Lubricant is harmful to the mechanical properties of the sintered materials. Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubrica...Lubricant is harmful to the mechanical properties of the sintered materials. Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant. Iron based samples were prepared by die wall lubricated warm compaction at 175 ℃, using a compacting pressure of 550 MPa. Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant. Admixed lubricant concentration ranging from 0 to 0.5% was tested. Extremely low admixed lubricant contents were used. Results show that in addition to the decrease in ejection forces, the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubricant content, then decreases with the decrease of admixed lubricant content. The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant. No scoring was observed in all die wall lubricated experiments.展开更多
Warm compaction behaviors and their affecting factors such as compaction temperature, compaction pressure and lubricant concentration were studied. Effect of die wall lubrication on the powder’s warm compaction behav...Warm compaction behaviors and their affecting factors such as compaction temperature, compaction pressure and lubricant concentration were studied. Effect of die wall lubrication on the powder’s warm compaction behavior was also studied. The use of smaller size colloidal graphite investigated can give a higher compact density and lesser spring back effect than the use of flake graphite.展开更多
Mechanical properties of the warm compacted alumina particulate reinforced powder metallurgy composite materials was compared with those of the materials obtained by conventional cold compaction. Factors affecting the...Mechanical properties of the warm compacted alumina particulate reinforced powder metallurgy composite materials was compared with those of the materials obtained by conventional cold compaction. Factors affecting the properties of the warm compacted material such as compaction temperature, lubricant content and alumina content were studied. A 3%(mass fraction) alumina particulate reinforced iron-base composite with a green density of 7.0 g/cm 3 can be obtained by pressing the powder with a pressure of 700 MPa at 175 ℃. The sintered materials have a density of 6.88 g/cm 3, a tensile strength of 512 MPa and an elongation of 1.3%. Results show that as alumina content increases, density and mechanical properties of the composite decrease.展开更多
In this paper, Ti（C,N）-based nano cermets were prepared by nano particles, and the effect of VC addition on the micmstructure and properties of Ti（C,N）-based nano cermets was investigated. The results showed that ...In this paper, Ti（C,N）-based nano cermets were prepared by nano particles, and the effect of VC addition on the micmstructure and properties of Ti（C,N）-based nano cermets was investigated. The results showed that there existed black-core grayish-rim strucmre as well as gray-core grayish-rim structure in VC-doped Ti（C,N）-based nano cermets. With the increase of VC addition, the number of gray cores in- creased, the lattice parameter of Ti（C,N） phase increased, the grain size decreased, the hardness and fracture toughness of Ti（C,N）-based nano cermets were enhanced, and nearly full densification could be achieved. However, excessive addition of VC to 1 wt% resulted in slight decrease in hardness and fracture toughness. Some deep dimples were found in the fracture surface of cermets with VC addition, which corresponded to ductile fracture.展开更多
Two cooling schemes （continuous cooling and interrupted cooling tests） were applied to investigate the cooling γ precipitation behavior in powder metallurgy superalloy FGH4096. The effect of cooling rate on cooling...Two cooling schemes （continuous cooling and interrupted cooling tests） were applied to investigate the cooling γ precipitation behavior in powder metallurgy superalloy FGH4096. The effect of cooling rate on cooling γ precipitation and the development of γ precipitates during cooling process were involved in this study. The ultimate tensile strength （ErrS） of the specimens in various cooling circumstances was tested. The experiential equations were obtained between the average sizes of secondary and tertiary γ precipitates, the strength, and cooling rate. The results show that they are inversely correlated with the cooling rate as well as the grain boundary changes from serrated to straight, the shape of secondary γ precipitates changes from irregular cuboidal to spherical, while the formed tertiary γ precipitates are always spherical. The interrupted cooling tests show that the average size of secondary γ precipitates increases as a linear function of interrupt temperature for a fixed cooling rate of 24℃/min. The strength first decreases and then increases against interrupt temperature, which is fundamentally caused by the multistage nucleation of γ precipitates during cooling process.展开更多
