The chemical composition variation of the TiAl-4722 alloys was examined in a batch of the industrial scale master ingots,and in the corresponding castings prepared by conventional vacuum arc remelting(VAR)combined wit...The chemical composition variation of the TiAl-4722 alloys was examined in a batch of the industrial scale master ingots,and in the corresponding castings prepared by conventional vacuum arc remelting(VAR)combined with induction skull melting(ISM)and investment casting processes.The content changes of major elements and interstitial elements were evaluated based on the chemical analysis at the top and bottom of the ingots and castings.Results show that the contents of C,N,H,Fe and Si have almost no change in the ingots and castings,suggesting that the chemical analysis on these elements can be based on the batch analysis.The O content keeps almost the same in different ingots,but exhibits relatively large differences in castings,which was probably influenced by the reaction between the shell mold and the molten alloy,and the spalling of face coat of the shell mold during casting.For the major elements of Al,Nb and Cr,the composition difference between the top and the bottom of the ingots is less than that of the castings.But for the O element,the trend is different,especially for the castings,suggesting that the investment casting is a homogenization process for Cr and Nb,but a differentiation process for O.The contents of major elements in castings fluctuate mainly in the same range as that in the ingots,indicating that the contents of the major elements are controllable during investment casting.展开更多
Positron lifetime spectra have been measured in binary Ni Al alloys with different chemical composition and NiAl alloys doped with Cr, Zr, Fe and Mg. The results indicate that in B2 NiAl and Ll 2 Ni 3Al alloys, some o...Positron lifetime spectra have been measured in binary Ni Al alloys with different chemical composition and NiAl alloys doped with Cr, Zr, Fe and Mg. The results indicate that in B2 NiAl and Ll 2 Ni 3Al alloys, some of the valance electrons of Ni and Al atoms are localized, which leads to a lower free electron density of the alloy. The mean free electron density of the binary Ni Al alloy decreases with increasing Al content. The open volume of defects on grain boundary of the Ni 3Al is larger than that of monovacancy or dislocation. Structural vacancies and microvoids are found in B2 NiAl alloys with Al content above 45%(mole fraction), and the concentration of the vacancies and open volume of microvoids will increase with higher Al content. The addition of Cr, Zr and Fe into a NiAl alloy can increase its mean free electron density and reduce the open volume of defects on its grain boundary, while with addition of Mg into the NiAl alloy, its mean free electron density decreases and open volume of boundary defects increases.展开更多
The influence of chemical composition on corrosion resistance of AZ91D magnesium alloys ingots has been investigated. Mass loss method was applied to evaluate the corrosion resistance of AZ91D alloys and the data were...The influence of chemical composition on corrosion resistance of AZ91D magnesium alloys ingots has been investigated. Mass loss method was applied to evaluate the corrosion resistance of AZ91D alloys and the data were analyzed by multiple regression. The results show that the corrosion resistance of this alloy can be improved by increasing Al, Zn and Mn in a certain degree, and will drop with increasing Si and heavy metals (Fe, Cu, Ni). It is found that ingots received from company F should be listed into unusable materials in terms of the corrosion resistance, while among the five suppliers, the only local company E supplied excellent AZ91D magnesium alloy ingots with the best corrosion resistance.展开更多
Multi-principal element solid solutions are prone to develop local chemical inhomogeneities,i.e.,chemi-cal order/clustering and/or compositional undulation.However,these structural details from short-range(first coupl...Multi-principal element solid solutions are prone to develop local chemical inhomogeneities,i.e.,chemi-cal order/clustering and/or compositional undulation.However,these structural details from short-range(first couple of nearest-neighbor atomic shells)to nanometer length scale are very challenging to re-solve in both experimental characterization and computer simulations.For instance,Monte Carlo model-ing based on density-functional-theory calculations is severely limited by the sample size and the sim-ulation steps practical in the simulations.Adopting the cluster expansion approach,here we systemati-cally reveal the local chemical inhomogeneity,including chemical order and compositional fluctuation,in three representative equiatomic TiZrNb-based body-centered cubic refractory high-entropy alloys(HEAs):TiZrNb,TiZrHfNb and TiZrHfNbTa.Ti-Zr pairs are found to exhibit the highest degree of chemical pref-erence among all atomic pairs.Such chemical short-range order(CSRO)induces an accompanying com-positional undulation,both extending to characteristic dimensions of the order of one nanometer.The chemical inhomogeneity trend uncovered for this series of TiZrNb-based HEAs is expected to impact their mechanical properties;e.g.,incorporating the CSRO effects in a current model significantly improves its agreement with experimental measured yield strength.展开更多
A Sb-Fe-carbon-fiber （CF） composite was prepared by a chemical vapor deposition （CVD） method with in situ growth of CFs us- ing Sb203/Fe2O3 as the precursor and acetylene （C2H2） as the carbon source. The Sb-Fe-C...A Sb-Fe-carbon-fiber （CF） composite was prepared by a chemical vapor deposition （CVD） method with in situ growth of CFs us- ing Sb203/Fe2O3 as the precursor and acetylene （C2H2） as the carbon source. The Sb-Fe-CF composite was characterized by X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM） and transmission electron microscopy （TEM）, and its electrochemical per- formance was investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The Sb-Fe-CF composite shows a better cycling stability than the Sb-amorphous-carbon composite prepared by the same CVD method but using Sb2O3 as the precur- sor. Improvements in cycling stability of the Sb-Fe-CF composite can be attributed to the formation of three-dimensional network structure by CFs, which can connect Sb particles firmly. In addition, the CF layer can buffer the volume change effectively.展开更多
基金the National Natural Science Foundation of China(Grant No.51671026)the State Key Lab of Advanced Metals and Materials,China(Grant No.2019-ZD05)。
文摘The chemical composition variation of the TiAl-4722 alloys was examined in a batch of the industrial scale master ingots,and in the corresponding castings prepared by conventional vacuum arc remelting(VAR)combined with induction skull melting(ISM)and investment casting processes.The content changes of major elements and interstitial elements were evaluated based on the chemical analysis at the top and bottom of the ingots and castings.Results show that the contents of C,N,H,Fe and Si have almost no change in the ingots and castings,suggesting that the chemical analysis on these elements can be based on the batch analysis.The O content keeps almost the same in different ingots,but exhibits relatively large differences in castings,which was probably influenced by the reaction between the shell mold and the molten alloy,and the spalling of face coat of the shell mold during casting.For the major elements of Al,Nb and Cr,the composition difference between the top and the bottom of the ingots is less than that of the castings.But for the O element,the trend is different,especially for the castings,suggesting that the investment casting is a homogenization process for Cr and Nb,but a differentiation process for O.The contents of major elements in castings fluctuate mainly in the same range as that in the ingots,indicating that the contents of the major elements are controllable during investment casting.
