Showing papers on "Powder metallurgy published in 1994"

Particle reinforced aluminium and magnesium matrix composites

Abstract: Particle reinforced metal matrix composites are now being produced commerically, and in this paper the current status of these materials is reviewed. The different types of reinforcement being used, together with the alternative processing methods, are discussed. Depending on the initial processing method, different factors have to be taken into consideration to produce a high quality billet. With powder metallurgy processing, the composition of the matrix and the type of reinforcement are independent of one another. However, in molten metal processing they are intimately linked in terms of the different reactivities which occur between reinforcement and matrix in the molten state. The factors controlling the distribution of reinforcement are also dependent on the initial processing method. Secondary fabrication methods, such as extrusion and rolling, are essential in processing composites produced by powder metallurgy, since they are required to consolidate the composite fully. Other methods, suc...

Recent development in the fabrication of metal matrix-particulate composites using powder metallurgy techniques

Abstract: It is advantageous to fabricate metal matrix-particulate composites (MMPCs) using powder metallurgy (PM) because the fabricated composites possess a higher dislocation density, a small sub-grain size and limited segregation of particles, which, when combined, result in superior mechanical properties. The various PM-related processes currently in use in the fabrication of MMPCs, are reviewed, outlining the common problems encountered in each of these fabrication processes. The more recently developed PM techniques to fabricate MMPCs are also discussed.

Shape memory TiNi synthesis from elemental powders

Abstract: Commercially, the shape memory alloy TiNi is produced either by vacuum induction melting or by vacuum arc remelting of the pure metal ingots. Powder metallurgy techniques provide an alternative fabrication route but problems arise in achieving chemical homogeneity. In this study TiNi compacts were cold-pressed from the blended elemental powders and sintered in vacuum for varying times at temperatures from 800 °C to 1000 °C. Two heating rates were used, 5 K min−1 and 10 K min−1. A TiNi microstructure could be produced after annealing at 1000 °c for 6 h, although some TiNi3 was still observed. This is likely to be difficult to completely remove as TiNi3 is thermodynamically more stable than TiNi. Thus, homogenization is unlikely to be completed by solid-state diffusion processes. The martensitic B19′ structure was observed to be highly oriented after processing.

Mechanical behavior of damage tolerant TiB whisker-reinforced in situ titanium matrix composites

Abstract: The results of a systematic study of the effects of alloying and microstructure on the mechanical behavior of in situ titanium matrix composites are reported in this paper. In situ composites are produced by alloying with B which promotes the formation of TiB whiskers during rapid solidification processing. The composite powders are subsequently compacted and extruded to align the whiskers prior to systematic heat treatment in the β and/or α + β phase fields. The processing conditions for the development of in situ composites with attractive combinations of strength, ductility, damage tolerance and creep resistance are thus established. The improvements in the composite properties are rationalized using simple micromechanics principles. The paper highlights the potential for the microstructural design of composites using micromechanics and conventional physical metallurgy principles.

Mechanical alloying of high-strength copper alloys containing TiB2 and Al2O3 dispersoid particles

Abstract: Considerable effort is being devoted to the development of high strength, high conductivity copper alloys both for applications in electronics as well as in aerospace, where the ability to remove heat and to retain a sufficient strength is of critical importance. Examples of such alloys are Cu-Cr-Zr and Cu-Ni-Sn alloys prepared by rapid solidification and by Osprey processing, in situ fabricated fiber-reinforced Cu-Cr, Fe, or Nb composites and mechanically alloyed Cu-bcc metal mixtures. The previously-examined mechanically alloyed materials showed good strength after consolidation of the milled powders but showed signs of structural instabilities at high temperatures due to coarsening of the dispersed bcc metal particles. The present study examined alloys prepared by milling and consolidating mixtures of copper with other elements which will produce stable compound phases (TiB[sub 2] and Al[sub 2]O[sub 3]) either during milling or during subsequent annealing. Such dispersed particles should be more resistant to coarsening than the earlier bcc metal particles and should lead to improved strength and stability after high temperature treatments.

