INFLUENCE OF TIN POWDER CHARACTERISTICS ON THE SINTERING OF IRON-TIN-COPPER POWDER COMPACTS

Abstract

In view of increasing industrial interest in the use of tin additions as an aid to the sintering of iron-based powder compacts, an examination has been made of the influence of the characteristics of the tin powder on sintering performance.

The effect of additions of narrow size-range fractions of atomized tin powder on the dimensional changes and tensile properties obtained on sintering Fe-Sn-Cu compacts made with –100 mesh (–152 μm) or – 300 mesh (– 53 μm) sponge iron and – 300 mesh (– 53 μm) atomized copper powders has been determined. The compacts contained tin and copper in the ratio 2:3. The narrow size fractions were separated from – 300 mesh tin powder by air elutriation. It was found that the use of coarse tin powder reduced the tensile strength of – 300 mesh iron-based Fe–1% Sn–1 ½% Cu compacts, but had no influence when this mixture was based on –100 mesh iron powder, or when the mixture composition was Fe–2% Sn–3% Cu. The effects have been examined in relation to the sintering mechanism by scanning electron microscopy and by X-ray microanalysis.     

THE CORRELATION BETWEEN RAW MATERIALS,PREPARATION CONDITIONS,AND PROPERTIES OF SINTERED IRON

Abstract

Three plain iron powders of different types (sponge-iron, atomized and electrolytic iron powder) were studied with respect to their sintering behaviour and to the influence of manufacturing parameters—i.e., compacting pressure, sintering temperature, and sintering atmosphere—on the microstructure and the properties of sintered compacts. The changes of length, electric conductivity, and strength during sintering are explained in physical and chemical terms. Technical sintering diagrams are presented. The influence of sintering atmospheres on the mechanical properties of sintered compacts is shown for the three types of powder. The correlation between pore structure and strength is discussed; analytical relationships are developed which are in agreement with the experimental results.     

THE EFFECT OF PHOSPHORUS ADDITIONS ON THE TENSILE,FATIGUE, AND IMPACT STRENGTH OF SINTERED STEELS BASED ON SPONGE IRON POWDER AND HIGH-PURITY ATOMIZED IRON POWDER

Abstract

The mechanisms operating during the sintering of iron-phosphorus PM alloys are discussed, as well as the factors contributing to the unique combination of strength, ductility, and toughness that is characteristic of these materials. Alloying methods are reviewed with special reference to powder compressibility, tool wear during compaction, and homogenization during sintering. The preferred production method is to add phosphorus in the form of a fine Fe₃P powder to iron powder. The mechanical properties of a number of sintered steels made with and without Fe₃P additions to sponge iron or to high-purity atomized iron powders are reported. Use of atomized powder makes it possible to reach extremely high density by single pressing and the resulting phosphorus-containing sintered steels have very high ductility and impact strength. The fatigue strength is related linearly to the tensile strength, with a correlation coefficient of 0·91. It is concluded that structural factors other than those that control ductility and toughness are responsible for the fatigue resistance of sintered steels.     

IRON-COPPER-TIN SINTERED COMPACTS

Abstract

A wide range of copper and tin powder additions to iron powder sintered compacts hasbeen studied. From mechanical-property tests it has been shown that when using sinteririg temperatures of 900–1100°C in nitrogen/10% hydrogen atmospheres there is an optimum copper: tin ratio of 15:2. The mechanical properties obtained from compacts pressed from iron mixed with 4% copper+tin in this ratio and sintered at 900°C were similar to those obtained from iron ?l0% copper powder compacts sintered at 1100°C. Moreover, the iron-copper-tin components showed improved dimensional accuracy.

In a further series of experiments, it was shown that tin additions to iron-copper alloy compacts increased the solubility of iron in the liquid phase at the sintering temperature and simultaneously decreased the rate of diffusion of copper into the iron particles. At the same time, tin improved the wettability of the liquid, reducing its surface tension and allowing it to disperse more completely throughout the matrix. The mechanical properties of compacts containing larger amounts of tin were decreased by the presence of brittle compounds, although the sintering rate was increased. It is concluded that the optimum properties of iron-copper-tin compacts are obtained by making correct additions of copper and tin to the iron powder and giving careful consideration to the sintering atmosphere.     

Volume changes accompanying the sintering of compacts from mixtures of titanium and iron powders

Conclusions The sintering of compacts from mixtures of titanium and iron powders at temperatures below the eutectic point is accompanied by their shrinkage, the sintering process being mainly determined by the particle size of the starting powders. During the sintering of compacts from mixtures of titanium and iron powders at temperatures exceeding the eutectic point the compacts grow in size, the extent of the growth depending on the particle size of the powders. This phenomenon may be attributed to the effect of heterodiffusion on sintering processes and to the crystallization pressure generated during the formation of intermetallic compounds.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 17–21, May, 1982.     

