Showing papers on "Powder metallurgy published in 1986"

Formation of amorphous alloys by the mechanical alloying of crystalline powders of pure metals and powders of intermetallics

Abstract: Amorphous powders of Ni32Ti68 and of Ni45Nb55 were synthesized by mechanical alloying (MA) starting from either a mixture of pure metal powders (in the appropriate molar ratio) or from powders of the crystalline intermetallics NiTi2 and Ni45Nb55, respectively. For both alloys, the peak temperature increase (above the average processing temperature) in the powder particles trapped between colliding balls is estimated at 38 K. Thus, the amorphization is attributed to a process other than the formation of local melts followed by the rapid solidification of these melts into the amorphous phase. The amorphization by MA starting from a mixture of pure crystalline powders is attributed to a solid state interdiffusion reaction, the kinetics of which is controlled by the excess point and lattice defects generated by plastic deformation. The amorphization by MA starting from powders of crystalline intermetallics is attributed to the accumulation of point and lattice defects which raise the free energy of the faulted intermetallic above that of the amorphous alloy.

Preparation of amorphous Ti1−xCux (0.10<x<=0.87) by mechanical alloying

Abstract: We show that amorphous alloy powders of Cu and Ti can be produced over a broad composition range by mechanical alloying of the elemental powders in a high-energy ball mill. The amorphous powders are compared with liquid-quenched amorphous alloys of the same compositions using the techniques of x-ray diffraction and thermal analysis of crystallization. The two types of samples are found to have similar characteristics. Chemical analysis shows that only trace amounts of impurities are introduced in the alloys by the milling process.

Reactivity of Dy2O3 and Tb4O7 with Nd15Fe77B8 powder and the coercivity of the sintered magnets

Abstract: The reaction of Dy2O3 or Tb4O7 with Nd15Fe77B8 powder during the sintering increases the coercivity of the sintered magnets. These oxides are reduced to metal during the sintering process, resulting in magnets with properties similar to those prepared from the Nd13.5Dy1.5Fe77B8 alloy.

Glass forming ability in mechanically alloyed Fe‐Zr

Abstract: Amorphous Fe‐Zr powders have been prepared by mechanical alloying in a powder mill. The samples are characterized by x‐ray diffraction, differential scanning calorimetry, and saturation magnetization measurements. The glass forming range reaches from 30 to 78 at. % Fe being much wider than for melt‐spun samples. Eutectic concentrations do not play any role. The results are compared with the glass forming ability predicted by free‐enthalpy diagram calculations based on the Miedema model [A. R. Miedema, Philips Tech. Rev. 36, 217 (1976)]. Amorphization by mechanical alloying seems to be a metastable equilibrium process neglecting intermetallic phases. Rather high crystallization temperatures are found in the concentration range which is not accessible by melt spinning.

Method for preparing fully dense, near-net-shaped objects by powder metallurgy

Abstract: A method of manufacture of objects by consolidation of powdered metals, alloys, ceramics, or their mixtures is disclosed. The method comprises the steps of preparing a shaped, preferably ceramic, shell, placing it inside a metal or ceramic can, filling both the shell and space between the shell and the can with powder, outgassing and sealing the can if necessary, heating the full can and pressing it to consolidate the powder into a dense form; and separating the densified object within the shell from the densified shapes between the shell and the can. During pressing, the ceramic shell does not consolidate or bond to the surrounding powder, thus acting as an easy parting surface as well as being a shape defining container for the object being consolidated. The method permits easy definition of desired shell shape and permits manufacture of complex shaped, fully densified objects in near-net-shape form.

Effect of annealing on the microstructure of sintered Nd‐Fe‐B magnets

Abstract: A transmission electron microscopy study of sintered Nd‐Fe‐B magnets after annealing above 650 °C shows the formation of a thin intergranular Nd‐rich layer extending to pockets of polycrystalline fcc Nd crystals The grain boundary phase acts as a pinning site for the magnetic domain walls and is necessary for good magnetic hardening On the other hand, the Nd1+eFe4B4 phase is an unavoidable product of the sintering process but need not be present for good coercivity

Rapidly Solidified Powder Aluminum Alloys

Abstract: This book begins with introductory invited papers establishing the need for RSP alloy development for use in aerospace and land vehicles. Tutorial papers on solidification theory and stereological characteristics follow. Topics covered include: use of rapidly solidified aluminium alloys in land vehicles; rapid solidification of highly undercooled aluminium powders; microstructure of supercooled submicrometae aluminium-copper alloy powder; and dynamic compaction of rapidly-solidified aluminium alloy-powders.

