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Effect of pore size and shape on endurance limit of sintered materials
PREPARATION OF TITANIUM ALUMINIDE FOILS BY ROLL COMPACTION OF ELEMENTAL POWDERS B. Kieback et al (Praunhofer Inst. for Applied Materials Research, Dresden, Germany). Production of TiAl foils, 70 mm by 0.7 to 2 mm thick, by roll compaction of elemental powders was described. The green foil was shown to be 80 to 90% dense. Process conditions were optimized to minimize density variations. Further rolling gave foil 200 urn thick. Production of structural materials and fibre filled composites was shown to be possible. MECHANICAL ALLOYING AND PHASE SYNTHESIS DURING SINTERING OF MOLYBDENUM DISILICIDE B. Kieback et al (Fraunhofer Inst. for Applied Materials Research, Dresden, Germany). The influence of mechanical activation on the synthesis of MoSiz was investigated. After 12 hours milling no MoSia was found but MoSi, formed at 1100°C. Increased milling times caused phase formation to start on heating to 600°C giving MoBSis, Mo:$i and MoSia. Further extension of milling times gave phase synthesis at lower temperatures. Sintered grain sizes were 2 to 8 urn. PROPERTIES AND STRUCTURES OF HIGH SPECIFIC STIFFNESS MECHANICALLY ALLOYED IRON ALUMINIDE R. Baccino et al (CEA/CERAM/CENG, Grenoble, France). Applications of iron aluminides were discussed with regard to the limitations imposed by ambient temperature brittleness and low creep resistance. A model of the properties was developed from experimental data and used to design a Fe-4Oat%Al alloy with enhanced mechanical properties. This was attributed to grain boundary strengthening and a stable ultrafine grain size. Aplications were discussed with respect to corrosion and creep. MICROSTRUCTURAL TRANSFORMATIONS DURING MECHANICAL ALLOYING OF TITANIUM ALLOY F.H. Froes et al (University of Idaho, Moscow, Idaho, USA). A study of the effects of mechanical alloying on prealloyed Ti-47at%Al-3XCr alloy powder was described. An ultrafine microstructure, with a crystallite size of 15 nm and partial amorphization was reported.
Porous materials PREPARATION AND CHARACTERIZATION OF POROUS ZIRCONIUM GETTERS A.R.M. Castro et al (COPESP, University City, Sao Paulo, Brazil). The use of ammonium carbonate in the production of sintered porous Zr, with a density of about 59%; was reported. The material had a controlled pore size distribution. The application was in a gas absorption device in a high pressure measuring instrument. EFFECT OF PORE SIZE AND SHAPE ON ENDURANCE LIMIT OF SINTERED MATERIALS B. Kubicki, V. Sundar (Central Queensland University, Rockhampton, Australia). A theory of fatigue in elasto-plastic materials with pores or inclusions was discussed. An attempt to determine the effect of endurance limit by analysis of plastic zones at inclusions was described. Stress intensity was considered. A critical value of stress was determined for varying pore sizes. Finite element methods and photoelasticity were used. PROPERTIES OF POROUS PARTS WITH LAYER OR GRADIENT STRUCTURES M. Joensson, P.Neumann (Krebsoge Sinterholding, Radevormwald, Germany). The use of centrifugal PM to make porous parts with layered or compositionally gradient structures was described. Effects of powder and process characteristics were determined. The experimental results were discussed with respect to structure, properties and uses. METHODS FOR THE PRODUCTION OF METALLIC FOAMS
A SINTERED VALVE SPRING COLLAR IN ALLOY STEEL A Arvand, A Haerian. A study of sintered 4%Ni-Z’%;Cu-0.5%Mo0.5% steel, intended to replace a forged or machined automotive part, was described. 200 000 specimens were made for test and only 7 were said to have failed. A 20% cost saving was reported for the PM part. FRACTURE TOUGHNESS TESTING OF POWDER METALLURGY MATERIALS D.I. Chen et al (University of Vienna, Vienna, Austria). Fracture toughness of a sintered 1.5!%Mo-0.7X steel was investigated as a function of porosity in the range 0 to 28%. It was reported that t.here was little crack growth prior to tensile fracture which was held to validate the test method. Toughness decreased with increased porosity. DEFORMATION BEHAVIOUR OF SINTERED STEELS UNDER INSTRUMENTED CHARPN IMPACT LOADING G. Straffelini et al (University of Trento, Trento, Italy). Impact strength of a range of steels, with varying %C and heat treatment, was studied on an instrumented Charpy machine. Impact energy dropped on passing from 0.2 to 0.3%X due to structural change. Impact strength was discussed in respect of energy absorbed, crack generation and growth, dynamic work hardening and fracture characteristics. FRACTURE TOUGHNESS OF PRECRACRED AND NOTCHED SINTERED STEELS
J. Baumeister et al (Praunhofer Inst, Bremen, Germany). Methods for production of metallic foams were described and analysed in which PM was thought to have high potential. Al foams, made by different techniques, were discussed with reference to structure, mechanical properties and applications.
