Showing papers on "Powder metallurgy published in 1989"

Formation of quasicrystals by mechanical alloying

Abstract: Quasi‐crystalline Al65Cu20Mn15 powder has been produced by mechanical alloying from crystalline elemental powders. The alloying process has been monitored by x‐ray diffraction, and the resulting product has been characterized by transmission electron microscopy. The quasi‐crystalline phase forms after about 90 h of milling. The crystallization temperature and enthalpy have been determined by differential scanning calorimetry. The results are compared with data for melt‐spun material.

Titanium diboride/titanium alloy metal matrix microcomposite material and process for powder metal cladding

Abstract: A titanium-based metal matrix microcomposite material About 1% to about 25% by weight TiB 2 is substantially uniformly incorporated in a titanium-based alloy matrix The microcomposite material is formed by sintering at a temperature selected to preclude diffusion of TiB 2 into the matrix The microcomposite material may be used in a process for cladding a macrocomposite structure

Sintering metal powders into structures without sintering aids

Abstract: Sintering metal powder in inert and/or reducing atmosphere has been found to result in a hard porous metal structure without the use of sintering aids. The oxidation resistance of the structure can be enhanced by the firing process comprised of the following steps: oxidation, reduction, and then inert gas sintering.

Synthesis and properties of ultrafine AlN powder by rf plasma

Abstract: High‐purity ultrafine AlN powder was synthesized by rf plasma through direct nitridation of Al. The specific surface area was about 30 m2 /g under typical experimental conditions. Ultrafine AlN powder showed excellent sinterability, compared with conventional AlN powders, whose particle sizes were more than 0.5 μm. The thermal conductivity for the sintered body reached 220 W/m K when sintered at 1900 °C, and 110 W/m K when sintered at 1400 °C, by using YF3 as a sintering aid.

An Experimental Determination of the Thermal Conductivity of a 304L Stainless Steel Powder Metallurgy Material

Abstract: The thermal conductivity of a 304L stainless steel powder metallurgy (P/M) material was experimentally determined to support research aimed at understanding the poor machining characteristics of P/M austenitic stainless steels. Thermal conductivity measurements were made on samples having relative densities ranging between 64 and 90% of theoretical density since workpieces requiring machining are often fabricated in that density range. The measurements were also made over a temperature range of 50 to 300C since workpiece temperatures can attain levels this high during the machining operation. The thermal conductivity was measured using an apparatus having a design based on the comparative method. The experimentally determined thermal conductivities were modeled by mathematical models found in the technical literature and modified for the present study. The thermal conductivity of this material increases with increasing relative density and temperature; it is also dependent on the matrix structure for a given porosity.

Method for developing enhanced texture in titanium alloys, and articles made thereby

Abstract: Enhanced crystallographic texture is developed in an alpha or alpha-beta titanium alloy having a dispersion of particles therein, by heating the alloy to essentially the all beta phase range and mechanically hot working the alloy in this range. The mechanical working is preferably accomplished by extrusion, rolling, or forging. The particles are stable during working, and prevent the formation of random texture in recrystallized beta phase grains at the working temperature. The particles are preferably oxides formed from rare earth elements such as erbium or yttrium, that are introduced into the alloy during manufacture. The alloys processed according to the invention are preferably prepared by powder metallurgy to achieve a uniform microstructure prior to working. A particularly suitable alpha-beta (but near alpha) titanium alloy contains aluminum, zirconium, hafnium, tin, columbium, molybdenum, tungsten, ruthenium, germanium, silicon, and erbium.

Nb/sub 3/Al wire produced by powder metallurgy and rapid quenching from high temperatures

Abstract: Powder-metallurgy-processed Nb-25-at.% Al wires were annealed at temperatures just below the melting temperature. Depending on anneal conditions, the entire Nb-Al part of the wire could be rapidly quenched as a metastable Al Nb(Al) solid solution with an Al concentration exceeding 23 at.%. This A2 phase is sufficiently ductile to be bent without incurring damage. A second anneal at 950 degrees C converted the A2 into A15. J/sub c/ was 10/sup 4/ A/cm/sup 2/ at 22 T, and T/sub c/ was 17.8 K. The rapid quenching of Nb-Al powder metallurgy processed wire is a possible alternative to obtain improved high-field properties. >

