粉末冶金温压的致密化机理

通过对铁粉的动态压制曲线、脱模力曲线、 X射线衍射、摩擦和润滑的研究, 揭示了温压的致密化机理： 温压成形过程可分为3个阶段, 在初期阶段, 粉末的颗粒重排过程占主导地位, 颗粒重排份额与冷压相比提高15%～31%; 而在后期, 温压致密化以塑性变形为主, 铁粉塑性变形程度的改善又为粉末颗粒的二次重排起了协调作用, 使铁粉获得最大程度的颗粒填充密度; 其间, 温压润滑剂对致密化起了重要作用, 它降低了摩擦因数, 改善了粉末和模壁、粉末和粉末之间的润滑条件, 有效地降低了粉末成形的摩擦阻力, 有利于粉末致密化的顺利进行.     

粉末冶金温压工艺的研究进展及其展望

综述了粉末冶金温压工艺的研究进展,概述了温压工艺的粉末原料、聚合物、温度、压力、烧结环节对温压工艺的影响和温压工艺的致密化机理。详细介绍了温压工艺的新进展—流动温压、高压温压等,并对其应用前景进行了展望。     

粉末冶金温压工艺的研究进展及展望

温压是一项以较低的成本制造高性能粉末冶金零件的新型成形技术，本文综述并讨论了温压工艺的粉末原料、聚合物、温度、压力、烧结环节及致密化机理。在此基础上，介绍了温压工艺的新发展——流动温压、高压温压等，并对其应用前景进行了展望。     

Model of Quasi-Isostatic Hot Pressing of SHS Products in the System Titanium ― Carbon ― Nickel. Part 1. Structural State and Rheological Model

Quasi-isostatic hot pressing of the products of self-propagating high-temperature synthesis (SHS) is considered. The temperature regime, and the aggregate and structural state of the SHS products of the Ti ― C ― Ni system are studied. A block model of the deformed volume is presented; parameters of the virtual field of plastic flow velocities are determined and an energy equation in the form of a variation functional is determined. Rheological models of the non-linearly viscous SHS products and the rigidly-plastic loose shell are considered within which the dual mechanism of compaction and the local nature of dispersed material particle deformation are taken into account.     

Model of Quasi-Isostatic Hot Pressing of SHS Products in the System Titanium ― Carbon ― Nickel. Part 1. Structural State and Rheological Model

Quasi-isostatic hot pressing of the products of self-propagating high-temperature synthesis (SHS) is considered. The temperature regime, and the aggregate and structural state of the SHS products of the Ti ― C ― Ni system are studied. A block model of the deformed volume is presented; parameters of the virtual field of plastic flow velocities are determined and an energy equation in the form of a variation functional is determined. Rheological models of the non-linearly viscous SHS products and the rigidly-plastic loose shell are considered within which the dual mechanism of compaction and the local nature of dispersed material particle deformation are taken into account.

     

Spray formation of high-density alloy-steel powder blanks

Powder blanks with densities of 96–98% of theoretical have been made under laboratory conditions with a URS-40 gas spray apparatus. The masses of such blanks are up to S kg, and the forming time is 4 sec. They can have any shape (flat or cylindrical), and they can be used either as final products or employed for forming sheet strip by metallurgical forming. The bending strength of the material is 1. S times higher than that in cast material by casting in a mold. Parameters have been identified that need to be monitored during the forming in order to obtain blanks with a given structure.     

铝粉末压制过程有限元模拟研究

根据粉末材料的塑性理论及Shima-Oyane屈服准则,利用体积可压缩有限元法,采用MARC有限元分析软件对铝粉的单向压制和双向压制过程进行了数值模拟。得到了粉末材料在压制过程中的变形特征、相对密度分布及粉末质点的流动规律,得到单向压制和双向压制的密度分布图,并对其差异进行了分析。模拟结果对揭示粉末压制过程机理,制订压制工艺都有显著意义。     

粉末热锻凸轮的数值模拟

凸轮作为装配式凸轮轴上的关键零部件之一,其制造技术很大程度上影响着凸轮轴及发动机的发展。采用验证实验的方法确认有限元法模拟粉末热锻凸轮的压制及热锻成形过程的合理性,在此基础上利用数值模拟法对凸轮的压制方式进行改进、优化热锻工艺参数。针对粉末压制成形工艺,对不同压制方式下(单向压制、双向压制、浮动压制、摩擦压制)的压坯密度进行模拟分析。而针对热锻工艺则研究分析锻压速度、摩擦因数、坯料加热温度、模具预热温度、坯料初始相对密度5组因素对锻件密度分布的影响,从而获得最佳的工艺方案。     

