The Co-Cr-W ternary system was critically assessed using the CALPHAD technique.The solution phases including the liquid,γ-Co,ε-Co and α-Cr were described by a substitutional solution model.The σ,μ and R phases we...The Co-Cr-W ternary system was critically assessed using the CALPHAD technique.The solution phases including the liquid,γ-Co,ε-Co and α-Cr were described by a substitutional solution model.The σ,μ and R phases were described by three-sublattice models of（Co,W）8（Cr,W）4（Co,Cr,W）18,（Co,Cr,W）7W2（Co,Cr,W）4 and（Co,W）27（Cr,W）14（Co,Cr,W）12,respectively,in order to reproduce their homogeneity ranges.A self-consistent set of thermodynamic parameters for each phase was derived.The calculated isothermal sections at 1 000,1 200 and 1 350 ℃ are in good agreement with the experimental data.A eutectoid reaction of R μ＋γ-Co＋σ in this ternary system was predicted to occur at 1 022 ℃.展开更多
The nucleation,variant selection,and orientation dependence of the strain-induced martensitic transformation(SIMT)process in biomedical Co-Cr-W-Ni alloys were investigated.The experimental results show that theε-hexa...The nucleation,variant selection,and orientation dependence of the strain-induced martensitic transformation(SIMT)process in biomedical Co-Cr-W-Ni alloys were investigated.The experimental results show that theε-hexagonal-close-packed phase was preferentially formed at theΣ3 twin boundaries and high-angle grain boundaries during the tensile process.The theoretical analysis shows that the variant selection of SIMT is governed by Schmid’s law.However,the SIMTedε-phase did not form equally on the two sides of the annealing twins,even though they had the same Schmid factor.This phenomenon is related to the mechanical work developed by the formation of theε-phase.Only the side which has both high Schmid factor and high mechanical work can initiate the SIMT process.A strong<111>fiber texture was formed,and theε-variants tended to appear in grains with orientations close to the<111>and<100>directions during the tensile process.These results can provide theoretical guidance for controlling the SIMT process of Co-Cr-W-Ni alloys to fabricate more reliable stents.展开更多
Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process.In this work,a novel nano-oxides dispersion strengthened Co2...Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process.In this work,a novel nano-oxides dispersion strengthened Co28 Cr9 W1.5 Si(wt.%)alloy,fabricated by laser powder bed fusion(LPBF),was comprehensively investigated.During the layer-by-layer featured process,in-situ formation of Si rich,amorphous,nano-oxide inclusions was observed,whose formation is ascribed to the high affinity of Si to oxygen.Meanwhile,distinctive body-centered cubic(BCC)Co5 Cr3 Si2 nano-precipitates with an 8-fold symmetry were also confirmed to appear.The precipitates,rarely reported in previous studied Co-Cr alloys,were found to tightly bond with the in-situ oxidization.Furthermore,the morphologies,the size distributions as well as the microstructure of the interface between the matrix and the inclusions were investigated in detail and their influence on the tensile deformation was also clarified.The existence of transition boundaries between these inclusions and the matrix strongly blocked the movement of dislocations,thereby increasing the strength of the alloy.It was understood that when the plastic deformation proceeds,the fracture occurs in the vicinity of the oxide inclusions where dislocations accumulate.A quantitative analysis of the strengthening mechanism was also established,in which an additional important contribution to strength(~169 MPa)caused by the effects of in-situ formed oxide inclusions was calculated.展开更多
Co30Cr8W1.6C3Ni1.4Si coatings were fabricated on Ti6Al4V alloy using a laser thermal spraying(LTS).The surface and cross-section morphologies,phases and bonding strength of obtained coatings were investigated using sc...Co30Cr8W1.6C3Ni1.4Si coatings were fabricated on Ti6Al4V alloy using a laser thermal spraying(LTS).The surface and cross-section morphologies,phases and bonding strength of obtained coatings were investigated using scanning electronic microscopy(SEM),X-ray diffraction(XRD),and scratch test,respectively.The effects of laser power on the coefficients of friction(COFs)and corrosive-wear behaviors of Co30Cr8W1.6C3Ni1.4Si coatings were investigated using a wear tester in 3.5%NaCl solution,and the electrochemical corrosion performance was analyzed using an electrochemical workstation.The experimental results show that the Co30Cr8W1.6C3Ni1.4Si coating is bonded with the substrate in the metallurgical form,and the bonding strengths of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W are 76.5,56.5,and 55.6 N,respectively.The average COFs of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W are 0.769,0.893,and 0.941,respectively;and the corresponding wear rates are 0.267×105,0.3178×105,and 0.325×105μm3/Nm,respectively,which increases with the increase of laser power,the wear mechanism is primarily abrasive wear.The corrosion potential of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W is-0.05,-0.25,and-0.31 V,respectively,higher than-0.45 V of substrate which enhances the electrochemical corrosion resistance of substrate.展开更多
基金Project(50771027)supported by the National Basic Research Program of ChinaProject(50771027)supported by the National Natural Science Foundation of China
文摘The Co-Cr-W ternary system was critically assessed using the CALPHAD technique.The solution phases including the liquid,γ-Co,ε-Co and α-Cr were described by a substitutional solution model.The σ,μ and R phases were described by three-sublattice models of（Co,W）8（Cr,W）4（Co,Cr,W）18,（Co,Cr,W）7W2（Co,Cr,W）4 and（Co,W）27（Cr,W）14（Co,Cr,W）12,respectively,in order to reproduce their homogeneity ranges.A self-consistent set of thermodynamic parameters for each phase was derived.The calculated isothermal sections at 1 000,1 200 and 1 350 ℃ are in good agreement with the experimental data.A eutectoid reaction of R μ＋γ-Co＋σ in this ternary system was predicted to occur at 1 022 ℃.