High density processing of high performance ferrous materials

Abstract: Density is a predominant factor in the performance of P/M components. Methods such as double press/double sinter, copper infiltration and powder forging have been employed to provide higher densities than traditional single press and sinter operations; however, their widespread use in constrained by cost and geometry considerations. A commercially proven method for obtaining single compaction/single sinter densities in the 7.25 to 7.55g/cm 3 range by means of the patented ANC0RDENSE TM technology is introduced. Conventional compaction pressures and sintering temperatures, typically not exceeding 50tsi (690MPa) or 2300 o F (1260 o C), respectively, are utilized. Resulting properties for several high performance materials are presented. Test results indicate that the new material system is a cost effective method of providing high density parts with outstanding physical properties. The process is shown to be applicable to a wide variety of high performance materials. Additionally, significant improvements in green strength and ejection forces are realized

Yield behavior of metal powder assemblages

Abstract: W e present experimental data on the compaction of powder metals using two powder systems with different powder particle morphologies. The data have been collected using biaxial and triaxial compaction systems that load powders radially in deformation space. Our results indicate that several current models proposed for powder metal compaction do not represent actual constitutive behavior. Additionally, the powders tested demonstrate a strong dependence on powder morphology and a possible associated dependence on interparticle cohesion. This dependence on cohesion may necessitate the use of an additional state variable beyond those of relative density and particle hardening ordinarily used to represent powder yield behavior.

Co-cr-mo powder metallurgy articles and process for their manufacture

Abstract: A powder metallurgy article formed from a Co-Cr-Mo alloy powder and a method for making the article are disclosed. The Co-Cr-Mo alloy powder contains, in weight percent, about 0.35 % max. C, about 1.00 % max. Mn, about 1.00 % max Si, about 26.0-30.0 % Cr, about 5.0-7.0 % Mo, about 3 % max Ni, about 0.25 % max. N, about 1.00 % max. Fe, about 0.01 % max. of oxide forming metals, and the balance is essentially Co. Within their respective weight percent limits C and N are controlled such that they satisfy the relationship: 62.866 + 360.93 x (%C) + 286.633 x (%N) - 682.165 x (%C)2 - 641.702 x (%N)2 » 120.

Chemically activated liquid phase sintering of tungsten-copper

Abstract: Liquid phase sintering of mixed W-Cu powders is hampered by the insolubility of tungsten in copper. In this study, the system properties were significantly improved by additions of less than 1w/o Co to the starting powder mixture. The effects of processing variables such as cobalt concentration, initial homogeneity, copper particle size, copper concentration, green density, heating rate, and sintering temperature were investigated. In response to these variables, density, strength, and microhardness were measured and related to microstructures, fracture surfaces, and grain sizes. The dependence of grain growth on activator concentration and sintering temperature is similar to that observed in the activated solid state sintering of tungsten with Co additions

Method for preparation of a functionally gradient material

Abstract: The invention provides a method for in-situ powder metallurgy processing of a functionally gradient material (FGM) which uses a preceramic polymer binder system with the metal and/or ceramic powders used to produce the intermediate layers of the composite. The invention also provides a method for controlling shrinkage of the functionally gradient material during processing while still preserving the desired density of the intermediate layers by controlling the preceramic polymer binder content within the functionally gradient material.

Hi-density sintered alloy

Abstract: A process of forming a sintered article for powder metal comprising blending carbon and ferro alloys and lubricant with compressible elemental iron powder, pressing said blended mixture to form sintering said article, and then high temperature sintering said article in a reducing atmosphere to produce a sintered article having a high density from a single compression.

