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。     

颗粒增强铝基复合材料热等静压近净成形有限元模拟

目的 建立可靠的模拟方法,以更高效地预测颗粒增强铝基复合材料(PRAMC)粉末热等静压中的形状变化和不同部位致密度的差异,解决传统实验试错方法适用性差且费时费力的问题,满足批量应用的需求。方法 以45%(体积分数)SiCp/6092Al复合材料为研究对象,构建了能预测粉末热等静压成形过程的有限元模型。使用Gurson-Tvergard-Needleman(GTN)模型作为粉末本构模型,建立了粉末尺度的代表性体积单元(RVE)对GTN模型进行修正。结果 通过对比GTN模型计算结果与实验结果,发现修正后的GTN模型能更准确地预测模型的最终变形尺寸,与修正前相比,相对误差降低了1.6%~2.9%。使用修正后的GTN模型对杯形回转体零件的热等静压成形过程进行预测,最终形状的计算结果与实验结果的相对误差仅为0.2%~3.1%,致密度分布的相对误差在0.5%以内。在探究包套厚度对热等静压过程的影响时发现,随着包套厚度的增大,热等静压过程中的屏蔽作用增强,内部粉体致密度下降。结论 为PRAMC热等静压近终形制备的形状和致密度控制问题提供了有限元预测工具,辅助优化了热等静压工艺和包套设计,降低了颗粒增强铝基复合材料热等静压近净成形过程开发的试错成本。     

Hot consolidation and mechanical properties of nanocrystalline equiatomic AlFeTiCrZnCu high entropy alloy after mechanical alloying

The present study is aimed to investigate the consolidation behaviour and mechanical properties of nanocrystalline equiatomic AlFeTiCrZnCu high entropy alloy after mechanical alloying. The consolidation was achieved by cold pressing with conventional sintering, vacuum hot pressing and hot isostatic pressing techniques. The microstructure and mechanical properties were evaluated. The hardness and compressive strength of nanocrystalline equiatomic AlFeTiCrZnCu high entropy alloy after vacuum hot pressing are 9.50 and 2.19 GPa and those after hot isostatic pressing are 10.04 and 2.83 GPa, respectively. The wear resistance is found to be higher than the commercially used materials such as Ni-hard faced alloy.     

Neue Kapseltechnik für Diamantverbundwerkstoffe mittels PVD‐Verfahren

Novel encapsulation technique for diamond composites using PVD‐process For machining of mineral materials diamond tools consisting of a steel body combined with diamond impregnated segments are used. Frequently, these segments are hot pressed. Other process routes are pressureless sintering of green compacts partly combined with hot isostatic pressing and hot isostatic pressing of encapsulated powder mixtures. The compaction effect of hot isostatic pressing require a low porosity of sintered components realized by using ultra‐fine metal powder or an impermeable capsule made of metal or glass. The Institute of Materials Engineering pursues a novel process route by physical vapor deposition of a coating on pressureless sintered composites. The thin coating acts as a capsule and guarantees the pressure transfer in the following hot isostatic pressing process. Although bronze powders with particle sizes up to 90 μm are used, the manufacturing of diamond composites with low porosities is possible. In comparison to conventional encapsulation‐techniques the main advantages of this novel process route are the use of comparatively coarse metal powders and a larger geometric flexibility.     

Transformation in metal materials during hot isostatic pressing

The paper presents a review of transformations in a number of metal materials during hot isostatic pressing which result in changes in the shape, density, morphology, and composition of the structural components of some metals, including cast, powder, and composite titanium alloys, heat-resistant nickel alloys, hard alloys of the WC-Co system, and also some aluminum and aluminide materials. Methods for studying the compaction processes using an eddy current dilatometric cell and differential barothermal analysis to determine the baric shift of the characteristic temperatures for some heat-resistant nickel alloys are described. The data on the practical application of hot isostatic pressing are presented, which makes it possible to fabricate the most important parts of gas turbines. It is shown that hot isostatic pressing causing transformations of different physicochemical origin should be considered as a necessary step of the production of metals to ensure their limiting strength characteristics.     

喷射成形多孔材料的致密化工艺综述

介绍了6种常用的喷射成形多孔材料致密化工艺,即热挤压、轧制、锻造、热等静压、楔形压制和陶粒压制工艺,重点介绍了各种工艺的原理、特点、优缺点以及针对某些缺点而采取的一些改进措施.发现热挤压、轧制、锻造、热等静压和陶粒压制工艺能单次使喷射成形多孔材料整体成形致密化,而楔形压制是一种通过局部小变形累积以实现整体成形致密化的工艺;楔形压制在致密化喷射成形大尺寸材料方面具有独到的优势.最后,探讨和展望了今后的发展方向.     