Particle size distribution effects on sintering rates

Abstract: Recent interest in the use of near‐monosize powders for ceramic processing has provoked questions concerning the dependence of the processing on the particle size distribution One such factor is the sintering rate of the compact produced from a powder with a narrow particle size distribution This issue is addressed theoretically by considering a log‐normal particle size distribution which is characterized by a mean particle size and a width parameter The sintering rates derived for model systems are examined for both the initial and intermediate stages, and these rates are found to be a strong function of the distribution width parameter The sintering ability of a compact decreases with a broader particle size distribution and this effect becomes dramatic in the intermediate stage when grain growth is considered

Process and apparatus to simultaneously consolidate and reduce metal powders

Abstract: A powder metallurgy consolidation process and apparatus for carrying out said process produces integral metal bodies by heating metal powder of a predetermined composition to a temperature sufficient to cause solid state interparticle bonding, while simultaneously maintaining a reactive fluid in contact with the metal powder. The metal powder is compacted to a density greater than 90% of the full theoretical density of the composition after the reactive fluid has been removed. The reactive fluid is selected to modify the powder particle surface chemistry in order to improve bondability and to obtain other properties as desired. Metal bodies which have been consolidated by the process are sufficiently dense to be mechanically hot worked and exhibit exceptionally low retained gas content.

Physics and chemistry of beryllium

Abstract: The combination of properties of beryllium which results in this very low Z element being a candidate for use in fusion reactors is reviewed. The occurrence, availability, and processing of beryllium from both bertrandite (domestic) and beryl (imported) ores are described. The available beryllium grades are characterized. The purity level of these grades, which are all unalloyed in the usual sense, is presented in detail. The crystallographic factors which establish the physical and mechanical characteristics are reviewed. Powder metallurgy techniques are used almost exclusively to provide beryllium with modest ductility at room temperature (e.g., 3% tensile elongation) and excellent strain capacity at elevated temperature (>40% tensile elongation at 400 °C). The metallurgical behavior of the powder metallurgy product is summarized. The physical properties of this low density metal (1.85 g/cm3) are reviewed with emphasis on the favorable thermal properties. Mechanical properties at room and elevated tempe...

Metallurgical Variables Influencing the Corrosion Susceptibility of a Powder Metallurgy SiCw/Al Composite

Abstract: Corrosion studies of a powder metallurgy (P/M) SiC whiskers (SiCw)/Al Aluminum Association (AA) 7091 aluminum composite material were performed. The plate material, which was heat treated to the T-6 and T-7 tempers by conventional methods, exhibited preferential corrosion of the surface layers up to 2-mm thick. The regions of corrosion susceptibility were determined to result from improper processing and thermal treatments. Cold-worked regions resulting from extrusion were not completely removed by the conventional solution treatment and thus appeared as more corrosion susceptible. Large void volume fraction and excessive segregation of SiCw was also noted. Electrochemical, microscopic, and analytical techniques were used in these investigations. Attempts were made to remove the cold-worked regions and study the resultant corrosion properties. A comparative analysis of these results is discussed.

Titanium carbide/titanium alloy composite and process for powder metal cladding

Abstract: A microcomposite material having a matrix of a titanium-base alloy, the material further including about 10-80% by weight TiC substantially uniformly dispersed in the matrix. Several methods of cladding a macrocomposite structure including pressing quantities of a matrix material and a microcomposite material composed of the matrix material and a compatible stiffener material into layers to form a multi-layered compact and sintering the multi-layered compact to form an integral metallurgical bond between the layers of the compact with diffusion but essentially no composition gradient between the layers. A multi-layered macrocomposite article composed of an alloy layer of a matrix material and a layer of a microcomposite material composed of the matrix material and a compatible stiffener material bonded together at the interface region between the layers, the interface region being essentially free of a composition gradient.

