难变形材料热静液挤压复合精密塑性成形工艺

目的 研究热静液挤压及其复合塑性变形工艺在高密度钨合金、钨铜合金、钛基复合材料及镁合金薄壁细管等难变形材料方面的制备。方法 通过对高密度钨合金难变形材料进行热静液挤压及旋转锻造等塑性成形,分析了材料在成形过程中的微观组织及性能变化规律和强化机制,制备出大长径比穿甲弹弹芯材料。在此基础上,将该复合塑性变形技术拓展至两相不互溶材料钨铜合金、钛基复合材料及大长径比镁合金毛细管等难变形材料方面的制备。结果 热静液挤压及其复合塑性变形工艺在粉末冶金难变形材料的致密化方面具有显著优势,获得材料不仅致密度高,而且有效实现了控形控性;对于镁合金薄壁细管成形而言,也可以实现组织与性能的有效调配,同时材料的精度较高。结论 热静液挤压及其复合塑性变形工艺在难变形材料的制备与成形方面具有独特的优势与广阔的应用前景。     

Titanium Alloys for Aerospace Applications

There is probably no other material more closely related to aerospace than titanium and its alloys. With a density of 4.5g/cm³, titanium alloys are only about half as heavy as steel or Ni‐based superalloys, yielding an excellent strength‐to‐weight ratio. Furthermore, they have exceptional corrosion resistance. The use of titanium alloys in the aerospace sector will be highlighted including airframe, engine, helicopter, and space applications.     

高温钛合金中杂质元素Fe的扩散行为及其对蠕变抗力的损害作用

高温钛合金是先进航空发动机压气机应用的理想材料,代替钢或镍基高温合金,可以显著提高发动机的推重比和服役性能.随着钛合金使用温度的提高,高温蠕变抗力越来越成为影响其使用温度和使用寿命最关键的力学性能.在400～600℃的温度范围内,钛合金的蠕变变形一般受位错攀移机制所控制,蠕变激活能近似等于有效扩散激活能,因此,扩散是影响钛合金高温蠕变抗力的最主要因素.杂质元素Fe在钛合金中具有反常大的扩散能力,是Ti自扩散系数的103～105倍,在Ti中的扩散可能受离解扩散机制所控制.钛合金中的微量Fe同时会显著促进Ti的自扩散,提高位错攀移速率,从而降低蠕变抗力.为了改善高温钛合金的蠕变性能,需要严格控制原材料如海绵钛和中间合金中杂质Fe的含量.     

粉末冶金难变形材料热静液挤压技术进展

综述了热静液挤压技术在烧结态粉末冶金难变形材料挤压成形与粉末体高致密化固结方面的研究进展。简述了热静液挤压工艺原理、工艺特点与适用范围,分析了热静液挤压润滑层形成的影响因素,介绍了热静液挤压润滑介质研制和热静液挤压技术在粉末冶金高比重钨合金、γ-TiAl基合金材料的挤压成形以及纳米晶铝合金、弥散强化铜合金、NdFeB永磁合金等金属粉末体材料的高致密化固结成形方面的应用,指出了热静液挤压工艺的技术优势与发展前景。     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.     

Precipitate coarsening and its effects on the hot deformation behavior of the recently developedγ’-strengthened superalloys

Recently,theγ’-strengthened superalloys are of great interests in high temperature applications due to their excellent high temperature strength which is derived from theγ’strengthening phase.For theseγ’-strengthened superalloys,the changes in morphology,size and distribution ofγ’precipitates due to coarsening during thermal exposure have a significant impact on the properties of alloys.This article briefly summarizes the recent advances on the coarsening behavior of gamma prime precipitates in the recently-developedγ’-strengthened superalloys and its effects on the hot deformation behavior of superalloys,drawing specific examples on Allvac^■718 Plus TM and Ni3 Al-based intermetallic superalloys.It is found that the particle size plays an important role in morphological evolution ofγ’precipitates.For instance,the morphology ofγ’precipitates evolves from cuboidal to strip-like or other complex structures in Ni3 Al-based intermetallic alloys,while theγ’precipitates in Allvac^■718 Plus alloy always present nearspherical morphology due to the relatively small initial particle size.The Lifshitz-Slyozof-Wagner(LSW)theory and its modifications,as well as Trans-Interface Diffusion Controlled(TIDC)theory have been applied to describing the coarsening kinetics ofγ’precipitates.Additionally,the hot deformation behavior ofγ’-strengthened superalloy is found to be greatly influenced by the coarsening ofγ’precipitates.     

