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Sintering and crystallization of strontium oxide-alumina-silica ceramics
It was noted that evaluation of flow properties of powders, less than 325 mesh, presents difficulties in ranking, although these have high flowability. It was suggested that a torque rheometer can detect differences in dry viscosify of non-agglomerated powders. A study of this to detect friction related differences between samples of gas atomized stainless steel powder, was described. Both fine samples, less than 325 mesh, and mixtures with larger particles were examined. Results from the torque rheometer and standard tests for flowability were compared. It was shown that the torque rheometer is of value in evaluat,ing flowabiliity of very fine powders. ON-LINE DROPLET FOR PRODUCTION SOLDER POWDERS
SIZE CONTROL OF SPHERICAL
J.C.Rocha, eJ.H.Chun. (Massachusetts Inst. of Technology, USA.) Production of uniform spherical solder particles, by a Uniform Droplet Spray technique was outlined. The need for precision in particle size for electronics applications was noted. Closed loop control of the process to make particles in the 75 to 1000 pm size range was discussed. Two parts of the system were identified, droplet size measurement and sphere size control. It was shown that the particle size can be controlled within +2.5% of the target size. The emphasis of the study was on particle sizes 250 to 800 pm.
Sin tering SINTERING OF MOLYBDENUM CIDE DOPED WITH NICKEL
DISILI-
I.H.Moon et al. (Hanyang University, Seoul, Korea.) Sintcring of ball milled MoSi,-(0.1 to 2)wt%Ni was investigated during hcating at 4, 8 and lG”C.min-’ and isothermally. The process was followed by X-ray diffraction and microscopy. GNi,Si was detected. The powder sintered readily at 1250 to 1300°C. Grain growth in the 2%Ni alloy was examined as a function of time during liquid phase sintering at 1400°C. SINTERING AND CRYSTALLIZATION OF STRONTIUM OXIDE-ALUMINA-SILICA CERAMICS Y.M.Sung et al. (I)aejon University, Korea.) A study of sintering of 50wt%(SrOSiOz)-5O%(SrO-A&O,-SiO,), prepared by melting and milling in an aZr0, mill was described. The glass transition and crystallization temperatures were determined and activation energy calculated. Powders were compacted and sintered
at 900°C and then at 1100°C. Densities and structures at’the sintered ceramics were measured. Effects of BaO, and TiO, additions were studied. The results were compared with data for stoichiometric SrO-A&O,-SiO, materials. MECHANICAL PROPERTIES AND SINTERING OF WATER ATOMIZED IRONCHROMIUM-MOLYBDENUM POWDERS C.Lindberg. (IIoganas AB, Hoganas, Sweden. 1 PM Cr-Mo st,eels were discussed with reference to mechanical properties, sintering characteristics, hardenability and the tendency for Cr to oxidize. It was shown that by preparing pre-alloyed 3%Cr-0.58Mo steel, pressing and sintering at 1120°C in N-H oxidation could be minimized. Yield strengths of 500 to 570 MPa and Vickers hardness of 220 to 260 could be attained at 0.3 to 0.4%C.
fliA1, with Cr, Mn and Mg alloy additions, was processed by mechanical alloying and sintered by a pulse discharge technique. Sintering was rapid. The best improvement in mechanical properties was obtained with 2%Cr. It was shown that the fracture strength increased with increased test temperature with Cr added. Mn had the reverse effect. MICROWAVE SINTERING AND CHARACTERIZATION OF POWDERED METALS R.Roy et al. (Pennsylvania University, USA. 1 1Jse of microwave sintering
was discussed and it was noted that few experiments have been done with metal powders. Green laboratory and commercial compacts were microwave sintered, typically, at 1100 to 1300°C for 5 to 30 min-
GRAVITY INDUCED DIMENSIONAL NON-UNIFORMITY TAKING GRAIN SEGREGATION INTO ACCOUNT
utes. ed to with with
E.A.Olevsky, sylvania State
Dimensional
R.M.German. USA.) University,
(Penn-
Liquid phase sintering, under simultaneous influence of surface tension and gravity, was analysed and mathematically modelled using continuum theory taking grain segregation into account. The model was applied to sintering of a porous cylindrical specimen. Shape distortion was characterized and compared wit,h experimental data for W-Fe-Ni samples. The effect of gravity segregation on dimensional non-uniformity was determined. The application of the study was shown to lie in the need for improved dimensional precision in sintered parts and to develop a model to give better tool design to achieve this. DIRECT OBSERVATION OF PM PARTS DURING SINTERING R.M.German ef al. (Pennsylvania State University, USA.) It was reported that in situ video imaging had been used to study densification and distortion during sintering of a range of alloys. Various phenomena were directly observed. The technique was said to provide a tool for process optimization. Results were correlated with data obtained by other methods.
