喷射沉积SiC_P/Al复合材料的塑性变形致密化与冶金缺陷消除研究进展

喷射沉积SiC_P/Al基复合材料具有优异的力学性能,但因孔隙、沉积颗粒边界、沉积颗粒表面的氧化皮等冶金缺陷无法完全消除而使其应用受限,消除冶金缺陷和改进致密化技术对于提高喷射沉积铝基复合材料的性能和扩大其应用尤为重要。本文论述了喷射沉积颗粒增强铝基复合材料的致密化技术,着重介绍了楔形压制工艺、陶粒轧制、旋球同步致密化等新型致密化技术;展望了喷射沉积铝基复合材料的发展趋势,认为热等静压、陶粒轧制的剪切作用小,不能完全消除孔洞和沉积颗粒边界等缺陷;提出颗粒增强铝基复合材料的喷射沉积制备与致密化同步进行有利于减少晶粒与弥散粒子的粗化,提高复合材料的力学性能和成形性能。采用旋球同步致密减少坯料孔隙,降低坯料沉积坯中的氧含量,再通过楔形压制实现沉积颗粒间的完全冶金结合。     

多层喷射沉积颗粒增强铝基复合材料的研究现状与发展趋势

通过多层喷射沉积技术制备颗粒增强铝基复合材料,强化了冷却效果,能获得细小均匀的显微组织,优化复合材料中增强相的分布及其与基体的结合状态。本文综述了喷射沉积颗粒增强铝基复合材料的发展现状;介绍了多层喷射沉积技术的原理与工艺参数;概述了喷射沉积颗粒增强Al-Zn—Mg系、Al—Fe系与Al-Si系复合材料;并介绍喷射沉积颗粒增强铝基复合材料的致密化技术,着重介绍在小吨位设备上致密大块多孔材料的楔形压制工艺、外框限制轧制、陶粒包覆轧制工艺和热压后轧制工艺;展望了喷射沉积铝基复合材料的的发展趋势,认为增强颗粒与基体界面的结合强度有待进一步提高,提出了多层喷射沉积技术将朝在可编程控制下制备组织均匀、细小且致密度高的大尺寸坯料方向发展,而致密化技术也将朝小吨位设备制备大尺寸致密材料的方向发展,认为热压和楔形压制作为预致密方式能有效提高大尺寸喷射沉积坯料的成形能力,有利于进一步成形。     

喷射沉积8009/SiCP铝合金的陶粒轧制成形性能研究

针对喷射沉积铝合金板坯含有一定量的孔隙、直接轧制时易出现板坯表面横裂及边裂的问题,探讨了一种新型的准等静压轧制工艺-陶粒轧制.主要研究在陶粒轧制工艺过程中传压介质对喷射沉积8009/SiCP铝合金板坯轧制成形性能的影响.结果表明,在陶粒轧制过程中合理设计、选取及控制传压介质,避免了板坯轧制变形过程中裂纹的形成,有效地提高了喷射沉积铝合金板坯的轧制成形性能.     

喷射沉积8009Al/SiCp复合材料楔形压制致密化

研究了喷射沉积8009Al/SiCp复合材料楔形压制致密化规律,通过光学显微镜(OM)、扫描电镜(SEM)、密度和硬度测试等手段研究了楔形压制过程中复合材料致密化机理。结果表明,多孔复合材料在楔形压制过程中,同时存在致密化和塑性变形两种现象,压制初期主要是致密化;多孔坯不同位置的致密度存在差异且表面摩擦力对致密化有影响;复合材料塑性变形过程中,孔洞及团聚的碳化硅粉末随基体金属的塑性流动得到破碎与分散。     

快速凝固Al-Fe系耐热铝合金的研究进展

通过快速凝固技术制备Al-Fe系耐热铝合金,可以获得弥散细小且在高温下扩散率低的第二相粒子,从而获得良好的耐热性能。本文综述了快速凝固Al-Fe系合金的发展现状,介绍了各系列Al-Fe合金,着重介绍了Al-Fe-V-Si合金及其复合材料;综述了制备合金的快速凝固技术的发展历程;概述了几种快速凝固Al-Fe系耐热铝合金常用的致密方法,并介绍了能在小吨位设备上致密大块多孔材料的楔形压制工艺、外框限制轧制和陶粒包覆轧制工艺;展望了快速凝固Al-Fe系耐热铝合金的发展趋势,认为合金的耐热性能有待进一步提高,提出了制备方法将朝高冷却速率下制备组织均匀且致密度高的大尺寸坯料方向发展,而致密化技术也将朝小型设备制备大尺寸致密材料的方向发展。     

喷射沉积多孔材料的轧制变形理论

根据"表观总应变能达到一个临界值时材料开始屈服"这一概念,研究和建立了多孔材料轧制塑性变形屈服准则,根据"多孔材料变形时质量不变"原理建立了轧制变形过程中高向变形与相对密度、高向变形与纵向变形、泊松比与相对密度的关系.理论预测与用喷射沉积制备的FVS0812耐热铝合金多孔材料的轧制结果符合得较好;建立了多孔材料轧制变形相对密度与高向应力的关系,提高多孔材料所处的压应力状态可以加速材料的致密化速度,改善多孔材料的轧制成形性能.     

