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Modified linear packing density model of powder particles
improve uniformity of die filling. The technique uses gas to ‘lubricate’ the powder particles. It is shown that the system enables the user to control powder delivery and to improve dimensional control.
Shtefing Laser processing R.Irving. lnt. J. Pot&r
MetaU., Vol 36, No 4, 2000,
69-74.
Use of lasers in processing powder metals was reviewed. Topics considered include direct light fabrication, selective laser sintering, direct metal deposition and laser engineered net shaping. Applications are described.
Monitoring transient liquid phase sintering of copper-tin by thermal analysis B.Reybum.SCorbin. (Universiry of Waterloo, Waterloo, Can&a.) 57-68
lnt. J. Powder M&l.,
Vd 36, No 5, 2C00,
Sintering of Cu-Sn powderswas investigated by thermal analysis. It is shown that there is little interdiffusion in the solid state and that the transient liquid phase sintering is dominated not by the amount of liquid present but by the time the liquid is there. Fine Cu powder promotes rapid conversion of the Sn rich liquid to intermediate phases. Sintering is slow with coarse Cu powder and the liquid phase persists. Effects of fluxes are considered.
Rapid rate sintering of dispersed systems v.v.skor&holL
M&dl. M&d. PCJU&r Ceram.(LJknzine),Vd 38, No 7-8, 2OC0,350-357. Rapid rate sintering of metal powder, W, was investigated. It is shown that this results in high density and uniformly fine grained structures. Structural evolution was statistically analysed in terms of randomly packed particles with variations in density. A new mechanism for particle rotation, grain boundary controlled and leading to uniform densification, is propcsed. Nonisothermal and rapid heating sintering are discussed.
Fundamentals Wallcoefficient of friction
by
modelling of die pressing R.Lursson et d. (L&l Sweden.) Pou&MetaU.,
Technical University, Lukd, Vol43, No 2,2000,132-138.
Friction in die pressing is discussed. The importance of lubrication is emphasized and difficulty in measuring die wall friction is noted. Modelling and experiment estimated a coefficient of friction. Two approaches are used for assessment of friction, a finite element method and an analytical technique. Experimental data were deduced for single action cold pressing of a cylinder.
www.metal-powder-net
Modelling of grain growth when inhibited by dispersed particles B.N.Kim. (National Research Inst. for Metals,Ibmaki,
Japnn.)ActaMater.Vol49, No 3, 2001, 543-552. Grain growth in particle dispersed materials was investigated by modeling interactions between grain boundaries and particles using finite element methods. Factors considered include interparticle distances, velocity effects of grain bounndary migration and grain boundary curvature. A relationahip between critical gram size and volume fraction of dispersedparticles is given. Prediction and experiment are compared. A modified Zener model is presented.
Determination of contact parameters for simulation of ball mills B.K.Mishra, C.V.R.Murty. (Indian Inst.of Technology, Kanpur, India.) Pourdpr Technology, Vol 115, No 3,
2001, 290-297. Use of discrete element methods in simulation of ball milling is discussed with regard to the need for correct establishment of interaction rules and contact parameters. Experiments using an ultra-fast load cell are described and used in deriving a model. Non-linear contact behaviour was used to deduce parameters that limit numerical integration. This procedure is considered unsuitable for ball milling. A process of linearisation is used to change the non-linear model to an analogous linear one. The study is illustrated by simulation of a ball . mill 545mm in diameter.
Analysis of movement of particles under laser radiation pressure S.Koyanak, S.Endoh. (Inst. for Resources and Envknment, k&i, Japan.) Powder Technology, Vol 116, No I, 2001,13-22.
Movement of powder particles, including Ni and A1203, under the influence of a weakly focused laser beam, was investigated with reference to particle separation. A model for mm size particles is proposed. The model was evaluated by experimental measurements.There was qualitative agreement for Ni particles, which were near spherical but for Al203 results depended on particle shape that was irregular.
Control of segregation problems in powder metal processing R.A.Bamum et d. (jenike andJohanson, Inc., Westford,
USA.) PM ScienceandTechnology Briefs,Vol2, No 2, 2oo0, l&--13. Mechanisms and types of segregation, by constituents of a powder mixture or by particle size, are reviewed. Some solutions to problems of segregation in existing situations and for new production facilities are described.
