Powder Metallurgy Materials Research Articles

New Aluminum Structural Materials for the 1980's

These new materials are the result of recent innovations in powder metallurgy technology and materials engineering. New production processes have been developed to compact powdered aluminum into billets which can be extruded, forged, or rolled into aluminum mill products. These new aluminum powder metals are also being mechanically alloyed and reinforced with whiskers and fibers to produce very unique structural properties. These new materials are generally superior in quality and corrosion resistance to conventional ingot aluminum mill products. Fiber-reinforced aluminum materials are being produced that are stronger and stiffer than steel, yet they weigh only 1/3 as much as steel. This paper summarizes these recent developments for: (1)Aluminum powder metal products; (2)aluminum whisker composite products; and (3)aluminum fiber composite products. A brief description of the production processes for each of these products is given, and some typical material properties are shown for specific products. Estimated future production volumes and prices of these materials are also examined.

Pressure drop in sheet porous powder-metallurgy materials

Pressure drop in sheet porous powder-metallurgy materials

Velocity of sound in sintered powder metallurgy materials

1. An equation has been derived analytically and confirmed experimentally, describing the dependence of the velocity of sound in powder materials on their porosity and conditions of their preparation and testing. 2. It is shown that the method of investigating the velocity of sound in powder materials may be employed for the physicochemical analysis of sintering processes.

Ways of increasing the range of application of powder metallurgy parts in diesel locomotive construction

motive parts produced at the plant increased 6.6 times, while the number of types of standard parts increased 3.4 times. During the first two years of the Ninth Five-Year Plan, the weight of parts used grew 1.4 times, attaining 55 tons in 1972. In 1973, the plant's estimated demand for parts produced by powder metallurgy techniques totaled one and a half million items. Each year, savings were made as a result of cuts in production costs made possible by the adoption of new powder metallurgy parts. The savings amounted to 116,100 rubles during the period of the Eighth Five-Year Plan and 39,000 rubles in the first two years of the Ninth Five-Year Plan (Fig. 1). Some of the parts used are shown in Fig. 2. Powder metallurgy materials are now used in the manufacture of 40 types of standard parts, including bushings of the louvers, brake linkage, spring suspension, and valves and seats of the oil system. Increased locomotive speeds and powers and the need for longer lives in parts operating in heavily stressed units of locomotives had necessitated comprehensive research and development work with the aim of improving the physical and mechanical properties of existing materials and developing new materials and fabrication processes which had not previously found application in industry.

PROPERTIES OF ALUMINIUM-TIN ALLOYS PRODUCED BY POWDER METALLURGY

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.

Structural Characterization of Powder Metallurgy and Composite Materials

Of the broad spectrum of new or advanced competitive engineering materials for structural applications, composites and high-density powder metallurgy (P/M) materials are perhaps of most interest. Rational development necessitates a thorough knowledge of the associated structure-property relationship; particular importance is vested in the role of microstructure on properties such as strength, creep resistance, ductility, toughness and fatigue resistance. Examination of structure in these materials presents a number of unique problems; however, intelligent application of the various techniques of optical and electron microscopy can provide a quantitative characterization. The primary objective here is to review these approaches and to illustrate observations by reference to metal-matrix composites and various P/M materials.

Effects of sintering temperature and time on results of spectral analysis

1. The temperature and time of sintering of Fe+Ni+Co+Cu, Fe+Ni, Fe+Co, and Fe+Cu powder metallurgy materials produced by the chemical alloying of iron powder have virtually no effect upon the results of spectral determinations of the alloying additions performed with the aid of high-frequency and high-frequency condensed-spark generators. In view of this, it is possible: a) to prepare, by the method described above, a single set of reference standards for the analysis of both cast materials and materials (containing chemically introduced alloying additions) sintered at any temperature and for any period of time; b) to employ for the analysis of sintered materials produced by the technique described, irrespective of their sintering temperature and time, cast reference standards of the same composition and structure. 2. The temperature at which powder metallurgy materials are sintered does not affect the results of spectral determinations of the impurities present in their base materials.

Mean contact stress in the densification rolling of powder metallurgy materials

Mean contact stress in the densification rolling of powder metallurgy materials

Pore size of powder metallurgy materials

1. Calculations are made of the mean pore sizes of thin sintered strips from titanium, stainless steel, and nickel powders. 2. It is demonstrated that, in the formula for calculating the mean pore size from the coefficient of permeability, the coefficient of pore tortuosity should be taken to be equal to 2.0–2.4. 3. The coefficient of pore tortuosity is unaffected by the porosity of the material or the ratio of the specimen thickness to the mean particle size of the starting metal powder.

