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.     

PROPERTIES OF ALUMINIUM-TIN ALLOYS PRODUCED BY POWDER METALLURGY

Abstract

Aluminium-tin powder-metallurgy alloys containing 20–40% Sn and 0–3% Cu were prepared by compaction and extrusion of prealloyed atomized powder. The powder-metallurgy (PM) material had a fine distribution of the tin phase and was stronger, with greater fatigue strength than an Al-20% Sn-1 % Cu cast alloy but was harder and less ductile. Heat-treatment reduced the hardness of the PM alloys to values comparable with those of the cast material, whereas the strength, although also reduced, remained superior to that of the cast product.     

OBSERVATIONS ON THE SINTERING OF COMPACTSFROM A MIXTURE OF IRON AND COPPER POWDERS

Abstract

Three grades of iron powder-an atomized steel powder, a sponge iron powder reduced from magnetite with carbon, and a powder reduced from mill scale with hydrogen were mixed with 3% of copper powder and pressed into compacts. The diametral dimensional changes of the compacts during sintering below and above the melting point of copper were measured, their microstructures examined, and both related to the characteristics of the powders, particularly their specific surface. During sintering below the melting point of copper, compacts of all three powders shrank. Micrographic examination showed that the copper is transported by solid-state diffusion along the surfacesand grain boundaries of the iron powder particles. During sintering above the melting point of copper, compacts of the atomized and the MH-100 sponge iron powders grew while those of the hydrogen reduced mill-scale powder shrank. This phenomenon is related to the different mode of penetration of liquid copper in the compacts from the three powders, observed in the microstructures of the compacts.     

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.     

EFFECTS OF PARTICLE SIZE ON THE SINTERING KINETICS IN TUNGSTEN POWDER

Abstract

An experimental study has been made of the effects of initial particle size on sintering kinetics in tungsten powder within the temperature range 1100–1500°C. Particle size, compacting pressure, sintering time and temperature all influence the rate of sintering. Isothermal changes in density and volume have been measured. The results indicate grain-boundary diffusion as the mechanism principally responsible for material transport in the case of particle sizes <4 μ Surface diffusion appears to bethe mechanism of material transport in compacts with particle sizes of 14– 16 μ The temperature-dependence of the rate of sintering is characterized by activation energies of 101± 2 and 72± 2 kcal/mole for fine particles (< 4 μ) and coarse particles (14–16 μ), respectively.     

316L不锈钢粉真空松装烧结的研究

研究了316L不锈钢粉注射成形等低压成形工艺的粉末真空松装烧结行为及其影响因素。通过添加石墨实现脱氧控碳,分析比较了气、水雾化粉真空松装还原烧结行为的差异。     

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.     

Structurization in sintering of antifriction powder materials based on iron-copper alloys

The paper studies the contact interaction of the components in powders Fe-(Cu + Sn), Fe-(Cu + Sn + P + Pb), and Fe + B-(Cu + Sn + P + Pb) during sintering in hydrogen at 920 °C. It is shown that this interaction is responsible for the formation of both the interphase boundary and the general structure that defines the performance characteristics of an antifriction material. The interface and the phase and chemical composition of the products of interaction are examined. It is established that the powder composition Fe + Cu + Sn + P + B + Pb sintered in hydrogen at 920 °C is a microheterogeneous material whose matrix, which takes up the major load during friction, includes two phases: one based on iron alloyed with boron (Fe₂B), copper, tin, and phosphorus and the other based on copper including tin in the form of α-solid solution, phosphorus in the form of Cu₃P, and iron. Lead uniformly distributed over the matrix volume is the antifriction component of the material.     

