Gas-atomized powders of three Fe-based glass-forming alloys were sprayed on mild steel substrates by atmospheric plasma spaying using the same spaying parameters. Microstructures, thermal stabilities and tribological ...Gas-atomized powders of three Fe-based glass-forming alloys were sprayed on mild steel substrates by atmospheric plasma spaying using the same spaying parameters. Microstructures, thermal stabilities and tribological properties of the sprayed coatings were analyzed. The coating performances showed a strong dependence on the intrinsic characters of the compositions, i.e., glass-forming ability （GFA） and supercooled liquid region （ATx）. The coatings tended to exhibit higher amorphous phase fraction for the composition with higher GFA and lower porosity for that with larger ATX. All the coatings exhibited superior wear resistance compared with the substrate. Higher wear resistance could be obtained in coatings with higher amorphous phase fraction, i.e. higher GFA of the composition. This study has important implications for composition selecting and optimizing in the fabrication of metallic glass coatings.展开更多
The room temperature compressive plasticity of Fe75MosP10Cs.3B1.7 bulk metallic glass （BMG） was improved from 0.5% to 1.8% by increasing the sample diameter from 1.5 mm to 2.0 mm. With increasing the sample diameter...The room temperature compressive plasticity of Fe75MosP10Cs.3B1.7 bulk metallic glass （BMG） was improved from 0.5% to 1.8% by increasing the sample diameter from 1.5 mm to 2.0 mm. With increasing the sample diameter to 2.0 mm, a heterogeneous microstructure with in-situ formed a-Fe dendrite sparsely distributed in the amorphous matrix can be attained. This heterogeneous mierostructure is conceived to be highly responsible for the enhanced global plasticity in this marginal Fe-based BMG.展开更多
In this paper,SmCo6.9 Hf0.1 as-cast alloys and ribbons with the addition of either graphite（C） or carbon nanotubes（CNTs） were prepared by arc melting and melt-spinning,respectively.The effects of adding carbon on ...In this paper,SmCo6.9 Hf0.1 as-cast alloys and ribbons with the addition of either graphite（C） or carbon nanotubes（CNTs） were prepared by arc melting and melt-spinning,respectively.The effects of adding carbon on the structure and magnetic properties SmCo6.9 Hf0.1 were investigated by means of X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,magnetic force microscopy（MFM） and vibrating sample magnetometer（VSM）.It was found that the microstructure and magnetic structure of SmCo6.9 Hf0.1 ribbons were changed obviously due to the introduction of C or CNTs,although their crystal structure was characterized as the same Sm（Co,Hf）7 single phase,no matter carbon was added or not.As a result,the magnetic properties of carbon-contained ribbons were enhanced in a certain degree.This was considered to be related to the refined equiaxed grains,small domain size and the pinning effect of C or CNTs-rich regions.The magnetic properties of SmCo6.9 Hf0.1（CNTs）0.05 ribbons reached Hc =12.5 kOe,Mr =57.0 emu/g and Mr/M2 T =0.788.展开更多
Ternary nickel cobaltite(NiCo2O4),as a promising electrode material for supercapacitors,has attracted increasing attention for its excellent electrochemical properties.In this study,novel NiCo2O4 nanosheets were ratio...Ternary nickel cobaltite(NiCo2O4),as a promising electrode material for supercapacitors,has attracted increasing attention for its excellent electrochemical properties.In this study,novel NiCo2O4 nanosheets were rationally designed and prepared using dealloying process,followed by an oxidation treatment.The as-prepared sample was characterized by microstructural and electrochemical techniques in view of its possible application in supercapacitors.The as-prepared sample exhibited high specific capacitance and excellent durability.The specific capacitance reached 663 F/g at 1 A/g and the rate capacitance high up to 73.6%when the current density increased from 1 A/g to 20 A/g.After 5000 cycles of galvanostatic charge-discharge durability test at 4 A/g,the capacity retention rate was 82.1%.The results indicate that versatile dealloying can be used to prepare robust electrode for supercapacitor application.展开更多