High Nb containing TiAl alloy was fabricated in argon atmosphere by reactive hot pressing process. Reaction mechanism was investigated by means of microstructural analyses and thermodynamic calculations. The results s...High Nb containing TiAl alloy was fabricated in argon atmosphere by reactive hot pressing process. Reaction mechanism was investigated by means of microstructural analyses and thermodynamic calculations. The results show that it is feasible to prepare high Nb containing TiAl alloy with fine lamellar colonies by reactive hot pressing process. The reaction between Ti and Al powders is dominant in Ti-Al-Nb system. Nb powders dissolve into the Ti-Al matrix by diffusion. Pore nests are formed in situ after Nb powders diffusion. The hot pressing atmosphere is optimized by thermodynamic calculations. Vacuum or argon protective atmosphere should be adopted.展开更多
The role of niobium in nickel-based superalloys is reviewed. The importance of niobium as a strengthener is discussed. New developments in nickel-based superalloys are also briefly mentioned, including some results th...The role of niobium in nickel-based superalloys is reviewed. The importance of niobium as a strengthener is discussed. New developments in nickel-based superalloys are also briefly mentioned, including some results that show improved resistance to sulfidation by niobium. Research results from a current program on the role of niobium in the Russian powder metallurgy alloy EP741NP are presented. Future research plans on the role of niobium in superalloys are also discussed.展开更多
Iron-based powder metallurgy material was prepared by warm compaction at 125 ℃ using a compacting pressure of 700 MPa. Sintering temperature ranging from 1 100 ℃ to 1 300 ℃ and sintering time ranging from 40 min to...Iron-based powder metallurgy material was prepared by warm compaction at 125 ℃ using a compacting pressure of 700 MPa. Sintering temperature ranging from 1 100 ℃ to 1 300 ℃ and sintering time ranging from 40 min to 80 min were used to study the effects of sintering parameters on the compacts. Die wall lubrication polytetrafluoroethylene(PTFE) emulsion was also applied in combination with warm compaction in hope to increase the compact density and the mechanical properties of the sintered material. Green and sintered density, spring back effect and sinter shrinkage were measured. Mechanical properties of both as-sinter and heat treated samples were also measured. Results show that mechanical properties of the sintered compacts increase with the increase of sintering temperature and sintering time. Sample prepared by die wall lubricated warm compaction always shows higher density and mechanical properties.展开更多
Nano-hydroxyapatite(nHA) and titanium(Ti) powders with different ratios were prepared by mechanical ball milling,and then sintered in vacuum environment. The microstructure and phase composition of Ti-based biocomposi...Nano-hydroxyapatite(nHA) and titanium(Ti) powders with different ratios were prepared by mechanical ball milling,and then sintered in vacuum environment. The microstructure and phase composition of Ti-based biocomposites with different contents of nHA(5% and 10%,in volume fraction) were investigated. Meanwhile,the phase composition of pure Ti was studied for contrast. The results show that Ti phase forms a finer continuous network microstructure with few porous after milling and sintering. The higher amount of nHA powders are added,the higher amount of porous are achieved,while the fracture morphology becomes coarser. The specimen with contents of 10% nHA has serious interface reaction after sintering at 1 100 ℃,it varies with the pure Ti specimen. Combined with the XRD and EDS analysis,it can be founded that elements Ca,P,O and Ti diffuse on the interface,and the phases of Ti,Ti2O,Ti5P3,CaTiO3 and TiOx can be ascertained in nHA/Ti composites.展开更多
The wear behavior of Ni-Cr-based alloys was investigated at ambient and elevated temperatures. The wear samples were prepared by metallurgical hot pressing. Wear tests were carried out on a general purpose wear testin...The wear behavior of Ni-Cr-based alloys was investigated at ambient and elevated temperatures. The wear samples were prepared by metallurgical hot pressing. Wear tests were carried out on a general purpose wear testing machine having a heating unit and pin-disc sample configuration. The counterface material was prepared from Al2O3 ceramics. The tests were carried out at room temperature(RT),200 ℃ and 600 ℃. The effects of temperatures on the tribological properties were determined by using optical microscopy,and X-ray diffractometry. The results show that at room temperature the worn surfaces of the alloys are characterized by mild scuffing and micro cracks,the action of nano-crystal structural wear debris on the worn surfaces is responsible for the reduction of friction. At 200 ℃,the friction coefficient is the highest. The worn surfaces of the alloys are adhesive and oxidative. At 600 ℃,the friction coefficient is reduced due to the effect of the oxides,tungstates and sulfides residue on the worn surface.展开更多
