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Numerical prediction of cracks in PM parts
abstracts could bc reduced by up to 70%. The alloy design aspect was to enhance microstructural homogeneity and toughness in finegrained materials. (;rain growth inhibitors, VC and Cr2C3, were used. Mechanical property variations were reduced.
High-performance PM materials Chemical behaviour of tungstenlanthanide composite materials K.Cadoret et al. (Thales Electron Devices, Thonon-les-Bains, France.) Crystallography and chemistry of W-lanthanide composite materials, for use as cathodes in powder grid tubes, was described. High-temperature X-ray diffraction and synchrotron radiation werc used to investigate phase formation and phase transitions in real time during heatmg and carburisation. Phase equilibria were deduced for WO~-La203. The W-lanthanide is shown to have improved stability and chemical homogeneity on cathode surfaces.
Mechanical properties of nickel aluminide made from mechanically alloyed or milled powders Y.D.Kim et al. (Hanyang University, Korea.) Samples of mechanically alloyed NiAI powder and milled Ni-A1 powder mixture were spark-plasma sintered. Densification behaviour and mechanical properties were determined. Densification characteristics were different for the two materials. Mechanically alloyed powder required 800"C to 900°C for densification to 98°/,, and the mixed milled powder started to densifv at 300°C and reached 99%. Structurcs of both were mamly NiA] with Ni~AI as a second phase. Fine grain size was found in the machanically alloyed samples. Mechanical properties were described.
Carburisation of molybdenumlanthanide materials W.Jinshu et al. (Beijing Polytechnic University, Beijing, China.) Carburisation of Mo-La20 ~ cathode materials was investigated by thermal analysis. The process was found be threestage. The first is controlled by chemical reaction, the second by chemical reaction and diffusion and the third bv diffusion alone. Activation energies and rate constants for the process were calculated.
36
February 2003
Preparation of nickel aluminide materials C.D.Vidu et al. (METAV S.A., Bucharest, Romania.) Synthesis of NiA1, five mixes, and Ni~AI, four mixes, from elemental powders was described. Various process parameters were investigated. The consolidated materials were characterised for microstructure and properties that were correlated with process conditions. It was suggested that these materials could replace Ni base alloys in aerospace high-temperature applications.
Shape distortion and dimensional precision in liquid-phase sintering of tungsten heavy alloys R.M.German et al. (Pennsylvania State University, USA.) Densification and shape distortion in liquid phasc sintered W-Ni-Cu alloys was investigated with regard to microstructural parameters. A pore forming agent, ethylene-bissteaaramide, was added, the amount added controlling the porosity and particle size the pore size. The tungsten content was varied and the Ni: Cu ratio was altered to change the dihedral angle. A distortion parameter was obtained by measurements. It was shown that distortion decreases with increase in solid volume, %W, and dihedral anglc. Initial porosity and pore size were found to have no effect on distortion. Suggestions were made for improvements to liquid-phase sintering.
General topics Methods for productionof nanostructured aluminium nitride ceramics P.Kisly et al. (Inst. for Superhard Materials, Kiev, Ukraine.) Sintering nf fine and coarse AIN powders, in tbe range 1000°C to 2000°C, was investigated. Topics discussed were; high rate of densification at small particle sizes and formation of AI oxy-nitride; mechanisms of grain growth recrystallisation at different stages of sintering; phase formation and formation of a polycrystaline microstructure during sintering after shock wave treatment. Formation of grains with high dislocation density was observed.
Preparation and properties of nano-dispersed carbonitrides of transition metals I.Zalite, J.Krastins. (Riga Technical University, Salaspils, Latvia.) It was reported that nano-dispersed carbonitridc powders, 50 to 200nm in size', of
one or more IV to VI transition metals, Ti, Nb, Cr etc, had been prepared by plasmachemical synthesis. Particles were shown to be single crystals with a high concentration of lattice defects. The powders had high chemical activity and sintered rapidly at low sintering temperatures. Examples were given.
Explosive compaction of nano-crystalline alumina powder P.Weimar, R.Pruemmer. (Karlsruhe University, Karlsruhe, Germany.) It was noted that nano-ceramics, grain sizes below 100nm, have special properties: high hardness, low friction and very small pores. This is difficult to retain during conventional processing. It was suggested that this problem could be solved by explosive compaction. Explosive compaction of nano-AI20.3 showed that near-full density could be attained. Electron microscopy showed that phase transitions occurred and sub-grain size diminished.
