The micro arc oxidation(MAO)coatings with different concentrations of Ca,P and Zn elements are successfully formed on the titanium substrate at the different applied voltages.After MAO treatment,the MAO coating exhibi...The micro arc oxidation(MAO)coatings with different concentrations of Ca,P and Zn elements are successfully formed on the titanium substrate at the different applied voltages.After MAO treatment,the MAO coating exhibits the porous surface structure and composed of anatase and rutile TiO2 phases.Meanwhile,the average size and density of micro-pores on the MAO coatings have been modified via the adjusting the applied voltages.In addition,the contents of the incorporated elements such as Zn,Ca and P elements in the MAO coatings have been optimized.The bonding strength test results reveal that the MAO coating shows higher bonding strength,which is up to 45±5 MPa.Compared to the pure Ti plate,the MAO coating formed at 350 and 400 V show good apatite-inducing ability.Meanwhile,the MAO coating containing Zn,Ca and P elements have better antibacterial ability for E.coli and S.aureus.Thus,the incorporation of Zn,Ca and P elements was an effective method to improve the antibacterial ability.Moreover,the concentrations of Zn,Ca and P elements could be adjusted with the changing of the applied voltages.As a result,the enhancement of the antibacterial ability on the MAO coating surfaces was depended on the comprehensive effect of the incorporated elements and the surface property of MAO coatings.展开更多
Additively manufactured(AM)metallic materials commonly possess substantial tensile surface residual stress,which is detrimental to the load-bearing service behavior.Recently,we demonstrated that deep cryogenic treatme...Additively manufactured(AM)metallic materials commonly possess substantial tensile surface residual stress,which is detrimental to the load-bearing service behavior.Recently,we demonstrated that deep cryogenic treatment(DCT)is an effective method for improving the tensile properties of CoCrFeMnNi high-entropy alloy(HEA)samples fabricated by laser melting deposition(LMD),by introducing high compressive residual stress and deformation microstructures without destroying the AM shape.However,carrying out the DCT in a single-step mode does not improve the residual stress gradients inherent from the LMD process,which are undesirable as the mechanical properties will not be homogeneous within the sample.In this work,we show that carrying out the DCT in a cyclic mode with repeated cryogenic cooling and reheating can significantly homogenize the residual stress in LMD-fabricated Co Cr Fe Mn Ni HEA,and improve tensile strength and ductility,compared with single-step DCT of the same cryogenic soaking duration.Under cyclic DCT,the thermal stress is re-elevated to a high value at each cryogenic cooling step,leading to the formation of denser and more intersecting reinforcing crystalline defects and hcp phase transformation,compared to single-step DCT of the same total cryogenic soaking duration in which the thermal stress relaxes towards a low value over time.The enhancement of defect formation in the cyclic mode of DCT also leads to more uniform residual stress distribution in the sample after the DCT.The results here provide important insights on optimizing DCT processes for post-fabrication improvement of mechanical properties of AM metallic net shapes.展开更多
基金This work was financially supported by Heilongjiang Provincial Youth Science Foundation(QC2013C043)National Basic Science Research Program(2012CB933900)the Fundamental Research Funds for the Central Universities(Grant no.HIT.NSRIF.2014002).
文摘The micro arc oxidation(MAO)coatings with different concentrations of Ca,P and Zn elements are successfully formed on the titanium substrate at the different applied voltages.After MAO treatment,the MAO coating exhibits the porous surface structure and composed of anatase and rutile TiO2 phases.Meanwhile,the average size and density of micro-pores on the MAO coatings have been modified via the adjusting the applied voltages.In addition,the contents of the incorporated elements such as Zn,Ca and P elements in the MAO coatings have been optimized.The bonding strength test results reveal that the MAO coating shows higher bonding strength,which is up to 45±5 MPa.Compared to the pure Ti plate,the MAO coating formed at 350 and 400 V show good apatite-inducing ability.Meanwhile,the MAO coating containing Zn,Ca and P elements have better antibacterial ability for E.coli and S.aureus.Thus,the incorporation of Zn,Ca and P elements was an effective method to improve the antibacterial ability.Moreover,the concentrations of Zn,Ca and P elements could be adjusted with the changing of the applied voltages.As a result,the enhancement of the antibacterial ability on the MAO coating surfaces was depended on the comprehensive effect of the incorporated elements and the surface property of MAO coatings.
基金the National Natural Science Foundation of China(Nos.52171154,and 51871076)the National Key Research and Development Programs of China(Nos.2018YFB1105200 and 2019YFA0209904)+1 种基金the Guangdong Province Basic and Applied Research Key Projects(Nos.2020190718102)the National Key R&D Programme,Ministry of Science and Technology of China(No.2019YFA0209)。
文摘Additively manufactured(AM)metallic materials commonly possess substantial tensile surface residual stress,which is detrimental to the load-bearing service behavior.Recently,we demonstrated that deep cryogenic treatment(DCT)is an effective method for improving the tensile properties of CoCrFeMnNi high-entropy alloy(HEA)samples fabricated by laser melting deposition(LMD),by introducing high compressive residual stress and deformation microstructures without destroying the AM shape.However,carrying out the DCT in a single-step mode does not improve the residual stress gradients inherent from the LMD process,which are undesirable as the mechanical properties will not be homogeneous within the sample.In this work,we show that carrying out the DCT in a cyclic mode with repeated cryogenic cooling and reheating can significantly homogenize the residual stress in LMD-fabricated Co Cr Fe Mn Ni HEA,and improve tensile strength and ductility,compared with single-step DCT of the same cryogenic soaking duration.Under cyclic DCT,the thermal stress is re-elevated to a high value at each cryogenic cooling step,leading to the formation of denser and more intersecting reinforcing crystalline defects and hcp phase transformation,compared to single-step DCT of the same total cryogenic soaking duration in which the thermal stress relaxes towards a low value over time.The enhancement of defect formation in the cyclic mode of DCT also leads to more uniform residual stress distribution in the sample after the DCT.The results here provide important insights on optimizing DCT processes for post-fabrication improvement of mechanical properties of AM metallic net shapes.