文摘Positron lifetime spectra have been measured in binary Ni Al alloys with different chemical composition and NiAl alloys doped with Cr, Zr, Fe and Mg. The results indicate that in B2 NiAl and Ll 2 Ni 3Al alloys, some of the valance electrons of Ni and Al atoms are localized, which leads to a lower free electron density of the alloy. The mean free electron density of the binary Ni Al alloy decreases with increasing Al content. The open volume of defects on grain boundary of the Ni 3Al is larger than that of monovacancy or dislocation. Structural vacancies and microvoids are found in B2 NiAl alloys with Al content above 45%(mole fraction), and the concentration of the vacancies and open volume of microvoids will increase with higher Al content. The addition of Cr, Zr and Fe into a NiAl alloy can increase its mean free electron density and reduce the open volume of defects on its grain boundary, while with addition of Mg into the NiAl alloy, its mean free electron density decreases and open volume of boundary defects increases.
文摘The influence of chemical composition on corrosion resistance of AZ91D magnesium alloys ingots has been investigated. Mass loss method was applied to evaluate the corrosion resistance of AZ91D alloys and the data were analyzed by multiple regression. The results show that the corrosion resistance of this alloy can be improved by increasing Al, Zn and Mn in a certain degree, and will drop with increasing Si and heavy metals (Fe, Cu, Ni). It is found that ingots received from company F should be listed into unusable materials in terms of the corrosion resistance, while among the five suppliers, the only local company E supplied excellent AZ91D magnesium alloy ingots with the best corrosion resistance.
基金J.D.and E.M.acknowledge XJTU for hosting their research at the Center for Alloy Innovation and Design(CAID).This work was funded by the Natural Science Foundation of China(No.12004294)National Youth Talents Program and the HPC platform of Xi’an Jiaotong University。
文摘Multi-principal element solid solutions are prone to develop local chemical inhomogeneities,i.e.,chemi-cal order/clustering and/or compositional undulation.However,these structural details from short-range(first couple of nearest-neighbor atomic shells)to nanometer length scale are very challenging to re-solve in both experimental characterization and computer simulations.For instance,Monte Carlo model-ing based on density-functional-theory calculations is severely limited by the sample size and the sim-ulation steps practical in the simulations.Adopting the cluster expansion approach,here we systemati-cally reveal the local chemical inhomogeneity,including chemical order and compositional fluctuation,in three representative equiatomic TiZrNb-based body-centered cubic refractory high-entropy alloys(HEAs):TiZrNb,TiZrHfNb and TiZrHfNbTa.Ti-Zr pairs are found to exhibit the highest degree of chemical pref-erence among all atomic pairs.Such chemical short-range order(CSRO)induces an accompanying com-positional undulation,both extending to characteristic dimensions of the order of one nanometer.The chemical inhomogeneity trend uncovered for this series of TiZrNb-based HEAs is expected to impact their mechanical properties;e.g.,incorporating the CSRO effects in a current model significantly improves its agreement with experimental measured yield strength.
基金supported by the Zijin Program of Zhejiang Universitythe Fundamental Research Funds for the Central Universities (No.2010QNA4003)+1 种基金the Ph.D. Program Foundation of the Ministry of Education of China (No.20100101120024)the Foundation of Education Office of Zhejiang Province, China (No.Y201016484)
文摘A Sb-Fe-carbon-fiber （CF） composite was prepared by a chemical vapor deposition （CVD） method with in situ growth of CFs us- ing Sb203/Fe2O3 as the precursor and acetylene （C2H2） as the carbon source. The Sb-Fe-CF composite was characterized by X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM） and transmission electron microscopy （TEM）, and its electrochemical per- formance was investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The Sb-Fe-CF composite shows a better cycling stability than the Sb-amorphous-carbon composite prepared by the same CVD method but using Sb2O3 as the precur- sor. Improvements in cycling stability of the Sb-Fe-CF composite can be attributed to the formation of three-dimensional network structure by CFs, which can connect Sb particles firmly. In addition, the CF layer can buffer the volume change effectively.