Sintering of ultrafine SiC powders prepared by plasma CVD

Abstract: Ultrafine SiC powders with a nanometre particle size were synthesized by r.f. plasma chemical vapour deposition (CVD) using a chemical system of SiH4−C2H4−Ar. The powder was also ultrapure with a grade of 99.999% purity. The product was polytype 3C−SiC and black in colour, in spite of its high purity, because of its ultrafine size. Silicon carbide is a difficult ceramic to sinter; it is possible to sinter it to full density with the aid of sintering additives. Ultrafine and ultrapure SiC powders were hot-pressed without sintering additives in the present study, in order to investigate the sintering behaviour. The CVD powders proved sinterable to 88% theoretical density without sintering additives. The present experiments revealed that powder treatment before firing was a key technology when using ultrafine powders as starting materials in the sintering process. The sintering behaviour of the powder was characterized by a large shrinkage. Phase transformation was negligible after hot pressing at 2200°C for 30 min.

Direct preparation of BaTiO3 powders from titanium metal by anodic oxidation under hydrothermal conditions

Abstract: Elaboration, par une nouvelle technique combinant reaction hydrothermique et oxydation electrochimique, de poudres de titanate de baryum.

Science of sintering : new directions for materials processing and microstructural control

Abstract: I. Fundamentals of Sintering.- Sintering of Ceramics.- The Main Trends in Study and Quantitative Description of the Sintering Processes.- Stereological Theory of Sintering.- A Stereology-Based Equation for Isotropic Shrinkage During Sintering by Viscous Flow.- A New Model for Initial Sintering of Oxide Powders under Controlled Gaseous Atmosphere.- Mechanism of Anisotropic Dimensional Changes During Sintering of Metal Powder Compact.- II. Controlled Preparation of Ceramic Powders.- Preparation of Well Defined Ceramic Powders.- Progress in Preparation of ZnO Based Varistor Ceramics.- Chemical Preparation of Alumina-Zirconia Powders for Low Temperature Sintering and Particulate Composites.- Evolution of Mullite from a Solgel Precursor.- The Role of Powder Calcination Conditions in the Sintering Behaviour of Calcined ZrO2 Powders.- Surface Effect of MgO Addition on Gamma Al2O3 Sintering.- III. Preparation and Sintering of Metallic Powders.- Principles of Atomization.- Dispersion Hardening of a Rapidly Solidified Copper Based Matrix.- Problem of Sintering Metallic Ultrafine Powders.- Sintering of Copper Ultrafine Powders.- Synthesis and Characterization of the Mixed and the Composite Ni-TiN Ultrafine Particles.- IV. Sintering of Multiphase Systems.- Phase Stability and Sintering of Multiphase Alloy Systems.- Solid State Sintering of Two Component Systems with Solubility.- Prognosis of Sintering of System W-Ni in the Presence of Liquid Phase.- Influence of Sintering and Termomechanical Treatment on Microstructure and Properties of W-Ni-Fe Alloys.- Removal of Ni-Activator from the Activated Sintered W-Compact by High Vacuum Treatment.- V. Pressure Sintering.- Explosive Compaction of Powders: Principle and Prospects.- Theoretical Aspects of High Pressure Sintering.- Dynamic Compaction of Amorphous Ni78P22.- The Prediction of HIP Parameters for Intermetallic Prealloyed Ni-Al Powder.- Defect Healing Mechanisms During Sinter/HIP of Polyphase Materials.- Residual Stress Characteristics of Ceramic Coatings and Their Cracking Behaviour.- VI. Rate Controlled Sintering.- Rate Controlled Sintering for Ceramics and Selected Powder Metals.- Application of Rate Controlled Sintering in the Production of ZrO2-Based Ceramic Materials.- Rate-Controlled Sintering of SiC with Additions of (a) Al2O3 + Y2O3 (b) B + C (c) B4C + C.- VII. Microstructure Control.- Grain Boundaries in Sintering.- Computer Simulation and Experimental Analysis of Abnormal Grain Growth in BaTiO3 Ceramics.- Pore Removal During Final Stage Sintering of Modified Yttria.- Thermoelectric Properties of Lead Tin Telluride Compacts.- Microstructural Development in Dense Si3N4 Ceramics.- Effect of Sintering Parameters on Microstructure and Properties of Sialon Materials.- VIII. Metals and Composite Processing.- Powder Processing of High Temperature Aluminide-Matrix Composites.- Differential Sintering.- Boron/Magnesium-Aluminium Machinable Composite.- Effect of "Inheritance" in Powder Metallurgy.- Hydrostatic Compaction of Fine Cobalt Powder.- Mechanical Properties of Cu-P Sintered Alloyed Steels: Study of the Copper Influence on Dimensional Changes.- IX. Sintering of Oxide Ceramics.- Ultra-Rapid Sintering of Ceramics.- Hydrothermal ZrO2 Powder and Its Sintering Behaviour.- Effect of Green Compact Pore Size Distribution on the Sintering of ?-Fe2O3.- Effect of Niobia on the Sintering of SnO2.- Kinetics and Mechanisms of Solid State Sintering of Alkaline Earth Titanates.- The Influence of Thermal Treatment on Polarization Behaviour of Bi4Ti3O12 Ceramics.- Changes of Electrical and Structural Characteristics of Cold Sintered Potassium Dihydrogen Arsenate with Temperature.- A Study of Isothermal Sintering and Properties of Magnesium Oxide from Sea Water.- X. High Temperature Superconductors.- Properties of High Tc Superconducting Oxides.- The Influence of Oxygen Stoichiometry on High-Tc YBa2Cu3Oy Superconductor Properties.- A Modified Noncontact Method for Critical Temperature Measurements of High Temperature Superconductors.- XI. Non-Oxide Ceramics.- On the Kinetics of Densification During Liquid Phase Sintering of Si3N4.- Stability of Pure and AlN-Alloyed Al2OC and Influence on Abrasive Properties of Al2O3-Al4C3-AlN Materials.- Preparation and Properties of ?/? Sialon Composites.- International Program Committee.- Contributors.