Spray Forming of Metal Matrix Composites

Abstract: Spray forming is emerging as a viable technology for the fabrication of discontinuously reinforced metal matrix composites. Advantages of this hybrid powder metallurgy approach reside in near net shape capability, the development of fine scale microstructures devoid of macrosegregation and porosity, and the presence of a uniform distribution of the reinforcing constituents in the matrix. In spray forming, interfacial properties are not compromised and the need to handle fine powder is eliminated. There are two primary adaptations of the Osprey process used in the processing of discontinuously reinforced metal matrix composites, namely reactive (in situ) spray forming, and inert spray forming. The former embraces spray processing with attendant gas–liquid reactions, liquid–liquid reactions, or liquid–solid reactions. In inert spray forming benign particles are injected into the metal spray. These approaches are analysed and their application to diverse metal matrix composites is described. It is de...

Mechanical alloying of Fe-Al intermetallics in the DO3 composition range

Abstract: Binary Fe-Al intermetallics with compositions ranging between 10 and 30 at% have been produced by mechanical alloying. The elemental powders were milled together resulting in the dissolution of the Al atoms into the Fe lattice. Subsequent heat treatment of the compacted powder resulted in the formation of the intermetallic. However, complete suppression of the DO3 (Fe3Al) structure in favour of the B2 (FeAl) structure was observed. The suppression of the DO3 structure is considered to be due to the presence of the high density of defects resulting from the heavy deformation incurred during milling. At Al compositions below 22 at%, X-ray diffraction revealed a b c c phase with lattice parameters varying between those of α-Fe and the B2 intermetallic. The structure tended towards that of α-Fe with lower Al contents indicating a decreasing number of Al atoms available to occupy B2 lattice sites. A fine grain size and evidence of tearing indicate that mechanically alloyed Fe-Al intermetallics in the DO3 composition range are ductile at room temperature.

Mechanical Alloying of BiTe and BiSbTe Thermoelectric Materials

Abstract: Two thermoelectric materials, BiTe and BiSbTe were prepared by mechanical attrition of elemental powders in a rare gas atmosphere. Nearly 20 min were required for the alloying of BiTe, while 10h were required for BiSbTe. After attrition, the average powder diameter of the BiSbTe alloy was in 1.4 μm, and the impurity content, measured by Inductively Coupled Argon Plasma Emission Spectrophotometer, xasless than 0.1 mass%. The MA powders were sintered by a hot pressing technique. Uniform elemental dispersions were measured by EPMA in BiSbTe alloys sintered at 623 K

High-energy NdFeB magnets and their applications

Abstract: In sintered NdFeB magnets, additive elements for increasing coercivity decrease residual magnetization. Also, fine magnetic powder oxidization prevents identification of the stoichiometry composition (Nd2Fei14B).To improve the magnetic properties of a sintered NdFeB magnet, the authors have developed a method involving two alloys. Magnetic Nd2Fei14Balloy and a rare- earth- rich alloy (including richer dysprosium content) are melted individually and mixed together after coarse pulverization. After the sintering process, dysprosium in the sintered body is enriched in each grain region near the grain boundary. The two- alloy method minimizes the liquid phase necessary to keep the coercive force at a useful level, and thus results in compositions closer to stoichiometry. The energy product of magnets having an inhomogeneous dysprosium distribution is typically 360 kj - m- 3(45 MG.Oe) at production level. The corrosion characteristics of cobalt- substituted NdFeB magnets also were investigated. These magnets are now used in voice coil motors for hard disk drives and contribute to shortening access time and hard- drive downsizing.

Compaction and sintering of ultrafine powders

Abstract: The properties of many particulate materials can be improved through the application of ultrafine powders. There are, however, many peculiarities associated with the consolidation (i.e. compaction and sintering) of these powders. In this article, the following aspects of ultrafine powders are considered: the influence of powder properties on the interparticle friction characteristics; the content of adsorbed gases and storage problems; the effect of compaction pressure on the density of silicon nitride and nickel powders; the sintering parameters of these powders; and selected properties of consolidaled nanocrystalline materials

Synthesis and microstructural evolution of Al-Ni-Fe-Gd metallic glass by mechanical alloying

