To tackle the common issue of green defects in material extrusion(MEX)additive manufacturing(AM)cemented carbides,warm isostatic pressing(WIP)was introduced to eliminate defects of MEX WC-9Co cemented carbide greens,t...To tackle the common issue of green defects in material extrusion(MEX)additive manufacturing(AM)cemented carbides,warm isostatic pressing(WIP)was introduced to eliminate defects of MEX WC-9Co cemented carbide greens,thereby improving both microstructure uniformity and mechanical properties of sintered bodies.The results indicate that WIP reduces defects in MEX greens,thus decreasing the dimensions and numbers of defects,modifying shapes of pores within sintered bodies,while preserving surface quality and shape characteristics.Compared with WC-9Co prepared via MEX followed by debinding and sintering(DS),the hardness of WC-9Co prepared using MEX-WIP-DS does not change significantly,ranging HV_(30)1494-1508,the transverse rupture strength increases by up to 49.3%,reaching 2998-3514 MPa,and the fracture toughness remains high,ranging 14.8-17.0 MPa·m^(1/2).The mechanical properties surpass comparable cemented carbides fabricated through other AM methods and are comparable to those produced by powder metallurgy.The integration of green WIP into MEX-DS broadens the MEX processing window,and improves the overall mechanical properties of MEX AM WC-Co cemented carbides.展开更多
The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains ...The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains are refined into triangular prism with sound edges via the process of spheroidization,but WC grain size has no evident change compared with that of untreated alloys.The phase transformation of Co phase from α-Co（FCC） to ε-Co（HCP） is observed in the cryogenically treated alloys,which is attributed to the decrease of W solubility in the binder（Co）.Deep cryogenic treatment enhances the hardness and bending strength of the alloys,while it has no significant effects on the density and cobalt magnetic performance.展开更多
The characteristics of hot filament chemical vapor deposition（HFCVD） diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentratio...The characteristics of hot filament chemical vapor deposition（HFCVD） diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentration. Orthogonal experiments were introduced to study the comprehensive effects of such three parameters on diamond films deposited on WC-Co substrates. Field emission scanning electron microscopy, atomic force microscopy and Raman spectrum were employed to analyze the morphology, growth rate and composition of as-deposited diamond films. The morphology varies from pyramidal to cluster features with temperature decreasing. It is found that the low total pressure is suitable for nano-crystalline diamond films growth. Moreover, the substrate temperature and total pressure have combined influence on the growth rate of the diamond films.展开更多
Two types of fatigue tests, a rotating bending fatigue test and a three- or four-point bending fatigue test, were carried out on a fine grained WC-Co cemented carbide to evaluate its fatigue crack growth behavior and ...Two types of fatigue tests, a rotating bending fatigue test and a three- or four-point bending fatigue test, were carried out on a fine grained WC-Co cemented carbide to evaluate its fatigue crack growth behavior and fatigue lifetime. From successive observations of the specimen surface during the fatigue process, it was revealed that most of the fatigue lifetime of the tested WC-Co cemented carbide was occupied with crack growth cycles. Using the basic equation of fracture mechanics, the relationship between the fatigue crack growth rate(da/dN) and the maximum stress intensity factor(Kmax) was derived. From this relation, both the values of the threshold intensity factor(Kth) and the fatigue fracture toughness(Kfc) of the material were determined. The fatigue lifetime of the WC-Co cemented carbide was estimated by analysis based on the modified linear elastic fracture mechanics approach. Good agreement between the estimated and experimental fatigue lifetimes was confirmed.展开更多
WC-10%Co （mass fraction） nanocomposite was synthesized by high energy planetary ball milling at balls to powder mass ratio of 15. For inhibition of growth of WC grains during sintering, TaC and VC were used as inhib...WC-10%Co （mass fraction） nanocomposite was synthesized by high energy planetary ball milling at balls to powder mass ratio of 15. For inhibition of growth of WC grains during sintering, TaC and VC were used as inhibitors. Hardness and fracture toughness results reveal that the addition of TaC increases the toughness of hard metal and VC increases the hardness of the sample due to the effective reduction of WC grain size. The effect of co-addition of 0.6% TaC and 0.7% VC on physical and mechanical properties of WC-10%Co sintered sample was investigated. The hardness of the sample is increased to HV30 1 787, which is 24% more than that of the inhibitor-free sample; the fracture toughness achieves 8.7 MPa·m^1/2, 35% higer then that of the inhibitor-free sample; the grain growth is inhibited and grain size achieves 0.38μ m.展开更多
The production of deep well-shaped WC-Co cemented carbide blocks via industrial powder pressing remains a challenging technical problem,primarily due to the unsuitability of the forming agent.The forming agent paraffi...The production of deep well-shaped WC-Co cemented carbide blocks via industrial powder pressing remains a challenging technical problem,primarily due to the unsuitability of the forming agent.The forming agent paraffin wax was modified through four types of modifiers,including organic high-molecular-mass resins,plasticizers,surfactants and lubricants.The qualitative screening of resin types was explored and an orthogonal experiment involving the combination of these four paraffin wax modifiers was conducted to obtain an optimized quantitative ratio of modifiers.The results reveal that the insertion of the small molecule chain of resin into the interstitial spaces of paraffin wax crystals is likely a crucial factor for improving the compatibility between the resin and paraffin wax.Through orthogonal experiments,the optimized formulation for the forming agent is determined:100 parts of 58#paraffin wax,15 parts of EVA-2,4 parts of DPHP,4 parts of oleic acid amide and 2 parts of stearic acid.This optimized formulation is applied to industrial production at one Chinese company,and qualified deep well-shaped cemented carbide products are achieved,which contain 90wt%WC and 10wt%Co.展开更多
