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Kinetics of binder burnout and oxide reduction in injection moulded iron parts
conditions on formation of precipitates was described. It was shown that precipitates such as Ti,Al,C, Ti,Al(C,N) and Ti,AlN are formed during heat treatment of mechanically alloyed Ti525at%Al and Ti-48%Al-2%Cr-2%Nb powders. Synthesis of precipitates depends on heat treatment temperature and concentrations of impurities and alloy elements, Cr and Nb. PROCESSING OF SILVER-ALUMINIUM BY MECHANICAL ALLOYING (National J.L.H.Estrada et al. Polytechnic Inst. of Mexico, Mexico.) Ag-(25, 35, 62.5 and SO)wt%Al powders were mechanically alloyed for 100 and 200 hours. The milled powders were characterized. Ag-25%Al showed a supersaturated face centred cubic solid solution after 100 hours. Ag-35%Al contained Ag,Al. Ag-(65.5 and 9O)%Al contained a mixture of phases in a face centred cubic solid solution matrix. IMPROVEMENT OF SILVER-TIN ELECTRICAL CONTACT ALLOY BY MECHANICAL ALLOYING H.Zoz et al. (Zoz GmbH, Germany.) Ag-CdO, used for electrical contacts, was discussed with regard to properties; the toxicity of Cd and the need to substitute Cd was emphasized. A study of AgSnO, was described. MA was used to process (Ag-33at%Snl-AgO powders, which were compacted and sintered to high density. The structure was SnO, in a Ag-rich matrix.
Sintering
atmospheres
SINTERING OF STEEL PARTS IN ENDOTHERMIC GAS AND NITROGENHYDROGEN ATMOSPHERES J.G.Marsden et al. (Air Products and Chemicals Inc, USA.) N based atmospheres were reviewed with regard to use of generators or blending of elemental gases, N and H. Widespread use of endo-gas generators is common in the PM industry, because of the perceived high cost of using blended elemental gases and lack of data concerning the advantages of N-H mixtures. An investigation to compare parts sintered in endothermic gas or blended N-H mixtures was described. N-H was shown to be beneficial over endo-gas. RESIDUAL GAS ANALYSIS OF VACUUM FURNACES FOR PM W.Li, R.L.Thomas. Inc, USA.)
(Cutler-Hammer
42 MPR December 1998
On-line analysis of residual gases in vacuum sintering furnaces was discussed with reference to applications such as debinding and out-gassing. A study, using quadruple mass spectroscopy, to determine gas composition in vacuum sintering furnaces was described. The alloy tested was a Cu-Cr electrical contact material. As process temperature was raised from ambient to 105O”C, H,O, H, CO and N were found in the residual gas at different temperatures.
Powder injection moulding PREDICTING RHEOLOGY OF FEEDSTOCKS WITH VARYING PARTICLE CHARACTERISTICS R.M.German et al. (Pennsylvania State University, USA.) Factors influencing the rheological characteristics of injection moulding feedstocks, including temperature and shear rate, particle shape, size distribution and volume fraction, were discussed. A model for prediction of viscosity of feedstocks, of varying powder characteristics, was proposed. Several variables are combined in a single rheological parameter. The model was validated for a range of feedstocks. It was shown that the study can be helpful in design of feedstock and formulation of the moulding cycle. COMBINED MODEL FOR VISCOSITY OF MIXTURES WITH LOW VISCOSITY BINDERS J.R.Jabbireddy, M.Vijayakumar. (Defence Metallurgical Research Laboratory, India.) Rheology of injection moulding feedstocks was reviewed with regard to factors involved. An equation, incorporating a range of parameters, for prediction of viscosity of feedstocks, was proposed. Capillary rheometry was used to study viscosity of feedstocks based on coarse SiO, or fine Also,, with a polymer-wax binder, under a range of conditions. Good agreement between experimental and predicted results was reported. The results were presented as iso-viscosity maps and applied to selection of processing regimes for injection moulding mixtures. NOVEL WATER DEBINDING METAL POWDER FEEDSTOCK R.Petcavich, X.Yang. (Planet Polymer Technologies Inc, USA.) It was reported that a novel water debindable injection moulding feedstock
had been developed. This avoids use of hazardous solvents or acids. The new binder is based on polyvinylalcohol-polyolefin blends, which improve moulding characteristics, green and brown strength, debinding and sintering. Details were given with examples of parts. HOLLOW PARTS MADE BY GAS ASSISTED INJECTION MOULDING U.Haupt, H.Walcher. (ARBURG, GmbH, Germany.) Solid and hollow injection moulded parts were reviewed. Gas assisted injection moulding was reported to facilitate production of hollow parts. Principles of operation, equipment, process parameters and their effect on part production were outlined. Advantages, such as lower material consumption, and limitations were discussed. KINETICS OF BINDER BURNOUT AND OXIDE REDUCTION IN INJECTION MOIJLDED IRON PARTS et al. (Illinois Inst. of P.Nash Technology, USA.) It is noted that the successful production of injection moulded Fe parts depends on process control in debinding, oxide reduction and sintering heat treatments. Thermogravimetry was used to investigate binder burnout and reduction of Fe,O, in a partial H atmosphere. It is shown that control of heating rates, dwell times and atmosphere flow rate lead to complete debinding, complete oxide reduction and densities in excess of 96%.