热等静压对第三代单晶高温合金DD33显微组织和持久性能的影响

对第三代DD33单晶高温合金进行标准热处理、热等静压以及不同制度的后续固溶和时效处理,并在850℃/650 MPa和1100℃/170 MPa条件下进行高温持久性能实验,使用金相显微镜(OM)、扫描电子显微镜(SEM)和X射线三维成像技术(XCT)等手段观察和表征不同状态的样品,研究了热等静压和热处理对这种合金显微组织和持久性能的影响。结果表明：铸态DD33单晶高温合金经过适当的热等静压和后续热处理工艺后,样品的组织形貌(γ′相尺寸、体积分数与立方化程度)与标准热处理态基本相同。与标准热处理态合金相比,热等静压处理后合金显微孔洞的体积分数和尺寸均显著降低,其体积分数从0.0190%降低到0.0005%,最大孔等效直径从36.9 μm减小到14.2 μm。在850℃/650 MPa和1100℃/170 MPa条件下热等静压后的样品持久寿命均显著延长。这表明,适当的热等静压和热处理能消除合金内部的显微孔洞缺陷,使其持久性能显著提高。     

Hot isostatic pressing of beta-alumina

The effect of hot isostatic pressing on the properties of sintered beta-alumina has been investigated. The mechanical strength is increased as compared with as-sintered material. The ionic resistivity is decreased by hot isostatic pressing but this has been shown to be related to the heat treatment rather than the application of pressure. The changes in mechanical and electrical properties are related to changes in ceramic microstructure.     

微量SiO2添加对Pr:Lu3Al5O12陶瓷光学及闪烁性能的影响

在制备透明陶瓷时, 广泛采用烧结助剂来提升陶瓷的光学质量。但烧结助剂的添加可能会恶化陶瓷的发光性能。本研究采用真空预烧结合热等静压烧结制备了0.25at%Pr:LuAG闪烁陶瓷, 研究了微量SiO₂烧结助剂对陶瓷光学及闪烁性能的影响。结果表明, 添加少于200 ppm的微量SiO₂(1 ppm表示添加量为1×10^-6 g/g)能有效促进热等静压过程中气孔的排出, 有效提升了Pr:LuAG陶瓷的光学性能。150 ppm SiO₂添加的Pr:LuAG陶瓷在400 nm处的直线透过率约为77%。同时研究了预烧温度及时间对Pr:LuAG陶瓷光学性能的影响。在实现完全闭气孔结构时, 进一步升高预烧温度或延长保温时间会降低热等静压过程中的致密化速率, 不利于气孔的排出, 从而降低了Pr:LuAG陶瓷的光学质量。此外, 添加微量SiO₂对Pr:LuAG陶瓷闪烁性能的影响较小。添加微量SiO₂结合热等静压烧结是制备Pr掺杂石榴石闪烁陶瓷的有效途径。     

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.     

热等静压工艺参数对ZTC4钛合金力学性能的影响

为了使ZTC4钛合金铸件具有较优的力学性能,系统地研究了热等静压温度、时间、压力等工艺参数对ZTC4钛合金铸板力学性能的影响.结果表明:热等静压工艺参数变化对ZTC4钛合金室温拉伸性能、弯曲性能都有影响,其中对ZTC4钛合金伸长率的影响最为明显,但对冲击性能影响不显著.综合考虑各因素,在920℃/125MPa/2h热等...     

Effect of hot isostatic pressing on mechanical properties and microstructure of 70–30 cupronickel castings

Abstract

The present work is part of an investigation into the use of hot isostatic pressing to recover 70–30 cupronickel castings. These alloys have particularly good corrosion resistance and, when strengthened with silicon and chromium, produce a material capable of use in very severe conditions of stress and massive corrosion. However, it is not possible to recover such castings by the application of repair welding, because of the possibility of reduced corrosion resistance in the vicinity of the weld. Hot isostatic pressing represents an alternative method of casting recovery. The results reported in the present work refer to the effect of hot isostatic pressing on mechanical properties, microstructure, and the level of segregation in the alloys. Hot isostatic pressing may be used to remove casting defects in the form of fine pores up to total porosity of 5%. However, in cases where porosity takes the form of very large defects, the mechanical properties of the recovered region are inferior to those of the originally sound material. This effect is probably associated with the presence of very finely distributed oxide particles in the originally defective parts of the casting. The optimum hot isostatic pressing temperature for the best overall combination of properties was 950°C.

MST/1732     

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.     

Mechanical and technological properties of vacuum plasma sprayed and hot isostatically pressed Composite materials

Ti/NiCr20TiAl and NiCoCrALY/IN617 composite materials have been produced by vacuum plasma spraying, Arc-PVD and hot isostatic pressing. Regarding their mechanical and technological properties they are dependent on the heat treatment during the production process. Therefore optimized strength properties can be obtained by using thermal age hardening base materials.     

