SINTER-HIP TREATMENT OF NANOCRYSTALLINE TUNGSTEN CARBIDE
A.Rosen et al. (Technion, Haifa, Israel.) Densification at the liquid/solid interface in Ar or vacuum sintered nanocrystalline WC-15%Co was studied. HIP was shown to reduce porosity after low pressure sintering. HIP sintering was at 800 to 1330°C and 10 MPa. Below 1100°C densification was too slow to be of practical application. Structure and properties were investigated. ABNORMAL GRAINED
GRAIN TUNGSTEN
GROWTH CARBIDE
OF CARBURIZED TUNGSTEN CARBIDE
Y.Doi et al. (Tokyo Tungsten Co Ltd, Tokyo, Japan.) The need for ultrafine carbide cermets was discussed with regard to properties and applications. The production of ultrafine WC by direct reduction and simultaneous carburization of WO, was investigated. It was reported that WC, 0.1 to 0.7 pm, had been made. Mechanical properties of WC cermets with grain growth inhibitors were measured. Vicker’s hardness of 2300 and K,, of 15 MPa.m1’2 were reported. STRENGTH TUNGSTEN
AND TOUGHNESS CARBIDE-COBALT
OF
A.V.Laptev. (Inst. for Problems of Materials Science, Kiev, Ukraine.) A study of solid state processing of WC-lGwt%Co was fine grained described. It was reported that high energy hot pressing resulted in high density but did not reduce porosity to zero. Decrease in process temperature resulted in increased porosity. Poor quality was obtained at densification temperatures below 1200°C. SINTERING OF WITH VANADIUM
CEMENTED CARBIDE
ELECTRO.NIC NIOBIUM ALLOYS
AND
APPROACH MOLYBDENUM
TO
A.Rosen et al. (Technion, Haifa, Israel.) Sintering of WC, without Co or grain growth inhibitors, was investigated in a dilatometer. It was reported that densification is influenced by particle size and size distribution, and method of powder preparation. Grain growth was shown to start at high temperatures and was negligible at 1100°C. PLASMA SPRAYED CARBIDE-COBALT
RECRYSTALLIZATION AND MOLYBDEmNUM
OF NANOCRYSTALLINE CARBIDE POWDER
TUNGSTEN COATINGS
Y.Borisov et al. (National Academy of Sciences, Kiev, Ukraine.) It was reported that WC-Co coatings had been deposited by supersonic airgas plasma spraying at 70 to 180 kW. The WC-Co particles had a velocity of 350 to 500 m.s-i. Effects of process parameters on composition and properties of the deposit were studied and reported to be: hardness, 7500 to 12 000; porosity, 0.5 to 1.5%; and bond strength, 100 to 150 MPa. A high rate of deposition was reported. PROPERTIES STRENGTHENED MOLYBDENUM
OF
OXIDE NICKEL-
OF TUNGSTEN ALLOYS
K.Okamoto et al. (Tokyo Tungsten Co Ltd, Toyama, Japan.) The effects of annealing atmosphere on recrystallization and grain growth in W, W-0,8wt%L,a,O,, MO and MO-TZM, were investigated in Ar and ArlOvol%H. In MO and W grain growth was more rapid in Ar than in Ar-H. The composites were less affected by atmosphere than the pure metals. Grains in W-La,O, retained their elongated shape. The possibilities that the composites may have good high temperature properties was noted. HIGH TEMPERATURE OF NICKEIL BASE
DEFORMATION SUPERALLOY
J.Zbiral. (Technical University, Vienna, Austria.) It was reported that MA, degassing and hot extrusion had been used to prepare oxide dispersion strengthened NiMO alloys. The alloys were shown to have higher strength owing to fine grain and homogeneous fine oxide dispersoids. The possibility of further strengthening by precipitation of a Ni-Mo phase was investigated. Effects of composition and process conditions on structure and properties were described.
L.Schultz et al. (Inst. fur Festkorper und Werkstofforschung, Dresden, Germany.) An investigation of deformation of an oxide dispersion strengthened Ni base superalloy was described. Various grain structures and fibre textures were studied. It was reported that creep was more affected by texture than grain aspect ratio. In fatigu’e tests grain structure determined fracture path but did not influence cyclic lifetimes. Life could be predicted from effect of orientation on Young’s modulu,s.
NITRIDING TITANIUM
MOLYBDENUM PRODUCED DEPOSITION
OF MOLYBDENUMALLOYS IN AMMONIA
CARBIDE
T.Tanase et al.(Mitsubishi Materials Corp, Saitama, Japan.) and densification of Sintering
face layer was shown to be yMo,N with an inner layer of KMo,N. The layer grew in accordance with a parabolic rate law. Vickers hardness at the surface was 1800, decreasing to 1600 with a sharp reduction at the interface between nitrided layer and the core.
M.Furui et al. (Nagoya University; Nagoya, Japan.) It was reported that investigations had been carried out to study elevated temperature mechanical and creep properties and resistance to molten Li of MO and Nb alloys. Some electronic parameters were calculated and used for prediction of properties. Elements to enhance resistance to corrosion by Li were selected. Based on calculation and experiment, MO and Nb alloys were designed for nuclear applications.
SINTERING TUNGSTEN
IN FINE
K.Hayashi, N.Matsuoka. (University of Tokyo, Tokyo, Japan.) A modelling study of grain growth in WC-Co, which consisted of a large proportion of fine grains and a very small amount of large grains, was described by means of differential equations. Sizes of the large grains were measured to assess abnormal grain growth in WCO.Swt%V-lO%Co. It was shown that the design of fine grained hardmetals is rational for a fine grain size of 0.5 pm. PROPERTIES ULTRAFINE
undoped and VC doped cemented carbides were compared. Both underwent 80% densification in the solid state but were slower in the doped alloy. Retarded densification was attributed to delayed diffusion in the Co. Grain growth occurred in the range 1000 to 1200°C and was slower in the doped material. The effect of VC was assumed to be due to interference in the solutioniprecipitation reaction by segregation on interfaces.
J.Takada et aZ. (Okayama University, Okayama, Japan.) MO and Mo-0.5wt%Ti alloys were nitrided at 1100°C in NH, and the microstructure investigated. The sur-
COATINGS BY VACUUM
ARC
B.B.Straumal et al. (Inst. of Solid State Physics, Moscow, Russia.) It was ahown that MO in the form of foils or coatings can be produced by vac-
MPR June 1998 37