Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance a...Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.展开更多
Selective laser melting(SLM)has the advantage in preparing supersaturated solid solutions due to its unique thermal field and high solidification rate.In this study,a face-centered cubic single-phase FeCrNi medium ent...Selective laser melting(SLM)has the advantage in preparing supersaturated solid solutions due to its unique thermal field and high solidification rate.In this study,a face-centered cubic single-phase FeCrNi medium entropy alloy(MEA)with an ultrahigh Cr content(~35 at.%)was additively manufactured by SLM.The as-built MEA shows a hierarchical microstructure of coarse columnar grains and submicron dislocation cell structures,where the cell boundaries are probed segregated with Cr and C and decorated with nano carbides.The appearance of these dislocation barriers results in an excellent combination of strength(σ_(0.2)=745 MPa,σ_(UTS)=1007 MPa)and ductility(ε_(f)=31%).The current MEA also shows a superb corrosion resistance with a corrosion current density of 0.06μA cm^(−2) in 3.5 wt.%NaCl solution,which is far lower than that of 316 L.The high content of solutioned Cr in the MEA ensures sufficient Cr supply to form an integrated Cr_(2)O_(3) passive film,and the large number of cell boundaries acting as the diffusion channels lead to the fast formation of a stable passive film over the alloy surface.展开更多
Laser surface melting（LSM） is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, an attempt of LSM on magnesium alloy with liquid...Laser surface melting（LSM） is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, an attempt of LSM on magnesium alloy with liquid nitrogen-assisted cooling（LNSC） was carried out to get the higher cooling rate and improve the surface properties. The experimental results were compared with those of Ar gas protection at room temperature. The samples after LSM with LNSC resulted in a thinner melted layer, a highly homogeneous, refined melted microstructure and formed a lot of worm-like nanocrystals and local amorphous structures. Microhardness of the melted layer with LNAC was improved to HV 90-148 as compared to HV 65-105 of the samples with Ar gas protection. The corrosion resistance of the melted layer in a 3.5% Na Cl solution（mass fraction） was improved because of the grain refinement and redistribution of β-Mg17Al12 phases following rapid quenching associated with the process.展开更多
Additively manufactured Ti-6Al-4V(TC4)parts have been successfully employed as artificial implants in dental and orthopedic surgery due to their excellent mechanical properties.However,the suboptimal corrosion resista...Additively manufactured Ti-6Al-4V(TC4)parts have been successfully employed as artificial implants in dental and orthopedic surgery due to their excellent mechanical properties.However,the suboptimal corrosion resistance limits their applications.The surface characterization and corrosion behavior of micro-arc oxidation(MAO)treated TC4 alloy prepared by selective electron beam melting(SEBM)and selective laser melting(SLM)technologies were compared.The corrosion resistance mechanism of SLM-MAO and SEBM-MAO was clarified through the analysis of the microstructure evolution,surface morphology,and electrochemical experiments.The results show that the anatase-type TiO_(2) is partially transformed into the slankite phase after MAO treatment.The surface roughness of SEBM sample was reduced by MAO coating,while the surface roughness of SLM sample increased after MAO,which is related to the difference between the microstructure of the deposited samples caused by different additive manufacturing technologies.When MAO time was 15 min,SLM-MAO and SEBM-MAO coating displayed the best and the worst corrosion resistance,respectively.展开更多
基金Foundation item： National Natural Science Foundation of China （50671081）
文摘Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.
基金supported by the National Natural Science Foundation of China(Nos.52020105013 and 51771232)the National Key Research and Development Plan of China(No.2016YFB0700302)
文摘Selective laser melting(SLM)has the advantage in preparing supersaturated solid solutions due to its unique thermal field and high solidification rate.In this study,a face-centered cubic single-phase FeCrNi medium entropy alloy(MEA)with an ultrahigh Cr content(~35 at.%)was additively manufactured by SLM.The as-built MEA shows a hierarchical microstructure of coarse columnar grains and submicron dislocation cell structures,where the cell boundaries are probed segregated with Cr and C and decorated with nano carbides.The appearance of these dislocation barriers results in an excellent combination of strength(σ_(0.2)=745 MPa,σ_(UTS)=1007 MPa)and ductility(ε_(f)=31%).The current MEA also shows a superb corrosion resistance with a corrosion current density of 0.06μA cm^(−2) in 3.5 wt.%NaCl solution,which is far lower than that of 316 L.The high content of solutioned Cr in the MEA ensures sufficient Cr supply to form an integrated Cr_(2)O_(3) passive film,and the large number of cell boundaries acting as the diffusion channels lead to the fast formation of a stable passive film over the alloy surface.
基金Project(51305292)supported by the National Natural Science Foundation of ChinaProject(2014-024)supported by Shanxi Scholarship Council of China
文摘Laser surface melting（LSM） is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, an attempt of LSM on magnesium alloy with liquid nitrogen-assisted cooling（LNSC） was carried out to get the higher cooling rate and improve the surface properties. The experimental results were compared with those of Ar gas protection at room temperature. The samples after LSM with LNSC resulted in a thinner melted layer, a highly homogeneous, refined melted microstructure and formed a lot of worm-like nanocrystals and local amorphous structures. Microhardness of the melted layer with LNAC was improved to HV 90-148 as compared to HV 65-105 of the samples with Ar gas protection. The corrosion resistance of the melted layer in a 3.5% Na Cl solution（mass fraction） was improved because of the grain refinement and redistribution of β-Mg17Al12 phases following rapid quenching associated with the process.
基金funded by the National Natural Science Foundation of China (Nos.51671152 and 51874225)the Industrialization Project of Shaanxi Education Department (18JCO19)+1 种基金the Key Research and Development Program of Shaanxi Province (2020ZDLGY13-10)the Science and Technology Plan Project of Xi'an (2020KJRC0048).
文摘Additively manufactured Ti-6Al-4V(TC4)parts have been successfully employed as artificial implants in dental and orthopedic surgery due to their excellent mechanical properties.However,the suboptimal corrosion resistance limits their applications.The surface characterization and corrosion behavior of micro-arc oxidation(MAO)treated TC4 alloy prepared by selective electron beam melting(SEBM)and selective laser melting(SLM)technologies were compared.The corrosion resistance mechanism of SLM-MAO and SEBM-MAO was clarified through the analysis of the microstructure evolution,surface morphology,and electrochemical experiments.The results show that the anatase-type TiO_(2) is partially transformed into the slankite phase after MAO treatment.The surface roughness of SEBM sample was reduced by MAO coating,while the surface roughness of SLM sample increased after MAO,which is related to the difference between the microstructure of the deposited samples caused by different additive manufacturing technologies.When MAO time was 15 min,SLM-MAO and SEBM-MAO coating displayed the best and the worst corrosion resistance,respectively.
