- Email: [email protected]
Thin tungsten disilicide film deposited from cast high purity targets
alloys contain a high proportion of intermetallic compounds. An Mg alloy, QE22, with 8 to 12 pm Sic particle reinforcements was studied. Spray formed billets were extruded and structures and properties determined. The results are discussed in relation to other PM materials. PHYSICAL PROPERTIES OF ALLOYS RELEVANT TO SPRAY FORMING A.P.Day et al. (National Physical Laboratory, Teddington, Middlesex, UK.) Powder Metal, Vol40, No 2, 1997, 131-134. It is reported that methods had been developed for measurement of properties of alloys needed for modelling of high temperature processes such as spray forming and atomization.
SEMINAR. The following Abstracts -1 seminar, which was held in Reutte,
NEEDLE CRYSTAL GROWTH DURING TUNGSTEN OXIDE REDUCTION J.Pfeifer et al. (Hungarian Academy of Sciences, Budapest, Hungary.) An investigation of growth and morphology of acicular W oxide crystals in during ammonium paratungstate microwave irradiation was described. Comparison was made with crystals observed in the reduction of W oxide to W powder. Thick columnar crystals made up of smaller needles were observed. The thin individual needles were mono-crystalline whiskers. A mechanism for crystal growth in microwave irradiation was suggested. ROLE OF CHROMIUM CARBIDE IN TUNGSTEN CARRIDE BASED IIARD coMPosITEs G.S.Upadhyaya, D.Banerjee. (Indian Inst. of Technology, Kanpur, India.) Small additions of Cr,C, in WC-Co were noted to improve corrosion resistance. A study of the effects of larger additions, up to Gwt%Cr&z and replacement of some of the Co by Ni, on densification and properties was described. Addition of Ni increased indentation fracture toughness and transverse rupture strength but did not aid densiflcation. INVESTIGATIONS OF FRACTURE MECHANICS OF MOLYBDENUM ALLOYS M.Rig et al, (Forschungszentrum Jiilich GmbH, Jiilich, Germany.) Static and dynamic fracture toughness, K,, and K,,, were determined for MO alloys TZM and Mo-B%Re at ambi-
ent temperature, 200 and 450°C. Modified fatigue pre-cracking was used with increasing loads. Test results were compared with materials with cut notches. For both alloys K,, was increased by a factor of 1.5 between ambient temperature and 450°C. Dynamic fracture toughness was 3 to 4 times higher than the static value and was independent of temperature. SOLID-STATE SYNTHESIS OF TUNGSTEN-RHENIUM BY MECHANICAL ALLOYING E.Y.Ivanov, B.D.Bryskin. (Rhenium Alloys Inc, Elyria, Ohio, USA.) An investigation of mechanical alloying and heat treatment of W-25wt%Re alloy powders was described. Two stages in MA were noted, formation of a dispersed composite and, later, a nanocrystalline solid solution. The o phase was precipitated by heat treatment. THIN TUNGSTEN DISILICIDE FILM DEPOSITED FROM CAST HIGH PURITY TARGETS E.D.Stinov et al. (Inst. of Solid State Physics, Chernogolovka, Russia.) It was reported that high purity WSi, target materials had been cast in vacuum and laser induced evaporation investigated. The object was to prepare thin WSi, films which were characterized for phase composition and electrical resistivity. SILICIDES FOR NIOBIUM PROTECTIVE COATINGS B.Berton et al. (Dassault Aviation, St. Cloud, France.) It was reported that a pack cementation process had been used to co-deposit Si, Ti, Cr and Fe coatings onto Nb and Nb alloys, with the object of improving oxidation resistance. Low oxidation resistance and catastrophic failure have been barriers to use of Nb at high temperatures. Alloying of Nb to improve oxidation resistance reduced mechanical properties and the protective coating was considered necessary. SINTERING AND ELECTRICAL CIIARACTERIZATION OF ANODIC FILMS OF NIOBIUM-TANTALUMALUMINIUM U.U.Gomes, J.N.F.de Holanda. (Advanced Materials Laboratory UENF, Campos, Brazil.) Investigations of sintering of prealloyed Nb-Ta-Al powders were described. Powders were made by alumino-thermic reduction of Nb and Ta pentoxides and mechanical comminution. Powders were die pressed and sintered. The sintered compacts were characterized in relation
to sintering
conditions. Anodizing phosphoric acid was investigated.
