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Production of powders for MIM by inert gas atomization
:)M
HOT PRESSED WEAR RESISTANT I R O N ~ H R O M I U M ALLOY WITH HARD PHASE MECHANICALLY ALLOYED SURFACE
B. Martner and E. Friedrich, (Dresden University of Technology, Germany). Production of a novel wear resistant material by impacting hard BC powder into the surface of relatively tough Fe(Cr) powder by ball milling was described. The composite powder was consolidated by hot pressing for a short time to minimize dissolution of BC into the matrix. Stresses and temperature generated during abrasion cause dissolution of BC in the surface layers and ensures the formation of a hard, wear resistant, surface. Process technology, structural changes and wear properties were reported.
LITERATURE
REVIEVt
Steel specimens, prepared from atomized powder were brazed or diffusion bonded in green and sintered conditions. Four brazing alloys were used and the strength and hardness of the joints, as a function of density, were compared with those of the parent metals.
Powder injection moulding COMPARISON OF INJECTION MOULDING OF POWDER/BINDER MIXTURES AND PLASTIC MATERIAL
B.O. Rhee and C.I. Chung, (Rensselaer Polytechnic Inst, Troy, N e w York, USA). It was noted that metal and ceramic materials are often injection moulded on machines designed for use with polymers. Design of machines was discussed with FORMING METHOD FOR A MULTILAYER regard to differences between polymers and PM COMPOSITE MATERIAL PIM feedstocks. Freezing times for both were c o m p a r e d experimentally and L.Y. Li and H.H. Wang, (Qingdao Research analytically. Possible solutions for the problem of premature freezing were Inst of PM, China). Uniaxial compaction for production of discussed. multilayer c o m p o s i t e s was described. STRUCTURE APPROACH TO Applications included oil impregnated INJECTION MOULDING OF POWDERb e a r i n g s and m e c h a n i c a l p a r t s with BINDER MIXTURES medium to high strength.
Joining technology DEVELOPMENT OF TECHNOLOGY FOR LASER WELDING OF SINTERED STEEL PARTS
Y. Mural et al, (Kobe Steel Ltd, Kobe, Japan). The use of C O 2 lasers for joining high C steel was described. Without a filler the joints were reported to contain defects, cracks and blowholes. The filler was selected to control martensite formation, promote deoxidation and fix S and N in the steel. Use of laser welding for 0.8% C steel and 0.6% C low alloy steel was reported. COPPER BRAZING OF PM COMPONENTS TO WROUGHT PARTS
B. Marzella et al, (Clarion Sintered Metals, Ridgeway, USA). The brazing of sintered and wrought steel sub-components was described. The P M steel was Cu infiltrated and it was reported the satisfactory joints were produced. Cost savings were claimed because of the reduction in finishing operations. The powder mixture, control of %C, sintered and green densities and assembly were discussed. JOINING OF IRON RASED PM COMPONENTS BY BRAZING AND DIFFUSION BONDING
B. Clausen and ICA. Thorsen, (Technical University of Denmark, Copenhagen, Denmark).
50 MPR November 1992
R.T. Fox et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). An outline of the objectives of PIM, the production components to c l o s e d i m e n s i o n a l t o l e r a n c e s with u n i f o r m microstructures and improved properties in a cost effective way was presented. The prerequisites for successful PIM, knowledge of the feedstock rheology and the effects of process parameters on the integrity of the part were discussed. Flow behaviour o f a r a n g e of f e e d s t o c k s was d e t e r m i n e d experimentally. Finite element methods were used to analyze the physical and mechanical properties. When applied to actual moulding trails causes of defects can be identified and avoided by proper control of m o u l d i n g p a r a m e t e r s and optimum moulding conditions established. NOVEL BINDER FOR RAPID DEBINDING OF POWDER INJECTION MOULDED SAMPLES
H.H. Andermann and A. van der Biest, (Leuven University, Belgium). The rapid removal of a novel binder from PIM compacts, without wicking or solvent was described. A cylindrical sample 13 mm x 10 ram, made from carbonyl Fe powder w a s d e b o u n d in 5 h o u r s w i t h o u t deformation, results for 316L stainless steel and alumina were also given. NOVEL PROCESS CONTROL METHODS FOR BINDERS BASED ON THERMOSET CONDENSATION RESINS G.M. Brasel and J.E. Duke, (Megamet Industries lnc, St. I~uis, USA).
