成形压力与粉末粒径对钨铜复合材料烧结性能的影响

为进一步提高钨铜合金的致密度和简化制备工艺,研究了粉末粒度与成形压力对无压烧结制备的W-15Cu复合材料致密度的影响.发现随着球磨时间延长,钨铜粉末发生明显的细化和圆化,粉末分布更为均匀,烧结活性有较大提高,合金性能更加优异,组织结构更加良好,致密度相应提高.通过对烧结试样密度和铜含量的测定,得到不同成形压力下材料致密度和铜含量随烧结温度的变化曲线,发现随着成形压力增大,材料的烧结致密度升高,铜流失的现象得到一定的控制.     

Effect of aluminum particle size on the volume changes experienced by compacts from a mixture of aluminum and copper powders during liquid-phase sintering

Conclusions The process of liquid-phase sintering of aluminum-copper powder compacts comprises two main stages — growth and shrinkage. Growth is due to diffusion of copper atoms from the liquid phase into the solid, with the formation of liquid interlayers at the grain and subgrain boundaries. Compacts from powder mixtures containing large aluminum particles exhibit increased growth in the first stage of sintering, which may be due to nonuniform reaction of the liquid phase on the peripheries of the particles, resulting in the appearance of local strains and further separation of the solid-phase particles.Translated from Poroshkovaya Metallurgiya, No. 9(285), pp. 23–27, Septmeber, 1986.     

Sintering of ultradisperse powders based on zirconium dioxide (review)

We consider the effect of the starting powder characteristics (purity, grain size and shape, size distribution, sintering aids content, etc.), green compact microstructure (density and porosity distribution), and processing parameters (including temperature, exposure time, rate of heating or cooling of the medium) on sintering of ultrafine ZrO₂-based powders. We discuss various sintering techniques: hydrothermal sintering, microwave sintering, hot pressing, sinter—forging, sinter-HIP, and gas-pressure sintering.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6, pp. 43–52, May–June, 1995.     

A Phenomenological Analysis of Sintering Mechanisms of W-Cu from the Effect of Copper Content on Densification Kinetics

The effect of addition of copper on the sintering of a W powder was systematically investigated by the analysis of dilatometric experiments on W and W-Cu compacts prepared with submicrometric powders. A pure W powder compact and a W-10 wt pct Cu powder compact with the same packing fraction of W particles were first studied, in order to analyze the effect of copper at fixed microstructure of the solid W particle packing. A more systematic set of experiments with different copper contents and W particle sizes was also qualitatively analyzed. A phenomenological model of sintering was developed and fitted in order to extrapolate the effect of copper content on sintering kinetics at fixed microstructure of the W particle skeleton. An interpretation of the sintering mechanisms was then proposed. Sintering of a W-Cu powder compact is the result of solid-state sintering of the W skeleton, enhanced by the capillary forces exerted by copper, with the superimposition of a particle rearrangement step after copper melting.     

Deformation of aluminum-copper powder solids during liquid-phase sintering

Conclusions During sintering with the participation of a liquid phase Al-Cu powder solids experience growth deformation in the first stage and shrinkage in the second. When the copper concentration in the mixture does not exceed the limit of solid-phase solubility at the sintering temperature, powder solids experience only growth; when the liquid phase is preserved during the whole period of sintering, growth is replaced by shrinkage. The growth of such powder solids during liquid-phase sintering is due to diffusion of copper atoms from the melt into aluminum particles, with the formation of solid solutions in these particles and of a liquid phase at grain boundaries. The deformation of powder solids in the shrinkage stage is brought about by dissolution of particles of the solid phase in the liquid and the particle regrouping process. The sign and magnitude of the deformation of powder solids during liquid-phase sintering are determined by Eq. (1).Translated from Poroshkovaya Metallurgiya, No. 8 (272), pp. 39–43, August, 1985.     

The effects of ultrasonic vibration on mechanical properties of tungsten particle-reinforced copper-matrix composites

W-Cu micro-powder mixtures usually have poor sinterability due to the relatively low solubility of W in both solid and liquid Cu. In fabricating W-Cu composites, an electroless copper plating process is often used to coat Cu on the W particle surface prior to the sintering process. Due to their small size W particles tend to agglomerate during the plating process, hence the individual particle may not be properly coated with Cu. In this study, ultrasonic vibration is applied in the electroless plating process to break up the agglomerations and restrain the powders from gathering, ensuring a uniform deposition of the Cu on individual W particle. W-Cu composite samples containing pure Cu and 6, 9 and 12 wt-% of Cu-coated W particles, respectively, are fabricated using a standard powder metallurgy technique. It is shown that the application of ultrasonic vibration in the activation and deposition steps of the electroless copper plating process prevents W powder agglomeration and ensures that each W particle is coated with Cu. As a result, the mechanical properties of the W-Cu composites are significantly improved. It is found that the optimal tensile strength and yield strength are obtained using a W reinforcement phase content of 9 wt-%.     