Low-temperature sintering and gas desorption of gold ultrafine powders

Abstract: Sintering and gas desorption phenomena were examined in ultrafine gold powders. Sintering characteristics were observed by means of Brunauer-Emmett-Teller specific surface area measurements, dilatometric measurements and SEM observations. The decrease in the surface area and shrinkage simultaneously occurred at approximately 360 K. H 2 O, CO 2 , H 2 and CO gases were mainly detected while heating the gold ultrafine powders at temperatures up to 873 K in a high vacuum. These gases were considered to be produced by surface reactions.

Sintering Behaviour of T42 Water Atomised High Speed Steel Powder Under Vacuum and Industrial Atmospheres with Free Carbon Addition

Abstract: (1989). Sintering Behaviour of T42 Water Atomised High Speed Steel Powder Under Vacuum and Industrial Atmospheres with Free Carbon Addition. Powder Metallurgy: Vol. 32, No. 4, pp. 291-299.

Elastic Moduli of Powder Metallurgy Steels

Abstract: Experimental data for the variations of elastic properties with porosity of powder metallurgy materials are reviewed briefly. Analytical and finite element models based on linear elasticity theory are shown to have mixed success in explaining the observations. An additional model is proposed based on mechanisms for generation of porosity during straining. Details of the model depend on whether the porosity is interconnected or disconnected. PM/0488

Method for the continuous fabrication of comminuted hydrogen storage alloy material negative electrodes

Abstract: An improved method for the continuous fabrication of metal-hydride, electrochemical, hydrogen storage alloy, negative electrodes for use in rechargeable nickel metal hydride cells. The improved method comprises the steps of reducing the size of a high hardness, metal hydride, hydrogen storage alloy by shattering it along natural fracture line thereof. The process next includes providing measured amounts of powered metal hydride electrochemical hydrogen storage alloy material and disposing said material upon a continuous wire mesh screen substrate. Thereafter, the powdered metal hydride electrochemical hydrogen storage alloy and wire mesh screen are subjected to a compaction process wherein they are rolled and pressed so as to form a single integral electrode web which is subsequently exposed to a high temperature sintering process in a chemically inert environment. The sintering process is designed to drive off excess moisture in the material while discouraging oxidation of the electrode web and set the electrode web state of charge.

