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Fractography and fracture mechanics of structural ceramics
density variations had little effect. conditions tensile Under optimum strength up to 400 MPa was attained. EFFECT OF STRUCTURE ON IMPACT AND WEAR OF SINTERED CIIROMIUM-MOLYBDENUM STEELS A.Molinari et al. (University of Trento, Trento, Italy.) Powder Metall., Vol47, No 3, 1999,235-241. Structure, mechanical properties and dry rolling-sliding wear resistance of Fe-3%-Cr 0.5%Mo, with and without 0.4%C, were investigated in as-sintered and in heat treated conditions. Graphite enhances sintering by reduction of oxides. The steels had a bainite-martensite structure after sintering and cooling at a ‘normal’ rate. Impact properties were increased by addition of C but diminished by heat treatment due to lower ductility of tempered martensite. Wear properties were influenced by hardness. Increased hardness reduces delamination and favours formation of a glazed surface during dry slidingrolling.
Cobalt MICROSTRUCTURE - PROPERTY RELATIONSHIPS IN HIP STELLITE M.H.Jacobs et al. (University of Birmingham, Birmingham, UK.) Powder Metall., Vol47, No 3, 1999,243-249. Investigations of structures and properties of Stellite, prepared by HIP, are described. The object was to compile a database to aid alloy choice for net shape part making. Attention is given to effects of powder characteristics on consolidation. HIP materials were characterized for structural parameters. Effects of process conditions on structure and properties are discussed with regard to process optimization.
Iron and steel STRUCTURE AND PROPERTIES OF SINTERED CARBON-MANGANESE STEELS A.S.Wronski et al. (Bradford University, Bradford, UK.) Powder Metall., Vol 47, No 3,1999,227-233. Mechanical properties of 2 to 4%Mn steels were investigated. Young’s modulus was 115 GPa or 153 GPa when measured by extensometer or by an ultrasonic method. Structures were free of oxide networks and were mostly pearlitic but variable. Tensile strengths of 300 to 600 MPa and transverse rupture strengths of 640 to 1260 MPa are reported. Results are analysed statistically. When processing was carefully controlled Weibull modulus was 17 for furnace cooled samples and six for
quenched. The variations in strengths were investigated. It is suggested that corrections for plasticity and Weibull analysis gives better correlation. LIQUID PHASE SINTERING OF IRON-COPPER-CARBON H.Kuroki et al. (Hiroshima University, Higashi-Hiroshima, Japan.) Int. J. Powder Metall., V0125, NO 2,1999,57-62. Driving forces for liquid phase sintering in Fe-Cu-C were investigated quantitatively and two mechanisms are identilied. C and particle shapes are considered. Under the influence of C a semi-permeable layer of liquid Cu is formed which inhibits diffusion of C but allows transport of Fe between particles which enhances sintering. Neck formation, in a columnar structure, is shown to be an example of liquid boundary migration.
Ceramic materials DENSIFICATION OF NANO-CRYSTALLINE TITANIA POWDER COMPACTS H.G.Kim, K.T.Kim. (University of Science and Technology, Pohang, Korea.) Acta Mater., Vo147, No 13, 1999,3561-3570. grain growth and Densification, phase transformations of nano-crystalline TiO, during pressureless sintering and hot pressing were investigated. A model is described that takes driving force and effects of pressure into account. A finite element procedure is used to compare predicted and experimental results. Good agreement is reported. TRANSITION OF @LUMINA &U&DNA BY MILLING
INTO
S.Boskovic et al. (Inst. of Nuclear Sciences, Belgrade, Yugoslavia.] Powder Technol., Vol 107, No l/2,2000,48-53. Intense milling of yAl,O, was investigated. It is reported that yAl,O, transforms into aAlsO,, with the 6 and 8 phases forming as intermediate stages in the process. The transformed oAl,O, is shown to have a distorted lattice with crystallites larger than those in the initial yAl,O,. In the initial stages of milling particle size of yAl,O, was reduced and porosity was eliminated. FRACTOGRAPIIY AND FRACTURE MECIIANICS OF STRUCTURAL CERAMICS J.Dusza, M.Steen. (Inst. for Advanced Materials, European Commission, Petten, The Netherlands.) Int. Muter. Rev.,Vol44., No 5,1999,165-216. Fracture and mechanical properties of high temperature structural ceramics are reviewed with reference to preparation and structural parameters.