Modelling and lifing of structural materials for future aeroengine components

This paper reports on some of the major research and development activities at the SMC into materials modelling of existing advanced high strength superalloys and the work in progress to understand the step change materials which will have to be introduced into future engines to meet the perceived performance requirements. These studies are aimed at developing appropriate lifing methodologies and ensuring safe service usage of these materials. Lifing models for dwell sensitive titanium alloys, powder metallurgy materials, single crystal alloys, metal matrix composites and intermetallic alloys are considered.     

Extrusion of AI–Zn–Mg–Cu–Zr alloys

Abstract

Four aluminium alloys of different zinc/magnesium ratio have been studied under various extrusion conditions. The alloys were cast in steel book moulds and subjected to initial thermomechanical treatments. Studies were made of hot extrusions and cold hydrostatic extrusions and in each case the changes in the extrusion parameters were analysed. An attempt has been made to explain some of the extrusion defects which appeared in various extruded sections. The extrusion speed was found to be crucial, since sections developed surface cracks at higher speeds. The extrusion speed was also found to vary inversely with the extrusion ratio, with higher speeds at low ratios. A well defined solute–depleted weld zone was observed on each of the four faces of a square tube extruded using a porthole die. Thermal treatment was not found to improve this weak weld zone. Tubes extruded using a floating-mandrel die withstood pressure testing up to 550 MPa.

MST/43     

Recent Progress in the Development of Gamma Titanium Aluminide Alloys

Intermetallic titanium aluminides offer an attractive combination of low density and good oxidation and ignition resistance with unique mechanical properties. These involve high strength and elastic stiffness with excellent high temperature retention. Thus, they are one of the few classes of emerging materials that have the potential to be used in demanding high‐temperature structural applications whenever specific strength and stiffness are of major concern. However, in order to effectively replace the heavier nickel‐base superalloys currently in use, titanium aluminides must combine a wide range of mechanical property capabilities. Advanced alloy designs are tailored for strength, toughness, creep resistance, and environmental stability. These concerns are addressed in the present paper through global commentary on the physical metallurgy and associated processing technologies of γ‐TiAl‐base alloys. Particular emphasis is paid on recent developments of TiAl alloys with enhanced high‐temperature capability.     

HOT CONSOLIDATION OF B2 NiAl and FeAl

Alloys based on B2 NiAl and FeAl are potential structural materials for high temperature applications. This paper summarizes some of the results from hot consolidation of these alloys in joint programs between CWRU and NASA Lewis Research Center. The major emphasis has been on using powders and consolidating them by hot extrusion and by hot pressing in order to obtain a range of microstructures. Alloying additions have been made in the elemental form as well as in the prealloyed forms. Oxide dispersion strengthening has been attempted. Dynamic recrystallization plays an important role in the microstructural development during hot consolidation of these alloys, the resulting grain size being controlled by powder variables as well as the processing parameters. Results of processing of cast alloys by hot extrusion techniques are also included for comparison.     

Mechanical property requirements for aero gas turbine materials

Abstract

The outstanding performance of current military and civil aero gas turbine engines is linked closely to the way in which modern design and manufacturing techniques have become totally integrated with materials designed specifically for operation within the hostile environment of a gas turbine. Advanced titanium alloys are used extensively throughout the compressor and nickel-base superalloys dominate materials application in the turbine. In spite of current achievements, the engine designer is still under severe competitive pressure to improve engine performance still further and this will inevitably lead to even more demanding material requirements. The present paper outlines the continuing trends in engine development and describes the impact these are having on materials technology in general and the mechanical property requirements of nickel-base superalloys in particular.