In the present investigation the possibility of using exfoliated graphite nanoplatelets (xGnP) as reinforcement in order to enhance the mechanical properties of Cu-based metal matrix composites is explored. Cu-based m...In the present investigation the possibility of using exfoliated graphite nanoplatelets (xGnP) as reinforcement in order to enhance the mechanical properties of Cu-based metal matrix composites is explored. Cu-based metal matrix composites reinforced with different amounts of xGnP were fabricated by powder metallurgy route. The microstructure, sliding wear behaviour and mechanical properties of the Cu-xGnP composites were investigated. xGnP has been synthesized from the graphite intercalation compounds (GIC) through rapid evaporation of the intercalant at an elevated temperature. The thermally exfoliated graphite was later sonicated for a period of 5 h in acetone in order to achieve further exfoliation. The xGnP synthesized was characterized using SEM, HRTEM, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The Cu and xGnP powder mixtures were consolidated under a load of 565 MPa followed by sintering at 850°C for 2 h in inert atmosphere. Cu-1, 2, 3 and 5 wt% xGnP composites were developed. Results of the wear test show that there is a significant improvement in the wear resistance of the composites up to addition of 2 wt% of xGnP. Hardness, tensile strength and strain at failure of the various Cu-xGnP composites also show improvement upto the addition of 2 wt% xGnP beyond which there is a decrease in these properties. The density of the composites decreases with the addition of higher wt% of xGnP although addition of higher wt% of xGnP leads to higher sinterability and densification of the composites, resulting in higher relative density values. The nature of fracture in the pure Cu as well as the various Cu-xGnP composites was found to be ductile. Nanoplatelets of graphite were found firmly embedded in the Cu matrix in case of Cu-xGnP composites containing low wt% of xGnP.展开更多
The densification behavior of a TiAl base alloy prepared by elemental powder metallurgy has been studied. It is found that a densification abnormality occurs at 1 400 ℃, i.e. the compact density decreases with the in...The densification behavior of a TiAl base alloy prepared by elemental powder metallurgy has been studied. It is found that a densification abnormality occurs at 1 400 ℃, i.e. the compact density decreases with the increase of hot pressing temperature. By microstructural observation, including optical microscopy and TEM, it has been concluded that the densification abnormality can be attributed to the different high temperature creep mechanisms induced by microstructure coarsening in the late period of densification.展开更多
The fracture behavior of the thermomechanical fatigue （TMF） of the powder metallurgical nickel based superalloy FGH96 was investigated under in-phase （IP） and out-of-phase （OP） loadings in the temperature range ...The fracture behavior of the thermomechanical fatigue （TMF） of the powder metallurgical nickel based superalloy FGH96 was investigated under in-phase （IP） and out-of-phase （OP） loadings in the temperature range from 550 ℃ to 720 ℃ and the mechanical strain amplitude range from 0.3% to 0.8%. The results show that the FGH96 TMF fracture character is intergranular for the IP samples and transgranular cleavage-like for the OP samples, at the same strain amplitude, the fatigue life is shorter for the IP than that for the OP samples that is related to crack propagation along grain boundary on the IP samples, the γ′ size is larger in the IP than that in the OP sample, which is related to the bulk diffusion processes accelerated by the tensile strain during the high temperature portion of the IP cycle. Dislocation pairs and stacking faults are main microstructures induced by IP TMF, and they are hindered by the grain boundary, which likely resulted in the crack propagation along the grain boundary in the IP samples.展开更多
文摘Lubricant is harmful to the mechanical properties of the sintered materials. Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant. Iron based samples were prepared by die wall lubricated warm compaction at 175 ℃, using a compacting pressure of 550 MPa. Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant. Admixed lubricant concentration ranging from 0 to 0.5% was tested. Extremely low admixed lubricant contents were used. Results show that in addition to the decrease in ejection forces, the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubricant content, then decreases with the decrease of admixed lubricant content. The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant. No scoring was observed in all die wall lubricated experiments.
文摘Warm compaction behaviors and their affecting factors such as compaction temperature, compaction pressure and lubricant concentration were studied. Effect of die wall lubrication on the powder’s warm compaction behavior was also studied. The use of smaller size colloidal graphite investigated can give a higher compact density and lesser spring back effect than the use of flake graphite.
文摘Mechanical properties of the warm compacted alumina particulate reinforced powder metallurgy composite materials was compared with those of the materials obtained by conventional cold compaction. Factors affecting the properties of the warm compacted material such as compaction temperature, lubricant content and alumina content were studied. A 3%(mass fraction) alumina particulate reinforced iron-base composite with a green density of 7.0 g/cm 3 can be obtained by pressing the powder with a pressure of 700 MPa at 175 ℃. The sintered materials have a density of 6.88 g/cm 3, a tensile strength of 512 MPa and an elongation of 1.3%. Results show that as alumina content increases, density and mechanical properties of the composite decrease.
