The microstructure, precipitate type, precipitate distribution and tensile strength of a ZL205 alloy, beforeand after ageing treatment, have been studied by means of optical microscopy and transmission electron micros...The microstructure, precipitate type, precipitate distribution and tensile strength of a ZL205 alloy, beforeand after ageing treatment, have been studied by means of optical microscopy and transmission electron microscopy.The results showed that the as-cast microstructure of the alloy was made up of α-Al and eutectic phase distributedat the grain boundaries. During ageing treatment, the tensile strength increased at first and then reduced with time,and the highest ultimate tensile strength was found to be around 488.2 MPa.展开更多
A novel in-situ process-Reaction Synthesis has been used to fabricate Al/TiC compos-ites,the phase constitute,microstructure and mechanical property of the Al/TiC composite have been investigated by the use of XRD and...A novel in-situ process-Reaction Synthesis has been used to fabricate Al/TiC compos-ites,the phase constitute,microstructure and mechanical property of the Al/TiC composite have been investigated by the use of XRD and SEM.It has been shown that the reaction synthesized TiC particu-late is submicron in size(about 0.1~0.8μpm),spherical in shape and smooth in surface.In macrostruc-ture the distribution of the TiC particulate in matrix is homogeneous,but in micostructure there is micro-segregation of the TiC particulate at the intergrannular.The cast structure become fine because of the existence of the TiC particulate.In addition«with the increasing of weight percentage of TiC partic-ulate in alloy,the yield strength and ultimate tensile strength of the composite increase significantly«e.g.at 15%TiC,117% and 103% increase respectively,in the same time the elongation of the composite is still more than 4.5%.In the end,the analysis has been done by SEM on the fracture morphology of the composite.The results show that the fracture is ductility,and mainly because of the cluster of TiC particulate to intergrannular and the synthesis of bar morphology Al_(3)Ti.展开更多
The optical microscope, scanning electron microscope and universal testing machine are used to investigate the effect of Zn content on the microstructure, mechanical properties and fracture behavior of Mg- Mn-Zn alloy...The optical microscope, scanning electron microscope and universal testing machine are used to investigate the effect of Zn content on the microstructure, mechanical properties and fracture behavior of Mg- Mn-Zn alloy. The results indicate that fine （Mg, Mn, AI）-containing phases are distributed uniformly in the Mg-Mn alloy matrix, while small amount of （Mg, Zn）-containing phases are formed in the matrix and the grain boundary becomes coarse when 1wt.% Zn is added. As the Zn content increases, the amount of （Mg, Zn）-containing phases increases, and the grain boundary becomes coarser. When the Zn content is between 3wt.%-5wt.%, slender （Mg, Zn）-containing phases precipitate at the grain boundary. The addition of Zn could reduce the grain size and enhance the mechanical properties of the alloy matrix, and both of the effects can be enhanced by increasing the Zn content further more. When the Zn content is more than 3wt.%, grain size stops decrease, the strength cannot be improved any more and elongation decreases significantly. The fracture behavior of Mg-Mn alloy appears to be cleavage fracture, and transforms into quasi-cleavage fracture as Zn is added. When Zn content exceeded 3wt.%, large amount of （Mg, Zn）-containing phases appear on the fracture face, and act as the crack sources.展开更多
In this paper,the effects of aluminum content,C/Ti ratio and the size of powders on the phase constitute and micrography of reaction synthesis of Al+Ti+C system have been studied by the use of XRD and SEM.It has been ...In this paper,the effects of aluminum content,C/Ti ratio and the size of powders on the phase constitute and micrography of reaction synthesis of Al+Ti+C system have been studied by the use of XRD and SEM.It has been shown that with the increase of aluminum content,in addition to TiC,Al_3Ti phase is also synthesised,and the content of Al_3Ti increase,and the size of TiC become fine,changing from 0.4-1.4μm.The increase of C/Ti ratio is favorable to the synthesis of TiC and can increase the Al content in which only TiC phase has formed,and has no effect on the micrography of TiC,but shows great in fluence on the micrography,of Al_3Ti.In addition,the size of titanium has no effect on the phase constitue and micrography,but the size of aluminum has great in fluence on them.With the increase of size of aluminum powder,Al_3Ti will be synthesised and its content increase also,so it is unfavorable to the synthesis of TiC.展开更多
The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent,met...The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent,metallic and ionic characters. For a quantitative analysis of the relative strength of these components,their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN,which coincides to that de-duced from the first-principles method.展开更多
文摘The microstructure, precipitate type, precipitate distribution and tensile strength of a ZL205 alloy, beforeand after ageing treatment, have been studied by means of optical microscopy and transmission electron microscopy.The results showed that the as-cast microstructure of the alloy was made up of α-Al and eutectic phase distributedat the grain boundaries. During ageing treatment, the tensile strength increased at first and then reduced with time,and the highest ultimate tensile strength was found to be around 488.2 MPa.