基金financially supported by the National Key R&D Program of China(No.2017 YFA 0403804).
文摘The nucleation,variant selection,and orientation dependence of the strain-induced martensitic transformation(SIMT)process in biomedical Co-Cr-W-Ni alloys were investigated.The experimental results show that theε-hexagonal-close-packed phase was preferentially formed at theΣ3 twin boundaries and high-angle grain boundaries during the tensile process.The theoretical analysis shows that the variant selection of SIMT is governed by Schmid’s law.However,the SIMTedε-phase did not form equally on the two sides of the annealing twins,even though they had the same Schmid factor.This phenomenon is related to the mechanical work developed by the formation of theε-phase.Only the side which has both high Schmid factor and high mechanical work can initiate the SIMT process.A strong<111>fiber texture was formed,and theε-variants tended to appear in grains with orientations close to the<111>and<100>directions during the tensile process.These results can provide theoretical guidance for controlling the SIMT process of Co-Cr-W-Ni alloys to fabricate more reliable stents.
基金supported by Guangdong Academy of Science Fund(No.2020GDASYL-20200101001)Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030006)the National Natural Science Foundation of China(Nos.51871132 and 51701171)。
文摘Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process.In this work,a novel nano-oxides dispersion strengthened Co28 Cr9 W1.5 Si(wt.%)alloy,fabricated by laser powder bed fusion(LPBF),was comprehensively investigated.During the layer-by-layer featured process,in-situ formation of Si rich,amorphous,nano-oxide inclusions was observed,whose formation is ascribed to the high affinity of Si to oxygen.Meanwhile,distinctive body-centered cubic(BCC)Co5 Cr3 Si2 nano-precipitates with an 8-fold symmetry were also confirmed to appear.The precipitates,rarely reported in previous studied Co-Cr alloys,were found to tightly bond with the in-situ oxidization.Furthermore,the morphologies,the size distributions as well as the microstructure of the interface between the matrix and the inclusions were investigated in detail and their influence on the tensile deformation was also clarified.The existence of transition boundaries between these inclusions and the matrix strongly blocked the movement of dislocations,thereby increasing the strength of the alloy.It was understood that when the plastic deformation proceeds,the fracture occurs in the vicinity of the oxide inclusions where dislocations accumulate.A quantitative analysis of the strengthening mechanism was also established,in which an additional important contribution to strength(~169 MPa)caused by the effects of in-situ formed oxide inclusions was calculated.
基金Funded by the Key Research and Development Project of Jiangsu Province(BE2016052)。
文摘Co30Cr8W1.6C3Ni1.4Si coatings were fabricated on Ti6Al4V alloy using a laser thermal spraying(LTS).The surface and cross-section morphologies,phases and bonding strength of obtained coatings were investigated using scanning electronic microscopy(SEM),X-ray diffraction(XRD),and scratch test,respectively.The effects of laser power on the coefficients of friction(COFs)and corrosive-wear behaviors of Co30Cr8W1.6C3Ni1.4Si coatings were investigated using a wear tester in 3.5%NaCl solution,and the electrochemical corrosion performance was analyzed using an electrochemical workstation.The experimental results show that the Co30Cr8W1.6C3Ni1.4Si coating is bonded with the substrate in the metallurgical form,and the bonding strengths of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W are 76.5,56.5,and 55.6 N,respectively.The average COFs of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W are 0.769,0.893,and 0.941,respectively;and the corresponding wear rates are 0.267×105,0.3178×105,and 0.325×105μm3/Nm,respectively,which increases with the increase of laser power,the wear mechanism is primarily abrasive wear.The corrosion potential of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W is-0.05,-0.25,and-0.31 V,respectively,higher than-0.45 V of substrate which enhances the electrochemical corrosion resistance of substrate.