In-moulding debinding, by the Megamet process, was described with regard to the process controls required. Green compacts were produced without the use of an i n j e c t i o n m o u l d i n g m a c h i n e . The importance of the relationship between the properties of the powder, binder and additives was emphasized. Control of green density was exercised through pressurization control and mould venting in a novel way. EFFECTS OF POWDER CHARACTERISTICS AND DEBINDING CONDITIONS ON DEFORMATION BEHAVIOUR OF INJECTION MOULDED COMPACTS DURING THERMAL DEBINDING
R. Miura and S. Takamori, (Japan Steel Works Ltd, Japan). The causes of distortion during debinding, the weight of the compact and viscous creep, were discussed. A n investigation of deformation in three-point bending of a beam was described. Effects of powder morphology and size distribution, bending moment, solid/binder ratio, heating rate, temperature and atmosphere were outlined. ATMOSPHERE PROCESS FOR THE CONTROL OF CARBON AND OXYGEN CONTENTS DURING DEBINDING OF INJECTION MOULDED STEEL
M.A. Phillips et al, (Liquid Air Corp, Countryside, Illinois, USA). The effects of binder decomposition during debinding in increasing the C content of alloys was discussed. This is partly offset by decarburization by reaction with O. The effect of gas composition of %C in Fe-2%Ni steels was evaluated. Precise C content could be attained by adjusting gas composition and debinding parameters. PROCESS PARAMETERS FOR A FAST CATALYTIC DEBINDING SYSTEM
D. Weinand and M. Blomacher, (BASF AG, Ludwigshafen, Germany). Catalytic debinding of injection moulded parts was discussed and was said to offer advantages over conventional debinding p r o c e s s e s . Th e p r o c e s s p a r a m e t e r s r e l e v a n t to e c o n o m i c a n a l y s i s w e r e investigated. Feedstock theology, thermal history, cycle time and green strength were considered. Continuous and discontinuous debinding were discussed. EVOLUTION OF GASES AND SINTERING BEHAVIOUR IN CARBONYL IRON POWDER FOR INJECTION MOULDING
S. Igarashi et al, Tokyo, Japan). It was noted contains volatile and O and that
(Sumitomo Metal Mining, that carbonyl Fe powder impurities including C, N little research had been
carried out on the effects of evolved gases on the sintering process~ An investigation, using gas chromatography of the evolved gases during sintering, was described. The relationship between the gases and the sintering behaviour was examined.
The importance of uniform powder/ binder distribution for quality of a PIM part was noted and the effects of process parameters on particle orientation and distribution and orientation in the PIM binder was described.
CHARACTERIZING POWDERS FOR METAL INJECTION MOULDING
FINITE DIFFERENCE MODEL F O R SIMULATION OF 3-DIMENSIONAL PIM
M. Tasovac, (Remington Arms Co, Hazen, USA). The p r o p e r t i e s of p o w d e r s a n d feedstock, relevant to MIM were discussed. Particle morphology, size distribution, density and residual element concentrations were included and methods for their determination were outlined. Powder characterization was discussed in relation to properties of MIM components.
C. Wang et al, (Metalworking Technolo~, Inc, USA). A numerical program for simulation of mould filling and heat transfer in PIM was described. The partial differential equations were solved for time dependent nonNewtonian flow and heat transfer by a finite difference method. Volume of liquid and imaginary particle methods were used to track advancement of the melt front. The technique was reported to be reliable and to be supported by experimental results.
DEFORMATION BEHAVIOUR OF MIM COMPACTS DURING SINTERING
H. Ohtsubo et ai, (Kawasaki Steel CorD, Kawasaki, Japan). The deformation, during sintering, of 316L stainless steel, m a d e from water atomized powder, was investigated by a three point bend test. Deformation was correlated with connectivity between particles. Sintering was in the range 900 to 1350°C and rapid deformation was reported at 1000°C. Particle surfaces were examined by electron microscopy and Auger spectroscopy. The reaction between C and D was considered to be responsible for the deformation by weakening the bond between particles. Finite element analysis was used to model the deformation and good agreement with experimental results was reported.
