The solidification microstructures of undercooled Ni90Cu10 alloys under different undercoolings were studied systematically by means of melt coating and cyclic superheating.In the obtained undercooling range,the solid...The solidification microstructures of undercooled Ni90Cu10 alloys under different undercoolings were studied systematically by means of melt coating and cyclic superheating.In the obtained undercooling range,the solidification structures of the two undercooled alloys have similar transformation processes,and there are two kinds of grain refinement structures under the conditions of low undercooling and high undercooling,respectively.The microstructures of the two grain refinement processes were analyzed in more detail by electronic backscattering diffraction technique.Under the condition of small undercooling,dendrite remelting is considered to be the main reason of grain refinement.However,under the condition of high undercooling,the existence of annealing twins and obvious migration of grain boundary are important evidences for the occurrence of recrystallization process.展开更多
The feasibility of using coral reef sand(CRS) in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are a...The feasibility of using coral reef sand(CRS) in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.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
The increasing demand for reducing vehicle weight in the automotive and aerospace industries has raised the need to develop improved structural aluminum-based alloys. Thus, horizontal solidification experiment with th...The increasing demand for reducing vehicle weight in the automotive and aerospace industries has raised the need to develop improved structural aluminum-based alloys. Thus, horizontal solidification experiment with the Al-7%Si-0.3%Mg(mass fraction) alloy was carried out. A water-cooled horizontal directional solidification device was developed and used. Microstructural characterization was carried out using traditional techniques of metallography, optical microscopy and SEM microscopy. The Thermo-Calc software was used to generate the solidification path of the investigated alloy with addition of 0.17% Fe(mass fraction). The effects of the thermal parameters such as the growth rate(VL), cooling rate(TC) and solidification local time(tSL) on the formation of the macrostructure and on the dendritic microstructure evolution were evaluated. A columnar to equiaxed transition(CET) was found for VL and TC values from 0.82 to 0.98 mm/s and from 1.71 to 2.55 ℃/s, respectively. The microstructure was characterized by the measurement of the primary and secondary dendrite arm spacings(λ1 and λ2, respectively). Experimental laws of λ1 =f(VL, TC) and λ2 =f(tSL) were proposed. It is observed that the interdendritic region is composed of the following eutectic mixture: a(Al)+Si+p-Al8 Mg3 Fe Si6+q-Mg2 Si.展开更多
The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys (Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15) synthesized via mechanical alloying by varying...The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys (Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15) synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth (RE) and transition metal (TM) elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.展开更多
Compositional dependences on microstructures and martensitic transformation behaviors in(Cu_(0.5)Zr_(0.5))_(100-x)Zn_x(x=1.5,2.5,4.5,7.0,10.0,and 14.0at.%)alloys were investigated.It was found that CuZr mart...Compositional dependences on microstructures and martensitic transformation behaviors in(Cu_(0.5)Zr_(0.5))_(100-x)Zn_x(x=1.5,2.5,4.5,7.0,10.0,and 14.0at.%)alloys were investigated.It was found that CuZr martensites were present in the present alloys.With increasing Zn content,the volume fractions of CuZr martensitic crystals and B2 CuZr phase gradually decrease and increase,respectively.With the addition of high Zn contents(i.e.,7.0,10.0,and 14.0at.%),the matrix proves to be eutectic.Thermal analysis results show that the initial martensitic transformation temperature(M_s)decreases from(412±5)K to(329±5)K as the Zn content increases from 1.5at.% to14.0at.%.The values of Msof Cu-Zr-Zn shape memory alloys are inversely proportional to the number and concentrations of valence electrons(i.e.,e_v/a and c_v),respectively,implying that the martensitic transformation in CuZrZn alloys could be of electronic nature.展开更多
基金Funded by the Basic Applied Research Projects in Shanxi Province(No.201801D221151)the Key R&D and Promotion Projects in Henan Province(No.212102210267)。
文摘The solidification microstructures of undercooled Ni90Cu10 alloys under different undercoolings were studied systematically by means of melt coating and cyclic superheating.In the obtained undercooling range,the solidification structures of the two undercooled alloys have similar transformation processes,and there are two kinds of grain refinement structures under the conditions of low undercooling and high undercooling,respectively.The microstructures of the two grain refinement processes were analyzed in more detail by electronic backscattering diffraction technique.Under the condition of small undercooling,dendrite remelting is considered to be the main reason of grain refinement.However,under the condition of high undercooling,the existence of annealing twins and obvious migration of grain boundary are important evidences for the occurrence of recrystallization process.