Titanium: Rapid solidification technology

Abstract: This book presents the papers given at a symposium on the solidification of titanium. Topics considered at the symposium included the development of novel titanium alloys, solidification structure, laser surface melting, powder metallurgy, yttrium tin particles, microstructure, dislocations, and the effects of heat treatment on fatigue crack growth.

Mechanical, Electrical, and Electrical Contact Properties of Cu–TiO2 Composites

Abstract: Cu–TiO2 particulate composites have been prepared from copper coated titania particles by the powder metallurgy route. The properties of composites containing 5–20 wt-%TiO2 are compared with those of composites of similar composition produced from uncoated particles. Microstructural studies showed that the coated particles have a reduced tendency to agglomerate when present in quantities up to 5 wt-%. The density of composites decreased, while their hardness and electrical resistivity increased, with increasing titania content. In all cases, composites made from coated particles possessed better properties than those produced from uncoated ones. Re-pressing and annealing of the composites resulted in an increase in properties. Cu–5TiO2 particulate composites could be suitable for use as electrical contacts in light duty applications. PM/0282

High-density alumina-zirconia sinter and process for its production.

Abstract: A high-density alumina-zirconia sinter, which comprises more than 60 mol % to 99 mol % of alpha-alumina, 1 mol % to less than 40 mol % of zirconia containing at least 65 % of a tetragonal crystal phase, and a transition metal oxide in an amount of 0.01-1 % in terms of an atomic ratio of a transition metal to the sum of aluminum and zirconium, and which has a remarkably high sintering density, high strength, high toughness, and high hardness useful as mechanical members, abrasion-resistant materials, cutting tools, etc. This sinter can be obtained by dispersing alpha-alumina powder or its precursor powder and zirconia powder or its precursor in a solution or suspension of a transition metal compound, and sintering the powder obtained from the resulting dispersion. Particularly preferable starting powders include alumina-zirconia composite powder obtained by mixing a dispersion of alpha-alumina powder in an aqueous solution of a zirconium salt with a precipitating agent, and calcining the obtained composite powder.

Spherical precious metal based powder particles and process for producing same

Abstract: A powdered material and a process for producing the material are disclosed. The powdered material consists essentially of precious metal based spherical particles which are essentially free of elliptical shaped material and elongated particles having rounded ends. The material has a particle size of less than about 20 micrometers. The process for making the spherical particles involves mechanically reducing the size of a starting material to produce a finer powder which is then entrained in a carrier gas and passed through a high temperature zone above the melting point of the finer powder to melt at least about 50% by weight of the powder and form spherical particles of the melted portion. The powder is directly solidified.

A powder-based approach to semisolid processing of metals for fabrication of die-castings and composites

Abstract: A technique is presented for the generation of a globular (non-dendritic) array of solid fragments surrounded by a solute-enriched liquid. This is based on the premixing, heat treatment and consolidation of different types of powder. The resultant slurries have then been injected into a die at high velocity. The technique offers promise in terms of the versatility with which the slurry microstructure can be controlled and the soundness of the resulting die-castings has been encouraging. Among the effects investigated are the role of solute diffusion, the importance of globule size and the nature of coarsening phenomena. Experiments have also been carried out on the incorporation of ceramic fibres into the product and this appears to offer promise as a composite fabrication route. The work described here concerns only aluminium-base material alloyed with magnesium, although the principles outlined are expected to apply to many other systems.

Pump liners and a method of cladding the same

Abstract: A method of cladding an internal cavity surface of a metal object is disclosed The method includes the steps: (a) applying a powder metal layer on said internal surface, the metal powder including metal oxide or oxides, borides and carbides, (b) filling a pressure transmitting and flowable grain into said cavity to contact said layer, (c) and pressurizing said grain to cause sufficient pressure transmission to the powder metal layer to consolidate same

Preparation of rare earth magnet

Abstract: PURPOSE:To improve magnetic characteristics by sintering after the powder of Nd, Fe, B system alloy whose main formation phase is Nd2Fe14B is mixed with the fine powder of (Ce, Pr, Nd), Fe, B system alloy and is molded. CONSTITUTION:Nd2Fe14B system magnetic alloy containing Nd, Fe and B as the main components is manufactured by powder metallurgy. In this process, the powder of Nd, Fe, B system magnetic alloy is mixed with 0-60wt% (0 is not included) of the powder of (Ce, Pr, Nd), Fe, B system magnetic alloy whose main formation phase is (Ce, Pr, Nd)2Fe14B and then is molded. This molded substance is sintered and represents improved magnetic characteristics as a product.