GRANULAR MODELLING OF STEEL POWDER FLOW AND COMPACTION IN MIM
T. Alzawa and J. Kihara, (University of Tokyo, Japan). The m o d e l l i n g of the m e c h a n i c a l behaviour of MIM green compacts was discussed with regard to the mechanical parameters employed and their application. A model was described in which the granular powders have local stiffness, the binder is represented by a pressure term and solution of m o m e n t u m equations provide d a t a c o n c e r n i n g m e c h a n i c a l behaviour.
STUDY OF PARTICLE ORIENTATION AND DlffrIHBUTION D U I I N G MELT FLOW IN INJECTION MOULDING
J.T. Lindt et al, (University of Pittsburg, USA).
LARGE SCALE PRODUCTION OF STAINLESS STEEL GEARS BY MIM H. Cohrt et al, (Schunk Sintermetalitechnik GmbH, Oberhausen, Germany). The production of small, 0.3 and 1 g gears in 316L stainless steel by MIM was described. MIM and stainless steel were chosen for corrosion resistance, part shape complexity, the need for mass production (30 000 per day) and the inability of other materials to withstand service conditions. Ready for assembly parts were reported to have been produced. All stages of the production were said to be subject to close quality control.
APPLICATION OF MIM TO HIGH PERFORMANCE PARTS
R. Schulten et al, (R. Zapp Werkstofltechnik GmbH, DQsseldorf, Germany). The use of MIM for the shaping of high performance parts in hard metals and high carbon and stainless steels was discussed with regard to costs compared with c o n v e n t i o n a l PM processes. Selected examples were reviewed and enhanced properties arising from the use of MIM reported.
FATIGUE PROPERTIES OF INJECTION MOULDED IRON-NICKEL AND 17-4PH ALLOYS
M.K. Bulger and A.R. Erickson, (FloMet Inc, USA). A study of the fatigue properties of Fe7%Ni and 17-4PH alloys was reported. S-N curves were produced by the use of reciprocating-bending tests. The fatigue properties were correlated with tensile properties, porosity and microstructure.
Oom~Ja~d~n mM I
HYDROffgATIC COMPACTION OF NANO-SIZED POWDERS M.Y. Tanakov et al, (Ultram International, USA). Deformation of nano-sized powders u n d e r low t e m p e r a t u r e h y d r o s t a t i c compaction was investigated. The observed low d e f o r m a b i l i t y was a t t r i b u t e d to irreversibility of plasticity and it was reported that the compaction pressures were higher t h a n for coarse powders. Finite element methods were used to calculate distribution of stresses and it was shown that sintering characteristics are modified by hydrostic compaction which also stimulates redistribution of impurity atoms.
M M $OVAL OF $ ~ C ACID FROM INJECTION MOULDED SPECIMEN$ OF STAINLESS STEEL
H.H. Angermann and O. van der Blest, (Leuven University, Belgium). Experimental studies of spherical 316L stainless steel powders with a stearic acid (SA)/polypropylene (PP)/polyethylene (PE) binder were described. It was found t h a t the debinding t e m p e r a t u r e s and kinetics of the SA differed from the PP and PE. The removal of SA was studied by thermogravimetric analysis under isothermal conditions. Diffusion of SA through the polymer to pore surfaces was said to be the controlling mechanism. Results were compared with those for SA/ PP and SA/PE binder mixtures.
PRODUCTION OF POWDERS FOR MIM BY I N E r r GAS ATOMIZATION
NJ.E. Adkins and G.P. Yiasenides, (BNFFulmer, Wantage, UK). The production of inert gas atomized powders for MIM was reviewed with regard to the qualities required in the powders and currently available commercial powders. Cleanliness and fineness of powders were considered. New developments in close coupled atomization of powders to meet the requirements of MIM were discussed. Particular reference was made to rare earth powders for magnetic applications and Ni aluminide for high temperature use.