Effects ofcontaminationonproperties of W-15Cu preparedfrom mechanically alloyed powders

Abstract

To eliminate the contamination of activator elements, such as Fe and Ni, W-15Cu compacts were prepared from mechanically alloyed powders using an attritor with a zirconia tank, balls and agitator arms. Coarse tungsten and copper powders, 9·9 μm and 13·3 μm, respectively, were milled to 1·26 μm composite powders after 145h of milling. The milled powder contained little free copper and was highly combustible in air. After sintering, the 50 vol.-% dense green compacts attained a density of 15·8g cm^-3 or 96·2%. The microstructure consists of uniformly interdispersed tungsten and copper. When stainless steel grinding balls were used, the powder was heavily contaminated with Fe and Ni. The contamination improved the density slightly, but the grain size and the electrical resistivity increased significantly as well. The sintering behaviours of the two composite powders were similar. Most densification occurred during heating before reaching the melting point of copper.     

INFLUENCE OF THIN OXIDE FILMS ON THE MECHANICAL PROPERTIES OF SINTERED METAL-POWDER COMPACTS

Abstract

The influence of thin oxide films, in the range 200–1200Å thick, on the mechanical properties of sintered iron, copper, and nickel powder compacts has been investigated. As the thickness of the oxide film on the metal powders increased, the properties studied, namely, densification parameter, hardness, and tensile strength improved and attained a maximum at a critical oxide-film thickness, the value of which was ～ 625 Å for iron and nickel and ～ 500 Å for copper. Further increase in thickness to ～ 1200 Å led to a gradual decline in the properties. The improvement in the properties obtained with powders having the optimum oxide thickness was independent of the sintering atmosphere. A probable explanation in terms of activated sintering is given.     

STUDIES OF THE SINTERING AND HOMOGENIZATION OF NICKEL-COPPER COMPACTS

Abstract

Studies are described of the progress of sintering and alloying in compacts of similar compositions made from nickel-coated copper, copper-coated nickel, and mixed nickel and copper powders. Density losses observed in the early stages of sintering were lower in magnitude and were more quickly recovered in the case of the composite powder compacts. Alloying by diffusion at both 1900 and 2200°F (1040 and 1205°C) progressed most rapidly in compacts prepared from nickel-coated copper powders, and the probable reasons for this observation are discussed in detail. Electrical resistivity was used to follow homogenization of the compacts, and samples were rendered nearly 100% dense by cold working and annealing before making resistivity measurements. Resistivity / sintering-time curves for dense specimens showed no maxima of the type reported by earlier investigators for porous compacts, which were attributed to alloying effects.     

SINTERING KINETICS OF OXIDE-FILMCOATED COPPER POWDER

Abstract

The sintering kinetics of pure copper powder and of copper powder coated with a critical oxide (CU₂O) film thickness (～,500Å), has been studied by following the densification of the compacts as a function of temperature and time in pure dry hydrogen and in vacuum. The activation energy for the sintering of pure copper powder in hydrogen was 55,000 cal/mole, suggesting that the volume self-diffusion mechanism predominates during the sintering process. In the case of the oxide-coated powder the corresponding value was 37,000 cal/mole. The high rate of sintering of the coated powder in hydrogen and in vacuum is explained in terms of an activated sintering mechanism.     

THE PROPERTIES OF POROUS NICKEL PRODUCED BY PRESSING AND SINTERING

Abstract

The effects of compacting pressure and of sintering temperature and time on the properties of porous sintered nickel compacts have been studied, using three carbonyl and two reduced nickel powders. For all five powders, the density of the green compacts and the porosity of the sintered compacts were linearly related to the log compacting pressure. Similar relationships with pressure were observed for strength and electrical conductivity.

Photomicrographs of sections through the sintered compacts made from the reduced nickel powders show that there are pores in two different size ranges, originating from the porosity between the original powder particles and the pores within the particles. It is concluded that sintered compacts from all five powders containing 40–50% porosity have adequate strength and conductivity for use in fuel-cell electrodes.     

THE PRESSING AND SINTERING PROPERTIES OF IRON POWDERS

Abstract

Some twenty different iron powders are available in Europe for the manufacture of sintered bearings and structural parts. These powders can be grouped under four headings: reduced, atomized, comminuted, and electrolytic. Details are given of the experience gained in testing these types of powder by the methods in common use in the metal-powder industry.

The influence of the data thus obtained on the processing, in particular the pressing and sintering conditions, of iron powders is discussed in detail. Consideration is given to the way in which the properties of the powders affect their sinterability, the pressing operation and tool design, and also the physical characteristics of the finished product.     