Structural changes accompanying the sintering of ultrafine aluminum nitride powders

Conclusions An electron-microscopical investigation has established that the sintering of compacts from an ultrafine plasma-chemical AlN powder is determined by the following processes: coagulation, with the formation of strong polycrystalline aggregates (1000–1400°C); coalescence, made possible by a geometric grain boundary match inside the aggregates, and formation of high-angle boundaries between aggregates (1200–1600°C); and collective recrystallization (above 1600°C). In an x-ray diffraction study annealing at temperatures above 1700°C was found to decrease the parameter c of AlN by 0.002 Å as a result of dissolution of oxygen in the lattice without affecting its parametera. The results of both electron-microscopical and x-ray diffraction studies show that annealing at temperatures above 1600°C increases the defectiveness of the wurtzite structure of AlN, brings about twinning and the formation of polytypal interlayers in recrystallized grains, and raises the concentration of other defects causing a broadening of lines in x-ray diffraction photographs. As a result of these phenomena the material experiences a strengthening at sintering temperatures of 1700–1800°C.Translated from Poroshkovaya Metallurgiya, No. 10(226), pp. 35–40, October, 1981.The authors wish to thank A. N. Pilyankevich for helpful discussion.     

Volume changes experienced by Al-Zn compacts during liquid-phase sintering

Conclusions The sintering of compacts from aluminum powders with zinc additions in the presence of a liquid phase is accompanied by their volume growth and a corresponding increase in their porosity. The volume growth of compacts from Al-Zn powder mixtures during liquid-phase sintering is mainly due to the Kirkendall effect, which manifests itself during the formation of a solid solution on the aluminum particles as a result of the diffusion of zinc atoms from the melt to the particles preceding their dissolution in the liquid phase. In general, the porosity of sintered compacts is satisfactorily described by Eq. (1). When, however, the zinc content of a compact does not exceed its limit of solid-phase solubility in aluminum at the sintering temperature, the process of dissolution of aluminum in the melt may be ignored. In such a case the end porosity of compacts is described by Eq. (2) with a correction for shrinkage due to a regrouping of particles. The extent to which the volume of compacts from an Al-Zn powder mixture grows during sintering increases with increasing mean aluminum powder particle size.Translated from Poroshkovaya Metallurgiya, No. 10 (238), pp. 11–16, October, 1982.     

Production of high-strength parts for constructional applications from multicomponent iron-base charges

Conclusions Calculation of the activity of carbon in multicomponent compositions enables a suitable choice to be made of compositions of alloyed charges made up of individual powdered elements (the base material being an iron powder), from which materials can be obtained with strength properties approaching those of rolled medium-alloy steels. The strength of such composites is determined by structure-formation processes, particularly those taking place in contact zones. The main role in these processes is played by the mobility of carbon.Translated from Poroshkovaya Metallurgiya, No. 11(239), pp. 61–64, November, 1982.     

钨铜热变形致密化工艺及组织性能研究

以W-40%Cu(质量分数)为原料,采用机械球磨-冷压制坯-液相烧结-热挤压的工艺,制备出微观组织均匀、性能优异的复合材料.在试验中,首先对W、Cu粉末进行机械球磨,之后分别进行压制、液相烧结;接着对烧结后坯料进行了一次热挤压、二次热挤压.结果表明:经过二次挤压后,材料的致密度、导电性以及硬度都得到较大提高,并且材料微观组织比较均匀.该工艺不仅可提高W-Cu复合材料的性能,而且还有效解决了此类不互溶材料致密化困难的问题.     

Sintering at a controlled rate as a method for regulating the microstructure of ceramics and similar sintered materials

This review is devoted to rate-controlled sintering (RCS) problems. It is shown that nonlinear nonisothermal sintering provides dense fine-grained materials based on ultrafine and submicron powders of different substances and mixtures of them. The theoretical and procedural bases of RCS as well as possible methods for a priori determination of its major parameter, i.e., maximum safe rate, are considered.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 1–10, March–April, 1994.     

注射成形W-Cu研究现状及产业化发展趋势

本文就高热导率钨铜复合材料的应用及最新制备方法——注射成形作了报道，集中对比介绍了JinChunKim、THKim，以及German等人在这方面的最新研究成果。注射成形作为一种新型的材料近净成形技术，有独特的优势，钨铜复合材料的注射成形技术必将成为今后钨铜复合材料的重要发展方向之一。但是由于钨铜复合材料的注射成形技术起步较晚，其工业化还需加倍努力实现。本文对W—Cu的产业化现状及趋势作了总结，提出了粉末冶金法为今后钨铜产业化发展的一条重要途径。     

Effect of cobalt addition on the liquid-phase sintering of W-Cu prepared by the fluidized bed reduction method

A new process, fluidized bed reduction (FBR) method, was applied for fabrication of uniform W-Cu sintered material. Liquid-phase sintering was carried out to obtain fully densified W-Cu composite, and the effect of cobalt addition on the sintering behavior was investigated. It was found that fully densified material could not be obtained even after sintering at 1200 °C for 4 hours in the case of 75W-25Cu, while more than 96 pct density could be obtained as soon as the sintering temperature reached 1200 °C when 0.5 wt pct cobalt was added prior to the sintering. It has been found that the wetting angle of the liquid copper is reduced significantly by the addition of cobalt, and the formation reaction of Co₇W₆ intermetallic compound at the surface of the tungsten powder is mainly responsible for the enhancement of the densification process.     