基金supported by the Key Project of Chinese Academy of Engineering(No.2019-XZ-11)the General Project of Chinese Academy of Engineering(No.2023-XY-18)+1 种基金the Open Fund of National Joint Engineering Research Center for Abrasion Control and Molding of Metal Materials of China(No.HKDNM201907)the Independent Project of State Key Laboratory of Powder Metallurgy,China。
文摘To tackle the common issue of green defects in material extrusion(MEX)additive manufacturing(AM)cemented carbides,warm isostatic pressing(WIP)was introduced to eliminate defects of MEX WC-9Co cemented carbide greens,thereby improving both microstructure uniformity and mechanical properties of sintered bodies.The results indicate that WIP reduces defects in MEX greens,thus decreasing the dimensions and numbers of defects,modifying shapes of pores within sintered bodies,while preserving surface quality and shape characteristics.Compared with WC-9Co prepared via MEX followed by debinding and sintering(DS),the hardness of WC-9Co prepared using MEX-WIP-DS does not change significantly,ranging HV_(30)1494-1508,the transverse rupture strength increases by up to 49.3%,reaching 2998-3514 MPa,and the fracture toughness remains high,ranging 14.8-17.0 MPa·m^(1/2).The mechanical properties surpass comparable cemented carbides fabricated through other AM methods and are comparable to those produced by powder metallurgy.The integration of green WIP into MEX-DS broadens the MEX processing window,and improves the overall mechanical properties of MEX AM WC-Co cemented carbides.
基金Project(12JJ8018)supported by the Natural Science Foundation of Hunan Province,China
文摘The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains are refined into triangular prism with sound edges via the process of spheroidization,but WC grain size has no evident change compared with that of untreated alloys.The phase transformation of Co phase from α-Co（FCC） to ε-Co（HCP） is observed in the cryogenically treated alloys,which is attributed to the decrease of W solubility in the binder（Co）.Deep cryogenic treatment enhances the hardness and bending strength of the alloys,while it has no significant effects on the density and cobalt magnetic performance.
基金Project(2012ZX04003-031)supported by the National Science and Technology Major Project,China
文摘The characteristics of hot filament chemical vapor deposition（HFCVD） diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentration. Orthogonal experiments were introduced to study the comprehensive effects of such three parameters on diamond films deposited on WC-Co substrates. Field emission scanning electron microscopy, atomic force microscopy and Raman spectrum were employed to analyze the morphology, growth rate and composition of as-deposited diamond films. The morphology varies from pyramidal to cluster features with temperature decreasing. It is found that the low total pressure is suitable for nano-crystalline diamond films growth. Moreover, the substrate temperature and total pressure have combined influence on the growth rate of the diamond films.
文摘Two types of fatigue tests, a rotating bending fatigue test and a three- or four-point bending fatigue test, were carried out on a fine grained WC-Co cemented carbide to evaluate its fatigue crack growth behavior and fatigue lifetime. From successive observations of the specimen surface during the fatigue process, it was revealed that most of the fatigue lifetime of the tested WC-Co cemented carbide was occupied with crack growth cycles. Using the basic equation of fracture mechanics, the relationship between the fatigue crack growth rate(da/dN) and the maximum stress intensity factor(Kmax) was derived. From this relation, both the values of the threshold intensity factor(Kth) and the fatigue fracture toughness(Kfc) of the material were determined. The fatigue lifetime of the WC-Co cemented carbide was estimated by analysis based on the modified linear elastic fracture mechanics approach. Good agreement between the estimated and experimental fatigue lifetimes was confirmed.
文摘WC-10%Co （mass fraction） nanocomposite was synthesized by high energy planetary ball milling at balls to powder mass ratio of 15. For inhibition of growth of WC grains during sintering, TaC and VC were used as inhibitors. Hardness and fracture toughness results reveal that the addition of TaC increases the toughness of hard metal and VC increases the hardness of the sample due to the effective reduction of WC grain size. The effect of co-addition of 0.6% TaC and 0.7% VC on physical and mechanical properties of WC-10%Co sintered sample was investigated. The hardness of the sample is increased to HV30 1 787, which is 24% more than that of the inhibitor-free sample; the fracture toughness achieves 8.7 MPa·m^1/2, 35% higer then that of the inhibitor-free sample; the grain growth is inhibited and grain size achieves 0.38μ m.
文摘The production of deep well-shaped WC-Co cemented carbide blocks via industrial powder pressing remains a challenging technical problem,primarily due to the unsuitability of the forming agent.The forming agent paraffin wax was modified through four types of modifiers,including organic high-molecular-mass resins,plasticizers,surfactants and lubricants.The qualitative screening of resin types was explored and an orthogonal experiment involving the combination of these four paraffin wax modifiers was conducted to obtain an optimized quantitative ratio of modifiers.The results reveal that the insertion of the small molecule chain of resin into the interstitial spaces of paraffin wax crystals is likely a crucial factor for improving the compatibility between the resin and paraffin wax.Through orthogonal experiments,the optimized formulation for the forming agent is determined:100 parts of 58#paraffin wax,15 parts of EVA-2,4 parts of DPHP,4 parts of oleic acid amide and 2 parts of stearic acid.This optimized formulation is applied to industrial production at one Chinese company,and qualified deep well-shaped cemented carbide products are achieved,which contain 90wt%WC and 10wt%Co.