Analysis of second phase particles in a powder metallurgy HIP nickel-base superalloy

Abstract: The nature of the second phase particles associated with LC Astroloy prepared using powder metallurgy techniques has been examined. The individual particles have been identified using energy dispersive X-ray analysis and convergent beam electron diffraction. Four distinct types of particles have been observed: a cubic MC carbide in which M is either titanium or titanium plus molybdenum, a monoclinic phase ZrO2, a trigonalα-Al2O3 and a tetragonal M3B2 phase in which M is molybdenum or molybdenum and chromium. The observations indicate that, although some MC carbides are associated with the ZrO2 phase, the majority of the prior particle boundary precipitates are separate entities. Hot isostatic pressing or subsequent heat treatments above or below the γ′ solvus were observed to have little effect on the incidence or distribution of the precipitation associated with the prior particle boundaries. In contrast, heat treatments above the γ′ solvus resulted in the dissolution of the M2B3 phase and its preferential precipitation on the grain boundaries.

Effect of consolidation route on structure and property control in rapidly solidified Al–Cr–Zr–Mn povvder alloy for high temperature service

Abstract: In this paper the authors describe a new rapidly solidified alloy which is capable of meeting the projected requirements of the aerospace industry. Initial studies using splat quenched particulates were carried out on the Al–Cr–Zr system. Microhardness tests indicated that these alloys age–hardened between 350 and 400°C and showed excellent thermal stability. Further alloy development and studies of fabrication behaviour were carried out using air atomized powder. Powders were consolidated by either conventional or hydrostatic extrusion. Microstructural changes during fabrication were identified and correlated with mechanical property data. The alloy can achieve the requirements of the aerospace industry provided microstructural development is controlled during fabrication.MST/233

Fabrication of hollow, cored, and composite shaped parts from selected alloy powders

Abstract: Alloy powder is packed into a mold which comprises a complex-shaped solid aphite inner core and a similarly complex-shaped thin glass outer wall. The mold is evacuated, sealed, and then heated to the alloy sintering temperature, the glass softens and applies an isostatic pressure on the alloy as the alloy particles consolidate. After the consolidation step, the mold and its contents are cooled and the glass and graphite materials are removed from the alloy object. This method is particularly useful for preparing complex fittings of Nitinol shape memory alloys.

Superalloy compositions with a nickel base

Abstract: Superalloy with a nickel base matrix having good mechanical properties whenot in respect of tensile strength, creep resistance, low cycle fatigue and resistance to crack-propagation of which the composition in percentages by weight is as follows: Cr 11 to 13; Co 8 to 17; Mo 6 to 8; Nb less than or equal to 1.5; Ti 4 to 5; Al 4 to 5; Hf less than or equal to 1; C, B, Zr each less than or equal to 500 ppm; Ni remainder to 100. The alloy can be manufactured advantageously by powder metallurgy techniques and used in the manufacture of turbo machine disks.

Manufacture of rare-earth magnet

Abstract: PURPOSE: To increase the strength and the density of a formed product at low pressure by sintering after alloy powder is mixed with 1W3wt% polyisobutylene, coated and pressed for forming. CONSTITUTION: When an R 2 Co 17 magnet alloy (R is yttrium or a rare earth element.) is manufactured by powder metallurgy, R 2 Co 17 alloy powder is mixed with 1W13wt% polyisobutylene and coated on the surface of the particles of the alloy and then, this is pressed for forming and sintered. The strength and the density of a formed product can be increased without affecting the characteristics of a magnet by forming in a magnetic field after the alloy powder wherein the main component is the R 2 Co 17 is mixed with the appropriate quantity polyisobutylene and coated. COPYRIGHT: (C)1987,JPO&Japio

Construction elements produced by powder metallurgy

Abstract: Structural component made of powder metallurgical materials, particularly temperature resistant alloys, nickel base alloys, are produced by injection molding or pressing. The sintering is divided into individual work steps for producing dense and smooth structural components which are true to shape.