EURO PM 2001. The following Abstracts are of papers presented at the 2001 European Congress on Powder Metallurgy, which was held in Nice, France, in October 2001.
Compaction modelling Materials characterisation modelling and validation for a multilevel ferrous PM part P.Brewin et al. (EPMA, Shrewsbury, UK.) A case study of compaction of a complex multi-level 'H' shaped ferrous part was described. Yield and friction properties of the powder were characterised., compaction was simulated and parts were produced. Computed and experimental results were compared. Density distribution agreed within 0.3gm/cm -~ to 0.5gm/cm "3 and punch force levels agreed within 20%.
User-friendly aspects of compaction modelling R.Maassen et al. (GKN Sinter Metals Service GmbH, Radevormwald, Germany.) It was noted that pressing of complex parts can be difficult, faults include undesired density variations and cracks in green compacts. Development of process modelling allows simulation of die compaction including prediction of density variations
metal-powder.net
although sotne lact()rs havu t l o t beeu considered. Rcquirelnents \yore sho\'~n to be
Numerical prediction of cracks in PM parts
Die compaction was analysed with regard to dcnsit~ variation. A modified model, sensitive to density and eccentricity of plastic potential was proposed. A finite element version allows avoidance of refreshing of the" mesh. Pressing diagrams were examined and density distribution defined. The significance of shear strain rates for formation of cracks was noted.
l.C.Cante, I.Oliver. (Technical University of Catalonia, Barcelona, Spain.)
High-density processing
mcorporaiion of simuhmon techniques into the r:mtilw ol design and developinent a l ] d eLlsC t)f tlSl2 illpUt of data and integration with press set up and control.
t:apability of a mnncrical simulation proccdure to predict crack formation in PM p a r t s \va~ demonstrated. 1,1sc was made of a Pow(:om program and experimental results, The program incorporates finite element smmlati(m codes based on large plastic det;:wntation theory Reference parts were simuiatcd and parts produced with 'L' shapcd designs, to provoke cracking.
Modelling of spring-back in green compacts I.M.Prado et al. (Polytechnic University of Cataluna, Barcelona, Spain.) Elastic bchaviour of green dic' conlpactcd samples was investigated using uniaxial c()nlprcssion tests ()n p r i s l n a t i c specimens. Linh)admg and i-cloadmg cvcles rcvealed mm-lincaitx and anisotropy of elastic responses. A model describing mechanical b e h a v i o u r in terlns Of strain tensor was proposed. ~.\ strtlcttn'al tensor was used to accotnlt t:or [ r a n s \ e r s c a n i s o t r o p y during compaction. Parantctcrs for the model x~erc determined cxperimentall):
Advances in finite element modelling l.Oliver et al. (Technical University of Catalonia, Barcelona, Spain.) It was reported that a new, finite elcment bascd nlethodology had been developed fi~l" powder transfer, compaction and ejecti(m of a PM part. A l)owCont program, based on large plastic deformation, contact-friction algorithms xxith remeshing strategies to avoid distortion of finite element nlesh was used. A user-friendly con> putcr was used for data input and visualisation of results. Details of the continuum mechanics, development of the finite element model and practical applications were presented.
Numerical analysis and prediction of defects in die compaction M.Shtern, O.Mikhailov. (Inst. for Problems of Materials Science, Kiev, Ukraine.)
metal-powder.net
Green turning of warm compacted PM steels A.Benner, P.Beiss. (Aachen University of Technology,Aachen, Germany.) It was noted that there had been Little study of machining of green warm compacted PM parts. Two warm compacted stccls were machmcd in thc green state. Criteria for satisfactory machining were shown to be surface quality and edge integrity The object of the investigation was to optimise the cutting process by study of effects of process and tool parametcrs.
Laboratory processing of steels to high density A.S.Wronski et al. (University of Bradford, Bradford, UK.) Means to incrcasc smtercd density of PM steels were hwestigated. Compaction pressures were 600MPa to 800MPa. One strategy was warm compaction, sintering, slow co(fling through the ferrite transition range and cold repressing. The other was to add B to promote liquid phase smtering. Cold rcsizmg raised density to 7.6gm/cm 4. 0.1 to 0.4%B gave densities up to 7.Sgm/cm -3. More than 0.4%B rcsuhed in formation of brittle intergranular fihns. Mechanical properties were described.