Modified linear packing density model of powder particles
W.Haibing et d. (Central South Ubniversity of Technoba, Changsha, China.) PM khnofogj, Vol19,
No3, 2001, 140-143.InChinese. An examination of the linear packing model for metal powders is described. The model was modified to obtain an improved fit with experimental data. Other models of packing are reviewed.
Copper Production and characterisation of bronze powders for bearing applications A.Cores et d. (CENIM, Madrid,Spain.)Rev. Metal. Madrid, Vol36, No 6, 2000,452-458. In Spanish.
Development of alloyed Cu-6S%Sn-4%ZnI.S%Pb powdersfor manufacture of bearings is reported. The material was characterized to establish optimum sintering conditions for a bearing for a compressor shaft.
Iron and steel Factor analysis of PM phosphorus steel B.Bergquist. (L&d Technical University, L&a, Swed,en.) Powder Me&L, Vol43, No 2,2COO,143-148. It is noted that alloy design and choice of process parameters may lead to difficulty in selecting best parameter settings. Thii can be improved by use of multi-variant statistics. Data from 4 studies of Fe-C-P are evaluated for process conditions and material properties by use of principal factor analysis. The results show how different properties interact.
Fatigue crack propagation in some PM steels R.A.Philips et d. (University of Nottingham, Nottingham, UK .) Pow& Metail., Vol43, No 2,2COO,149-156. Fatigue crack growth was investigated in a range of PM steels with reference to density. Property and structure data was available. Paris exponents for steady state crack growth depended on density and were 8 to 18 for 90% density and 2.6 to 4 for full density. Fe-O.S%C failed by progressivefracture of sintering necks at 90% density. other steels, with smaller plastic zones, fail partly by fracture of necks and partly through particles. At full density failure is partly by true fracture and partly by cleavage
Corrosion modes in PM ferritic stainless steels M.C.Bman, B.A.Shaw.(Pennsyluanin State University, USA.) 1nt.J. PouderMetdI., Vo/36,No4,2ooO,57-68. Corrosion of PM ferritic stainless steels was investigated and comparison was made with wrought materials. Electrochemical tests showed that the PM alloys had the lower open current potentials, higher densities and lower passivity.These are attributed to crevice corrosion mechanisms in pores and precipitation of
MPR February 2002
39
Shtefing Laser processing R.Irving. lnt. J. Pot&r
MetaU., Vol 36, No 4, 2000,
69-74.
Use of lasers in processing powder metals was reviewed. Topics considered include direct light fabrication, selective laser sintering, direct metal deposition and laser engineered net shaping. Applications are described.
Monitoring transient liquid phase sintering of copper-tin by thermal analysis B.Reybum.SCorbin. (Universiry of Waterloo, Waterloo, Can&a.) 57-68
lnt. J. Powder M&l.,
Vd 36, No 5, 2C00,
Sintering of Cu-Sn powderswas investigated by thermal analysis. It is shown that there is little interdiffusion in the solid state and that the transient liquid phase sintering is dominated not by the amount of liquid present but by the time the liquid is there. Fine Cu powder promotes rapid conversion of the Sn rich liquid to intermediate phases. Sintering is slow with coarse Cu powder and the liquid phase persists. Effects of fluxes are considered.
Rapid rate sintering of dispersed systems v.v.skor&holL
M&dl. M&d. PCJU&r Ceram.(LJknzine),Vd 38, No 7-8, 2OC0,350-357. Rapid rate sintering of metal powder, W, was investigated. It is shown that this results in high density and uniformly fine grained structures. Structural evolution was statistically analysed in terms of randomly packed particles with variations in density. A new mechanism for particle rotation, grain boundary controlled and leading to uniform densification, is propcsed. Nonisothermal and rapid heating sintering are discussed.
Fundamentals Wallcoefficient of friction
by
modelling of die pressing R.Lursson et d. (L&l Sweden.) Pou&MetaU.,
Technical University, Lukd, Vol43, No 2,2000,132-138.
