Preparation of ultrafine cemented tungsten carbides by direct carburzation of oxides

Preparation of ultrafine cemented tungsten carbides by direct carburzation of oxides

RESINTERING STEELS OF CONVENTIONAL PM R.J.Wendell, A.C.Taylor. (ICM/Krebsoge, USA.) Results of the effects of resintering, in endothermic gas, of p...

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RESINTERING STEELS

OF CONVENTIONAL

PM

R.J.Wendell, A.C.Taylor. (ICM/Krebsoge, USA.) Results of the effects of resintering, in endothermic gas, of pressed-and-sintered PM steels at a density of 6.75 g.cm-” were presented. Comparisons were made with single sintered and high temperature sintered materials. Benefits of resintering were discussed. MOLYBDENUM STRUCTURAL STEELS ALLOYED BY DIFFERENT METHODS l&Weiss et al. (University of Vienna, Vienna, Austria) It was reported that 1.5%Mo-0.7%C steel had been prepared from elemental or prealloyed powders by sintering at a range of temperatures. Mechanical properties were determined. The importance of homogeneity was emphasized. At moderate sintering temperatures the prealloyed materials were more homogeneous. The elemental powders required higher tempertures to attain this degree of homogeneity. After sintering at 1230°C little difference in homogeneity was found MO being homogenized through a transient liquid phase. Impact and fatigue properties were better after the higher temperature sintering.

Soft magnetic

materials

ROLE OF SECONDARY OPERATIONS MANUFACTURE OF SOFT MAGNETIC AUTOMOTIVE PARTS

IN

.J.B.Ryan et al. (Windfall Products Inc., StMary’s, USA.) Engineering design requirements for magnetic automotive parts were reviewed with regard to the need for secondary manufacturing operations and the effect of these on properties. The elfects of a range of secondary operations were described and discussed. SOFT MAGNETIC COMPOSITE MATERZALS FOR AC ELECTICAL APPLICATIONS D.E.Gay et al. (General Motors Carp, USA.) Fabrication of magnetic composites, which have an advantage over laminated sheet steel stacks, was discussed with respect to powder characteristics, microstructure, magnetic properties, deformation during compaction and heat treatment. Metal/polymer blends were considered. Important properties and techniques were identified. Problems impeding widespread use were examined. PM MATERIALS APPLICATIONS

FOR AC MAGNETIC

H.G.Rutz et al. (Hoeganaes USA.)

42

MPR July/August

Corp, Riverton,

1997

ANCORSTEEL insulated powders were discussed with reference to applications requiring limitation of eddy currents at high frequencies. The development of these powders was reviewed wit,h consideration of

MORPHOLOGICAL CHAR.ACTERIZATION OF IRON POWDERS AND ESTIMATION OF DENSITY

magnetic and physical properties. Potential applications of parts made by PM were described.

T.Itoh, Y.Wanibe. (Nagoya University, Nagoya, Japan.) A new concept for characterization of powders was introduced with a simulation of random packing of spheres for any size distribution. Fe powders were investigated with regard to particle shape and apparent density of random packing. A method to estimate density of random packed nonspherical powders was suggested.

CHEMICAL AND ELECTRICAL INSULLATION OF FINE IRON PARTICLES GAlexandre, Platere. (CEA, France.) The eflects of phosphate treatment of fine, less than 10 pm, Fe powders on electrical and corrosion properties were discussed. Effects of phosphating conditions on properties were investigated. It was reported that oxidation resistance up to 400°C was improved but heat treatment was essential. Applications were outlined. EFFECT OF SINTERING CONDITIONS ON PROPERTIES OF WARM COMPACTED IRON-PHOSPHORUS STEELS J.B.Ryan et al. (Windfall Products Inc., St.Mary’s, USA.) A series of Fe-P powders was prepared, some with additions of Cu and C. The powders were warm compacted and sintered in belt or vacuum furnaces. Effects of sintering conditions on magnetic and mechanical properties were determined. Recommendations concerning the use of Fe-0.45%’ alloys were made.

Powder

characterization

PRECISION OF SCREEN ANALYSIS MEASUREMENT OF PARTICLE SIZE DISTRIBUTION IN METAL POWDER A.B.Backensto, C.B.Thompson. (SCM Metal Products Inc., Cleveland, Ohio, USA.) Sieve analysis for determination of particle size distribution in powders was reviewed with reference to standards and precision. It was reported that twelve laboratories had collaborated in studies intended to develop a precision statement. Protocols, test results and analysis were reviewed and a new precision statment was presented. EFFECTS OF POWDER CIIAR.ACTERISTICS ON PARTICLE SIZE MEASUREMENTS R.G.Iacocca, P.Downs, (Pennsylvania State University, USA.) Instruments for the measurement of particle size were reviewed. It was noted that there were differences in algorithms used by differing methods leading to variations in data. A study of effects of sampling methods and particle shape and size on test results was described.

Cemented

carbides

PREPARATION OF ULTRAFINE CEMENTED TUNGSTEN CARBIDES BY DIRECT CARBURZATION OF OXIDES Z.Zou et al. (Powder Metallurgy Research Inst., China.) Investigations of WC- lO%Co were described. The precedure involved high activity WO, which was directly carburized below 1100°C to a powder 0.15 urn in size. Sinter HIP was used for consolidation. The sintered compacts were reported to reach a Rockwell hardness of 92.7A, compared with conventional WC-1O’XCo at 89 to QOA. Process kinetics were investigated and the influence of various factors were discussed. It was shown that 92’% of the densification occured in the solid state due to the high activity of the WC. FATIGUE CERMETS

OF HARDMETALS

AND

W.Heinrich et al. (Kennametal Hertel, Germany.) Failure of hardmetal and ceramic cutting tools under alternating loads was discussed. It was reported that these materials have high resistance to cyclic loading. Studies of fatigue and microstructural damage were described. A summary of present knowledge of fatigue of hardmetals and ceramics was given and possible improvements outlined. EFFECT OF TUNGSTEN CARBIDE SIZE ON MECHANICAL PROPERTIES OF TUNGSTEN CARBIDE-COBALT B.KKim et al. (Korea Inst. of Machinery and Materials, Korea.) It was reported that homogeneous nanoscale WC-Co powder had been made by a new process. Near full density was attained in 20 minutes sintering at 1400°C with small additions of VC or VC-TaC. Properties were shown to bc good due to fine structure and homogeneity. ROMANIAN BARDMETAL PRODUCTION P.Nicolae, I.Popovici. (Carmesin SA, Romania.)