Abstract: Amorphous Al[sub 80]Ni[sub 8]Fe[sub 4]Gd[sub 8] quaternary powders are successfully produced using the mechanical alloying (MA) technique, suggesting that powder metallurgy techniques may be used in the manufacture of aluminum-transition metal-rare earth metallic glasses as high-strength, low-density engineering materials. Detailed investigations into the microstructural evolution of the amorphous phase from elemental powders are presented, employing scanning and transmission electron microscopy, as well as, analytical techniques. The results show that it is possible to amorphize higher-order systems by MA, and the observations of the amorphization reaction support the interdiffusion-based model developed from studies of simple binary systems, with certain adjustments. The resulting amorphous powder demonstrates good thermal stability, and consolidated amorphous bulk material up to 93% dense are easily produced. Mechanical properties of the amorphous phase are evaluated, including measurement of Vickers hardness and fracture toughness. K[sub c] is found to lie in the range of 1-5 MPa/m[sup 1/2], identifying the produced powder as the brittle-type amorphous phase seen in earlier work. Dispersed ductile nanocrystals improve the fracture toughness at the expense of Vickers hardness.

High density ferrous power metal alloy

Abstract: A method for producing high density and/or high surface density ferrous powder metal parts has the steps of: compacting a iron-containing powder substantially free of graphite at room temperature and at about 40-50 tsi; sintering the green compact in an inert, non-oxidizing environment at a temperature of about 2050°-2300° F.; repressing the sintered compact at room temperature at about 60 tsi; carburizing the repressed compact at high temperature to form a layer of relatively high carbon concentration to a depth of at least about 0.010 inches; and immediately quenching the hot carburized compact followed by a tempering treatment.

Rapid consolidation of BiPbSrCaCuO powders by a plasma activated sintering process

Abstract: A new rapid powder consolidation technique—plasma activated sintering (PAS)—was used to obtain high density disk-shaped bulk superconductor samples in the BiPbSrCaCuO system. Different powder precursors prepared by the glass-ceramic route, sol-gel processing, and solid state reactions were investigated. Results of density, hardness, and critical superconducting transition temperature were compared after PAS processing of powder precursors. Microstructures showing oriented grains of the 2223 phase were obtained as a result of PAS densification in very short time frames ( ).

New Mg-based amorphous alloys in MgY-misch metal systems

Abstract: New amorphous alloys in the MgYMm (where Mm denotes misch metal) system were found to form in the composition range 2.5–15 at.% Y and 0%–8% Mm by melt spinning. The highest tensile fracture strength is 530 MPa for Mg 88.5 Y 7.5 Mm 4 and the amorphous alloy also exhibits good corrosion resistance which is superior to that for the commercial AZ91 (MgAlZn) alloy. The application of powder metallurgy processing consisting of high pressure gas atomization and warm extrusion to an Mg 95.5 Y 2.5 Mm 2 alloy with good bending ductility even in a crystallized state caused the formation of a bulk alloy with a yield strength of 560 MPa at room temperature and 410 MPa at 523 K. The elevated-temperature strength is much superior to that for the heat-resistant type of MgYNd alloy (WE54A-T6). The high strength is presumably due to the formation of a finely mixed structure consisting of Mg, Mg 12 (Ce, Nd), Mg 17 La 2 and Mg 24 Y 5 . Thus the MgYMm alloy is attractive because of the features of the high elevated-temperature strength combined with its light weight and good corrosion resistance.

Consolidation of atomized NiAl powders by plasma activated sintering process

Abstract: There are several attributes that make NiAl intermetallics attractive for high temperature structural applications. First, NiAl combines higher temperature capabilities than superalloys, at a density 33% lower than superalloys. Second, among high temperature, high strength intermetallic compounds, NiAl has the special advantage of inherent oxidation resistance. For consolidation purposes, there are different avenues to decrease the high temperature exposure: to trade off high temperatures or long heating times by high applied pressure or to accelerate the densification process by plasma generation. The former approach is applied in some non-conventional consolidation techniques such as Ceracon process in which short-time high pressure application may compensate for high temperatures or long times. Additionally, the quasi-isostatic pressure application in the Ceracon process imparts shearing components of the applied stress that break down the surface oxides, thus permitting efficient particle bonding during subsequent consolidation. Another avenue that is being explored as a short time densification technique -- Plasma Activated Sintering (PAS) -- comprises an initial plasma generation step to prepare particle surfaces for further densification. PAS has been recently explored as a consolidation method for low diffusivity materials.

