Y_2O_3 dispersion strengthened iron-based powders and oxide dispersion strengthened(ODS) alloys were prepared by hydrothermal synthesis and spark plasma sintering(SPS),respectively.The effects of Y_2O_3,vibratory mill...Y_2O_3 dispersion strengthened iron-based powders and oxide dispersion strengthened(ODS) alloys were prepared by hydrothermal synthesis and spark plasma sintering(SPS),respectively.The effects of Y_2O_3,vibratory milling treatment,and Ti element on the microstructure and mechanical properties of the materials were investigated by scanning electron microscope(SEM) and micro-electronic universal tester.The results show that the best mechanical properties are obtained with 1 wt.% Y_2O_3 addition.The size of agglomerated particles can be decreased to a certain degree by vibratory milling treatment.With the addition of Ti element,the tensile strength and hardness of the samples were improved.展开更多
Considerable progress has been achieved in friction stir welding （FSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development ...Considerable progress has been achieved in friction stir welding （FSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, FSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. Compared to traditional fusion welding, FSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, FSW has the capability of fabricating steel joints with excellent toughness and strength. For example, unfavorable phase transformations that usu- ally occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during FSW of thick steels, optimization of microstructure and properties can be attained by controlling the heat input and post-weld cooling rate.展开更多
Pure Fe, Cr, AI, Ti elemental powders and prealloyed Y203 powder were processed by high energy mechanical milling. The compositions of the mixed powders are designed as Fe-18Cr-0.2Ti-0.35Y2O3 and Fe-18Cr-5Al-0.2Ti-0.3...Pure Fe, Cr, AI, Ti elemental powders and prealloyed Y203 powder were processed by high energy mechanical milling. The compositions of the mixed powders are designed as Fe-18Cr-0.2Ti-0.35Y2O3 and Fe-18Cr-5Al-0.2Ti-0.35Y2O3 in weight percent. The asmilled powders were consolidated by hot extrusion at 1423 K. The dispersed oxide particles were identified to be titania ＋ yttria for Al-free oxide dispersion strengthened （ODS） steel and alumina ＋ yttria for Al-added ODS steel, respectively. The ultimate tensile strength of Al-free ODS steel was higher than that of Al-added ODS steel over the temperature range of 298-973 K, because of the difference in number density and size of thermally stable oxide particles dispersed in both steel matrices. The strength in the longitudinal direction was lower than that in the transverse direction, probably due to anisotropy of the microstructure with elongated grains in the hot-extrusion direction for the 18%Cr-ODS steels with and without 5% Al.展开更多
A new Ni+Zr co-alloyed FeCrAl-ODS(oxide-dispersion-strengthened)ferritic alloy was fabricated by ball-milling and hot-isostatic-pressing.Using electron microscopy and atom probe tomography,the dispersive formation of ...A new Ni+Zr co-alloyed FeCrAl-ODS(oxide-dispersion-strengthened)ferritic alloy was fabricated by ball-milling and hot-isostatic-pressing.Using electron microscopy and atom probe tomography,the dispersive formation of high density core-shelled nano-particles of various sizes was confirmed with a common B2-NiAl shell.Among which,median-sized nano-particles(20-50 nm)typically have an Y_(4)Al_(2)O_(9)nano-core of<~20 nm,ultra-fine nano-particles(<~20)nm have an Y_(4)Zr_(3)O_(12)nano-core of<~10 nm,and larger-sized nano-particles(50-100 nm)incorporate an ultra-fine Y_(4)Al_(2)O_(9)nano-core and a few ultra-fine Y_(4)Zr_(3)O_(12)nano-oxides.All these nano-phases were highly coherent with the ferritic matrix.No large Y--Al-O nano-oxides were formed.The total number density of ultra-fine nano-particles was estimated as~2×10^(23)m^(-3)with a mean size of 6.3 nm only,and accordingly,the new alloy achieved an excellent combination of strength and ductility at high temperatures.展开更多
基金supported by the Major State Basic Research Development Program of China (973 Program) (No. 2008cb7178020)the State Key Laboratory for Advanced Metals and Materials of the University of Science and Technology Beijing
文摘Y_2O_3 dispersion strengthened iron-based powders and oxide dispersion strengthened(ODS) alloys were prepared by hydrothermal synthesis and spark plasma sintering(SPS),respectively.The effects of Y_2O_3,vibratory milling treatment,and Ti element on the microstructure and mechanical properties of the materials were investigated by scanning electron microscope(SEM) and micro-electronic universal tester.The results show that the best mechanical properties are obtained with 1 wt.% Y_2O_3 addition.The size of agglomerated particles can be decreased to a certain degree by vibratory milling treatment.With the addition of Ti element,the tensile strength and hardness of the samples were improved.
文摘Considerable progress has been achieved in friction stir welding （FSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, FSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. Compared to traditional fusion welding, FSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, FSW has the capability of fabricating steel joints with excellent toughness and strength. For example, unfavorable phase transformations that usu- ally occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during FSW of thick steels, optimization of microstructure and properties can be attained by controlling the heat input and post-weld cooling rate.
文摘Pure Fe, Cr, AI, Ti elemental powders and prealloyed Y203 powder were processed by high energy mechanical milling. The compositions of the mixed powders are designed as Fe-18Cr-0.2Ti-0.35Y2O3 and Fe-18Cr-5Al-0.2Ti-0.35Y2O3 in weight percent. The asmilled powders were consolidated by hot extrusion at 1423 K. The dispersed oxide particles were identified to be titania ＋ yttria for Al-free oxide dispersion strengthened （ODS） steel and alumina ＋ yttria for Al-added ODS steel, respectively. The ultimate tensile strength of Al-free ODS steel was higher than that of Al-added ODS steel over the temperature range of 298-973 K, because of the difference in number density and size of thermally stable oxide particles dispersed in both steel matrices. The strength in the longitudinal direction was lower than that in the transverse direction, probably due to anisotropy of the microstructure with elongated grains in the hot-extrusion direction for the 18%Cr-ODS steels with and without 5% Al.
基金This work was financially supported by the National MCF Energy R&D Program of China(No.2018YFE0306100).The computational resources at Hefei Advanced Computing Center and the High Performance Computing Center of Central South University are also highly appreciated.
文摘A new Ni+Zr co-alloyed FeCrAl-ODS(oxide-dispersion-strengthened)ferritic alloy was fabricated by ball-milling and hot-isostatic-pressing.Using electron microscopy and atom probe tomography,the dispersive formation of high density core-shelled nano-particles of various sizes was confirmed with a common B2-NiAl shell.Among which,median-sized nano-particles(20-50 nm)typically have an Y_(4)Al_(2)O_(9)nano-core of<~20 nm,ultra-fine nano-particles(<~20)nm have an Y_(4)Zr_(3)O_(12)nano-core of<~10 nm,and larger-sized nano-particles(50-100 nm)incorporate an ultra-fine Y_(4)Al_(2)O_(9)nano-core and a few ultra-fine Y_(4)Zr_(3)O_(12)nano-oxides.All these nano-phases were highly coherent with the ferritic matrix.No large Y--Al-O nano-oxides were formed.The total number density of ultra-fine nano-particles was estimated as~2×10^(23)m^(-3)with a mean size of 6.3 nm only,and accordingly,the new alloy achieved an excellent combination of strength and ductility at high temperatures.
