A novel binder system for hardmetal powder extrusion moulding (PEM) process has been developed. The binder system comprises a major fraction of a mixture of low molecular weight components (LMWCs) and a minor fraction...A novel binder system for hardmetal powder extrusion moulding (PEM) process has been developed. The binder system comprises a major fraction of a mixture of low molecular weight components (LMWCs) and a minor fraction of very finely dispersed polymer. The feedstocks are mixed as a thick slurry at a suitable temperature and are rapidly homogenized by stirring at an adequate shear force. The binders are removed by thermal debinding. The thermal debinding mechanism has been investigated by thermogravimetry (TG) and differential thermogravimetry (DTG). At the first stage of debinding, the LMWCs are removed. These open up pore channels which allows much faster removal of the remaining polymer component during the subsequent stage. The microstructures of the moulded green parts were observed by scanning electron microscopy (SEM). The debound samples were sintered at different temperatures, and the sintered samples properties were measured.展开更多
Hardmetals are tungsten carbide(WC)-based composites,which are made of WC as a hard phase and transition metals such as Co,Fe,or/and Ni as ductile binder matrices.Their properties can be mainly tailored through the gr...Hardmetals are tungsten carbide(WC)-based composites,which are made of WC as a hard phase and transition metals such as Co,Fe,or/and Ni as ductile binder matrices.Their properties can be mainly tailored through the grain sizes of the sintered carbides and the amount of metallic binder.As successful tool materials,hardmetals are widely applied in metal cutting,wear applications,chipless forming,stoneworking,wood,and plastic working.In 2017,about two-thirds of tungsten consumption(including recycled materials)were produced for hardmetals in the world.This paper briefly introduces the development of manufacturing technology on WC-Co hardmetals from three aspects:powder preparation,bulk densifica-tion,and performance characterization.Two special WC-Co hardmetals are also described:cobalt-enrichment zone(CEZ)hardmetals,and binderless hardmetals.Furthermore,the development prospects for manufacturing techniques of hardmetals are also presented in the end.展开更多
WC-8Co hardmetals with different proportions of prismatic WC grains and plate-like WC grains were directly produced through sintering the W-C-8Co ele- mental powder mixture which was fabricated by dielectric barrier d...WC-8Co hardmetals with different proportions of prismatic WC grains and plate-like WC grains were directly produced through sintering the W-C-8Co ele- mental powder mixture which was fabricated by dielectric barrier discharge plasma (DBDP)-assisted milling. The morphology of prepared WC-8Co hardmetals, geometry and the preferential orientation of plate-like WC were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The results demon- strate that the microstructure and mechanical properties of the sintered hardmetals are related to the morphology of W grain which is dependent on DBDP-milling time. The DBDP for 1 h (DBDP-1 h)-milled W-C-Co powder contains granular W particles that tend to form prismatic WC grains, while the DBDP for 3 h (DBDP-3 h)-milled powder contains lamellar W particles that generate plate-like WC grains. By adjusting the weight ratio of DBDP-1 h powder and DBDP-3 h powder in W-C-8Co mixture, the proportion of plate-like WC in the hardmetals can be controlled, and relatively high transverse rupture strength (TRS) is obtained as the proportion of plate-like WC grain in the hardmetals is about 35 % in present experimental condition.展开更多
Rare earth-doped WC-Co cemented carbides with low carbon-containing level were prepared by adding mischmetal (mainly containing lanthanum and cerium) in the form of cobalt pre-alloyed powder during ball-milling.After ...Rare earth-doped WC-Co cemented carbides with low carbon-containing level were prepared by adding mischmetal (mainly containing lanthanum and cerium) in the form of cobalt pre-alloyed powder during ball-milling.After sintering, the sinter skin (exterior) was observed and analyzed by scanning electron microscopy(SEM)and energy disperse X-ray spectroscopy(EDXS). The results show that during the sintering process lanthanum and cerium are separated and cerium predominantly migrates towards the surface forming precipitates containing oxygen.Thermodynamic analysis and polarization of cerium atom caused by the strong interaction between cerium atoms and high energy carbon atoms were used in explaining the observed phenomenon.展开更多
Using the microwave sintering technology, the effects of phosphorus (P) additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only ...Using the microwave sintering technology, the effects of phosphorus (P) additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only 0.3wt% P additions, full density WC-10Co cermets were obtained at temperature of 1250℃, which is 70 ℃ lower than that of the undoped counterparts. Lower sintering temperature can result in finer WC grain growth; therefore, the P-doped WC-10Co alloys exhibited higher hardness than the undoped ones. But at the same time, P doping could lead to sacrifice of fracture toughness ofWC-10Co cemented carbides.展开更多
基金This research was supported by the National Natural Science Foundation of China (grant No.5964120, No.69971007). The financial support is gratefully acknowledged.