in
DEFECTS IN FABRICATION AND PROPERTIES OF RHENIUM FOILS Y.Weihong et al. (Northwest Inst. for Non-Ferrous Metal Research, Xi’an Shaanxi, China.) Technology for fabrication of Be foils, 0.02 to 0.09 mm thick, was investigated with regard to quality of powder (99.99% pure), process conditions, structure and properties of the foil. Defects arising during processing were identified. Measures to minimize incidence of defects in processing were outlined. NEAR SURFACE POROSITY IN SINTERED REFRACTORY METALS B.A.Gnesin et al. (Inst. of Solid State Physics, Chernogolovka, Russia.) Cross-sections of sintered MO, Nb, doped W and un-doped W were examined by scanning electron microscopy to determine distribution of porosity, which was very uneven. Notably there was a high incidence of large, often interconnected, pores near the surface. Reasons for these regions of high porosity were discussed. QUALITY EVALUATION OF STARTING MATERIAL FOR ROLLING TUNGSTEN RIBBONS Y.Weihong et al. (Northwest Inst. for Non-Ferrous Metal Research, Xi’an Shaanxi, China.) Quality of W wires for rolling into ribbons was evaluated by a range of methods. Wires were rolled to assess rollability and incidence of defects. Eddy current testing could inspect correctly but could not identify the defect type in reject materials which would not roll satisfactorily. Ribbons 0.63 mm by 0.25 mm by 150 m were rolled from defectfree wire. CORRELATION OF STRUCTURE AND PROPERTIES OF FUSED TUNGSTEN CARBIDE R.L.Orban. (Technical University of Cluj-Napoca, Cluj-Napoca, Romania.) Structure and properties of fused WC were studied as a function of %C. From phase equilibria the alloy should be a quasi-eutectoid of WC and W,C and the proportion of phases was determined. Elastic modulus, flexural strength and Vicker’s hardness were measured. EFFECT OF ORDERING ON STRUCTURE AND PROPERTIES OF VANADIUM CARRIDE V.N.Lipatnikov, P.Etmayer. (Russian Academy of Sciences, Ekaterinburg, Russia.)
MPR May 1998 39
SEMINAR. The following Abstracts -1 seminar, which was held in Reutte,
NEEDLE CRYSTAL GROWTH DURING TUNGSTEN OXIDE REDUCTION J.Pfeifer et al. (Hungarian Academy of Sciences, Budapest, Hungary.) An investigation of growth and morphology of acicular W oxide crystals in during ammonium paratungstate microwave irradiation was described. Comparison was made with crystals observed in the reduction of W oxide to W powder. Thick columnar crystals made up of smaller needles were observed. The thin individual needles were mono-crystalline whiskers. A mechanism for crystal growth in microwave irradiation was suggested. ROLE OF CHROMIUM CARBIDE IN TUNGSTEN CARRIDE BASED IIARD coMPosITEs G.S.Upadhyaya, D.Banerjee. (Indian Inst. of Technology, Kanpur, India.) Small additions of Cr,C, in WC-Co were noted to improve corrosion resistance. A study of the effects of larger additions, up to Gwt%Cr&z and replacement of some of the Co by Ni, on densification and properties was described. Addition of Ni increased indentation fracture toughness and transverse rupture strength but did not aid densiflcation. INVESTIGATIONS OF FRACTURE MECHANICS OF MOLYBDENUM ALLOYS M.Rig et al, (Forschungszentrum Jiilich GmbH, Jiilich, Germany.) Static and dynamic fracture toughness, K,, and K,,, were determined for MO alloys TZM and Mo-B%Re at ambi-