Casting defects and high temperature fatigue life of IN 713LC superalloy

High-cycle high temperature fatigue life of a superalloy IN 713LC in as cast state and after hot isostatic pressing was experimentally determined for symmetrical cycling and cycling with tensile mean stress of 300 MPa. Fatigue tests were conducted at 800 °C in laboratory air. It has been found that the hot isostatic pressing improves the fatigue life. Large casting defects are sites of fatigue crack initiation in both states of the alloy. The hot isostatic pressing reduces the size of casting defects, however the broad scatter band of the lifetime data remains. Determination of casting defects size by optical microscopy on metallographic sections and an analysis of the size distribution by extreme value statistics indicates two types of defects: (i) small isolated defects and (ii) defect clusters consisting of complicated interconnected shrinkages in the three-dimensional space. The size distribution of both types of defects follows the extreme value statistics. This enables to estimate the maximum size of a defect likely to occur in a defined volume. The predicted maximum defect size in a volume of a fatigue specimen reasonable corresponds to the size of defect observed on the fracture surface of failed specimen.     

热等静压烧结Nd-Fe-B永磁体

热等静压烧结通常用来促进合金致密化和细化组织。本文尝试对Nd32．54Dy0．5Fe65．36Al0．6B1.0预烧结体分别进行热等静压烧结和常规烧结，旨在研究热等静压烧结能否促进Nd-Fe-B合金的致密化和晶粒细化。首次发现；高温热等静压烧结时，预烧结样品内的部分富Nd液相外流，在样品内形成空洞，被高压Ar气填充，造成样品不能收缩，磁体的密度比常规烧结磁体的低，力学性能明显恶化；且液相外流引起晶粒转动，导致取向度降低，最终磁体的剩磁和磁能积降低。     

Effect of processing conditions on the characteristics of pores in hot isostatically pressed alumina

Effect of processing conditions on the characteristics of residual pores was studied with an optical microscope in hot isostatically pressed translucent alumina ceramics. Green bodies formed by isostatic pressing were sintered at 1300, 1400 and 1600°C and then hot isostatically pressed at a temperature 50°C below the respective sintering temperature for 1 h at 100 MPa. All specimens were fully dense within experimental accuracy (±0.1%), and the grain size increased with increasing sintering/hot isostatic pressing temperatures. A variety of pores were found in all specimens. The distribution of pores was uniform at various locations within the specimen. The pore population decreased with increasing pore size, but was finite in the size range exceeding 84 m. The pores in this range increased with increasing sintering/hot isostatic pressing temperature. Except for these large pores, the pore population was similar under all processing conditions.     

Physical vapour deposition coating processes for encapsulation of powder metal components before hot isostatic pressing

Abstract

Application of coatings by plasma vapour deposition involving electron beam evaporation and ion plating onto green powder metal compacts has been studied as a potential method for encapsulating powder metal products before hot isostatic pressing. The deposition of defect free coatings is essential if this concept is to provide a reliable encapsulation technique. Coating structures are therefore discussed in terms of the plasma processing conditions and surface roughness of the powder substrate. It is shown that the most promising approach is a combined coating and sinter–hot isostatic pressing cycle, which enables defects within the coating to be removed by the formation of a transient liquid phase.

MST/1455     

络合溶胶-凝胶法制备氧化物弥散强化 12Cr钢中氧化物的形成机制

以乙二胺四乙酸(EDTA)为络合剂, 采用EDTA络合溶胶-凝胶法向氩气雾化制备的预合金粉末中添加Y₂O₃, 复合粉通过热等静压致密化, 锻造后固溶处理, 制得化学成分为Fe-12Cr-2.5W-0.25Ti-0.2V-0.4Y₂O₃ (0.4Y₂O₃/12Cr, 质量分数, %)的氧化物弥散强化(ODS) 铁素体钢(12Cr)。采用SEM、FE-SEM、XRD对复合粉末、热等静压态和锻造态Y₂O₃/12Cr铁素体钢中的氧化物的形成过程和行为进行了分析和表征。结果表明: 化学法制备的Y₂O₃弥散强化0.4Y₂O₃/12Cr铁素体钢中氧化物的形成机制有络合热分解机制、界面反应机制和再析出机制。通过选择合适的工艺参数和机械分散作用可获得细小均匀的氧化物强化相。      

Comparison between slip-casting and uniaxial pressing for the fabrication of translucent yttria ceramics

Slip casting and uniaxial pressing were compared as first consolidation stages prior to cold isostatic pressing (CIP) to produce translucent yttria ceramics. In the first step, yttria slurries suitable for slip casting were prepared. The viscosity was optimized with respect to the starting agglomeration state, amount of dispersant, milling time, and number of milling balls. Secondly, pellets were prepared either by slip casting or uniaxial pressing and then cold-isostatically pressed. Finally, the pellets were made translucent by a combination of pre-sintering and hot isostatic pressing (HIP). Although slip-cast and pressed samples exhibited similar green-body densities after CIP and pre-sintering, the samples prepared by slip casting were more homogeneous in terms of translucency and microstructure throughout their bodies. This was attributed to the ability of slip casting to minimize density gradients during packing, and to the beneficial effect of ball-milling to remove larger agglomerates before casting. Therefore, slip casting as a first consolidation stage prior to CIP appears to be more suitable than uniaxial pressing in order to prepare homogeneous optical ceramics.