CeO2-Gd2O3纳米复合粉的模压成形行为研究

测定了CeO2-Gd2O3纳米复合粉压制过程中压坯密度与成形压力的关系曲线。成形压力低于100MPa时。压坯密度随压力的增大而急剧增加；成形压力继续增大，压坯密度随压力的变化减慢。由压坯密度一压力对数关系曲线可知，粉末中团粒的屈服强度为44．7MPa。另外，粉末的压制规律遵循黄培云双对数方程。     

Model of Quasi-Isostatic Hot Pressing of SHS Products in the System Titanium ― Carbon ― Nickel. Part 2. Results of Modelling and Experimental Studies

Results are provided for modelling and experimental studies of hot quasi-isostatic pressing of SHS products of the system Ti C Ni. Good conformity is demonstrated between experimental data and calculated results using a rheological model for nonlinearly-viscous synthesis products. The model considers presence of a melt and the local nature of solid phase particle flow. Quantitative estimates are obtained for compaction of different zones of the loose shell, the force characteristics of the process, and the nonisostatic coefficient. This information is of interest for production planning and optimization of SHS product compaction.     

Plastic strain of powder components in unclosed volumes

During free compaction, extrusion, and bending of powder blanks, the material is under conditions of nonuniform stress and strain and is subject to compression and tension. A form of plasticity theory is developed for such a body that includes the tension and compression applied to the material. The trends in this theory form the basis for three technological hot-pressing processes. They have been used to prepare spherical layers for tractor hydraulic pump systems (the component is formed by compaction and at various stages is subject to various deformation schemes: uniaxial tension, free compaction, and hydrostatic nonuniform compression), and the same basis has been applied to gear forks for tractors (forming in a semi-open die in two stages: in the first, the state of stress varies from hydrostatic compression to uniaxial, while in the second the material is densified under conditions of hydrostatic compression), as well as to the polar sprocket for an automobile alternator (the process involves plastic bending of the flat elements, with changes produced under tension and adjustment of the material on a convex free surface followed by compression and densification on a concave one).Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 25–31, May–June, 1995.     

粉末净成形压制工艺优化及三维复杂零件结构设计的数值模拟

基于粉末连续体,运用MSC.Marc有限元软件对粉末净成形压制工艺进行优化,并对减重齿轮的结构设计进行数值模拟。通过与实验数据对比分析,验证了材料模型及仿真模拟的可靠性,在此基础上利用有限元软件研究分析压制方式、压制速度、摩擦系数、压制温度、保压时间等五组因素对压坯密度分布的影响。结果表明,压制方式是最显著的影响因子,采用双向压制、温压成形、低压制速度、小摩擦系数及保压方式的组合压制工艺能有效地改善粉体的密度分布。利用有限元软件对减重齿轮的结构进行优化设计,研究圆环高径比与压坯相对密度的关系,并确定减重孔最佳尺寸。结果表明,采用强制摩擦压制方式代替浮动压制方式,可有效改善孔洞薄壁处密度。此外,结合Workbench有限元软件对减重齿轮进行结构力学模拟仿真,分析薄壁处的受力情况,以满足对齿轮强度的要求。     

Investigation of warm compaction and sintering behaviour of aluminium alloys

Abstract

The effects of warm compaction on the green density and sintering behaviour of aluminium alloys were investigated. Particular attention is paid to prealloyed powders, i.e. eutectic and hypereutectic Al-Si alloys, regarding their potential applications in the automotive industry. The effects of chemical composition, alloying method, compacting temperature and the amount of powder lubricant were studied. The compaction behaviour was examined by an instrumented die enabling simultaneous measurement of density, die wall friction coefficient, the triaxial stresses acting on the powder during the course of compaction and ejection pressure. The sintering behaviour was studied via dilatometeric analysis as well as normal batch sintering. The results show that warm compaction could be a promising way to increase the green density of aluminium alloys, especially prealloyed powders, and to decreased imensional instability during sintering. Moreover, it reduces the sliding friction coefficient and the ejection force during the powder shaping process. This paper presents the significant advantages and drawbacks of using the warm compaction process for commercial PM aluminium alloys.     