文摘A novel binder system for hardmetal powder extrusion moulding (PEM) process has been developed. The binder system comprises a major fraction of a mixture of low molecular weight components (LMWCs) and a minor fraction of very finely dispersed polymer. The feedstocks are mixed as a thick slurry at a suitable temperature and are rapidly homogenized by stirring at an adequate shear force. The binders are removed by thermal debinding. The thermal debinding mechanism has been investigated by thermogravimetry (TG) and differential thermogravimetry (DTG). At the first stage of debinding, the LMWCs are removed. These open up pore channels which allows much faster removal of the remaining polymer component during the subsequent stage. The microstructures of the moulded green parts were observed by scanning electron microscopy (SEM). The debound samples were sintered at different temperatures, and the sintered samples properties were measured.
基金the Major Special Projects of Fujian Science and Technology Plan(Grant No.2017HZ0001-1)。
文摘Hardmetals are tungsten carbide(WC)-based composites,which are made of WC as a hard phase and transition metals such as Co,Fe,or/and Ni as ductile binder matrices.Their properties can be mainly tailored through the grain sizes of the sintered carbides and the amount of metallic binder.As successful tool materials,hardmetals are widely applied in metal cutting,wear applications,chipless forming,stoneworking,wood,and plastic working.In 2017,about two-thirds of tungsten consumption(including recycled materials)were produced for hardmetals in the world.This paper briefly introduces the development of manufacturing technology on WC-Co hardmetals from three aspects:powder preparation,bulk densifica-tion,and performance characterization.Two special WC-Co hardmetals are also described:cobalt-enrichment zone(CEZ)hardmetals,and binderless hardmetals.Furthermore,the development prospects for manufacturing techniques of hardmetals are also presented in the end.
基金financially supported by the Guangdong Provincial Natural Science Foundation(No. 2014A030310395)the Fundamental Research Funds for the Central Universities(No.2014ZB0020)
文摘WC-8Co hardmetals with different proportions of prismatic WC grains and plate-like WC grains were directly produced through sintering the W-C-8Co ele- mental powder mixture which was fabricated by dielectric barrier discharge plasma (DBDP)-assisted milling. The morphology of prepared WC-8Co hardmetals, geometry and the preferential orientation of plate-like WC were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The results demon- strate that the microstructure and mechanical properties of the sintered hardmetals are related to the morphology of W grain which is dependent on DBDP-milling time. The DBDP for 1 h (DBDP-1 h)-milled W-C-Co powder contains granular W particles that tend to form prismatic WC grains, while the DBDP for 3 h (DBDP-3 h)-milled powder contains lamellar W particles that generate plate-like WC grains. By adjusting the weight ratio of DBDP-1 h powder and DBDP-3 h powder in W-C-8Co mixture, the proportion of plate-like WC in the hardmetals can be controlled, and relatively high transverse rupture strength (TRS) is obtained as the proportion of plate-like WC grain in the hardmetals is about 35 % in present experimental condition.
基金Project (2004036428) supported by the Postdoctoral Science Foundation of China project supported by the Postdoctoral Science Foundation of Central South University+1 种基金 project (50323008) supported by the National Natural Science Foundation of China project (04JJ3084) supported the Natural Science Foundation of Hunan Province
文摘Rare earth-doped WC-Co cemented carbides with low carbon-containing level were prepared by adding mischmetal (mainly containing lanthanum and cerium) in the form of cobalt pre-alloyed powder during ball-milling.After sintering, the sinter skin (exterior) was observed and analyzed by scanning electron microscopy(SEM)and energy disperse X-ray spectroscopy(EDXS). The results show that during the sintering process lanthanum and cerium are separated and cerium predominantly migrates towards the surface forming precipitates containing oxygen.Thermodynamic analysis and polarization of cerium atom caused by the strong interaction between cerium atoms and high energy carbon atoms were used in explaining the observed phenomenon.
基金the National Key Technology R&D Program of MOST,China(2003BA328C)the National Natural Science Foundation of China(50472043)Natural Science Foundation of Hubei Province(2006ABA312,2006ABA316)
文摘Using the microwave sintering technology, the effects of phosphorus (P) additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only 0.3wt% P additions, full density WC-10Co cermets were obtained at temperature of 1250℃, which is 70 ℃ lower than that of the undoped counterparts. Lower sintering temperature can result in finer WC grain growth; therefore, the P-doped WC-10Co alloys exhibited higher hardness than the undoped ones. But at the same time, P doping could lead to sacrifice of fracture toughness ofWC-10Co cemented carbides.