are investigation Methods of summarized. Relationships between strength, Weibull modulus and defect distribution and possibilities for strength improvement are discussed. Fractographic appearances and toughare described. mechanisms ening Fracture toughness/structure relationships are discussed. Fatigue and property degradation are considered with regard to loading, creep, crack growth, oxidation and corrosion. The role of fracture studies in development of advanced ceramics with increased reliability is described. MECIIANICAL PROPERTIES AND STRUCTURES OF ALUMINA MADE BY CENTRIFUGAL COMPACTION H.Y.Suzuki et al. (Hiroshima University, Higashi-Hiroshima, Japan.) J. Jpn Sot. Powder/Powder Metall., Vol 46, NO 4, 1999,331-338. (In Japanese.) High purity Al,O, was mixed with water, high speed centrifugally compacted and sintered in air at 1150 to 1500 “C. Structures and properties were determined as functions of density. Equations linking structural parameters and properties are deduced and used to estimate the best combination of grain size and density M.ACIIINARILITY OF GREEN ALUMINA COMPACTS E.Sentoku et al. (Kanazawa Technical College, Kanazawa, Japan.) J. Jpn Sot. PowderlPowder Metall., Vol 46, NO 4, 1999,417-421. (In Japanese.) Machining of green Al,O, compacts was investigated with respect to cutting mechanisms, cutting forces and cracking of the machined surfaces, using orthogonal cutting geometry. Cutting speed was 0.8 m.si, depth of cut was 0.5 to 0.4 mm and chamfer angles were from -20” to +5”. Trans- and inter-granular cracking was detected at small and large cuts respectively
Coatings PROCESSING OF ALUMINIUMSILICON CARBIDE POWDERS FOR PLASMA SPRAYING K.Ghosh et al. (University of British Columbia, Vancouver, Canada.) Int J. Powder Metall., Vo125, No 2,1999,27-35. Use of Al in automotive engine parts is discussed with reference to surface properties and the need for protective coatings. It is reported that 6061Al alloy-sic powders had been mechanically alloyed, prior to plasma spraying with an axial feed torch. Adhesion to the substrate, hardness and wear properties are evaluated.
MPR November
2000 43
Cobalt MICROSTRUCTURE - PROPERTY RELATIONSHIPS IN HIP STELLITE M.H.Jacobs et al. (University of Birmingham, Birmingham, UK.) Powder Metall., Vol47, No 3, 1999,243-249. Investigations of structures and properties of Stellite, prepared by HIP, are described. The object was to compile a database to aid alloy choice for net shape part making. Attention is given to effects of powder characteristics on consolidation. HIP materials were characterized for structural parameters. Effects of process conditions on structure and properties are discussed with regard to process optimization.
Iron and steel STRUCTURE AND PROPERTIES OF SINTERED CARBON-MANGANESE STEELS A.S.Wronski et al. (Bradford University, Bradford, UK.) Powder Metall., Vol 47, No 3,1999,227-233. Mechanical properties of 2 to 4%Mn steels were investigated. Young’s modulus was 115 GPa or 153 GPa when measured by extensometer or by an ultrasonic method. Structures were free of oxide networks and were mostly pearlitic but variable. Tensile strengths of 300 to 600 MPa and transverse rupture strengths of 640 to 1260 MPa are reported. Results are analysed statistically. When processing was carefully controlled Weibull modulus was 17 for furnace cooled samples and six for
quenched. The variations in strengths were investigated. It is suggested that corrections for plasticity and Weibull analysis gives better correlation. LIQUID PHASE SINTERING OF IRON-COPPER-CARBON H.Kuroki et al. (Hiroshima University, Higashi-Hiroshima, Japan.) Int. J. Powder Metall., V0125, NO 2,1999,57-62. Driving forces for liquid phase sintering in Fe-Cu-C were investigated quantitatively and two mechanisms are identilied. C and particle shapes are considered. Under the influence of C a semi-permeable layer of liquid Cu is formed which inhibits diffusion of C but allows transport of Fe between particles which enhances sintering. Neck formation, in a columnar structure, is shown to be an example of liquid boundary migration.
