An analytical model is established to study the influence of lattice distortion and fraction of Hf on the yield strength of the BCC TiNbTaZrHfx multi-component high entropy alloys （HEAs）. Meanwhile, the mechanism of...An analytical model is established to study the influence of lattice distortion and fraction of Hf on the yield strength of the BCC TiNbTaZrHfx multi-component high entropy alloys （HEAs）. Meanwhile, the mechanism of solid solution strengthening caused by lattice distortion is also discussed in the HEA. The distorted unit cell is introduced to indicate the lattice distortion effects induced by the differences of the atomic size and shear modulus by doping other elements in Ti-based metal. The results show that the calculated values of the alloying yield strength considering the path of least resistance are obtained with regard to various grain sizes for the equiatomic TiNbTaZrHf HEA, which is well in line with the experimental results. Furthermore, it is predicted that the alloying yield strength is the largest value in the case of the same grain size for the Hf atomic fraction of 0.122. The meaningful modeling could provide a theoretical method to investigate the yield strength and alloying design of other BCC HEAs in the future.展开更多
The influence of pre-deformation and heat treatment on mechanicalproperties of as-extruded ZK60 alloy was investigated.The experimentalresults indicated that the solid solution,pre-cold rolling and artificialaging tre...The influence of pre-deformation and heat treatment on mechanicalproperties of as-extruded ZK60 alloy was investigated.The experimentalresults indicated that the solid solution,pre-cold rolling and artificialaging treatments remarkably improved the mechanicalstrength of alloys compared with the asextruded condition.Especially,pre-cold rolling in 5% reduction combined with artificialaging at 150 ℃ for 20 h was determined as the optimum heat treatment condition,which resulted in a yield strength of 333 MPa with an increment of 87 MPa and ultimate tensile strength of 373 MPa.High density of nanoscale precipitates in α-Mg matrix observed in this sample was beneficialto enhancing the strength.The as-extruded sample showed a typicalbrittle fracture while the solution treated sample exhibited ductile-fragile failure characterized by cleavage fractures,river patterns,and tear ridges.And the sample after pre-cold rolling combined with aging presented more equiaxialdimples with a great amount of cracked particles in them.The above-mentioned observations were analyzed in terms of microstructure and possible strengthening mechanism in the extruded ZK60 alloy.展开更多
Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory...Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory of solids and molecules (EET). Calculation shows that yttrium is on the fifth hybrid level and magnesium is on the third one in pure metal crystals. By comparing with aluminum in Mg-Al alloy, it is shown that the reason why the solution strengthening effect of yttrium is better than that of aluminum in Mg-Al alloy is the enhanced bond energy according to EET. And it is concluded from EET analysis that intermetallics Mg_(24)Y_5 can significantly improve the properties of magnesium alloys because yttrium atoms occupy the centers of the octahedron and Mg-Y bonds efficiently strengthen the alloy matrix.展开更多
To evaluate stress corrosion cracking（SCC） mechanism of low alloy ultra-high strength steel 30CrMnSiNi2 A in environment containing NaCl, SCC behavior of the steel in 3.5wt% NaCl solution is investigated by slow str...To evaluate stress corrosion cracking（SCC） mechanism of low alloy ultra-high strength steel 30CrMnSiNi2 A in environment containing NaCl, SCC behavior of the steel in 3.5wt% NaCl solution is investigated by slow strain rate technique（SSRT） with various strain rates and applied potentials, surface analysis technique, and electrochemical measurements. SCC susceptibility of the steel increases rapidly with strain rate decreasing from 1 · 10 5s 1to 5 · 10 7s 1, and becomes stable when strain rate is lower than 5 · 10 7s 1. SCC propagation of the steel in the solution at open circuit potential（OCP） needs sufficient hydrogen which is supplied at a certain strain rate.Fracture surface at OCP has similar characteristics with that at cathodic polarization 1000 mVSCE, which presents characteristic fractography of hydrogen induced cracking（HIC）.All of these indicate that SCC behavior of the steel in the solution at OCP is mainly controlled by HIC rather than anodic dissolution（AD）.展开更多
基金support from the National Natural Science Foundation of China (No. 11372103 and 11572118)the Hunan Provincial Science Fund for Distinguished Young Scholars (No. 2015JJ1006)+1 种基金the Fok Ying-Tong Education Foundation, China (No. 141005)the project of Innovation-driven Plan of Central South University, the State Key Laboratory of Powder Metallurgy
文摘An analytical model is established to study the influence of lattice distortion and fraction of Hf on the yield strength of the BCC TiNbTaZrHfx multi-component high entropy alloys （HEAs）. Meanwhile, the mechanism of solid solution strengthening caused by lattice distortion is also discussed in the HEA. The distorted unit cell is introduced to indicate the lattice distortion effects induced by the differences of the atomic size and shear modulus by doping other elements in Ti-based metal. The results show that the calculated values of the alloying yield strength considering the path of least resistance are obtained with regard to various grain sizes for the equiatomic TiNbTaZrHf HEA, which is well in line with the experimental results. Furthermore, it is predicted that the alloying yield strength is the largest value in the case of the same grain size for the Hf atomic fraction of 0.122. The meaningful modeling could provide a theoretical method to investigate the yield strength and alloying design of other BCC HEAs in the future.