The microstructural evolution of a Mg-10Ni-2Mm（molar fraction,%）（Mm=Ce,La-rich mischmetal） hydrogen storage alloys applied with various solidification rates was studied.The results show that the grain size of melt...The microstructural evolution of a Mg-10Ni-2Mm（molar fraction,%）（Mm=Ce,La-rich mischmetal） hydrogen storage alloys applied with various solidification rates was studied.The results show that the grain size of melt-spun ribbon is remarkably reduced by increasing the solidification rate.The microcrystalline,nanocrystalline and amorphous microstructures are obtained by applying the surface velocities of the graphite wheel of 3.1,10.5 and 20.9 m/s,respectively.By applying the surface velocity of the graphite wheel of 3.1 m/s,the melt-spun specimen obtains full crystalline with a considerable amount of coarse microcrystalline Mg and Mg2Ni except for some Mm-rich particles.The amount of nanocrystalline phases significantly increases with increasing the surface velocity of the wheel to 10.5 m/s,and the microstructure is composed of a large amount of nanocrystalline phases of Mg and Mg2Ni particles.A mixed microstructure containing amorphous and nanocrystalline phases is obtained at a surface velocity of the wheel of 20.9 m/s.The optimal microstructure with a considerable amount of nanocrystalline Mg and Mg2Ni in an amorphous matrix is expected to have the maximum hydrogen absorption capacity and excellent hydrogenation kinetics.展开更多
采用 Al-(3．4—15)%Bi(质量分数)难混溶合金进行了快速连续凝固实验,研究了 Bi 含量和凝固速率对快速连续凝固组织的影响．结果表明,少量富 Bi 相粒子尺寸随着 Bi 含量的增加而增大,提高凝固速率有助于制备少量富 Bi 相粒子均匀分布的...采用 Al-(3．4—15)%Bi(质量分数)难混溶合金进行了快速连续凝固实验,研究了 Bi 含量和凝固速率对快速连续凝固组织的影响．结果表明,少量富 Bi 相粒子尺寸随着 Bi 含量的增加而增大,提高凝固速率有助于制备少量富 Bi 相粒子均匀分布的难混溶合金．通过分析富 Bi 粒子尺寸分布,发现沿试样轴向和径向方向粒子平均直径变化不大,试样表层处粒子尺寸较小．研究表明,快速连续凝固是制备均质难混溶合金的有效途径．展开更多
Directional solidification experiments were carried out with Al-Pb alloys under the effect of a direct current （DC）. The experimental results show that the DC causes a migration of the minority phase droplets （MPDs...Directional solidification experiments were carried out with Al-Pb alloys under the effect of a direct current （DC）. The experimental results show that the DC causes a migration of the minority phase droplets （MPDs） from the middle part to the surface region of the sample, Samples with either a finely dispersed microstructure or a shell/ core structure were obtained by solidifying the alloy under the effect of the properly selected DC densities, A model was developed to describe the microstructure evolution in an immiscible alloy directionaliy solidified under the effect of the DC. The microstructure formation in the AI-Pb alloys was calculated. The numerical results are in favorable agreement with the experimental ones. They demonstrate that the DC affects the microstructure formation mainly through changing the spatial motions of the MPDs and the temperature field of the melt in front of the solid/liquid interface. The formation mechanisms of the finely dispersed microstructure as well as the shell/core structure were sufficiently clarified.展开更多
This paper briefly reviews the recent research on the near rapid directional solidification and microstructure superfining. The morphology transitions and the corresponding mechanical properties are presented. The cri...This paper briefly reviews the recent research on the near rapid directional solidification and microstructure superfining. The morphology transitions and the corresponding mechanical properties are presented. The critical velocities relevant to the morphology transitions are comprehensively given. Meanwhile the solidification characteristics near absolute stability limit are studied.It can be clearly seen that the superfine microstructures possess extremely better properties compared with the conventional microstructures.展开更多
Al 4.95%Zn alloy is directionally solidified in a modified Bridgman apparatus with higher temperature gradient to investigate response of cellular/dendritic microstructures and primary spacing to the variation of grow...Al 4.95%Zn alloy is directionally solidified in a modified Bridgman apparatus with higher temperature gradient to investigate response of cellular/dendritic microstructures and primary spacing to the variation of growth velocity under near rapid directional solidification condition. The results show that, with increasing growth rate, there exists a transition from dendrite to fine cell and a wide distribution range in primary cellular/dendritic spacing at the given temperature gradient. The maximum, λ max , minimum, λ min , and average primary spacing, λ , as functions of growth velocity, v , can be given by λ max =12 340 v -0.835 3 , λ min =2 953.7 v -0.771 7 , λ =7 820.3 v -0.833 3 , respectively. , as functions of growth velocity, v , can be given by λ max =12 340 v -0.835 3 , λ min =2 953.7 v -0.771 7 , λ =7 820.3 v -0.833 3 , respectively.展开更多