THE POWDER METALLURGY OF RUTHENIUM

Abstract

An investigation of the powder metallurgy of ruthenium is described, from the reduction of ammonium ruthenium chloride to the working of sintered compacts. The powder properties measured were specific surface area, by a simplified BET method, and tap density. The dependence of these properties on the conditions of reduction has been determined. The surface area of powders varies from 1 to 10 m²/g in the temperature-of-reduction range 700-350°C. The tap density is also variable (1–3 g/c.c.) and is generally related to the surface area. The effects of compacting pressure and temperature on sintering are described, the progress of sintering being observed by measurements of the “open” and “closed” porosity present in samples. Compact densities up to 95% of theoretical can be obtained by sintering at 1500°C. The selection of powder properties and compacting pressures to be used in the production, by vacuum sintering at 1500°C, of high-density compacts for working, is governed by the necessity to maintain open porosity during the heating cycle up to at least 1200°C, as considerable gas evolution occurs at this temperature; at the same time it is essential that good densification shall have occurred even at this stage. These conditions can be met by using powder with a surface area of 2–5 m²/g and compacting pressures in the range 0·5–25 tons/in ².

Observations on the hot working of sintered compacts indicate that ease of working is related to the surface area of the powder.     

Fe-Cu及Fe-Cu-C合金的烧结特性

对还原铁粉与铜粉、电解铁粉与铜粉的混合粉压坯的烧结特性进行了研究,探讨了在不同烧结温度下压坯尺寸的变化规律和碳对压坯异常膨胀的抑制作用。表明,不论还原铁粉还是电解铁粉与铜粉的混合压坯,烧结时均出现异常膨胀现象,而含铜约8%(Wt)时膨胀量最大。添加碳能抑制铗和铜的互扩散,从而抑制烧结Fe-Cu合金的异常膨胀,抑制效应随含碳量增加而增大。     

Production,sintering, and application of nanocrystalline iron–copper additions in a powder steel

A method is proposed for activated sintering of a sprayed iron powder by the coalescence of pressed particles through fine-grained layers based on iron–copper nanodispersed (ND) additions. The mechanical properties of composite materials containing 2% Fe–Cu ND addition are higher than those of the materials prepared from a mixture of standard powders by a factor of 1.5.     

SOME MECHANICAL PROPERTIES OF SAE 1045 STEEL JOINTS BONDED WITH SINTERED COMPACTS

Abstract

The physical and mechanical properties of plain steel (SAE 1045) butt joints, bonded with a sintered alloy as a filler material, are described. Sintered alloys were made from two types of iron powders–electrolytic and Swedish sponge– with various additions ranging from 7 to 20 wt.-% of an electrolytic copper powder, a prealloyed bronze powder (90% Cu+ 10% Sn), and a mechanically mixed elemental bronze powder.

The results showed that the tensile strength was not reduced as drastically as that of the copper-brazed joints, when the thickness of the bonding material (sintered alloy) was increased. The highest bond strength in tensile and fatigue testing was obtained with the sintered alloys comprising iron powder and 10 wt.-% pre alloyed bronze powder. The results indicate that there is a practical possibility of brazing steel using sintered compact as a filler material under a neutral or a reducing atmosphere.     

THE DRIVING FORCE FOR SHRINKAGE IN COPPER POWDER COMPACTS DURING THE EARLY STAGES OF SINTERING

Abstract

The shrinkage behaviour of compacts from irregular copper powder during the initial stages of sintering has been determined by a dilatometric method. The effects of compacting pressure and of external load during sintering at a constant heating rate of 3°C/min upon shrinkage were observed. The residual stresses present on the surface of compacts heated at the same rate to temperatures of 200, 300, 400, 500, and 600°C were also measured. It was observed that shrinkage starts at temperatures where considerable residual stresses in the surface of the compacts are still present, and that this temperature also depends upon the external stress applied during sintering. Residual and externally applied stresses complement each other in shifting the temperature of start of shrinkage to lower values with increasing stress. It is concluded that, in the low-temperature range up to 400°C, residual and externally applied stresses, rather than surface-tension forces, cause shrinkage.     