基金Funded by the National Natural Science Foundation of China(No.51571043)the International Science&Technology Cooperation Program of China(No.2014DFG52810)the Fundamental Research Funds for the Central Universities(No.106112015CDJZR135515)
文摘The influence of pre-deformation and heat treatment on mechanicalproperties of as-extruded ZK60 alloy was investigated.The experimentalresults indicated that the solid solution,pre-cold rolling and artificialaging treatments remarkably improved the mechanicalstrength of alloys compared with the asextruded condition.Especially,pre-cold rolling in 5% reduction combined with artificialaging at 150 ℃ for 20 h was determined as the optimum heat treatment condition,which resulted in a yield strength of 333 MPa with an increment of 87 MPa and ultimate tensile strength of 373 MPa.High density of nanoscale precipitates in α-Mg matrix observed in this sample was beneficialto enhancing the strength.The as-extruded sample showed a typicalbrittle fracture while the solution treated sample exhibited ductile-fragile failure characterized by cleavage fractures,river patterns,and tear ridges.And the sample after pre-cold rolling combined with aging presented more equiaxialdimples with a great amount of cracked particles in them.The above-mentioned observations were analyzed in terms of microstructure and possible strengthening mechanism in the extruded ZK60 alloy.
文摘Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory of solids and molecules (EET). Calculation shows that yttrium is on the fifth hybrid level and magnesium is on the third one in pure metal crystals. By comparing with aluminum in Mg-Al alloy, it is shown that the reason why the solution strengthening effect of yttrium is better than that of aluminum in Mg-Al alloy is the enhanced bond energy according to EET. And it is concluded from EET analysis that intermetallics Mg_(24)Y_5 can significantly improve the properties of magnesium alloys because yttrium atoms occupy the centers of the octahedron and Mg-Y bonds efficiently strengthen the alloy matrix.
基金financial support from the National Natural Science Foundation of China (No. 51171011)
文摘To evaluate stress corrosion cracking（SCC） mechanism of low alloy ultra-high strength steel 30CrMnSiNi2 A in environment containing NaCl, SCC behavior of the steel in 3.5wt% NaCl solution is investigated by slow strain rate technique（SSRT） with various strain rates and applied potentials, surface analysis technique, and electrochemical measurements. SCC susceptibility of the steel increases rapidly with strain rate decreasing from 1 · 10 5s 1to 5 · 10 7s 1, and becomes stable when strain rate is lower than 5 · 10 7s 1. SCC propagation of the steel in the solution at open circuit potential（OCP） needs sufficient hydrogen which is supplied at a certain strain rate.Fracture surface at OCP has similar characteristics with that at cathodic polarization 1000 mVSCE, which presents characteristic fractography of hydrogen induced cracking（HIC）.All of these indicate that SCC behavior of the steel in the solution at OCP is mainly controlled by HIC rather than anodic dissolution（AD）.