An experimental study on the microstructures of a rapid directionally solidified metallo-eutectic Sn-Cu alloy was carried out. This material is an important alloy that is used as a lead-free solder. The results showed...An experimental study on the microstructures of a rapid directionally solidified metallo-eutectic Sn-Cu alloy was carried out. This material is an important alloy that is used as a lead-free solder. The results showed that the kinetic undercooling due to the rapid solidification process led to the formation of a pseudoeutectic zone, whereas the hypereutectic reaction produced the regular lamellar structure in the hypereutectic Sn-1.0Cu alloy. The corresponding arm spacing in the obtained lamellar phases decreased gradually with the increase of the applied cooling rate, which corresponded well with the prediction of a rapid directional solidification model.展开更多
In order to investigate the response of cellular spacing to the variation of growth velocity under near-rapid directional solidification condition, Al-0.53wt%Zn alloy is directionally solidified with Bridgman apparatu...In order to investigate the response of cellular spacing to the variation of growth velocity under near-rapid directional solidification condition, Al-0.53wt%Zn alloy is directionally solidified with Bridgman apparatus. The results show that at the given temperature gradient the obtained microstrvctures are all cells and there exists a wide distribution range of cellular spacing. The maximum, λmax, minimum, λmin, and average cellular spacing, λ, as functions of growth rate, V, can be given by λmax=948.51V-0.4961, λmin= 661.16V-0.5015 and λ=412.41V-0.5049, respectively. The experimental results are compared with that predicted by KGT model, and a good agreement is found. Moreover,it is found that the average cellular spacing is also remarkably history-dependent.展开更多
基金supported by the National Basic Research Program of China (Grant No. 2007CB613900)the National Natural Science Foundation of China (Grant No. 51071008)the Fundamental Research Funds for the Central Universities
文摘Gas-atomized powders of three Fe-based glass-forming alloys were sprayed on mild steel substrates by atmospheric plasma spaying using the same spaying parameters. Microstructures, thermal stabilities and tribological properties of the sprayed coatings were analyzed. The coating performances showed a strong dependence on the intrinsic characters of the compositions, i.e., glass-forming ability （GFA） and supercooled liquid region （ATx）. The coatings tended to exhibit higher amorphous phase fraction for the composition with higher GFA and lower porosity for that with larger ATX. All the coatings exhibited superior wear resistance compared with the substrate. Higher wear resistance could be obtained in coatings with higher amorphous phase fraction, i.e. higher GFA of the composition. This study has important implications for composition selecting and optimizing in the fabrication of metallic glass coatings.
基金Foundation item: Project (SWU110046) supported by the Startup Foundation for Doctors of Southwest University, ChinaProjects (XDJK2012C017,CDJXS11132228, CDJZR10130012) supported by the Fundamental Research Funds for the Central Universities, China+1 种基金Project (CSTS2006AA4012) supported by the Chongqing Science and Technology Commission, ChinaProject (T201112) supported by Shenzhen Key Laboratory of Special Functional Materials,Shenzhen University,China
文摘The room temperature compressive plasticity of Fe75MosP10Cs.3B1.7 bulk metallic glass （BMG） was improved from 0.5% to 1.8% by increasing the sample diameter from 1.5 mm to 2.0 mm. With increasing the sample diameter to 2.0 mm, a heterogeneous microstructure with in-situ formed a-Fe dendrite sparsely distributed in the amorphous matrix can be attained. This heterogeneous mierostructure is conceived to be highly responsible for the enhanced global plasticity in this marginal Fe-based BMG.