State
The sintered compacts were reporthave unifurmly distributed porosity properties improved in comparison conventionally process materials.
control
COMPARISON OF CONVENTIONAL AND MICROWAVE SINTERED FERROUS ALLOYS M.J.Yang, R.M.German. (Pennsylvania State University, USA.) FC0208, Fe-Cu-C, and FN0208, Fe-
Ni-C steels were conventionally and microwave sintered at a range of temperatures after pressing at 552 and 690 MPa. The sintered samples were characterizcd for properties, dimensions, SC! and structure. Microwave sintering was reported to result in higher strength and hardness but worse dimensional control and non-uniform microstructure. The need for further investigation of microwave sintering was emphasized. PREDICTION OF DIMENSIONAL CHANGE DURING SINTERING OF STEEL R.M.German et al. (Pennsylvania State University, USA. 1 It was reported that a model had been applied to the prediction of dimensional change during sintering of FC0208, Fe-Cu-C steel. The model incor-
Novel sintering techniques
porates mechanisms involved in sintering and was validated by dilatometry. The predictions were shown to be in agreement with data from industrial processing.
EFFECT OF ALLOYING ON flITANIUM ALUMINIDE PREPARED BY PULSE DISCHARGE SINTERING
EFFECT OF SEVERAL PARAMETERS ON PART DISTORTION DURING SINTERING
T.Abe et al. (Tohoku National Industrial Research Inst., Sendai, Japan.)
A.Vovan, Canada.)
M.Guillot.
(Lava1
University,
MPR June 2000
37
SIZE CONTROL OF SPHERICAL
J.C.Rocha, eJ.H.Chun. (Massachusetts Inst. of Technology, USA.) Production of uniform spherical solder particles, by a Uniform Droplet Spray technique was outlined. The need for precision in particle size for electronics applications was noted. Closed loop control of the process to make particles in the 75 to 1000 pm size range was discussed. Two parts of the system were identified, droplet size measurement and sphere size control. It was shown that the particle size can be controlled within +2.5% of the target size. The emphasis of the study was on particle sizes 250 to 800 pm.
Sin tering SINTERING OF MOLYBDENUM CIDE DOPED WITH NICKEL
DISILI-
I.H.Moon et al. (Hanyang University, Seoul, Korea.) Sintcring of ball milled MoSi,-(0.1 to 2)wt%Ni was investigated during hcating at 4, 8 and lG”C.min-’ and isothermally. The process was followed by X-ray diffraction and microscopy. GNi,Si was detected. The powder sintered readily at 1250 to 1300°C. Grain growth in the 2%Ni alloy was examined as a function of time during liquid phase sintering at 1400°C. SINTERING AND CRYSTALLIZATION OF STRONTIUM OXIDE-ALUMINA-SILICA CERAMICS Y.M.Sung et al. (I)aejon University, Korea.) A study of sintering of 50wt%(SrOSiOz)-5O%(SrO-A&O,-SiO,), prepared by melting and milling in an aZr0, mill was described. The glass transition and crystallization temperatures were determined and activation energy calculated. Powders were compacted and sintered
at 900°C and then at 1100°C. Densities and structures at’the sintered ceramics were measured. Effects of BaO, and TiO, additions were studied. The results were compared with data for stoichiometric SrO-A&O,-SiO, materials. MECHANICAL PROPERTIES AND SINTERING OF WATER ATOMIZED IRONCHROMIUM-MOLYBDENUM POWDERS C.Lindberg. (IIoganas AB, Hoganas, Sweden. 1 PM Cr-Mo st,eels were discussed with reference to mechanical properties, sintering characteristics, hardenability and the tendency for Cr to oxidize. It was shown that by preparing pre-alloyed 3%Cr-0.58Mo steel, pressing and sintering at 1120°C in N-H oxidation could be minimized. Yield strengths of 500 to 570 MPa and Vickers hardness of 220 to 260 could be attained at 0.3 to 0.4%C.