MST/512     

Development of non-flammable high strength extruded Mg-Al-Ca-Mn alloys with high Ca/Al ratio

A series of non-flammable high strength Mg-Al-Ca-Mn alloys with high Ca/Al ratio were fabricated by water-cooled casting and hot extrusion. Microstructure and mechanical properties were investigated to study the effect of hot extrusion. The experimental results showed that hot extrusion significantly improved the mechanical properties by grain refinement and precipitates. Ignition temperature was measured by furnace test, and the highest temperature is up to approximately 1040?°C due to the composite oxide layer consisting of CaO and MgO. In addition, a laboratory-scale flame test was conducted to evaluate the flammability of smaller specimens. These alloys exhibited marvelous flame resistance attributed to the protective effect of dense and stable oxide film.     

Microstructure and Properties of As-Cast Mg–2.0Sn–1.0Zn–1.0Y–0.3Zr Alloys at Different Extrusion Ratios

Herein, the effect of hot extrusion with different extrusion ratios (λ = 6, 8, 10, and 12) on the microstructure evolution and properties of as-cast Mg–2.0Sn–1.0Zn–1.0Y–0.3Zr magnesium alloys, using optical microscopy (OM), scanning electron microscopy (SEM), immersion corrosion and electrochemical corrosion experiment, and tensile testing, is investigated. The results show that the Mg₁₄SnY and Mg₆SnY precipitated phases exist in the alloy before and after extrusion. After hot extrusion, the second phase of the alloy is broken into particles along the extrusion direction, whereas the grain size is significantly reduced, and dynamic recrystallization and deformed grains exist in the microstructure. The mechanical properties of the extruded alloy improve, but the corrosion resistance weakens. When the extrusion ratio is λ = 10, the extruded alloy exhibits relatively good mechanical properties and corrosion resistance. The corrosion behaviors of the extruded alloys are affected by both the grain size and galvanic corrosion. In the initial stage of corrosion, intergranular corrosion plays a major role in reducing the corrosion resistance of the extruded alloys. With prolonged corrosion time, galvanic corrosion has a more significant effect on weakening the corrosion resistance of the extruded alloys.     

有色金属固态回收技术的研究进展

有色金属固态回收避免了重熔,且回收率高、成本低及回收件力学性能优良,具有人的应用前景.介绍了有色金属固态回收技术的原理、特点,重点结合铝合金、镁合金的固态回收研究现状,详细介绍了常规挤压、轧制、循环塑性加工等固态回收技术的研究进展.最后对有色金属固态回收技术的研究和发展提出了一些建议.     

Aluminium and silicon base coatings for high temperature alloys—Process development and comparison of properties

The paper is concerned with systematic studies on the formation of overlay coatings on nickel and iron base superalloys to improve their resistance against high temperature oxidation and hot corrosion. In contrast to the simpler case of aluminizing nickel base alloys, the problems arising in aluminizing iron base superalloys and in siliconizing nickel base alloys have not yet been solved.A new and economical coating procedure is presented, which involves a reaction sintering process of unalloyed powder mixtures to obtain overlay coatings. The influence of the compositions of the layer and the substrate on the chemical compatibility of the whole layer composite is described in detail. It is shown that overlay coatings containing high concentrations of silicon can only be applied on nickel base superalloys if elements that are able spontaneously to form reaction barriers are present within the substrate alloy (e.g. aluminium) or in the as-preformed interlayer. Refractory metals have proved to be the most advantageous.To obtain a ductile coating, silicon-rich donor phases in the form of isolated precipitates were incorporated into a matrix containing low concentrations of silicon. These coating systems can also be applied to improve the aluminization of iron base alloys. The high temperature oxidation and corrosion behaviours of the coated samples were tested in burner gas or air at 1000°C and in molten salts at 900°C.     