基金Funded by the Fundamental Research Funds for the Central Universities(WUT:142201001)
文摘The feasibility of using coral reef sand(CRS) in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.
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.
基金financial support provided by IFPA-Federal Institute of Education, Science and Technology of Pará, UFPA-Federal University of Pará, and CNPq-The Brazilian Research Council (Grants 472745/2013-1, 308784/2014-6 and 302846/2017-4)FAPESPA-Amazon Foundation of Support to Study and Research (Grants ICAAF 064/2016)CAPES-Coordination of Superior Level Staff Improvement, Brazil
文摘The increasing demand for reducing vehicle weight in the automotive and aerospace industries has raised the need to develop improved structural aluminum-based alloys. Thus, horizontal solidification experiment with the Al-7%Si-0.3%Mg(mass fraction) alloy was carried out. A water-cooled horizontal directional solidification device was developed and used. Microstructural characterization was carried out using traditional techniques of metallography, optical microscopy and SEM microscopy. The Thermo-Calc software was used to generate the solidification path of the investigated alloy with addition of 0.17% Fe(mass fraction). The effects of the thermal parameters such as the growth rate(VL), cooling rate(TC) and solidification local time(tSL) on the formation of the macrostructure and on the dendritic microstructure evolution were evaluated. A columnar to equiaxed transition(CET) was found for VL and TC values from 0.82 to 0.98 mm/s and from 1.71 to 2.55 ℃/s, respectively. The microstructure was characterized by the measurement of the primary and secondary dendrite arm spacings(λ1 and λ2, respectively). Experimental laws of λ1 =f(VL, TC) and λ2 =f(tSL) were proposed. It is observed that the interdendritic region is composed of the following eutectic mixture: a(Al)+Si+p-Al8 Mg3 Fe Si6+q-Mg2 Si.
基金financial support obtained from the Science and Engineering Research Board,Department of Science & Technology,Government of India(SB/S3/ME/0044/2013)Sponsored Research and Industrial Consultancy,Indian Institute of Technology Kharagpur,India(GAF)
文摘The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys (Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15) synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth (RE) and transition metal (TM) elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.
基金Item Sponsored by National Natural Science Foundation of China(51501103)Fundamental Research Funds for the Central Universities on Northwestern Polytechnical University of China(GEKY1008)
文摘Compositional dependences on microstructures and martensitic transformation behaviors in(Cu_(0.5)Zr_(0.5))_(100-x)Zn_x(x=1.5,2.5,4.5,7.0,10.0,and 14.0at.%)alloys were investigated.It was found that CuZr martensites were present in the present alloys.With increasing Zn content,the volume fractions of CuZr martensitic crystals and B2 CuZr phase gradually decrease and increase,respectively.With the addition of high Zn contents(i.e.,7.0,10.0,and 14.0at.%),the matrix proves to be eutectic.Thermal analysis results show that the initial martensitic transformation temperature(M_s)decreases from(412±5)K to(329±5)K as the Zn content increases from 1.5at.% to14.0at.%.The values of Msof Cu-Zr-Zn shape memory alloys are inversely proportional to the number and concentrations of valence electrons(i.e.,e_v/a and c_v),respectively,implying that the martensitic transformation in CuZrZn alloys could be of electronic nature.