Experimental data on the rupturing pressure of porous powder metallurgy materials

1. Curves of rupturing pressure as a function of powder particle size, compaction pressure, and specimen thickness and diameter were constructed for porous parts compacted from stainless steel and nickel powders. 2. Empirical relations were established enabling rupturing pressures to be calculated for the filtration of compressed gas with filters of any diameter. 3. The rupturing pressure of a filter depends on the gas flow velocity and on the pressure-generating medium employed.

Modern powder metallurgy materials and prospects for further development

Modern powder metallurgy materials and prospects for further development

Comparative creep-rupture properties of tungsten-25% rhenium consolidated by arc-melting and powder-metallurgy techniques

The creep-rupture properties of W-25% Re materials consolidated by arc-melting and powder-metallurgy techniques have been compared at 1650 ° and 2200 °C for rupture times up to 1000 h. At comparable stresses, powder-metallurgy material has a shorter rupture life and lower rupture ductility than arc-melted material. On the basis of secondary creep rate, powder-metallurgy material is weaker than arc-melted material at 1650 °C but stronger at 2200 °C. Optical and electron metallography showed that voids form at grain boundaries in both materials. In the powder-metallurgy material, grain boundaries appear to be immobile, and massive growth of voids initiates fracture with very little deformation. In the arc-melted material, grain boundaries appear to be mobile, and fracture seems to be forestalled by their ability to move. The relative creep rates can be explained on the basis of void growth and grain size.

Technique for the simultaneous friction and wear study of powder metallurgy materials

Technique for the simultaneous friction and wear study of powder metallurgy materials

Electron microscopical investigation of the structure of metallic films during heating

1. A new technique for the direct heating of thin metallic objects in the electron microscope to temperatures of 850–900°C has been developed and used in investigations. The possibility has been established of studying gradual changes in the structure and phases of thin metallic foils during continuous heating, which may prove to be extremely useful in researches into the synthesis of new powder metallurgy materials and also into external friction of metals. 2. An account is given of the main structural changes occurring during the continuous heating of pure copper, nickel, and iron; these changes must be allowed for in investigations of phase transformations that may take place in compounds based on these metals. 3. It has been established that the recrystallization processes observed during heating in vapordeposited-nickel films correspond with the parallel processes occurring in the same temperature range in foils electrolytically reduced in thickness and annealed outside the electron microscope. 4. A characteristic phase (Fe3C) formation phenomenon was detected during the heating of iron. It appears to be closely linked with the reaction of iron with oil-vapor decomposition products in the heating space.

Dispersion-strengthened zirconium alloys

Inert particle strengthening concepts were extended to zirconium-base alloys. By using powder metallurgy techniques inert particles of Y 2O 3 were mechanically dispersed in a Zircaloy-2 matrix. Hot-hardness, elevated-temperature tensile, 343°C creep, and 400°C steam corrosion data for the resulting materials were obtained and interpreted. The elevated temperature yield strength of Zircaloy-2 was increased. Much of the increase was related to oxygen contamination. However, significant strengthening, in excess of that caused by oxygen, was shown to have been caused by inert particle dispersion. The 343°C, steady-state creep rates of dispersion-strengthened Zircaloy-2 were markedly lower than those for wrought Zircaloy-2. Yttria dispersants were noted to have some adverse effect on corosion resistance in 400°C steam. Oxygen contamination is the major technological problem with regard to the development of dispersion-strengthened zirconium powder metallurgy materials. Alloy additions of Be are suggested as a means of minimizing both the corrosion and oxygen contamination problems.

Tensile properties of tungsten-3% rhenium from 1400° to 2900°C in vacuum

The tensile properties of recrystallized, doped powder-metallurgy tungsten-3% rhenium rod have been determined from 1370° to 2930°C in vacuum at a strain rate of 0.02/min. A comparison is made with recrystallized, doped powder-metallurgy tungsten, which shows comparatively poor ductility, and plasma-flame single-crystal tungsten, a very ductile material. The variation of strain-hardening exponent with temperature is shown for the two powder-metallurgy materials. Tungsten-3% rhenium has the highest strength and the lowest ductility of the three materials. At a test temperature of ⋍ 50% of the absolute melting point, both tungsten-3% rhenium and powder-metallurgy tungsten show decreased ductility and intercrystalline fracture associated with void formation and growth. Ductility does not increase with increasing temperature above ⋍ 65% of the absolute melting point for tungsten- 3% rhenium, as it does for powder-metallurgy tungsten, and this is attributed to the absence of stress-induced grain growth during testing.