M A T I I / . M A T I C ~ U , I ~ ] U S I O N FOE POWDER MIXTURE COMPEE881BHJTY P. Molera et al, (University of Barcelona, Spain). Compressibility of powders is defined as
MPR November 1992 51
HOT PRESSED WEAR RESISTANT I R O N ~ H R O M I U M ALLOY WITH HARD PHASE MECHANICALLY ALLOYED SURFACE
B. Martner and E. Friedrich, (Dresden University of Technology, Germany). Production of a novel wear resistant material by impacting hard BC powder into the surface of relatively tough Fe(Cr) powder by ball milling was described. The composite powder was consolidated by hot pressing for a short time to minimize dissolution of BC into the matrix. Stresses and temperature generated during abrasion cause dissolution of BC in the surface layers and ensures the formation of a hard, wear resistant, surface. Process technology, structural changes and wear properties were reported.
LITERATURE
REVIEVt
Steel specimens, prepared from atomized powder were brazed or diffusion bonded in green and sintered conditions. Four brazing alloys were used and the strength and hardness of the joints, as a function of density, were compared with those of the parent metals.
Powder injection moulding COMPARISON OF INJECTION MOULDING OF POWDER/BINDER MIXTURES AND PLASTIC MATERIAL
B.O. Rhee and C.I. Chung, (Rensselaer Polytechnic Inst, Troy, N e w York, USA). It was noted that metal and ceramic materials are often injection moulded on machines designed for use with polymers. Design of machines was discussed with FORMING METHOD FOR A MULTILAYER regard to differences between polymers and PM COMPOSITE MATERIAL PIM feedstocks. Freezing times for both were c o m p a r e d experimentally and L.Y. Li and H.H. Wang, (Qingdao Research analytically. Possible solutions for the problem of premature freezing were Inst of PM, China). Uniaxial compaction for production of discussed. multilayer c o m p o s i t e s was described. STRUCTURE APPROACH TO Applications included oil impregnated INJECTION MOULDING OF POWDERb e a r i n g s and m e c h a n i c a l p a r t s with BINDER MIXTURES medium to high strength.
Joining technology DEVELOPMENT OF TECHNOLOGY FOR LASER WELDING OF SINTERED STEEL PARTS
Y. Mural et al, (Kobe Steel Ltd, Kobe, Japan). The use of C O 2 lasers for joining high C steel was described. Without a filler the joints were reported to contain defects, cracks and blowholes. The filler was selected to control martensite formation, promote deoxidation and fix S and N in the steel. Use of laser welding for 0.8% C steel and 0.6% C low alloy steel was reported. COPPER BRAZING OF PM COMPONENTS TO WROUGHT PARTS
B. Marzella et al, (Clarion Sintered Metals, Ridgeway, USA). The brazing of sintered and wrought steel sub-components was described. The P M steel was Cu infiltrated and it was reported the satisfactory joints were produced. Cost savings were claimed because of the reduction in finishing operations. The powder mixture, control of %C, sintered and green densities and assembly were discussed. JOINING OF IRON RASED PM COMPONENTS BY BRAZING AND DIFFUSION BONDING
B. Clausen and ICA. Thorsen, (Technical University of Denmark, Copenhagen, Denmark).
50 MPR November 1992
R.T. Fox et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). An outline of the objectives of PIM, the production components to c l o s e d i m e n s i o n a l t o l e r a n c e s with u n i f o r m microstructures and improved properties in a cost effective way was presented. The prerequisites for successful PIM, knowledge of the feedstock rheology and the effects of process parameters on the integrity of the part were discussed. Flow behaviour o f a r a n g e of f e e d s t o c k s was d e t e r m i n e d experimentally. Finite element methods were used to analyze the physical and mechanical properties. When applied to actual moulding trails causes of defects can be identified and avoided by proper control of m o u l d i n g p a r a m e t e r s and optimum moulding conditions established. NOVEL BINDER FOR RAPID DEBINDING OF POWDER INJECTION MOULDED SAMPLES
H.H. Andermann and A. van der Biest, (Leuven University, Belgium). The rapid removal of a novel binder from PIM compacts, without wicking or solvent was described. A cylindrical sample 13 mm x 10 ram, made from carbonyl Fe powder w a s d e b o u n d in 5 h o u r s w i t h o u t deformation, results for 316L stainless steel and alumina were also given. NOVEL PROCESS CONTROL METHODS FOR BINDERS BASED ON THERMOSET CONDENSATION RESINS G.M. Brasel and J.E. Duke, (Megamet Industries lnc, St. I~uis, USA).