TiAl合金气雾化制粉及热等静压成形研究进展

概述了TiAl合金气雾化制粉及热等静压成形的主要研究成果。在TiAl合金粉末制备方面,重点介绍了气雾化制粉工艺、粉末粒度控制、粉末氧含量控制和粉末组织特征。针对热等静压技术,介绍了TiAl合金粉末热等静压致密化过程及机理,总结了采用热等静压近净成形工艺制备TiAl合金转捩片的研究成果。结合粉末冶金TiAl合金研究进展,提出了未来TiAl合金粉末制备及成形技术的发展方向。     

改善喷射沉积多孔材料开裂行为工艺的研究

介绍了多孔金属材料的致密化过程及塑性变形,分析了其轧制开裂行为规律,研究了多孔金属材料在外框限制轧制中的轧制过程及避免多孔材料开裂的工艺措施.     

运动器件中的粉末冶金零件

美国每年用于运动器具的花费高达170.64亿美元,无论是专业的还是业余的运动器材均要求降低成本,因此粉末冶金制造技术有着很大的吸引力,此文主要介绍重量轻的钛合金和高比重钨的粉末冶金运动器件.钛粉末冶金工艺有两种:一是元素粉末混合法,二是预合金法.现在这两种工艺都可通过金属注射成形(MIM)和激光成形来实现.元素粉末混合法成本低,但多数情况下材料性能较差;预合金法成本较高,但材料的机械性能相当于铸锻件.此外,粉末成形工艺还有冷、热等静压、粉末轧制和挤压、喷射成形和气相沉积等.     

NiTi形状记忆合金的加工方法

对NiTi形状记忆合金的多种加工方法如锻造、热挤压、轧制和拉拔、冷加工、粉末成形、包套碎片挤压成形、溅射沉积加工等进行了详细介绍.     

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。     

Mechanisms of Polycrystalline CVD ZnS Densification during Hot Isostatic Pressing

The densification kinetics of CVD ZnS are studied during hot isostatic pressing by monitoring the porosity of the material. The process is shown to be accompanied by significant microstructural changes. The results indicate that, during hot isostatic pressing, both the diffusional coalescence and plastic deformation mechanisms are operative.     

Effect of Phase Transformation on Densification During Hot Isostatic Pressing

Densification of mixed phases which undergo phase transformation at elevated temperatures during hot isostatic pressing is described. The effect of the phase transformation on the densification process is shown relative to the densification characteristics of the major phase component of the mixed system. The densification of a mixed phase system undergoing phase transformation is compared using the mechanism maps for hot isostatic pressing of the single phase material. Densification of mixed phase systems undergoing phase transformation, such as homogenization with Kirkendall Effect, is considerably slower than its constituent single phase material. The tendency to generate Kirkendall pores due to homogenization of chemically different materials opposes the normal densification process, thus slowing down the densification process.     

PROCESSING AND PERFORMANCE OF SEVERAL SiC WHISKER-REINFORCED Al2O3 MATRIX COMPOSITES

The influence of different SiC whiskers on the processing and performance of Al₂O₃ matrix composites were investigated. Three types of commercial SiC whiskers produced in the United States were used. The composites contained 30 v/o of SiC whisker and were consolidated by both hot pressing (HP) and hot pressing followed by hot isostatic pressing (HP/HIP) techniques. The microstructure, mechanical properties, fracture behavior and toughening mechanisms of the composites were evaluated. The results show that the whisker types and processing techniques have profound effect on the densification and the properties of the composites.     

Effect of glass container encapsulation on deformation and densification behavior of metal powders during hot isostatic pressing

Hot isostatic pressing process consolidates metal powders to produce fully dense parts with complex geometries. Deformation behavior of compacts during hot isostatic pressing process typically is anisotropic for powders encapsulated in metal containers. Therefore, post-processing processes are required to fabricate the parts with required shape and dimension. This paper reports the effect of glass container encapsulation on deformation and densification behavior of 316 L stainless steel powder and nickel-based superalloy powder during hot isostatic pressing. Finite element calculations from Abaqus – finite element analysis (FEA) were compared with measured deformed shapes of powder compacts. Finally, samples deformed in glass containers were compared with those in metal containers to study the capabilities of glass containers to form near-net-shape parts. Glass containers transmitted all the pressure applied to the compacts and did not induce the Mises stress to the compacts that leads to homogeneous distribution of relative density over the compacts. Glass containers showed more homogeneous densification and uniform deformation of compacts compared to the conventional metal containers.     