A model for the thermal properties

Thermal properties are important to several applications for powder metallurgy products. For example, liquid-phase sintered tungsten-copper composites are used in microelectronic packaging to obtain a high thermal conductivity in a low thermal expansion material. This article addresses modeling the thermal properties for composites fabricated by liquid-phase sintering. A computational cell is constructed with interlinked phases, consisting of a core of low thermal expansion material (tungsten) and a edge network of high thermal conductivity phase (copper). This structure is used to calculate the composition effects on the coefficients of thermal expansion and thermal conductivity. The results are applied to prior reports on W-Cu and used as a basis to identify several candidate high thermal conductivity systems for future development.     

Effect of liquid phase on the densification of tungsten-copper and molybdenum-copper pseudoalloys in sintering

The paper examines how the amount of the liquid phase influences the densification of loose W-Cu and Mo-Cu powder mixtures in liquid-phase sintering at 1200°C, with the content of the low-melting component ranging from 20 to 90 wt.%. It is observed that the density grows continuously with increasing amount of the liquid phase in both W-Cu and Mo-Cu systems. It is shown that samples sintered with a great amount of the liquid phase in the W-Cu and Mo-Cu systems retain their shape.     

Structure and properties of copper-titanium-aluminum composites produced by thermoreactive sintering

Conclusions The process of formation of composites in the Cu-Ti-Al system during thermoreaetive sintering has a diffusional character, and the resultant microstructure therefore consists of various intermetallic compounds and remains of the starting components. Varying the titanium content of these composites brings about both quantitative and qualitative changes in their structure. The most homogeneous structure is obtained in alloys with 35–45% Ti, whose end products contain the least amount of the starting components. Composites with 15–30% Ti are characterized by a comparatively high level of physicomechanical properties. These alloys can be recommended as matrix materials for the working layers of superhard abrasive tools.Translated from Poroshkovaya Metallurgiya, No. 3(255), pp. 53–56, March, 1984.     

Structure and properties of sintered nickel-molybdenum strip

Conclusions The powder rolling method enables NMoZh-30-5 type alloys to be produced whose mechanical properties are comparable to those of cast and rolled alloys. Uniformity of microstructure and properties in finished strips is achieved by sintering rolled bars for a long time (not less than 10–18 h). By employing cold plastic working with reductions of 20–70% and varying the grain size in the range 0.01–0.03 mm, it it possible to regulate the mechanical properties of such an alloy.Translated from Poroshkovaya Metallurgiya, No. 1(217), pp. 35–41, January, 1981.     

BDensification and Diffusion Bonding of W-CuComposites by HIP Processing

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Dilatometric investigations of the processes of liquid-phase sintering of materials of the Cu-Sn system

Conclusions The shrinkage of Cu-Sn powder compacts during liquid-phase sintering, which is due to dissolution of copper particles in molten metal and their regrouping, is preceded by growth caused by preferential diffusion of tin atoms from the liquid phase to the solid. The process of regrouping of solid-phase particles as a result of the destruction of the rigid skeleton of a compact at a high tin content at the instant of appearance of molten metal fails to manifest itself explicitly. The possibility cannot be ruled out that regrouping takes place at the instant of diffusional growth of compacts and, superimposing itself on the latter process, is responsible for the extent of relative growth being dependent on starting porosity.Translated from Poroshkovaya Metallurgiya, No. 9(261), pp. 27–31, September, 1984.     

Production and properties of brass-base P/M constructional materials. A review

Conclusions The best processing properties are exhibited by brass powders manufactured by the diffusional impregnation technique, using a zinc powder, brass swarf, or a copper-zinc master alloy as a point source. However, as this is a very labor-intensive process, normally preference should be given to melt atomization as a method of manufacture of brass powders. Brass P/M parts produced by the conventional method consisting of pressing a powder and sintering the resultant compacts have porosities of not less than 7–10%, and consequently this method is not widely used for the production of constructional brass parts. The sintering of compacts from copper and copper-zinc master alloy powders gives more stable zinc contents compared with the sintering of compacts from copper and zinc powders; the greatest stability of chemical composition is exhibited by sintered compacts from a homogenized brass powder. The formation of diffusional porosity accompanying the evaporation of zinc may be prevented by performing sintering in the presence of a liquid phase (which appears in the presence of a phosphorus or lead addition), saturating the sintering atmosphere with zinc vapor, and adding carbonates or halides of alkali and rare-earth metals to starting powders. The mechanical properties of materials can be markedly improved by eliminating their porosity. This may be achieved by subjecting porous preforms to hot forging, which enables brass P/M parts to be obtained whose mechanical properties are comparable to those of cast parts.Translated from Eoroshkovaya Metallurgiya, No. 3(255), pp. 56–64, March, 1984.