ent temperature, 200 and 450°C. Modified fatigue pre-cracking was used with increasing loads. Test results were compared with materials with cut notches. For both alloys K,, was increased by a factor of 1.5 between ambient temperature and 450°C. Dynamic fracture toughness was 3 to 4 times higher than the static value and was independent of temperature. SOLID-STATE SYNTHESIS OF TUNGSTEN-RHENIUM BY MECHANICAL ALLOYING E.Y.Ivanov, B.D.Bryskin. (Rhenium Alloys Inc, Elyria, Ohio, USA.) An investigation of mechanical alloying and heat treatment of W-25wt%Re alloy powders was described. Two stages in MA were noted, formation of a dispersed composite and, later, a nanocrystalline solid solution. The o phase was precipitated by heat treatment. THIN TUNGSTEN DISILICIDE FILM DEPOSITED FROM CAST HIGH PURITY TARGETS E.D.Stinov et al. (Inst. of Solid State Physics, Chernogolovka, Russia.) It was reported that high purity WSi, target materials had been cast in vacuum and laser induced evaporation investigated. The object was to prepare thin WSi, films which were characterized for phase composition and electrical resistivity. SILICIDES FOR NIOBIUM PROTECTIVE COATINGS B.Berton et al. (Dassault Aviation, St. Cloud, France.) It was reported that a pack cementation process had been used to co-deposit Si, Ti, Cr and Fe coatings onto Nb and Nb alloys, with the object of improving oxidation resistance. Low oxidation resistance and catastrophic failure have been barriers to use of Nb at high temperatures. Alloying of Nb to improve oxidation resistance reduced mechanical properties and the protective coating was considered necessary. SINTERING AND ELECTRICAL CIIARACTERIZATION OF ANODIC FILMS OF NIOBIUM-TANTALUMALUMINIUM U.U.Gomes, J.N.F.de Holanda. (Advanced Materials Laboratory UENF, Campos, Brazil.) Investigations of sintering of prealloyed Nb-Ta-Al powders were described. Powders were made by alumino-thermic reduction of Nb and Ta pentoxides and mechanical comminution. Powders were die pressed and sintered. The sintered compacts were characterized in relation
to sintering
conditions. Anodizing phosphoric acid was investigated.
in
DEFECTS IN FABRICATION AND PROPERTIES OF RHENIUM FOILS Y.Weihong et al. (Northwest Inst. for Non-Ferrous Metal Research, Xi’an Shaanxi, China.) Technology for fabrication of Be foils, 0.02 to 0.09 mm thick, was investigated with regard to quality of powder (99.99% pure), process conditions, structure and properties of the foil. Defects arising during processing were identified. Measures to minimize incidence of defects in processing were outlined. NEAR SURFACE POROSITY IN SINTERED REFRACTORY METALS B.A.Gnesin et al. (Inst. of Solid State Physics, Chernogolovka, Russia.) Cross-sections of sintered MO, Nb, doped W and un-doped W were examined by scanning electron microscopy to determine distribution of porosity, which was very uneven. Notably there was a high incidence of large, often interconnected, pores near the surface. Reasons for these regions of high porosity were discussed. QUALITY EVALUATION OF STARTING MATERIAL FOR ROLLING TUNGSTEN RIBBONS Y.Weihong et al. (Northwest Inst. for Non-Ferrous Metal Research, Xi’an Shaanxi, China.) Quality of W wires for rolling into ribbons was evaluated by a range of methods. Wires were rolled to assess rollability and incidence of defects. Eddy current testing could inspect correctly but could not identify the defect type in reject materials which would not roll satisfactorily. Ribbons 0.63 mm by 0.25 mm by 150 m were rolled from defectfree wire. CORRELATION OF STRUCTURE AND PROPERTIES OF FUSED TUNGSTEN CARBIDE R.L.Orban. (Technical University of Cluj-Napoca, Cluj-Napoca, Romania.) Structure and properties of fused WC were studied as a function of %C. From phase equilibria the alloy should be a quasi-eutectoid of WC and W,C and the proportion of phases was determined. Elastic modulus, flexural strength and Vicker’s hardness were measured. EFFECT OF ORDERING ON STRUCTURE AND PROPERTIES OF VANADIUM CARRIDE V.N.Lipatnikov, P.Etmayer. (Russian Academy of Sciences, Ekaterinburg, Russia.)
MPR May 1998 39