R. Roberti et al (Polytechnic of Milan, Milan, Italy). Progress in the development of sintered structural materials was discussed in the light of low ductility and the need to improve this and methods of assessing toughness. The fracture toughness of two steels, precracked and notched, was investigated as functions of porosity, carburizing and notch root radius.
Steek
Sinterhg
FATIGUE OF SINTERED SPECIMENS IN AXIAL LOADING WITH SUPERIMPOSED BENDING
DENSIFICATION OF MOLYBDENUM DISILICIDE BY REACTIVE SINTERING AND HOT PRESSING
J. Bendixen (Danish Technological Inst., Taastrup, Denmark). Samples of P alloyed steel, in two densities, three surface treatments and with or without 0.2%C, were fatigue tested in uniaxial loading with bending imposed due to specimen out of flatness. A correction proceedure was developed to compare the data.
Y-S. Kim et al (Hong Ik University, Seoul, Korea). A study of densification and synthesis of MoSiz by a thermal explosion mode of self propagating high temperature synthesis was described. Pressure was applied during synthesis and alloy elements added to enhance densification to near full density. MPR July/August
1995
37
Porous materials PREPARATION AND CHARACTERIZATION OF POROUS ZIRCONIUM GETTERS A.R.M. Castro et al (COPESP, University City, Sao Paulo, Brazil). The use of ammonium carbonate in the production of sintered porous Zr, with a density of about 59%; was reported. The material had a controlled pore size distribution. The application was in a gas absorption device in a high pressure measuring instrument. EFFECT OF PORE SIZE AND SHAPE ON ENDURANCE LIMIT OF SINTERED MATERIALS B. Kubicki, V. Sundar (Central Queensland University, Rockhampton, Australia). A theory of fatigue in elasto-plastic materials with pores or inclusions was discussed. An attempt to determine the effect of endurance limit by analysis of plastic zones at inclusions was described. Stress intensity was considered. A critical value of stress was determined for varying pore sizes. Finite element methods and photoelasticity were used. PROPERTIES OF POROUS PARTS WITH LAYER OR GRADIENT STRUCTURES M. Joensson, P.Neumann (Krebsoge Sinterholding, Radevormwald, Germany). The use of centrifugal PM to make porous parts with layered or compositionally gradient structures was described. Effects of powder and process characteristics were determined. The experimental results were discussed with respect to structure, properties and uses. METHODS FOR THE PRODUCTION OF METALLIC FOAMS
A SINTERED VALVE SPRING COLLAR IN ALLOY STEEL A Arvand, A Haerian. A study of sintered 4%Ni-Z’%;Cu-0.5%Mo0.5% steel, intended to replace a forged or machined automotive part, was described. 200 000 specimens were made for test and only 7 were said to have failed. A 20% cost saving was reported for the PM part. FRACTURE TOUGHNESS TESTING OF POWDER METALLURGY MATERIALS D.I. Chen et al (University of Vienna, Vienna, Austria). Fracture toughness of a sintered 1.5!%Mo-0.7X steel was investigated as a function of porosity in the range 0 to 28%. It was reported that t.here was little crack growth prior to tensile fracture which was held to validate the test method. Toughness decreased with increased porosity. DEFORMATION BEHAVIOUR OF SINTERED STEELS UNDER INSTRUMENTED CHARPN IMPACT LOADING G. Straffelini et al (University of Trento, Trento, Italy). Impact strength of a range of steels, with varying %C and heat treatment, was studied on an instrumented Charpy machine. Impact energy dropped on passing from 0.2 to 0.3%X due to structural change. Impact strength was discussed in respect of energy absorbed, crack generation and growth, dynamic work hardening and fracture characteristics. FRACTURE TOUGHNESS OF PRECRACRED AND NOTCHED SINTERED STEELS
J. Baumeister et al (Praunhofer Inst, Bremen, Germany). Methods for production of metallic foams were described and analysed in which PM was thought to have high potential. Al foams, made by different techniques, were discussed with reference to structure, mechanical properties and applications.
R. Roberti et al (Polytechnic of Milan, Milan, Italy). Progress in the development of sintered structural materials was discussed in the light of low ductility and the need to improve this and methods of assessing toughness. The fracture toughness of two steels, precracked and notched, was investigated as functions of porosity, carburizing and notch root radius.
Steek
Sinterhg
FATIGUE OF SINTERED SPECIMENS IN AXIAL LOADING WITH SUPERIMPOSED BENDING
DENSIFICATION OF MOLYBDENUM DISILICIDE BY REACTIVE SINTERING AND HOT PRESSING
J. Bendixen (Danish Technological Inst., Taastrup, Denmark). Samples of P alloyed steel, in two densities, three surface treatments and with or without 0.2%C, were fatigue tested in uniaxial loading with bending imposed due to specimen out of flatness. A correction proceedure was developed to compare the data.
Y-S. Kim et al (Hong Ik University, Seoul, Korea). A study of densification and synthesis of MoSiz by a thermal explosion mode of self propagating high temperature synthesis was described. Pressure was applied during synthesis and alloy elements added to enhance densification to near full density. MPR July/August
1995
37