Influence of microstructure on fracture toughness of cold work tool steels W.Liebfahrt et al. (BOhler Edelstah[ GmbH, Kapfenberg, Austria.) Structure and mechanical properties of cold work tool steels were discussed. Structures of hard carbide particles in a martensitic matrix confer hardness and wear resistance and should have adequate fracture toughness. Increase in carbide content increases hardness and wear resistance but reduces toughness. Plane strain fracture toughness was investigated with regard to carbide particle content, size and distribution using quantitative scanning electron microscopy. Sizes of crack tip plastic zones
were calculated and compared with carbide interparticle separation. Composition was less critical than carbide particle characteristics.
Effect of niobium on structure and properties of PM high-speed steels H.Chung et al. (Ajou University, Gyunggi, Korea.) It was noted that PM high-speed steels could be made with higher % N b than cast/wrought alloys. F.ffects of 0 to 5 w t % N b on structure and properties of PM high-speed steels were investigated. Highest Rockwell hardness attained was 66C at l%Nb. Bcnd strength decreased with increased %Nb. Hardness, wear resistancc and resistance to thermal softening at 600"C was greater than fi,r steels without Nb.
Impact resistance and properties of PM high-density stainless steel G.L.Garagnani, M.Rosso. (Polytecnico of Torino, Torino, Italy.) Porosity was shown to impose a limitation to good propertics in sintcred materials. Means of reducing porosity were identified. A novel method involving reactive sintering of stainless steel was presented. Studics to optintise processing to cause reactive sintermg were described. Pressing was at 500MPa or 7f)0MPa. Sintering was either, I hour at l I g0"(] in pure H, 1 hour in vacuum at 1250"C or 30 minutes at less than 1275<'(i in a pusher furnace in N - 5 0 % H . Samples with increased density and rcsistancc properties were obtained.
Isostatic pressing A high-pressure cell for isostatic pressing of ceramic powders C.S.Dumitru et al. (University of Craiova, Craiova, Romania.) Aspects of high pressures, experimental problems and industrial practice of isostatic pressing were reviewed. A high-pressure cell fnr isostatic pressing was described. Working method, performance and test results were presented. Solutions were given for industrial exploitation.
Rapid tooting and prototyplng Advances in materials for direct metal laser sintering F.Petzold et aL (Fraunhofer Inst., IFAM.,Bremen, Germany.)
February 2003 ~
37
High-performance PM materials Chemical behaviour of tungstenlanthanide composite materials K.Cadoret et al. (Thales Electron Devices, Thonon-les-Bains, France.) Crystallography and chemistry of W-lanthanide composite materials, for use as cathodes in powder grid tubes, was described. High-temperature X-ray diffraction and synchrotron radiation werc used to investigate phase formation and phase transitions in real time during heatmg and carburisation. Phase equilibria were deduced for WO~-La203. The W-lanthanide is shown to have improved stability and chemical homogeneity on cathode surfaces.
Mechanical properties of nickel aluminide made from mechanically alloyed or milled powders Y.D.Kim et al. (Hanyang University, Korea.) Samples of mechanically alloyed NiAI powder and milled Ni-A1 powder mixture were spark-plasma sintered. Densification behaviour and mechanical properties were determined. Densification characteristics were different for the two materials. Mechanically alloyed powder required 800"C to 900°C for densification to 98°/,, and the mixed milled powder started to densifv at 300°C and reached 99%. Structurcs of both were mamly NiA] with Ni~AI as a second phase. Fine grain size was found in the machanically alloyed samples. Mechanical properties were described.
Carburisation of molybdenumlanthanide materials W.Jinshu et al. (Beijing Polytechnic University, Beijing, China.) Carburisation of Mo-La20 ~ cathode materials was investigated by thermal analysis. The process was found be threestage. The first is controlled by chemical reaction, the second by chemical reaction and diffusion and the third bv diffusion alone. Activation energies and rate constants for the process were calculated.
36
February 2003
Preparation of nickel aluminide materials C.D.Vidu et al. (METAV S.A., Bucharest, Romania.) Synthesis of NiA1, five mixes, and Ni~AI, four mixes, from elemental powders was described. Various process parameters were investigated. The consolidated materials were characterised for microstructure and properties that were correlated with process conditions. It was suggested that these materials could replace Ni base alloys in aerospace high-temperature applications.
