up to 96 hours in still air. Above 1300 “C oxidation pits were formed on the surface. Y and Al diffused to the surface.
Characteristics of silicon nitride powder - effects on composites with alumina and yttria Y.LJkyo et al. (Toyota Central Research Labs, Aichi,
Japan.) J. Jpn Sot. Powder/PowderMetal., Vol47, No 3, X00, 257-263. (Zn]apanese.) Composites containing Y-a’-S-Al-O-N and p’ Si-Al-O-N were prepared by hot pressing Y,O,-AlN-Si,N4 powders. Ten types of S&N, were used to determine the effect of Si,N, characteristics. The 0 content of the Si,N, had a large influence on sintering and on the proportion of Y-a’ Si-Al-O-N after sintering. 0 did not affect the lattice parameters of Si-Al-O-N.
Y.Kanekoet al. (Sumitmno Special Metals Co Ltd,
OS&, Japan.) J. Jpn Sot. Powder/Powder Metal., Vol 47, No 2, 2000, 139-145. (InJapanese.) Studies aimed at improving performance of Nd-Fe-B magnets by increasing the proportion of the NdzFe14B phase, control of microstructure to be dense and fine, and attainment of high levels of anisotropy of the Nd-Fe-B phase are described. This was achieved by improvements in powder production and use of CIP in processing.
Anisotropy in manganese-aluminiumcarbon magnets
Y.Tanaka et al. (Sanyo Special Steel Co Ltd, Himeji, .Japn.) J. Jpn Sot. Powder/PowderMetal., Vol47, No 2, 2000, 146-150. (In japanese.) It is reported that Mn-Al-C magnets had been prepared from gas atomized powders by extrusion at 580 to 720 “C and 0.005 to Fabrication of compositionally 0.05 se1 strain rate to determine the effects of graded nickel-alumina by spark particle size, temperature and strain rate on plasma sintering anisotropy. Anisotropy increased at lower temperature and strain rate and smaller particle K.Kikuchiet al. (TohokuUniversity, Send& Japan.) J. Jpn Sot. Powder/PowderMetall., Vol47, No 3, 2CC0, size. The findings are discussed in terms of 302-307. (In]apanese.) dynamic recrystallization. Production of graded Ni-A&O, materials is described. The part comprises two Ni outer layPhase transformations in ers and an A&O, core with graded composite manganesealuminiumcarbon layers between, and was consolidated by spark magnets plasma sintering. The requirements of the Y.Tanaka et al. (Sanyo Special Steel Co Ltd, Himeji, device were to provide high heat flux between a Japan.) J. Jpn Sot. Powder/Powder Metal., Vof 47, No heat source and a sink, to be electrically insulat2, 2000, 220-227. (InJapanese.) ing and to be free of thermal stresses. Magnetic and other properties of Mn-Al-C magnets are discussed with reference to the Synthesis of titanium diboride effects of cooling rate during gas atomization to titanium carbonitride composites powder. Phase transformations, E to Z, were H.Taimauu et al. (Akita University, Akita, Japan.) J. found in the alloys at 487 and 547 “C. The Jpn Sot. Powder/PowderMetall., Vol47, No 3, 2000, temperature difference is attributed to regions 308:314. (In Japanese.) of differing composition. Activation energy It is reported that TiB,-TI(C,N) composites was determined as 277 kJ mol-’ and was not had been made from BN, B4C and Ti powders affected by addition of Ni. by spark plasma sintering. Density increased with N content and reached a maximum of Magnetic properties of 99.1%. Young’s modulus, Vickers hardness and iron-aluminium during mechanical fracture toughness were measured. alloying
Mechanical characterization of zirconianickel alloy composites
M.Hashii, K.Tokumicsu. (University of Tokyo, Japan.) J. Jpn Sot. Powder/Powder Metall., Vol47, No 3, 2000, 287-290. (In Japanese.)
U.Paik et al. (Hanyang University, Seoul, Korea.) J. Alloys/Compounds,No 313, 2000, 248-257. Partially stabilized ZrO,, a Ni-&Al-Y alloy and composites made of these were prepared by plasma activated sintering. Mechanical prope ties were evaluated ,to test the effects of alloy:ceramic ratio in the ceramic and sintering temperature. There was a marked increase in fracture toughness at more than 6Ovol% of the alloy.
Elemental Fe-50at%Al powders were mechanically alloyed. Magnetic and structural changes were determined as functions of milling time. Magnetic properties changed from ferro- to Pam-magnetic as milling proceeded. Magnetic spectra are described.
Electrical and magnetic materials Development and production of high performance neodymium-iron-boron magnets
MPR July/August 2001
Preparation of manganesesilicon mechanical alloying and pulse current sintering
K.Ozaki et al. (National IndustriaI Research Inst., Nagoya, Japan.) J. Jpn Sot. Powder/Powder Metall., Vol 47, No 3, 2000, 327-331. (In Japanese.)
Mg-Si alloys, for thermo-electric applications, were prepared by mechanical alloying of elemental powders and pulsed current
sintering. The non-stoichiometric phase, MgSi, 75 started to form at 525 “C and there was fuil conversion at 625 “C.
Hard matetials and tool steels Preparation of boron carbide based cermets L.Leuin et al. (Ben-Gurion University, Beer-Sheua, Israel.) Inc. J. Refract. Metals/Hard Mater., Vol 18, No 2/3, 2000, 131-135.
A study of the effects of X0, on sintering B4C is described. X0, and B4C react’ at 1500 “C to form non-stoichiometric B,C,0x, XB, and oxides of C. At 2000 “C TiB, enhances sintering. With 4Chvt%XO, sintering at 2190 “C results in 95% density with a fine grained structure. The two-phase composite can be sintered to a range of density and infiltrated. With Al a Vickers hardness of 2500 can be attained with a flexural strength of 350 to 750 MPa depending on %Al. Heating at a high temperature in a carburizing atmosphere results in reversion of B&_ to B4C.
Developments in production and use of polycrystalline diamond and boron nitride M.W.Cook, P.K.Bossom. (De Beers Induwial Diamond Co Ltd, Ascot, UK.) Inc. J. Refract. Metals/Hard Mater., Vol 18, No 213, 2000, 147-152.
Use of polycrystalline diamond and polycrystalline cubic BN is reviewed with regard to the range of products available and their quality. Fabrication and applications, current and future trends are discussed. Developments of new grades are shown to enhance performance and improve efficiency of manufacture, notably the use of thinner diamond coatings.
L.Chen et al. (Austrian Research Centre, Seibersdorf, Austria.) Int. J. Refractory Metals Hard Materials, Vol 18, No 2-3, 2CO0, 153-161. The role of N in improving hardmetals and cermets, by optimizing structures, is discussed and it is noted that nitriding/de-nitriding affects sintering. A study of WC-TiC-TiN-, WC-TGTIN-Coand WC-Ti(C,N)TaC/NbC-Co/Ni- alloys is described. From the results of the study new cutting tools were developed including layered/graded materials. The object was to control metallurgical reactions during processing of properly designed material compositions.
Reaction hot pressed alumina-titanium carbide composites L.Chen, E.Kny. (Ausnian Research Centre, Seibersdorf, Austria.) Int. J. Refractory Metals Hard Materials, Vol 18, No2-3, 2000, 163-167.
of the reaction