EFFECT OF POROSITY ON THE FATIGUE BEHAVIOUR OF SINTERED PRECIPITATED NICKEL POWDER

Abstract

Groups of specimens with nominally 4% and 12% porosity have been prepared from fine (?240 + 300), medium (?200 + 240), and coarse (?150 ? 200) mesh sieve fractions of Sherritt-Gordon nickel powder by die compaction, preliminary sintering, re-pressing, and finally sintering at 1573K (1300°C). Irrespective of porosity content and the powder fraction from which they were prepared, all specimens exhibited a mixture of rounded and film-like porosity. The film-like porosity was more extensive in the more porous specimens, but in all specimens markedly influenced the fatigue behaviour. The development of persistent film-like porosity is attributed to the botryoidal form of the powder particles. The endurance limits of the less-porous specimens were almost identical, irrespective of the powder fractions from which they were prepared. However, the endurance limits of the more-porous specimens made from the coarse powder fraction were significantly lower than those made from the fine and medium powder fractions. The endurance limits of the less-porous specimens were much higher than those of the more-porous specimens and the endurance ratios were significantly higher. In all specimens, fatigue fractures were intergranular. The influence of film-like porosity on the fatigue behaviour is discussed.     

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.     

SOME PROPERTIES OF TIN PREPARED FROM TIN POWDER BY EXTRUSION

Abstract

Tin containing a fine dispersion of oxide has been prepared by the extrusion of atomized tin powder into rod. The oxide dispersion was stable up to ≮ 200°C and its presence influenced the grain growth of the tin. The hardness and tensile-strength values of the extruded tin powder were about twice those of cast tin and were independent of the oxide content of the powder within the range 0·2-1·5 wt.-%. This indicated that the dispersion of the oxide, governed by the particle size of the powder, was of more importance than the thickness of the oxide films.

Stress-to-rupture tests at 150°C showed the material made from powder to be markedly superior to either unalloyed tin or a tin–6% antimony alloy. The best Eltress-to-rupture properties were obtained in dispersion-hardened material heat-treated to give a fibrous structure of relatively large grains, elongated in the extrusion direction. Possible applications of dispersion-hardened tin are briefly considered.     

STUDIES ON THE ACTIVATION-SINTERING OF IRON POWDER

Abstract

A study of the sintering behaviour of iron compacts containing additions of tin up to 1 wt.-% has been made. A tensile strength of 234 MN/m² (34 x 10³ lbf/in²) has been achieved with an optimum tin addition of 0·5 wt.-%, sintering being carried out for 10 min at 1100°C (1373 K) in a reactive halide atmosphere. Combination of the two ‘activating’ techniques (addition of tin and sintering in a reactive atmosphere) permits current properties to be attained at considerably lower sintering temperatures or sintered densities, and is much more effective than when they are applied individually. A tensile strength of 165·3 MN/m² (24 x 10³lbf/in²), achieved by sintering at 1200°C (1473 K) for 10 min with an addition of 0·5 wt.-% tin can be obtained by reactive-sintering the same composition at 900°C (1173 K) for 10 min. Alternatively, the density of the part can be reduced from 6·7 to 6·2 g/cm³ with no loss of strength or elongation. Tin in excess of 0·5 wt.-% causes deterioration in properties under the sintering conditions studied and a reason for this is cited. The improvements in properties are lost also if admixed lubricant is used in the compactionprocess.     

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.     

Phase and structure changes during the sintering of compacts of high-speed steels obtained from powders with various rates of solidification

An investigation was made of the phase and structure transformations in compacts of high-speed steel R6M5F3 powder fractions ?630+50 μm at the temperatures of solid-phase (1160–1220°C) and liquid-phase (1240°C) sintering. The structure of the compacts was crystalline or quasicrystalline, depending on the degree of superheating and cooling rate of the melt during powder spraying. This was related to the presence of a cellular structure in particles of a critical size in the powder. Compacts of powder with the cellular structure experienced higher shrinkage during solid-phase sintering as a result of structre relaxation and recrystallization. The driving force of these processes is the change in chemical potential arising from the decomposition of highly supersaturated metastable solid solutions, and the excess grain-boundary energy of the quasicrystalline matrix structure.