基金financially supported by National Natural Science Foundation of China (No.50874076 and No.51074110)the Scientist Serving Enterprise Action Plan from Ministry of Science and Technology (No.2009GJF00030)
文摘In this paper, Ti（C,N）-based nano cermets were prepared by nano particles, and the effect of VC addition on the micmstructure and properties of Ti（C,N）-based nano cermets was investigated. The results showed that there existed black-core grayish-rim strucmre as well as gray-core grayish-rim structure in VC-doped Ti（C,N）-based nano cermets. With the increase of VC addition, the number of gray cores in- creased, the lattice parameter of Ti（C,N） phase increased, the grain size decreased, the hardness and fracture toughness of Ti（C,N）-based nano cermets were enhanced, and nearly full densification could be achieved. However, excessive addition of VC to 1 wt% resulted in slight decrease in hardness and fracture toughness. Some deep dimples were found in the fracture surface of cermets with VC addition, which corresponded to ductile fracture.
文摘Two cooling schemes （continuous cooling and interrupted cooling tests） were applied to investigate the cooling γ precipitation behavior in powder metallurgy superalloy FGH4096. The effect of cooling rate on cooling γ precipitation and the development of γ precipitates during cooling process were involved in this study. The ultimate tensile strength （ErrS） of the specimens in various cooling circumstances was tested. The experiential equations were obtained between the average sizes of secondary and tertiary γ precipitates, the strength, and cooling rate. The results show that they are inversely correlated with the cooling rate as well as the grain boundary changes from serrated to straight, the shape of secondary γ precipitates changes from irregular cuboidal to spherical, while the formed tertiary γ precipitates are always spherical. The interrupted cooling tests show that the average size of secondary γ precipitates increases as a linear function of interrupt temperature for a fixed cooling rate of 24℃/min. The strength first decreases and then increases against interrupt temperature, which is fundamentally caused by the multistage nucleation of γ precipitates during cooling process.
基金Project(704008) supported by the Key Grant Project of Chinese Ministry of Education Project(NCET-04-01017) supported by the Program for New Century Excellent Talents in University, China
文摘High Nb containing TiAl alloy was fabricated in argon atmosphere by reactive hot pressing process. Reaction mechanism was investigated by means of microstructural analyses and thermodynamic calculations. The results show that it is feasible to prepare high Nb containing TiAl alloy with fine lamellar colonies by reactive hot pressing process. The reaction between Ti and Al powders is dominant in Ti-Al-Nb system. Nb powders dissolve into the Ti-Al matrix by diffusion. Pore nests are formed in situ after Nb powders diffusion. The hot pressing atmosphere is optimized by thermodynamic calculations. Vacuum or argon protective atmosphere should be adopted.
文摘The role of niobium in nickel-based superalloys is reviewed. The importance of niobium as a strengthener is discussed. New developments in nickel-based superalloys are also briefly mentioned, including some results that show improved resistance to sulfidation by niobium. Research results from a current program on the role of niobium in the Russian powder metallurgy alloy EP741NP are presented. Future research plans on the role of niobium in superalloys are also discussed.
文摘Iron-based powder metallurgy material was prepared by warm compaction at 125 ℃ using a compacting pressure of 700 MPa. Sintering temperature ranging from 1 100 ℃ to 1 300 ℃ and sintering time ranging from 40 min to 80 min were used to study the effects of sintering parameters on the compacts. Die wall lubrication polytetrafluoroethylene(PTFE) emulsion was also applied in combination with warm compaction in hope to increase the compact density and the mechanical properties of the sintered material. Green and sintered density, spring back effect and sinter shrinkage were measured. Mechanical properties of both as-sinter and heat treated samples were also measured. Results show that mechanical properties of the sintered compacts increase with the increase of sintering temperature and sintering time. Sample prepared by die wall lubricated warm compaction always shows higher density and mechanical properties.