Shape distortion and dimensional precision in liquid-phase sintering of tungsten heavy alloys R.M.German et al. (Pennsylvania State University, USA.) Densification and shape distortion in liquid phasc sintered W-Ni-Cu alloys was investigated with regard to microstructural parameters. A pore forming agent, ethylene-bissteaaramide, was added, the amount added controlling the porosity and particle size the pore size. The tungsten content was varied and the Ni: Cu ratio was altered to change the dihedral angle. A distortion parameter was obtained by measurements. It was shown that distortion decreases with increase in solid volume, %W, and dihedral anglc. Initial porosity and pore size were found to have no effect on distortion. Suggestions were made for improvements to liquid-phase sintering.
General topics Methods for productionof nanostructured aluminium nitride ceramics P.Kisly et al. (Inst. for Superhard Materials, Kiev, Ukraine.) Sintering nf fine and coarse AIN powders, in tbe range 1000°C to 2000°C, was investigated. Topics discussed were; high rate of densification at small particle sizes and formation of AI oxy-nitride; mechanisms of grain growth recrystallisation at different stages of sintering; phase formation and formation of a polycrystaline microstructure during sintering after shock wave treatment. Formation of grains with high dislocation density was observed.
Preparation and properties of nano-dispersed carbonitrides of transition metals I.Zalite, J.Krastins. (Riga Technical University, Salaspils, Latvia.) It was reported that nano-dispersed carbonitridc powders, 50 to 200nm in size', of
one or more IV to VI transition metals, Ti, Nb, Cr etc, had been prepared by plasmachemical synthesis. Particles were shown to be single crystals with a high concentration of lattice defects. The powders had high chemical activity and sintered rapidly at low sintering temperatures. Examples were given.
Explosive compaction of nano-crystalline alumina powder P.Weimar, R.Pruemmer. (Karlsruhe University, Karlsruhe, Germany.) It was noted that nano-ceramics, grain sizes below 100nm, have special properties: high hardness, low friction and very small pores. This is difficult to retain during conventional processing. It was suggested that this problem could be solved by explosive compaction. Explosive compaction of nano-AI20.3 showed that near-full density could be attained. Electron microscopy showed that phase transitions occurred and sub-grain size diminished.
EURO PM 2001. The following Abstracts are of papers presented at the 2001 European Congress on Powder Metallurgy, which was held in Nice, France, in October 2001.
Compaction modelling Materials characterisation modelling and validation for a multilevel ferrous PM part P.Brewin et al. (EPMA, Shrewsbury, UK.) A case study of compaction of a complex multi-level 'H' shaped ferrous part was described. Yield and friction properties of the powder were characterised., compaction was simulated and parts were produced. Computed and experimental results were compared. Density distribution agreed within 0.3gm/cm -~ to 0.5gm/cm "3 and punch force levels agreed within 20%.
User-friendly aspects of compaction modelling R.Maassen et al. (GKN Sinter Metals Service GmbH, Radevormwald, Germany.) It was noted that pressing of complex parts can be difficult, faults include undesired density variations and cracks in green compacts. Development of process modelling allows simulation of die compaction including prediction of density variations
metal-powder.net
although sotne lact()rs havu t l o t beeu considered. Rcquirelnents \yore sho\'~n to be
Numerical prediction of cracks in PM parts
Die compaction was analysed with regard to dcnsit~ variation. A modified model, sensitive to density and eccentricity of plastic potential was proposed. A finite element version allows avoidance of refreshing of the" mesh. Pressing diagrams were examined and density distribution defined. The significance of shear strain rates for formation of cracks was noted.
l.C.Cante, I.Oliver. (Technical University of Catalonia, Barcelona, Spain.)
High-density processing
mcorporaiion of simuhmon techniques into the r:mtilw ol design and developinent a l ] d eLlsC t)f tlSl2 illpUt of data and integration with press set up and control.
t:apability of a mnncrical simulation proccdure to predict crack formation in PM p a r t s \va~ demonstrated. 1,1sc was made of a Pow(:om program and experimental results, The program incorporates finite element smmlati(m codes based on large plastic det;:wntation theory Reference parts were simuiatcd and parts produced with 'L' shapcd designs, to provoke cracking.