Method for producing a nickel-base superalloy

Abstract: A method of forming a Ni-base superalloy suitable for use as the material for gas turbine disks or the like has a composition containing, by weight, 0.01 to 0.15% of C, 15 to 22% of Cr, 3 to 6% of Mo, 3 to 6% of W, 5 to 15% of Co, 1.0 to 1.9% of Al, 1.5 to 3.0% of Ti, 3.0 to 6.0% of Ta, 0.001 to 0.020% of B and the balance substantially Ni except inevitable impurities. This alloy is produced using the conventional ingot making and a hot working process including working at a reducing ratio greater than or equal to 10%, first above the γ solvus temperature, and then during cooling to the recrystallization temperature and then subjected to direct aging without solid-solution treatment. As a result, the alloy exhibits excellent strength properties well comparable to those of expensive alloys produced by powder metallurgy process.

Flake materials in coating compositions

Abstract: A cured coating composition and substrate coated with the cured coating composition which coating is based upon an aqueous acid binder solution containing phosphate and chromate and/or molybdate ions into which has been dispersed a blend of metallic powder particles of three primary dimensions and flat metal flake materials, which can be applied to a substrate part to be coated more uniformly and thickly than conventional metal flake coatings, and which imparts better corrosion and impact resistance than conventional powder metal coatings.

Investigation of M2 High Speed Steel Produced by Osprey Process

Abstract: Microstructural and property assessments have been undertaken on spray deposited M2 high speed steel in the as deposited condition and after hot forging. The response of the material to hardening treatment has also been studied. The microstructure of the as deposited material showed a small grain size with a cellular carbide network. Subsequent hot forging produced a uniform dispersion of fine (0·5–2 μm) carbides. Austenitising the as deposited sample at 1200°C resulted in spheroidisation of the continuous grain boundary M6C carbide film. EDX analysis showed the resultant spheroidised particles to be predominantly vanadium rich MC. No significant differences were observed between the hardening response of M2 high speed steel produced conventionally and by spray deposition. The bend strength values of spray deposited M2 were isotropic and similar to those observed for powder metallurgy samples. PM/0487

Manufacture of iron base powder mixed material for powder metallurgy

Abstract: PURPOSE: To manufacture iron base mixed powder for powder metallurgy having a little segregation in the composition and a little fluidity variation with time by adding fatty acid and metallic soap and mixing at the time of manufacturing raw material for powder metallurgy by mixing the other metal powder, graphite powder, etc., to the iron series powder. CONSTITUTION: Cu powder, graphite powder, etc., according to the aim, are added to Fe series metal powder as the raw material for powder metallurgy and further, the metallic soap of zinc stearate, etc., as lubricator at the time of pressurize-compacting is added and mixed. In this case, in order to prevent the development of segregation caused by difference of sp. gr. of the graphite, etc., in the mixed raw material, at first, after adding and uniformly mixing the fatty acid of oleic acid, etc., to and with the iron powder, additive of Cu powder, graphite powder, etc., and the metallic soap of the zinc stearate, etc., as the lubricant are added and further, mixed. During mixing, while generating cofused material of the fatty acid and metallic soap, this is cooled to solidify the cofused material and the Cu powder and graphite powder are stuck on the surface of iron powder with this bonding force. Successively, further the metallic soap is added and sufficiently mixed and the iron base powder raw material having a little segregation of Cu and graphite and a little fluidity variation with time, is manufactured. COPYRIGHT: (C)1991,JPO&Japio

Particle‐Reinforced Magnesium Alloys

Abstract: Particle reinfored MMC’s are interesting in application in arduous enviroments. Advantages of these composites are increased modulus, strength, high temperature properties and wear restistance. The thermal expansion is reduced. In this paper the microstructures and properties of composites with different particle additions, eg Sic, TiB2, Ti(C,N), AlN and Al2O3-platelets produced by powder metallurgy techniques are dicussed.

Process for pretreating metal in preparation for compacting operations

Abstract: A pretreating process in powder metallurgy for preparing powders for compacting or densifying operations includes the steps of mixing powder metals with solid lubricants and optionally with liquid solvents to form a mixture and heating the resulted mixture prior to compacting or densifying to a temperature greater than room temperature and below the softening temperature of the solid lubricants.