基金Project (2006B35801001) supported by the Science and Technology Key Project of Guangdong Province, China
文摘Nano-hydroxyapatite(nHA) and titanium(Ti) powders with different ratios were prepared by mechanical ball milling,and then sintered in vacuum environment. The microstructure and phase composition of Ti-based biocomposites with different contents of nHA(5% and 10%,in volume fraction) were investigated. Meanwhile,the phase composition of pure Ti was studied for contrast. The results show that Ti phase forms a finer continuous network microstructure with few porous after milling and sintering. The higher amount of nHA powders are added,the higher amount of porous are achieved,while the fracture morphology becomes coarser. The specimen with contents of 10% nHA has serious interface reaction after sintering at 1 100 ℃,it varies with the pure Ti specimen. Combined with the XRD and EDS analysis,it can be founded that elements Ca,P,O and Ti diffuse on the interface,and the phases of Ti,Ti2O,Ti5P3,CaTiO3 and TiOx can be ascertained in nHA/Ti composites.
基金Project(K1703060819) supported by the National Defence Basic Research of China
文摘The wear behavior of Ni-Cr-based alloys was investigated at ambient and elevated temperatures. The wear samples were prepared by metallurgical hot pressing. Wear tests were carried out on a general purpose wear testing machine having a heating unit and pin-disc sample configuration. The counterface material was prepared from Al2O3 ceramics. The tests were carried out at room temperature(RT),200 ℃ and 600 ℃. The effects of temperatures on the tribological properties were determined by using optical microscopy,and X-ray diffractometry. The results show that at room temperature the worn surfaces of the alloys are characterized by mild scuffing and micro cracks,the action of nano-crystal structural wear debris on the worn surfaces is responsible for the reduction of friction. At 200 ℃,the friction coefficient is the highest. The worn surfaces of the alloys are adhesive and oxidative. At 600 ℃,the friction coefficient is reduced due to the effect of the oxides,tungstates and sulfides residue on the worn surface.
文摘In the present investigation the possibility of using exfoliated graphite nanoplatelets (xGnP) as reinforcement in order to enhance the mechanical properties of Cu-based metal matrix composites is explored. Cu-based metal matrix composites reinforced with different amounts of xGnP were fabricated by powder metallurgy route. The microstructure, sliding wear behaviour and mechanical properties of the Cu-xGnP composites were investigated. xGnP has been synthesized from the graphite intercalation compounds (GIC) through rapid evaporation of the intercalant at an elevated temperature. The thermally exfoliated graphite was later sonicated for a period of 5 h in acetone in order to achieve further exfoliation. The xGnP synthesized was characterized using SEM, HRTEM, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The Cu and xGnP powder mixtures were consolidated under a load of 565 MPa followed by sintering at 850°C for 2 h in inert atmosphere. Cu-1, 2, 3 and 5 wt% xGnP composites were developed. Results of the wear test show that there is a significant improvement in the wear resistance of the composites up to addition of 2 wt% of xGnP. Hardness, tensile strength and strain at failure of the various Cu-xGnP composites also show improvement upto the addition of 2 wt% xGnP beyond which there is a decrease in these properties. The density of the composites decreases with the addition of higher wt% of xGnP although addition of higher wt% of xGnP leads to higher sinterability and densification of the composites, resulting in higher relative density values. The nature of fracture in the pure Cu as well as the various Cu-xGnP composites was found to be ductile. Nanoplatelets of graphite were found firmly embedded in the Cu matrix in case of Cu-xGnP composites containing low wt% of xGnP.
文摘The densification behavior of a TiAl base alloy prepared by elemental powder metallurgy has been studied. It is found that a densification abnormality occurs at 1 400 ℃, i.e. the compact density decreases with the increase of hot pressing temperature. By microstructural observation, including optical microscopy and TEM, it has been concluded that the densification abnormality can be attributed to the different high temperature creep mechanisms induced by microstructure coarsening in the late period of densification.
基金Item Sponsored by National Science and Technology Pillar Programin the 11th Five-Year Plan of China (2006225)
文摘The fracture behavior of the thermomechanical fatigue （TMF） of the powder metallurgical nickel based superalloy FGH96 was investigated under in-phase （IP） and out-of-phase （OP） loadings in the temperature range from 550 ℃ to 720 ℃ and the mechanical strain amplitude range from 0.3% to 0.8%. The results show that the FGH96 TMF fracture character is intergranular for the IP samples and transgranular cleavage-like for the OP samples, at the same strain amplitude, the fatigue life is shorter for the IP than that for the OP samples that is related to crack propagation along grain boundary on the IP samples, the γ′ size is larger in the IP than that in the OP sample, which is related to the bulk diffusion processes accelerated by the tensile strain during the high temperature portion of the IP cycle. Dislocation pairs and stacking faults are main microstructures induced by IP TMF, and they are hindered by the grain boundary, which likely resulted in the crack propagation along the grain boundary in the IP samples.