Thermomechanical processing of a nickel-base superalloy powder compact

Some means by which the grain size and flow strength of nickel-base superalloy powder .compacts can be controlled during processing have been examined. The compacts were prepared by hot isostatic pressing and their flow behaviour studied by constant true strain rate compression testing under conditions simulating isothermal forging. It was found that the selection of a finer starting powder results in slight lowering of flow strength at forging temperatures. Prior cold working of the compact by hydrostatic extrusion also leads to small reductions in strength at these temperatures. Both the . grain size and flow strength may change substantially during plastic deformation at forging temperatures. This depends on the conditions of strain rate and temperature. Under all the testing conditions examined this transient flow behaviour is followed by a stesdy state regime of flow during which neither the grain size nor the flow strength continue to change. These observations and their practical implications are discussed.     

Modeling of conventional hot compaction and Spark Plasma Sintering based on modified micromechanical models of porous materials

Numerous micromechanical models have been proposed to describe the behavior of porous materials. Cocks, 1989, Ponte-Castaneda, 1991, Duva and Crow, 1992, Sofronis and McMeeking, 1992 have proposed different elliptic strain rate potentials which are mainly valid for small porosity (below 10% in general). In the present contribution, the domain of validity of the micromechanical models has been extended to the range of porosity [0; 50%] which allows their use for the modeling of consolidation process at elevated temperatures and pressures. The proposed modification introduces three new parameters that can be calibrated using compression, hot pressing and hot isostatic pressing tests. Lead and boron materials are considered and model parameters have been identified based on experimental works of Nicolle (1999) for boron and of Geindreau et al. (1999a) for lead. In particular, it is shown that the densification of the two materials can be well estimated during hot pressing and hot isostatic pressing. In consequence, the proposed modification permits the use of micromechanical models for the investigation of hot compaction process. Next, the Spark Plasma Sintering (SPS) of lead is considered. The application of an intense electric current generates large heating rates in the sample. Therefore, the compaction of the material can be achieved in a relatively short time period, making the SPS a very promising technique to elaborate nanostructured materials. A thermal–electrical–mechanical simulation has been proposed, the material behavior of the porous sample being described by the proposed modified model. An important outcome of the simulation is the possibility to present maps of temperature and porosity. It is shown that, temperature heterogeneities inside the sample lead to heterogeneities in the relative density of the final product.     

Fabrication of Al-Si controlled expansion alloys by unique combination of pressureless sintering and hot forging

The present work reports the synthesis of Al-X wt.% Si (X = 20, 30, 40 and 50) alloys by a unique combination of pressureless sintering (PLS) and hot forging at 800 and 1000 MPa forging pressures with 37.5 and 50% deformation, respectively, in a specially designed die. The effect of hot forging parameters on densification, hardness, compressive strength and microstructures of the alloys was studied as well as suitably compared with the conventional PLS alloys. The ‘PLS + forged’ alloys, specifically 50% deformed at 1000 MPa, yielded excellent densification and subsequent very good mechanical properties. The combination of hot forging pressure and temperature enabled the high densification due to pore collapse, fracturing of Si particles leading to Al flow between the fractured Si particles and better interfacial diffusion between Si and Al. Moreover, the alloys showed excellent electrical conductivity (~67% of that of pure Al), low coefficient of thermal expansion (CTE) and high thermal conductivity (TC) at par with the same alloys prepared with other methods, like spark plasma sintering, hot pressing and Osprey techniques.     

石墨烯增强镍基粉末高温合金复合材料的力学性能

采用湿混法将石墨烯纳米片分散到高温合金粉末中,并采用热等静压+热挤压+等温锻造+热处理的方法制备出FGH96镍基粉末高温合金。结果表明:石墨烯纳米片在高温合金中分散均匀,初步发现在后续的热工艺过程中并未发生变性;添加0.1%(质量分数)的石墨烯后,室温抗拉强度和屈服强度分别提高了58MPa和43MPa,塑性从21.0%提高到37.3%;650℃条件下抗拉强度和屈服强度分别提高了58MPa和28MPa,塑性从18.5%提高到26.5%。此外对石墨烯增强FGH96镍基高温合金力学性能的作用机制也进行了进一步分析。