Method of making powder metal helical gears

Abstract: A method includes the steps of compacting powder metal to form a powder metal blank, and forming gear teeth on the powder metal blank by rolling the powder metal blank between rolling dies rotating about parallel axes. The step of forming gear teeth on the powder metal blank by rolling includes the steps of rotating the rolling dies about parallel axes and maintaining the distance between the parallel axes constant during forming of the gear teeth on the powder metal blank. Powder metal gears having 45° helical gear teeth are cold rolled. Herringbone gears and pinion gears are made with the 45° helical powder metal gears.

Structures and properties of rapidly solidified MgCa based alloys

Abstract: With the aim of developing new light weight and high strength materials, rapidly solidified flakes of MgCa based alloys with or without ternary additions such as Zn, Si and Ce were produced by atomizing the alloy melt and subsequent splat-quenching on a water-cooled copper roll. The flakes were consolidated by hot extrusion. Metallographic structures and constituent phases were examined for both rapidly solidified flakes and powder metallurgical (PM) materials, and mechanical properties were evaluated for PM materials. The rapidly solidified flakes show fine dendritic cell structures with the cell size ranging from 0.2 to 2 μm. Hardness increased on heating the flakes of MgCa binary alloys at 373–473 K, presumably due to precipitation of Mg2Ca from extended solid solution of Ca in Mg. No such hardness increase is observed in the ternary alloys. After consolidation, fine grained structures with fine dispersions of intermetallic compounds are observed in all extruded PM materials. The highest tensile strength of 483 MPa was obtained in Mg-5mass%Ca-5mass%Zn PM material with 2% tensile elongation. The tensile strength decreases and elongation increases significantly with rising test temperature. At elevated temperatures. A PM material of MgCa binary alloys shows lower tensile strength than alloys with ternary additions. Nearly superplastic elongation of 200% is observed in Mg-5mass%Ca-5mass%Zn PM materials at 573 K.

Stress-strain behavior and shape memory effect in powder metallurgy TiNi alloys

Abstract: The shape memory properties of the TiNi alloy produced by a powder metallurgical method have been evaluated from tensile stress-strain curves. The contamination of the powders during atomization can be suppressed by applying the Plasma Rotating Electrode Process (P-REP), so that the compact made by Hot Isostatic Pressing (HIP) is expected to exhibit the shape memory effect identical to the typical alloy grown from melt. The fracture behavior of the P/M alloy is also studied, and the improvement of fracture strength of the P/M alloy is attempted.

Wick-debinding in powder injection molding

Abstract: Powder injection moulding offers the possibility of producing powder compacts of intricate shape and design at the cost of the additional step of debinding. In order to reduce the duration of debinding, capillary extraction of the binder by wick powder may be employed. The present investigation examines the influence of four variables in the wicking process in order to optimize it: specimen height, temperature, time, and wick powder size. The results confirm some aspects of a theorelical model accepted for injection moulding, the dependence on height, and on temperature through the binder viscosity

Laminated metal structure

Abstract: The invention concerns a laminated structure (1) obtained by high isostatic pressing, comprising a first metallic outer layer (2) (produced by powder metallurgy) on one side, a second metallic outer layer (3) on the other side which can form a brittle intermetallic phase and/or a brittle ordered phase with the first side, and a ductile metallic intermediate layer (4), whereby the layers possess mutually different coefficients of thermal expansion and whereby the intermediate layer (4) acts as a diffusion barrier against the formation of the aforementioned brittle intermetallic phases or ordered phases. The invention also concerns a manufacturing method for the structure and an application of same as a cathode in a plasma sputtering unit.