Ceramic materials DENSIFICATION OF NANO-CRYSTALLINE TITANIA POWDER COMPACTS H.G.Kim, K.T.Kim. (University of Science and Technology, Pohang, Korea.) Acta Mater., Vo147, No 13, 1999,3561-3570. grain growth and Densification, phase transformations of nano-crystalline TiO, during pressureless sintering and hot pressing were investigated. A model is described that takes driving force and effects of pressure into account. A finite element procedure is used to compare predicted and experimental results. Good agreement is reported. TRANSITION OF @LUMINA &U&DNA BY MILLING
INTO
S.Boskovic et al. (Inst. of Nuclear Sciences, Belgrade, Yugoslavia.] Powder Technol., Vol 107, No l/2,2000,48-53. Intense milling of yAl,O, was investigated. It is reported that yAl,O, transforms into aAlsO,, with the 6 and 8 phases forming as intermediate stages in the process. The transformed oAl,O, is shown to have a distorted lattice with crystallites larger than those in the initial yAl,O,. In the initial stages of milling particle size of yAl,O, was reduced and porosity was eliminated. FRACTOGRAPIIY AND FRACTURE MECIIANICS OF STRUCTURAL CERAMICS J.Dusza, M.Steen. (Inst. for Advanced Materials, European Commission, Petten, The Netherlands.) Int. Muter. Rev.,Vol44., No 5,1999,165-216. Fracture and mechanical properties of high temperature structural ceramics are reviewed with reference to preparation and structural parameters.
are investigation Methods of summarized. Relationships between strength, Weibull modulus and defect distribution and possibilities for strength improvement are discussed. Fractographic appearances and toughare described. mechanisms ening Fracture toughness/structure relationships are discussed. Fatigue and property degradation are considered with regard to loading, creep, crack growth, oxidation and corrosion. The role of fracture studies in development of advanced ceramics with increased reliability is described. MECIIANICAL PROPERTIES AND STRUCTURES OF ALUMINA MADE BY CENTRIFUGAL COMPACTION H.Y.Suzuki et al. (Hiroshima University, Higashi-Hiroshima, Japan.) J. Jpn Sot. Powder/Powder Metall., Vol 46, NO 4, 1999,331-338. (In Japanese.) High purity Al,O, was mixed with water, high speed centrifugally compacted and sintered in air at 1150 to 1500 “C. Structures and properties were determined as functions of density. Equations linking structural parameters and properties are deduced and used to estimate the best combination of grain size and density M.ACIIINARILITY OF GREEN ALUMINA COMPACTS E.Sentoku et al. (Kanazawa Technical College, Kanazawa, Japan.) J. Jpn Sot. PowderlPowder Metall., Vol 46, NO 4, 1999,417-421. (In Japanese.) Machining of green Al,O, compacts was investigated with respect to cutting mechanisms, cutting forces and cracking of the machined surfaces, using orthogonal cutting geometry. Cutting speed was 0.8 m.si, depth of cut was 0.5 to 0.4 mm and chamfer angles were from -20” to +5”. Trans- and inter-granular cracking was detected at small and large cuts respectively
Coatings PROCESSING OF ALUMINIUMSILICON CARBIDE POWDERS FOR PLASMA SPRAYING K.Ghosh et al. (University of British Columbia, Vancouver, Canada.) Int J. Powder Metall., Vo125, No 2,1999,27-35. Use of Al in automotive engine parts is discussed with reference to surface properties and the need for protective coatings. It is reported that 6061Al alloy-sic powders had been mechanically alloyed, prior to plasma spraying with an axial feed torch. Adhesion to the substrate, hardness and wear properties are evaluated.
MPR November
2000 43