Alloying element addition SYNTHESIS AND DENSIFICATION OF TUNGSTEN-SILICA COMPOSITES R.M.German. (Pennsylvania State University, USA.) An investigation of W-lOvol%SiO, was described. The objectives were to attain full density and incorporate the SiO, within the W grains and not at grain boundaries. Powders were prepared by mechanical alloying and compaction was by die pressing and CIP. Ni was added to the powder as a sintering enhancer. HIP was used to attain high density. Microstructures were examined by optical and electron microscopy with energy dispersion. 40% of the SiO, was intergranular and 99% density was reached. Further work is needed to improve the distribution of SiO,.
Sintering
atmospheres
SINTERING OF STEEL PARTS IN ENDOTHERMIC GAS AND NITROGENHYDROGEN ATMOSPHERES J.G.Marsden et al. (Air Products and Chemicals Inc, USA.) N based atmospheres were reviewed with regard to use of generators or blending of elemental gases, N and H. Widespread use of endo-gas generators is common in the PM industry, because of the perceived high cost of using blended elemental gases and lack of data concerning the advantages of N-H mixtures. An investigation to compare parts sintered in endothermic gas or blended N-H mixtures was described. N-H was shown to be beneficial over endo-gas. RESIDUAL GAS ANALYSIS OF VACUUM FURNACES FOR PM W.Li, R.L.Thomas. Inc, USA.)
(Cutler-Hammer
42 MPR December 1998
On-line analysis of residual gases in vacuum sintering furnaces was discussed with reference to applications such as debinding and out-gassing. A study, using quadruple mass spectroscopy, to determine gas composition in vacuum sintering furnaces was described. The alloy tested was a Cu-Cr electrical contact material. As process temperature was raised from ambient to 105O”C, H,O, H, CO and N were found in the residual gas at different temperatures.
Powder injection moulding PREDICTING RHEOLOGY OF FEEDSTOCKS WITH VARYING PARTICLE CHARACTERISTICS R.M.German et al. (Pennsylvania State University, USA.) Factors influencing the rheological characteristics of injection moulding feedstocks, including temperature and shear rate, particle shape, size distribution and volume fraction, were discussed. A model for prediction of viscosity of feedstocks, of varying powder characteristics, was proposed. Several variables are combined in a single rheological parameter. The model was validated for a range of feedstocks. It was shown that the study can be helpful in design of feedstock and formulation of the moulding cycle. COMBINED MODEL FOR VISCOSITY OF MIXTURES WITH LOW VISCOSITY BINDERS J.R.Jabbireddy, M.Vijayakumar. (Defence Metallurgical Research Laboratory, India.) Rheology of injection moulding feedstocks was reviewed with regard to factors involved. An equation, incorporating a range of parameters, for prediction of viscosity of feedstocks, was proposed. Capillary rheometry was used to study viscosity of feedstocks based on coarse SiO, or fine Also,, with a polymer-wax binder, under a range of conditions. Good agreement between experimental and predicted results was reported. The results were presented as iso-viscosity maps and applied to selection of processing regimes for injection moulding mixtures. NOVEL WATER DEBINDING METAL POWDER FEEDSTOCK R.Petcavich, X.Yang. (Planet Polymer Technologies Inc, USA.) It was reported that a novel water debindable injection moulding feedstock
had been developed. This avoids use of hazardous solvents or acids. The new binder is based on polyvinylalcohol-polyolefin blends, which improve moulding characteristics, green and brown strength, debinding and sintering. Details were given with examples of parts. HOLLOW PARTS MADE BY GAS ASSISTED INJECTION MOULDING U.Haupt, H.Walcher. (ARBURG, GmbH, Germany.) Solid and hollow injection moulded parts were reviewed. Gas assisted injection moulding was reported to facilitate production of hollow parts. Principles of operation, equipment, process parameters and their effect on part production were outlined. Advantages, such as lower material consumption, and limitations were discussed. KINETICS OF BINDER BURNOUT AND OXIDE REDUCTION IN INJECTION MOIJLDED IRON PARTS et al. (Illinois Inst. of P.Nash Technology, USA.) It is noted that the successful production of injection moulded Fe parts depends on process control in debinding, oxide reduction and sintering heat treatments. Thermogravimetry was used to investigate binder burnout and reduction of Fe,O, in a partial H atmosphere. It is shown that control of heating rates, dwell times and atmosphere flow rate lead to complete debinding, complete oxide reduction and densities in excess of 96%.
Alloying element addition SYNTHESIS AND DENSIFICATION OF TUNGSTEN-SILICA COMPOSITES R.M.German. (Pennsylvania State University, USA.) An investigation of W-lOvol%SiO, was described. The objectives were to attain full density and incorporate the SiO, within the W grains and not at grain boundaries. Powders were prepared by mechanical alloying and compaction was by die pressing and CIP. Ni was added to the powder as a sintering enhancer. HIP was used to attain high density. Microstructures were examined by optical and electron microscopy with energy dispersion. 40% of the SiO, was intergranular and 99% density was reached. Further work is needed to improve the distribution of SiO,.