fliA1, with Cr, Mn and Mg alloy additions, was processed by mechanical alloying and sintered by a pulse discharge technique. Sintering was rapid. The best improvement in mechanical properties was obtained with 2%Cr. It was shown that the fracture strength increased with increased test temperature with Cr added. Mn had the reverse effect. MICROWAVE SINTERING AND CHARACTERIZATION OF POWDERED METALS R.Roy et al. (Pennsylvania University, USA. 1 1Jse of microwave sintering
was discussed and it was noted that few experiments have been done with metal powders. Green laboratory and commercial compacts were microwave sintered, typically, at 1100 to 1300°C for 5 to 30 min-
GRAVITY INDUCED DIMENSIONAL NON-UNIFORMITY TAKING GRAIN SEGREGATION INTO ACCOUNT
utes. ed to with with
E.A.Olevsky, sylvania State
Dimensional
R.M.German. USA.) University,
(Penn-
Liquid phase sintering, under simultaneous influence of surface tension and gravity, was analysed and mathematically modelled using continuum theory taking grain segregation into account. The model was applied to sintering of a porous cylindrical specimen. Shape distortion was characterized and compared wit,h experimental data for W-Fe-Ni samples. The effect of gravity segregation on dimensional non-uniformity was determined. The application of the study was shown to lie in the need for improved dimensional precision in sintered parts and to develop a model to give better tool design to achieve this. DIRECT OBSERVATION OF PM PARTS DURING SINTERING R.M.German ef al. (Pennsylvania State University, USA.) It was reported that in situ video imaging had been used to study densification and distortion during sintering of a range of alloys. Various phenomena were directly observed. The technique was said to provide a tool for process optimization. Results were correlated with data obtained by other methods.
State
The sintered compacts were reporthave unifurmly distributed porosity properties improved in comparison conventionally process materials.
control
COMPARISON OF CONVENTIONAL AND MICROWAVE SINTERED FERROUS ALLOYS M.J.Yang, R.M.German. (Pennsylvania State University, USA.) FC0208, Fe-Cu-C, and FN0208, Fe-
Ni-C steels were conventionally and microwave sintered at a range of temperatures after pressing at 552 and 690 MPa. The sintered samples were characterizcd for properties, dimensions, SC! and structure. Microwave sintering was reported to result in higher strength and hardness but worse dimensional control and non-uniform microstructure. The need for further investigation of microwave sintering was emphasized. PREDICTION OF DIMENSIONAL CHANGE DURING SINTERING OF STEEL R.M.German et al. (Pennsylvania State University, USA. 1 It was reported that a model had been applied to the prediction of dimensional change during sintering of FC0208, Fe-Cu-C steel. The model incor-
Novel sintering techniques
porates mechanisms involved in sintering and was validated by dilatometry. The predictions were shown to be in agreement with data from industrial processing.
EFFECT OF ALLOYING ON flITANIUM ALUMINIDE PREPARED BY PULSE DISCHARGE SINTERING
EFFECT OF SEVERAL PARAMETERS ON PART DISTORTION DURING SINTERING
T.Abe et al. (Tohoku National Industrial Research Inst., Sendai, Japan.)
A.Vovan, Canada.)
M.Guillot.
(Lava1
University,
MPR June 2000
37