Friction in die pressing is discussed. The importance of lubrication is emphasized and difficulty in measuring die wall friction is noted. Modelling and experiment estimated a coefficient of friction. Two approaches are used for assessment of friction, a finite element method and an analytical technique. Experimental data were deduced for single action cold pressing of a cylinder.
www.metal-powder-net
Modelling of grain growth when inhibited by dispersed particles B.N.Kim. (National Research Inst. for Metals,Ibmaki,
Japnn.)ActaMater.Vol49, No 3, 2001, 543-552. Grain growth in particle dispersed materials was investigated by modeling interactions between grain boundaries and particles using finite element methods. Factors considered include interparticle distances, velocity effects of grain bounndary migration and grain boundary curvature. A relationahip between critical gram size and volume fraction of dispersedparticles is given. Prediction and experiment are compared. A modified Zener model is presented.
Determination of contact parameters for simulation of ball mills B.K.Mishra, C.V.R.Murty. (Indian Inst.of Technology, Kanpur, India.) Pourdpr Technology, Vol 115, No 3,
2001, 290-297. Use of discrete element methods in simulation of ball milling is discussed with regard to the need for correct establishment of interaction rules and contact parameters. Experiments using an ultra-fast load cell are described and used in deriving a model. Non-linear contact behaviour was used to deduce parameters that limit numerical integration. This procedure is considered unsuitable for ball milling. A process of linearisation is used to change the non-linear model to an analogous linear one. The study is illustrated by simulation of a ball . mill 545mm in diameter.
Analysis of movement of particles under laser radiation pressure S.Koyanak, S.Endoh. (Inst. for Resources and Envknment, k&i, Japan.) Powder Technology, Vol 116, No I, 2001,13-22.
Movement of powder particles, including Ni and A1203, under the influence of a weakly focused laser beam, was investigated with reference to particle separation. A model for mm size particles is proposed. The model was evaluated by experimental measurements.There was qualitative agreement for Ni particles, which were near spherical but for Al203 results depended on particle shape that was irregular.
Control of segregation problems in powder metal processing R.A.Bamum et d. (jenike andJohanson, Inc., Westford,
USA.) PM ScienceandTechnology Briefs,Vol2, No 2, 2oo0, l&--13. Mechanisms and types of segregation, by constituents of a powder mixture or by particle size, are reviewed. Some solutions to problems of segregation in existing situations and for new production facilities are described.
Modified linear packing density model of powder particles
W.Haibing et d. (Central South Ubniversity of Technoba, Changsha, China.) PM khnofogj, Vol19,
No3, 2001, 140-143.InChinese. An examination of the linear packing model for metal powders is described. The model was modified to obtain an improved fit with experimental data. Other models of packing are reviewed.
Copper Production and characterisation of bronze powders for bearing applications A.Cores et d. (CENIM, Madrid,Spain.)Rev. Metal. Madrid, Vol36, No 6, 2000,452-458. In Spanish.
Development of alloyed Cu-6S%Sn-4%ZnI.S%Pb powdersfor manufacture of bearings is reported. The material was characterized to establish optimum sintering conditions for a bearing for a compressor shaft.
Iron and steel Factor analysis of PM phosphorus steel B.Bergquist. (L&d Technical University, L&a, Swed,en.) Powder Me&L, Vol43, No 2,2COO,143-148. It is noted that alloy design and choice of process parameters may lead to difficulty in selecting best parameter settings. Thii can be improved by use of multi-variant statistics. Data from 4 studies of Fe-C-P are evaluated for process conditions and material properties by use of principal factor analysis. The results show how different properties interact.
Fatigue crack propagation in some PM steels R.A.Philips et d. (University of Nottingham, Nottingham, UK .) Pow& Metail., Vol43, No 2,2COO,149-156. Fatigue crack growth was investigated in a range of PM steels with reference to density. Property and structure data was available. Paris exponents for steady state crack growth depended on density and were 8 to 18 for 90% density and 2.6 to 4 for full density. Fe-O.S%C failed by progressivefracture of sintering necks at 90% density. other steels, with smaller plastic zones, fail partly by fracture of necks and partly through particles. At full density failure is partly by true fracture and partly by cleavage
Corrosion modes in PM ferritic stainless steels M.C.Bman, B.A.Shaw.(Pennsyluanin State University, USA.) 1nt.J. PouderMetdI., Vo/36,No4,2ooO,57-68. Corrosion of PM ferritic stainless steels was investigated and comparison was made with wrought materials. Electrochemical tests showed that the PM alloys had the lower open current potentials, higher densities and lower passivity.These are attributed to crevice corrosion mechanisms in pores and precipitation of
MPR February 2002
39