Effect of nickel on sintering processes in the Ti-Fe system. Part I

Conclusions Diffusional interaction in the Ti-Fe-Ni system is more vigorous than that in the Ti-Fe system. The temperature of the first ternary eutectic point in the Ti-Fe-Ni system, determined by the contact melting method, is 1040°C. During the sintering of compacts from a mixture of Ti, Fe, and Ni powders at temperatures above the eutectic point growth is observed, whose extent depends on the sintering temperature and the particle size of the powder employed: The smaller the particle size and the higher the sintering temperature, the smaller is the growth.Translated from Poroshkovaya Metallurgiya, No. 7(247), pp. 34–39, July, 1983.     

The Effect of Cooling Rate on the Strength of Sintered Fe—Cu Compacts

Abstract

The effect of cooling rate from the sintering temperature upon the tensile strength of compacts from a mixture of iron and copper powder was investigated. The compacts were pressed at 450 and 390 MPa and sintered in hydrogen at 1120°C for 40 min. The copper content of the compacts varied from 0 to 12%. For alloys with Cu content >4% the tensile strength was found to be strongly dependent upon the cooling rate in the temperature range between 850 and 600°C, with rapidly cooled specimens being considerably stronger. In specimens with 8%Cu the tensile strength increased from 206 to 343 MPa when the cooling rate was increased from 10 to 200 degC min^?1. In specimens with 2%Cu cooling rates above and below 600 degC min^?1 appear to influence the tensile strength. Possible explanations for the observed effects of cooling rate upon tensile strength in sintered Fe–Cu alloys are discussed.     

Linear shrinkage of metal powder compacts during sintering

Summary The influence exerted by various factors (particle size, particle size distribution, ultrafine powder addition, sintering temperature, etc.) on the linear shrinkage ratio during sintering was examined. Electrolytic, atomized, and ultrafine copper powders, as well as electrolytic iron powder, were used.     

Dilatometric analysis of thermal debinding of injection moulded iron compacts

Abstract

The less than desired tolerance control of powder injection moulded compacts is a result of inconsistent dimensional changes in the compacts accumulated during moulding, debinding, and sintering. This study investigated the in situ length changes and their causes during thermal debinding on compacts which have been solvent debound. The dilatometric analysis showed that the specimen shrank in the early stage between 250 and 370°C, not because of sintering, but through the loss of N, C, and O in the carbonyl iron powder. At temperatures between 370 and 450°C, the specimen expanded owing to the carburisation of the iron powder. The length change was also influenced by the heating rate, debinding atmosphere, and the amount of the backbone binder. These dilatometric results are helpful in establishing the guidelines in designing binder compositions and debinding schedules.     

Use of certain binders to increase the strength of green compacts

The effect of additives of certain binders to produce an increase in the strength of compacts of copper and iron powders is experimentally investigated. The best results are obtained upon the addition of 5 mass% polyvinylacetate to the powder. Through the use of this binder it becomes possible to saw and drill powder compacts prior to sintering.     

Influence of Powder Type and Density on Pore Closure and Surface Hardness Changes Resulting from Steam Treatment of Sintered Iron

Abstract

Two types of Höganäs iron powder – sponge, and atomized with very high compressibility (ASC), after compaction to densities of 6·0, 6·4, and 6·8 Mg m^?3 and sintering under standard conditions were subjected to steam oxidation at 450, 525, and 600°C. The progress of oxidation was studied by measurement of weight gain and hardness. X-ray methods were used to determine the type of oxide present after treatment. During steam oxidation the type of powder has an important influence on the extent of pore closure and on the morphology of the oxide produced. The kinetics of oxidation were always faster for sponge iron than for atomized iron and there was a corresponding increase in the rate of pore closure and in surface hardness. For effective sealing of surface pores components should be of high density and be steam treated at 600°C but for attainment of maximum hardness components should be of low density and be steam treated at 525°C.     

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.     

Nature of the growth of Al-Cu powder compacts during liquid-phase sintering

Conclusions Arresting the process of liquid-phase sintering of aluminum-copper system powder compacts by rapid cooling does not affect the character of the volume changes experienced by them during subsequent sintering under the same temperature conditions. In the growth stage a decrease in the crystal lattice parameter of aluminum and an appreciable broadening of an x-ray line have been observed, caused by the formation of aluminum base solid solutions. These findings bear out the hypothesis that the growth of aluminum-copper powder compacts above their eutectic melting point is mainly due to diffusion of copper from the liquid phase into aluminum particles.Translated from Poroshkovaya Metallurgiya, No. 5(305), pp. 16–19, May, 1988.     

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.