文摘A novel in-situ process-Reaction Synthesis has been used to fabricate Al/TiC compos-ites,the phase constitute,microstructure and mechanical property of the Al/TiC composite have been investigated by the use of XRD and SEM.It has been shown that the reaction synthesized TiC particu-late is submicron in size(about 0.1~0.8μpm),spherical in shape and smooth in surface.In macrostruc-ture the distribution of the TiC particulate in matrix is homogeneous,but in micostructure there is micro-segregation of the TiC particulate at the intergrannular.The cast structure become fine because of the existence of the TiC particulate.In addition«with the increasing of weight percentage of TiC partic-ulate in alloy,the yield strength and ultimate tensile strength of the composite increase significantly«e.g.at 15%TiC,117% and 103% increase respectively,in the same time the elongation of the composite is still more than 4.5%.In the end,the analysis has been done by SEM on the fracture morphology of the composite.The results show that the fracture is ductility,and mainly because of the cluster of TiC particulate to intergrannular and the synthesis of bar morphology Al_(3)Ti.
文摘The optical microscope, scanning electron microscope and universal testing machine are used to investigate the effect of Zn content on the microstructure, mechanical properties and fracture behavior of Mg- Mn-Zn alloy. The results indicate that fine （Mg, Mn, AI）-containing phases are distributed uniformly in the Mg-Mn alloy matrix, while small amount of （Mg, Zn）-containing phases are formed in the matrix and the grain boundary becomes coarse when 1wt.% Zn is added. As the Zn content increases, the amount of （Mg, Zn）-containing phases increases, and the grain boundary becomes coarser. When the Zn content is between 3wt.%-5wt.%, slender （Mg, Zn）-containing phases precipitate at the grain boundary. The addition of Zn could reduce the grain size and enhance the mechanical properties of the alloy matrix, and both of the effects can be enhanced by increasing the Zn content further more. When the Zn content is more than 3wt.%, grain size stops decrease, the strength cannot be improved any more and elongation decreases significantly. The fracture behavior of Mg-Mn alloy appears to be cleavage fracture, and transforms into quasi-cleavage fracture as Zn is added. When Zn content exceeded 3wt.%, large amount of （Mg, Zn）-containing phases appear on the fracture face, and act as the crack sources.
文摘In this paper,the effects of aluminum content,C/Ti ratio and the size of powders on the phase constitute and micrography of reaction synthesis of Al+Ti+C system have been studied by the use of XRD and SEM.It has been shown that with the increase of aluminum content,in addition to TiC,Al_3Ti phase is also synthesised,and the content of Al_3Ti increase,and the size of TiC become fine,changing from 0.4-1.4μm.The increase of C/Ti ratio is favorable to the synthesis of TiC and can increase the Al content in which only TiC phase has formed,and has no effect on the micrography of TiC,but shows great in fluence on the micrography,of Al_3Ti.In addition,the size of titanium has no effect on the phase constitue and micrography,but the size of aluminum has great in fluence on them.With the increase of size of aluminum powder,Al_3Ti will be synthesised and its content increase also,so it is unfavorable to the synthesis of TiC.
基金Supported by the National Natural Science Foundation of China (Grant No. 10702060)the Ministry of Science and Technology of China (2005CB724400 and 2005CB724404)
文摘The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent,metallic and ionic characters. For a quantitative analysis of the relative strength of these components,their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN,which coincides to that de-duced from the first-principles method.