流动温压制备不锈钢十字件的试验研究

流动温压成形技术是在传统温压成形工艺的基础上,结合粉末注射成形工艺的优点而发展起来的一种制备粉末冶金复杂件的新型近终形成形技术。用常规的17-4P不锈钢粉,利用流动温压制备出十字形试样,并对脱脂工艺和烧结试样的成形工艺、显微结构、密度、硬度等进行了分析。结果表明,通过流动温压成形技术,可以制备出高性能和低成本的结构复杂件。     

Springback behavior of tailor rolled blank in U-shape forming

The springback of tailor rolled blanks with quenching and partitioning steels was investigated.In order to find out the springback behavior and related influence factors for the novel sheets,both experimental and simulation methods have been used to compare and analyze the springback characteristics of equal thickness blanks and tailor rolled blanks in U-channel forming.From the results,the overall springback angles of tailor rolled blanks at thin and thick sides are respectively 106.79° and 99.705°,which are both lower than those of the corresponding equal thickness blanks.Due to the existence of the thickness transition zone,the stress distribution in thin and thick sides of blanks is changed.The location of dangerous region in thin side of tailor rolled blanks is closer to the end of side,and the thick side moved to the middle of straight wall,which are different with the equal thickness blanks.Afterwards,the released quantitles of tangential stress and strain per unit section of blank are adopted to calculate relative springback angles and give novel evaluation criteria for qualitatively analyzing the amount of springback angles.By comparing the results,it shows that the tangential strain method is more suitable for the actual situation.     

Characterisation of the Forming Behaviour of Patchwork Blanks

In order to satisfy the increasing demand for environmental sustainability and passengers’ safety, automotive manufacturers are more and more obliged to develop improved body concepts for lighter but also safer vehicles. At the same time, production costs have to be minimised in order to cope with the international market. Besides the application of new materials and innovative production processes mainly the use of tailor‐made semi‐finished products such as tailored welded blanks, tailored rolled blanks or tailored tubes can contribute substantially to this objective. Furthermore, for the production of sheet metal components with a load adapted material distribution, the patchwork blank technique represents a potential alternative to the widely‐used concept of tailored blanks. But even if patchwork blanks offer some additional advantages, this innovative technique has hardly found its way into series production due to a number of unsolved challenges regarding their formability and numerical modelling of corresponding forming processes. In this contribution the forming behaviour of welded patchwork blanks is investigated by means of experimental trials and finite element analyses. In order to simulate the forming processes of patchwork blanks accurately, knowledge about the characteristics of the weld metal, including the weld bead and the heat affected zone, is essential. For this purpose, Martens hardness measurements, which allow the analysis of the weld seam and the determination of the lateral extension of the heat affected zone, have been carried out. Subsequently, uniaxial tensile tests with longitudinally welded samples have been applied to characterise the constitutive behaviour of the weld metal. The results obtained from these experimental investigations have been implemented to different finite element models for patchwork blank forming processes. A comparison of the numerical results with experimental data obtained from a series of Nakajima tests allows a validation of the presented modelling techniques. It can be stated that the accuracy of the finite element analysis may be improved if the modified material properties along the weld seam are considered in the numerical model.     

压制方式和烧结工艺对置氢Ti6Al4V粉末烧结体组织和性能的影响

采用磁脉冲成形和模压成形2种方法对置氢Ti6Al4V粉末进行轴向压制,然后在保护气氛下烧结,研究压制方式和烧结工艺对烧结体真空退火后组织/性能的影响.结果表明:磁脉冲压实的不同氢含量粉末坯体烧结并真空退火后的相对密度、硬度和抗压强度分别比传统模压500 MPa下压制的高8%～13%、9～17 HRA和254～1033M...     

Self-propagating high-temperature synthesis metallurgy of pipes with wear-resistant protective coating with the use of industrial wastes of metallurgy production

The possibility of utilizing the industrial wastes of the metallurgical production and secondary raw materials (aluminum) by organizing self-propagating high-temperature synthesis (SHS) and obtaining metal pipes with an inner ceramic coating is investigated. The main production operations of the preliminary preparation of the starting raw materials are worked out and functional coatings providing high abrasive resistance are revealed. The results of testing the samples showed that the durability of the pipes with the deposited coating increases by a factor of more than 20. The possibility of forming highly energy-effective SHS technology of processing the industrial wastes of metallurgical production and obtaining pipes with a high abrasive resistance is shown.     

Producing multicomponent SHS-compacted cathodes based on refractory titanium compounds for vacuum-arc coatings

The technological features of and a device for manufacturing multicomponent cathodes of arc evaporators using SHS compaction are considered. Physically, an SHS-compacted cathode is a four-layer function-gradient product and consists of a metallic base in the form of a water-cooled bottom part of a regular cathode, an evaporating operating layer, an intermediate layer, and the SHS solder layer required for joining the synthesized material with the base. Compositions and weight characteristics of layers that allow us to produce defect-free multicomponent SHS-compacted cathodes based on stainless steel are presented.