Modelling of spring-back in green compacts I.M.Prado et al. (Polytechnic University of Cataluna, Barcelona, Spain.) Elastic bchaviour of green dic' conlpactcd samples was investigated using uniaxial c()nlprcssion tests ()n p r i s l n a t i c specimens. Linh)admg and i-cloadmg cvcles rcvealed mm-lincaitx and anisotropy of elastic responses. A model describing mechanical b e h a v i o u r in terlns Of strain tensor was proposed. ~.\ strtlcttn'al tensor was used to accotnlt t:or [ r a n s \ e r s c a n i s o t r o p y during compaction. Parantctcrs for the model x~erc determined cxperimentall):
Advances in finite element modelling l.Oliver et al. (Technical University of Catalonia, Barcelona, Spain.) It was reported that a new, finite elcment bascd nlethodology had been developed fi~l" powder transfer, compaction and ejecti(m of a PM part. A l)owCont program, based on large plastic deformation, contact-friction algorithms xxith remeshing strategies to avoid distortion of finite element nlesh was used. A user-friendly con> putcr was used for data input and visualisation of results. Details of the continuum mechanics, development of the finite element model and practical applications were presented.
Numerical analysis and prediction of defects in die compaction M.Shtern, O.Mikhailov. (Inst. for Problems of Materials Science, Kiev, Ukraine.)
metal-powder.net
Green turning of warm compacted PM steels A.Benner, P.Beiss. (Aachen University of Technology,Aachen, Germany.) It was noted that there had been Little study of machining of green warm compacted PM parts. Two warm compacted stccls were machmcd in thc green state. Criteria for satisfactory machining were shown to be surface quality and edge integrity The object of the investigation was to optimise the cutting process by study of effects of process and tool parametcrs.
Laboratory processing of steels to high density A.S.Wronski et al. (University of Bradford, Bradford, UK.) Means to incrcasc smtercd density of PM steels were hwestigated. Compaction pressures were 600MPa to 800MPa. One strategy was warm compaction, sintering, slow co(fling through the ferrite transition range and cold repressing. The other was to add B to promote liquid phase smtering. Cold rcsizmg raised density to 7.6gm/cm 4. 0.1 to 0.4%B gave densities up to 7.Sgm/cm -3. More than 0.4%B rcsuhed in formation of brittle intergranular fihns. Mechanical properties were described.
Influence of microstructure on fracture toughness of cold work tool steels W.Liebfahrt et al. (BOhler Edelstah[ GmbH, Kapfenberg, Austria.) Structure and mechanical properties of cold work tool steels were discussed. Structures of hard carbide particles in a martensitic matrix confer hardness and wear resistance and should have adequate fracture toughness. Increase in carbide content increases hardness and wear resistance but reduces toughness. Plane strain fracture toughness was investigated with regard to carbide particle content, size and distribution using quantitative scanning electron microscopy. Sizes of crack tip plastic zones
were calculated and compared with carbide interparticle separation. Composition was less critical than carbide particle characteristics.
Effect of niobium on structure and properties of PM high-speed steels H.Chung et al. (Ajou University, Gyunggi, Korea.) It was noted that PM high-speed steels could be made with higher % N b than cast/wrought alloys. F.ffects of 0 to 5 w t % N b on structure and properties of PM high-speed steels were investigated. Highest Rockwell hardness attained was 66C at l%Nb. Bcnd strength decreased with increased %Nb. Hardness, wear resistancc and resistance to thermal softening at 600"C was greater than fi,r steels without Nb.
Impact resistance and properties of PM high-density stainless steel G.L.Garagnani, M.Rosso. (Polytecnico of Torino, Torino, Italy.) Porosity was shown to impose a limitation to good propertics in sintcred materials. Means of reducing porosity were identified. A novel method involving reactive sintering of stainless steel was presented. Studics to optintise processing to cause reactive sintermg were described. Pressing was at 500MPa or 7f)0MPa. Sintering was either, I hour at l I g0"(] in pure H, 1 hour in vacuum at 1250"C or 30 minutes at less than 1275<'(i in a pusher furnace in N - 5 0 % H . Samples with increased density and rcsistancc properties were obtained.
Isostatic pressing A high-pressure cell for isostatic pressing of ceramic powders C.S.Dumitru et al. (University of Craiova, Craiova, Romania.) Aspects of high pressures, experimental problems and industrial practice of isostatic pressing were reviewed. A high-pressure cell fnr isostatic pressing was described. Working method, performance and test results were presented. Solutions were given for industrial exploitation.
Rapid tooting and prototyplng Advances in materials for direct metal laser sintering F.Petzold et aL (Fraunhofer Inst., IFAM.,Bremen, Germany.)
February 2003 ~
37