In-moulding debinding, by the Megamet process, was described with regard to the process controls required. Green compacts were produced without the use of an i n j e c t i o n m o u l d i n g m a c h i n e . The importance of the relationship between the properties of the powder, binder and additives was emphasized. Control of green density was exercised through pressurization control and mould venting in a novel way. EFFECTS OF POWDER CHARACTERISTICS AND DEBINDING CONDITIONS ON DEFORMATION BEHAVIOUR OF INJECTION MOULDED COMPACTS DURING THERMAL DEBINDING
R. Miura and S. Takamori, (Japan Steel Works Ltd, Japan). The causes of distortion during debinding, the weight of the compact and viscous creep, were discussed. A n investigation of deformation in three-point bending of a beam was described. Effects of powder morphology and size distribution, bending moment, solid/binder ratio, heating rate, temperature and atmosphere were outlined. ATMOSPHERE PROCESS FOR THE CONTROL OF CARBON AND OXYGEN CONTENTS DURING DEBINDING OF INJECTION MOULDED STEEL
M.A. Phillips et al, (Liquid Air Corp, Countryside, Illinois, USA). The effects of binder decomposition during debinding in increasing the C content of alloys was discussed. This is partly offset by decarburization by reaction with O. The effect of gas composition of %C in Fe-2%Ni steels was evaluated. Precise C content could be attained by adjusting gas composition and debinding parameters. PROCESS PARAMETERS FOR A FAST CATALYTIC DEBINDING SYSTEM
D. Weinand and M. Blomacher, (BASF AG, Ludwigshafen, Germany). Catalytic debinding of injection moulded parts was discussed and was said to offer advantages over conventional debinding p r o c e s s e s . Th e p r o c e s s p a r a m e t e r s r e l e v a n t to e c o n o m i c a n a l y s i s w e r e investigated. Feedstock theology, thermal history, cycle time and green strength were considered. Continuous and discontinuous debinding were discussed. EVOLUTION OF GASES AND SINTERING BEHAVIOUR IN CARBONYL IRON POWDER FOR INJECTION MOULDING
S. Igarashi et al, Tokyo, Japan). It was noted contains volatile and O and that
(Sumitomo Metal Mining, that carbonyl Fe powder impurities including C, N little research had been
carried out on the effects of evolved gases on the sintering process~ An investigation, using gas chromatography of the evolved gases during sintering, was described. The relationship between the gases and the sintering behaviour was examined.
The importance of uniform powder/ binder distribution for quality of a PIM part was noted and the effects of process parameters on particle orientation and distribution and orientation in the PIM binder was described.
CHARACTERIZING POWDERS FOR METAL INJECTION MOULDING
FINITE DIFFERENCE MODEL F O R SIMULATION OF 3-DIMENSIONAL PIM
M. Tasovac, (Remington Arms Co, Hazen, USA). The p r o p e r t i e s of p o w d e r s a n d feedstock, relevant to MIM were discussed. Particle morphology, size distribution, density and residual element concentrations were included and methods for their determination were outlined. Powder characterization was discussed in relation to properties of MIM components.
C. Wang et al, (Metalworking Technolo~, Inc, USA). A numerical program for simulation of mould filling and heat transfer in PIM was described. The partial differential equations were solved for time dependent nonNewtonian flow and heat transfer by a finite difference method. Volume of liquid and imaginary particle methods were used to track advancement of the melt front. The technique was reported to be reliable and to be supported by experimental results.
DEFORMATION BEHAVIOUR OF MIM COMPACTS DURING SINTERING
H. Ohtsubo et ai, (Kawasaki Steel CorD, Kawasaki, Japan). The deformation, during sintering, of 316L stainless steel, m a d e from water atomized powder, was investigated by a three point bend test. Deformation was correlated with connectivity between particles. Sintering was in the range 900 to 1350°C and rapid deformation was reported at 1000°C. Particle surfaces were examined by electron microscopy and Auger spectroscopy. The reaction between C and D was considered to be responsible for the deformation by weakening the bond between particles. Finite element analysis was used to model the deformation and good agreement with experimental results was reported.
