Production and properties of constructional parts from copper and copper alloy powders. A review

Conclusions Conventional methods of manufacture enable constructional copper alloy parts to be produced with a porosity of 10–15%. However, such parts do not exhibit high electrical conductivity and corrosion resistance, good brazing qualities, and stability of properties with time and at ambient temperature fluctuations. To improve their characteristics, it is necessary to reduce their porosity to not more than 3–5%. This can be achieved by employing high-energy methods of densification, in particular hot and cold forging. There is therefore an urgent need to study the processes of deformation of sintered blanks, determine optimum chemical compositions of materials, and develop methods of determining optimum blank sizes and shapes for forging.-Brasses are ductile at room temperature, but at 500–700°C they become less ductile than -brasses. At temperatures above 500°C the latter are less strong and hence more ductile than at room temperature. To obtain the best results, parts from -brass powders should be produced by cold forging and those +-brasses by hot forging. For hot forging it is best to use compacts from powders with a zinc content of 32–38%, which at room temperature are of the -modification and possess good formability. After heating for forging the -phase (an unordered solid solution) appears in their structure, which improves the workability of compacts in the hot state. Under these conditions their hightemperature ductility increases twofold. Hot-forged parts are also amenable to heat treatment (aging).Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 44–53, March, 1982.     

Production of tungsten-based composite materials from mechanically activated powders

The effects of the composition and metal additives on the compressibility of mechanically activated tungsten-based powder mixtures, the volume changes upon sintering, and the structure and strength of high-temperature composite materials are studied.     

Production of metal powders from melts by centrifugal atomization

Conclusions A study was made of centrifugal atomization of molten metals in argon at low argon consumption rates [(5.2–7.5) · 10^–3 NTP m³/kg]. Output with a single injector attained 30–40 kg/h. Increasing the molten metal head to 0.6–0.8 MPa and decreasing the nozzle diameter to 0.3 mm substantially increased the fineness of the powders. Raising the head still further influenced the effectiveness of atomization to a smaller extent, and decreasing the nozzle diameter to less than 0.3 mm coarsened the powders. Powders of magnesium, aluminum, and Br020 alloy. (20% Sn-Cu bronze) produced by centrifugal atomization of superheated (by about 30–50°K) melts in an inert atmosphere (argon) had spherical particle shapes, which imparted to them good flowability. The oxygen content of the powders was low (less than 0.08%).Translated from Poroshkovaya Metallurgiya, No. 12(276), pp. 5–10, December, 1985.     

Production and properties of metal-PTFE antifriction materials from atomized bronze powders

Conclusions An investigation into the sinterability of loosely poured atomized bronze powders has established that the porosity of resultant sintered bronze skeletons depends on the particle size and shape. The shape of the bronze powder particles has some effect on the antifriction characteristics of a metal -PTFE material, but its coefficient of friction and wear resistance are affected more strongly by the composition of a solid lubricant introduced into the pores of its sintered skeleton. Using a nonspherical rather than spherical bronze powder gives a bronze saving of 15–20% without affecting the good antifriction properties of metal-PTFE materials, by increasing the porosity of their skeletons. Replacing molybdenum disulfide with graphite substantially increases the wear resistance of two-layer metal-PTFE materials and markedly decreases their cost, since the price of molybdenum disulfide is more than 20 times that of graphite.Translated from Poroshkovaya Metallurgiya, No. 9(273), pp. 30–34, September, 1985.     

Production of powders of cast iron shavings and special features of production of components from these powders. III. Structure and strength of heat-treated alloys

Conclusions Quenching the specimens from 800°C does not lead to the redistribution of the carbide in the volume of the alloys of the iron-cast iron system. The most homogeneous structure of the alloys is formed only in quenching from 900°C. However, quenching from 1000°C increases the size of voids and causes supinating of the alloys, although their homogeneity increases.Heat treatment increases the tensile strength of the alloys which contain 10–50% of low-alloy cast iron. The alloys quenched from 800°C have the maximum strength after tempering of 300°C, whereas the alloys quenched from 900 and 1000°C with a maximum strength at tempering temperatures of 250 and 200°C, respectively.The highest hardness was recorded for the alloys after quenching from 900°C. All the alloys quenched from 800, 900, and 1000°C are characterized by sufficiently higher hardenability to a depth of 4mm.An increase of the tempering temperature of the alloys in the range 200–300°C reduces their impact toughness. This fact is not in agreement with the generally recognized interpretations. However, an increase of the cast iron content usually greatly reduces the KC value of the specimens, regardless of the quenching and tempering temperatures.Translated from Poroshkovaya Metallurgiya, No. 1(325), pp. 47–53, January, 1990.     

Production of abrasive powders from a silicon nitride base material

Conclusions Optimum conditions of preparation of abrasive powders using scrap from the manufacture of Silinit-R tool material have been determined. The strength of grains of powders investigated is comparable to or higher than, depending on their size, that of AS15 and AS6 synthetic diamond grains. The energy of rupture of their grains substantially exceeds that of grains of a silicon carbide abrasive powder, and grows with increasing filler content. Silinit with the maximum filler content is superior in abrasive ability to titanium carbide or titanium boride but inferior to Kubonit. Abrasive powders from Silinit tool material are suitable for the manufacture of abrasive tools.Translated from Poroshkovaya Metallurgiya, No. 12(300), pp. 26–31, December, 1987.     

NiAl powder alloys: I. Production of NiAl powders

The influence of five methods of production of Ni₅₀Al₅₀ powder alloys on the processes occurring during reactive alloy formation of nickel monoaluminide during heating is considered. It is shown that, when powder mixtures obtained by agitation in ball mills and cladded composite powders with a low level of internal stresses are used, it is possible to produce a material with a nearly equilibrium phase composition in the course of reactive sintering due to an exothermic effect with the participation of a liquid phase (aluminum melt) in the reaction. The sintered material is porous and has an island structure. Mechanical alloying in a high-energy ball mill (attritor) results in the formation of layered Ni/Al granules with a developed interface and a high level of internal stresses and defects, which makes it possible to decrease the temperatures of initiation of reactive interaction by ∼300°C. This interaction develops in the solid phase according to a slow diffusive mechanism leading to the formation of intermediate nickel aluminides and hindering the achievement of equilibrium phase composition. The microingot granules (∼80 wt % particles 100–400 μm in size) produced by melt spraying by gases (N, Ar) has the composition of the melt, but grain boundaries are depleted of aluminum in comparison with the volume. The NiAl powders (∼90 wt % particles <40 μm in size) produced by combined hydride-calcium reduction are characterized by a highly homogeneous nickel and aluminum distribution, and their composition is close to equilibrium. These two types of powders are selected as the initial material for investigating the compacting and production of NiAl-based alloys.