Effect of impurities on the weldability of powder metallurgy, electron-beam melted and arc-melted molybdenum and its alloys

Abstract: Welds of various molybdenum metals and alloys were examined by bend tests between 183 and 333 K, and the fracture surfaces were observed by scanning electron microscopy and Auger electron spectroscopy. In PM-Mo, blow holes were formed but weldability was improved by selecting high-purity powder, which contained low concentrations in oxides forming impurities, to reduce the total content of oxygen. Nitrogen segregated to grain boundaries promoted intergranular brittleness in PM-Mo. However, in EB-Mo, AM-Mo, Mo 0.56%Nb and TZM, nitrogen was hardly detected and carbon segregation was always present at grain boundaries. Carbon segregation and carbide precipitation were found to strengthen the grain-boundary cohesion and improve the ductility.

Method for producing alpha titanium alloy pm articles

Abstract: A method for producing a titanium alloy powder metallurgy article having high resistance to loading and creep at high temperature is described and comprises the steps of simultaneously pressing a preselected quantity of titanium alloy powder at from 15 to 60 ksi and heating the powder to a temperature just below the beta transus temperature of the alloy to promote beta to alpha phase transformation in the alloy, and then slowly cooling the compacted powder under pressure.

On the formation of potassium bubbles in tungsten rod

Abstract: The microstructure of tungsten wire that is manufactured for use as lamp filaments has been studied by a number of researchers. The author demonstrates that one of the most important features of the microstructure is the potassium bubbles, approximately 500 A in diameter, that are aligned in rows in the direction of wire drawing. These bubbles pin the grain boundaries as they migrate down the length of the wire, giving rise to an interlocking grain structure in the recrystallized wire. If these bubbles were not present, a bamboo structure would form which would then rapidly fail during operation of the lamp as a result of grain boundary sliding. The potassium which forms these bubbles is incorporated into the tungsten during sintering of the powder metallurgy ingot.

Sintering behaviour of NdFeB magnets

Abstract: The dimensional changes that occur during the sintering of NdFeB magnets were investigated using a high-temperature vacuum dilatometer. These measurements were made on samples produced by the conventional powder metallurgical method and on compacts produced using hydrogen decrepitation (HD) as a premilling technique. The amount of shrinkage at a given temperature was found to be greater for the HD compact, with pronounced contractions being observed at the temperatures where hydrogen is desorbed. Shrinkage measurements, carried out on sintered compacts produced with a range of alignment fields, revealed anisotropic shrinkage of the compact, with the increased growth being along the a-axis direction. In sintering experiments NdFeB magnets were cooled at different rates to room temperature and subsequently given a postsintering heat treatment. The results of the experiments showed that the intrinsic coercivity decreases linearly with increasing cooling rate. However, when the samples were annealed for 1 h at 650 degrees C all coercivity values came up to the same level, more or less nullifying the influence of the previous cooling rate. >

Rate Controlled Sintering for Ceramics and Selected Powder Metals

Abstract: After almost a quarter-century of research and development at NCSU, the process optimization method for densification of ceramics now known as Rate Controlled Sintering (RCS) has more-or-less ‘come of age’. For a wide range of ceramic materials, it has been found to provide an efficient and effective means for determining near-optimum (though typically non-linear) temperature-time pathways for densification. In doing so, it appears to beneficially influence and regulate the ‘path of morphological change,’ thereby facilitating refinement and control of final sintered micro­structures. More recently, it has also been found useful for the sintering of a special class of high-porosity metal compacts (e.g., those that have been formed by injection molding).

Role of Molybdenum in Promoting Densification During Vacuum Sintering of T1 Grade High Speed Steel Powders

Abstract: It is shown that densification during vacuum sintering of T1 type high speed steel powders is due to the presence of a liquid phase and that sinter-ability is influenced by the molybdenum content of the T1 powder, with 0·5 wt-% being essential for satisfactory sintering behaviour. The results of differential thermal analysis, sintering trials, and microstructural studies carried out on three batches of T1 powder containing <0·02, 0·26, and 0·51 wt-%Mo are discussed with reference to phase diagrams. Sintering behaviour and sintered microstructures can be correlated with phase diagram predictions. For sintering to full density to occur, the solidus temperature must be exceeded. Optimal sintering occurs within the austenite + carbide + liquid region. The amount of liquid is also important. Increasing the molybdenum content changes the position of the solidus, promoting sintering through the formation of a larger volume fraction of liquid at the sintering temperature. PM/0491