and rolled materials. The superplastic elongation of the spray-formed and rolled material was relatively low, being in the range of 250 to 300 pct. The deformation behavior is discussed in light of the presence of porosity in the microstructure.     

晶界在超塑性变形中的作用

超塑性材料所具有的微细晶粒组织,意味着材料的单位体积内存在着大量的晶界。本文结合作者及其合作者近几年来所进行的研究工作,详细地论述了晶界在超塑性变形中所起的重要作用。