基金supported by General Program from the National Natural Science Foundation of China(51271072)National Science Fund for Young(51301056)+1 种基金Key Program from the Science and Technology Research for Colleges and Universities in Hebei Province(ZH2011202)Hebei Natural Science Foundation of China(E2013202030)
文摘In this paper,SmCo6.9 Hf0.1 as-cast alloys and ribbons with the addition of either graphite（C） or carbon nanotubes（CNTs） were prepared by arc melting and melt-spinning,respectively.The effects of adding carbon on the structure and magnetic properties SmCo6.9 Hf0.1 were investigated by means of X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,magnetic force microscopy（MFM） and vibrating sample magnetometer（VSM）.It was found that the microstructure and magnetic structure of SmCo6.9 Hf0.1 ribbons were changed obviously due to the introduction of C or CNTs,although their crystal structure was characterized as the same Sm（Co,Hf）7 single phase,no matter carbon was added or not.As a result,the magnetic properties of carbon-contained ribbons were enhanced in a certain degree.This was considered to be related to the refined equiaxed grains,small domain size and the pinning effect of C or CNTs-rich regions.The magnetic properties of SmCo6.9 Hf0.1（CNTs）0.05 ribbons reached Hc =12.5 kOe,Mr =57.0 emu/g and Mr/M2 T =0.788.
基金Supported by the National Natural Science Foundation of China(No.51661018).
文摘Ternary nickel cobaltite(NiCo2O4),as a promising electrode material for supercapacitors,has attracted increasing attention for its excellent electrochemical properties.In this study,novel NiCo2O4 nanosheets were rationally designed and prepared using dealloying process,followed by an oxidation treatment.The as-prepared sample was characterized by microstructural and electrochemical techniques in view of its possible application in supercapacitors.The as-prepared sample exhibited high specific capacitance and excellent durability.The specific capacitance reached 663 F/g at 1 A/g and the rate capacitance high up to 73.6%when the current density increased from 1 A/g to 20 A/g.After 5000 cycles of galvanostatic charge-discharge durability test at 4 A/g,the capacity retention rate was 82.1%.The results indicate that versatile dealloying can be used to prepare robust electrode for supercapacitor application.
基金Project(2007DFA50590)supported by the International S&T Cooperation Projects the Norwegian Research Council for financial support
文摘The microstructural evolution of a Mg-10Ni-2Mm（molar fraction,%）（Mm=Ce,La-rich mischmetal） hydrogen storage alloys applied with various solidification rates was studied.The results show that the grain size of melt-spun ribbon is remarkably reduced by increasing the solidification rate.The microcrystalline,nanocrystalline and amorphous microstructures are obtained by applying the surface velocities of the graphite wheel of 3.1,10.5 and 20.9 m/s,respectively.By applying the surface velocity of the graphite wheel of 3.1 m/s,the melt-spun specimen obtains full crystalline with a considerable amount of coarse microcrystalline Mg and Mg2Ni except for some Mm-rich particles.The amount of nanocrystalline phases significantly increases with increasing the surface velocity of the wheel to 10.5 m/s,and the microstructure is composed of a large amount of nanocrystalline phases of Mg and Mg2Ni particles.A mixed microstructure containing amorphous and nanocrystalline phases is obtained at a surface velocity of the wheel of 20.9 m/s.The optimal microstructure with a considerable amount of nanocrystalline Mg and Mg2Ni in an amorphous matrix is expected to have the maximum hydrogen absorption capacity and excellent hydrogenation kinetics.