GRANULAR MODELLING OF STEEL POWDER FLOW AND COMPACTION IN MIM
T. Alzawa and J. Kihara, (University of Tokyo, Japan). The m o d e l l i n g of the m e c h a n i c a l behaviour of MIM green compacts was discussed with regard to the mechanical parameters employed and their application. A model was described in which the granular powders have local stiffness, the binder is represented by a pressure term and solution of m o m e n t u m equations provide d a t a c o n c e r n i n g m e c h a n i c a l behaviour.
STUDY OF PARTICLE ORIENTATION AND DlffrIHBUTION D U I I N G MELT FLOW IN INJECTION MOULDING
J.T. Lindt et al, (University of Pittsburg, USA).
LARGE SCALE PRODUCTION OF STAINLESS STEEL GEARS BY MIM H. Cohrt et al, (Schunk Sintermetalitechnik GmbH, Oberhausen, Germany). The production of small, 0.3 and 1 g gears in 316L stainless steel by MIM was described. MIM and stainless steel were chosen for corrosion resistance, part shape complexity, the need for mass production (30 000 per day) and the inability of other materials to withstand service conditions. Ready for assembly parts were reported to have been produced. All stages of the production were said to be subject to close quality control.
APPLICATION OF MIM TO HIGH PERFORMANCE PARTS
R. Schulten et al, (R. Zapp Werkstofltechnik GmbH, DQsseldorf, Germany). The use of MIM for the shaping of high performance parts in hard metals and high carbon and stainless steels was discussed with regard to costs compared with c o n v e n t i o n a l PM processes. Selected examples were reviewed and enhanced properties arising from the use of MIM reported.
FATIGUE PROPERTIES OF INJECTION MOULDED IRON-NICKEL AND 17-4PH ALLOYS
M.K. Bulger and A.R. Erickson, (FloMet Inc, USA). A study of the fatigue properties of Fe7%Ni and 17-4PH alloys was reported. S-N curves were produced by the use of reciprocating-bending tests. The fatigue properties were correlated with tensile properties, porosity and microstructure.
Oom~Ja~d~n mM I
HYDROffgATIC COMPACTION OF NANO-SIZED POWDERS M.Y. Tanakov et al, (Ultram International, USA). Deformation of nano-sized powders u n d e r low t e m p e r a t u r e h y d r o s t a t i c compaction was investigated. The observed low d e f o r m a b i l i t y was a t t r i b u t e d to irreversibility of plasticity and it was reported that the compaction pressures were higher t h a n for coarse powders. Finite element methods were used to calculate distribution of stresses and it was shown that sintering characteristics are modified by hydrostic compaction which also stimulates redistribution of impurity atoms.
M M $OVAL OF $ ~ C ACID FROM INJECTION MOULDED SPECIMEN$ OF STAINLESS STEEL
H.H. Angermann and O. van der Blest, (Leuven University, Belgium). Experimental studies of spherical 316L stainless steel powders with a stearic acid (SA)/polypropylene (PP)/polyethylene (PE) binder were described. It was found t h a t the debinding t e m p e r a t u r e s and kinetics of the SA differed from the PP and PE. The removal of SA was studied by thermogravimetric analysis under isothermal conditions. Diffusion of SA through the polymer to pore surfaces was said to be the controlling mechanism. Results were compared with those for SA/ PP and SA/PE binder mixtures.
PRODUCTION OF POWDERS FOR MIM BY I N E r r GAS ATOMIZATION
NJ.E. Adkins and G.P. Yiasenides, (BNFFulmer, Wantage, UK). The production of inert gas atomized powders for MIM was reviewed with regard to the qualities required in the powders and currently available commercial powders. Cleanliness and fineness of powders were considered. New developments in close coupled atomization of powders to meet the requirements of MIM were discussed. Particular reference was made to rare earth powders for magnetic applications and Ni aluminide for high temperature use.
M A T I I / . M A T I C ~ U , I ~ ] U S I O N FOE POWDER MIXTURE COMPEE881BHJTY P. Molera et al, (University of Barcelona, Spain). Compressibility of powders is defined as
MPR November 1992 51