Intermetallic Alloys Based on Orthorhombic Titanium Aluminide

Orthorhombic titanium aluminides represent the youngest class of alloys emerging out of the group of titanium aluminides. These new materials are based on the ordered orthorhombic phase Ti₂AlNb, which was discovered for the first time in the late 1980s as a constituent in a Ti₃Al‐base alloy. In the 1990s primarily simple ternary Ti–Al–Nb orthorhombic alloys were investigated in countries such as the US, UK, India, France, Japan, and Germany. The drive was mainly provided by jet engine manufacturers and related research labs looking for a damage‐tolerant, high‐temperature, light‐weight material. This follows the aim of further extending the use of lower density titanium‐base materials in temperature regimes, where heavy nickel‐base superalloys are the only alternative today. The present understanding of microstructure–property relationships for orthorhombic titanium aluminides reveals an attractive combination of low and high temperature loading capabilities. These involve high room‐temperature ductility and good formability, high specific elevated temperature tensile and fatigue strength, reasonable room‐temperature fracture toughness and crack growth behavior, good creep, oxidation, and ignition resistance combined with a low thermal expansion coefficient. This article reviews the aspects of composition–microstructure–property relationships in comparison to near‐α titanium, TiAl, and nickel‐base alloys. Special emphasis is also placed on the environmental degradation of the mechanical properties.     

Glass forming ranges of cobalt-base thin film alloys

The glass forming ranges of cobalt-base binary and ternary thin film alloys containing zirconium, titanium, niobium, molybdenum, vanadium and silicon have been studied in the cobalt-rich region. The minimum solute concentration for glass formation decreased with increasing difference in atomic radii or Pauling's electronegativity, as well as the cooling rate. Cobalt-base binary alloys readily showing glass formation are shown on the glass formation diagram. The values of atomic size effect in alloys sputtered at room temperature were about 0.065, and decreased with increase of cooling rate. The value was decreased in alloys having a large heat of formation. In ternary cobalt alloys containing zirconium, niobium, molybdenum and vanadium, the glass forming range could not be interpreted as the concept of atomic size effect alone.     

钛合金中ω相变的研究进展

钛合金中的ω相及其相变对合金的组织性能影响较大,因此近年来ω相变也成为钛合金研究中的热点问题之一。从ω相的形成、分解、组织形貌以及ω相辅助α形核的角度总结归纳了相关研究报道,对比了相关模型观点的优缺点,阐述了ω相目前仍存在的学术分歧。     

热挤压工艺对AZ31镁合金晶粒大小及性能的影响

对商用AZ31镁合金挤压棒材进行了不同工艺参数的挤压变形,系统研究了挤压工艺参数对AZ31镁合金晶粒大小以及性能的影响,并对镁合金组织的微晶尺寸进行了金相定量分析.研究结果表明,热变形可有效细化晶粒,但对AZ31镁合金晶粒细化是有限度的;对已通过热挤压变形晶粒细化的AZ31镁合金进一步进行大的塑性变形,其晶粒不但没有进一步的细化反而比挤压前略有长大.     

热等静压技术在镍基铸造高温合金领域的应用研究

镍基铸造高温合金是航空发动机与燃气轮机生产制造过程中应用的主要材料之一,在航空航天、能源工业、船舶舰艇等领域有着广泛的应用。现代航空工业的飞速发展离不开高温合金综合性能的快速提升,而热等静压技术在镍基铸造高温合金领域的应用对镍基铸造高温合金综合性能的改进方面发挥了举足轻重的作用。本文介绍了热等静压技术的工作原理与应用发展历史,总结了热等静压技术在镍基铸造高温合金领域的研究应用现状,重点阐述了热等静压技术对铸造高温合金的致密化作用机理与组织性能影响、热等静压对长期服役镍基铸造高温合金组织修复研究以及实现两种镍基高温合金扩散连接的应用优势与研究成果。同时指出热等静压技术研究中存在的一些问题及国内热等静压技术在镍基铸造高温合金领域的发展趋势。