文摘采用 Al-(3．4—15)%Bi(质量分数)难混溶合金进行了快速连续凝固实验,研究了 Bi 含量和凝固速率对快速连续凝固组织的影响．结果表明,少量富 Bi 相粒子尺寸随着 Bi 含量的增加而增大,提高凝固速率有助于制备少量富 Bi 相粒子均匀分布的难混溶合金．通过分析富 Bi 粒子尺寸分布,发现沿试样轴向和径向方向粒子平均直径变化不大,试样表层处粒子尺寸较小．研究表明,快速连续凝固是制备均质难混溶合金的有效途径．
基金the financial support from the National Natural Science Foundation of China(Nos. 51071159,51031003,51271185 and u0837601)
文摘Directional solidification experiments were carried out with Al-Pb alloys under the effect of a direct current （DC）. The experimental results show that the DC causes a migration of the minority phase droplets （MPDs） from the middle part to the surface region of the sample, Samples with either a finely dispersed microstructure or a shell/ core structure were obtained by solidifying the alloy under the effect of the properly selected DC densities, A model was developed to describe the microstructure evolution in an immiscible alloy directionaliy solidified under the effect of the DC. The microstructure formation in the AI-Pb alloys was calculated. The numerical results are in favorable agreement with the experimental ones. They demonstrate that the DC affects the microstructure formation mainly through changing the spatial motions of the MPDs and the temperature field of the melt in front of the solid/liquid interface. The formation mechanisms of the finely dispersed microstructure as well as the shell/core structure were sufficiently clarified.
文摘This paper briefly reviews the recent research on the near rapid directional solidification and microstructure superfining. The morphology transitions and the corresponding mechanical properties are presented. The critical velocities relevant to the morphology transitions are comprehensively given. Meanwhile the solidification characteristics near absolute stability limit are studied.It can be clearly seen that the superfine microstructures possess extremely better properties compared with the conventional microstructures.
文摘Al 4.95%Zn alloy is directionally solidified in a modified Bridgman apparatus with higher temperature gradient to investigate response of cellular/dendritic microstructures and primary spacing to the variation of growth velocity under near rapid directional solidification condition. The results show that, with increasing growth rate, there exists a transition from dendrite to fine cell and a wide distribution range in primary cellular/dendritic spacing at the given temperature gradient. The maximum, λ max , minimum, λ min , and average primary spacing, λ , as functions of growth velocity, v , can be given by λ max =12 340 v -0.835 3 , λ min =2 953.7 v -0.771 7 , λ =7 820.3 v -0.833 3 , respectively. , as functions of growth velocity, v , can be given by λ max =12 340 v -0.835 3 , λ min =2 953.7 v -0.771 7 , λ =7 820.3 v -0.833 3 , respectively.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50401003), Fok Ying Tong Education Foundation (No. 104015), and the Natural Science Foundation of Tianjin City (No. 033608811).
文摘An experimental study on the microstructures of a rapid directionally solidified metallo-eutectic Sn-Cu alloy was carried out. This material is an important alloy that is used as a lead-free solder. The results showed that the kinetic undercooling due to the rapid solidification process led to the formation of a pseudoeutectic zone, whereas the hypereutectic reaction produced the regular lamellar structure in the hypereutectic Sn-1.0Cu alloy. The corresponding arm spacing in the obtained lamellar phases decreased gradually with the increase of the applied cooling rate, which corresponded well with the prediction of a rapid directional solidification model.
文摘In order to investigate the response of cellular spacing to the variation of growth velocity under near-rapid directional solidification condition, Al-0.53wt%Zn alloy is directionally solidified with Bridgman apparatus. The results show that at the given temperature gradient the obtained microstrvctures are all cells and there exists a wide distribution range of cellular spacing. The maximum, λmax, minimum, λmin, and average cellular spacing, λ, as functions of growth rate, V, can be given by λmax=948.51V-0.4961, λmin= 661.16V-0.5015 and λ=412.41V-0.5049, respectively. The experimental results are compared with that predicted by KGT model, and a good agreement is found. Moreover,it is found that the average cellular spacing is also remarkably history-dependent.
