Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. Th...Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. The experimental results show that the addition of 1.0% Y is beneficial to the formation of TiC particles; Al-Ti-C-1.0Y consists of rod-like and blocky TiAl3, TiC, Al3Y and α-Al matrix. Y is found around TiC particles in Al-Ti-C-0.5Y master alloy while blocky (AlTiY) phase appears in Al-Ti-C-1.0Y master alloy. Al3Y with dendritic morphology and small blocky Al2Y except for TiC are found in Al-Ti-C-2-0Y master alloy.展开更多
X-ray microanalysis,convergent beam electron diffraction(CBD)and selected area electron diffraction(SAD)studies on the structures and compositions of the constituent phases in 2024 series Al alloys have been conducted...X-ray microanalysis,convergent beam electron diffraction(CBD)and selected area electron diffraction(SAD)studies on the structures and compositions of the constituent phases in 2024 series Al alloys have been conducted.Partial substitution of alloying elements is found to occur in all the constituent phases,which cause small deviations from the stoichiometric com- positions reported in these ternary compounds.The dominant phase is α-Al_(12)(FeMn)_3Si which has a body center cubic crystal structure with the Im■ space group and a=1.25 nm.The next dominant phase is Cu_2FeAl_7 which has a primitive tetragonal crystal structure with the P4/mnc space group and a=0.6336 nm,c=1.487 nm.The minor phase is α'-Al_(12)Fe_3Si hav- ing α primitive cubic crystal structure with the Pm■ space group and α=1.27 nm.展开更多
Through microstructure observation and X-ray diffraction analysis, the equilibrium phase constituents of Al-Zn alloy that contains 2 at. pct Cu at room temperature have been determined as Al-based solid solution (α),...Through microstructure observation and X-ray diffraction analysis, the equilibrium phase constituents of Al-Zn alloy that contains 2 at. pct Cu at room temperature have been determined as Al-based solid solution (α), Zn-based solid solution and AI4Cu3Zn phase (T'-phase), which are different from a phase, Zn phase and CuZn4 phase originally believed. It is determined that the products of discontinuous precipitation transformation below 277℃ are not the equilibrium phase constituents, but the metastable phases made up of a phase, Zn phase and CuZn4 phase. The phase constituents after discontinuous precipitation of AIZn-2Cu alloy would transform to the ones in equilibrium status: Al-based solid solution (α) in fcc structure, Zn-based solid solution in hcp structure and AI4Cu3Zn phase (T'-phase) ultimately through plastic deformation at room temperature and re-heating treatment below 277℃.展开更多
Based on analytical data of mineral phase constituents at three sections from Tern Lake, West Lake and Kitezh Lake in the Fildes Peninsula of King George Island, Antarctica, the characteristics of mineral phase consti...Based on analytical data of mineral phase constituents at three sections from Tern Lake, West Lake and Kitezh Lake in the Fildes Peninsula of King George Island, Antarctica, the characteristics of mineral phase constituents, material source and their environmental implication have been discussed. Research results indicate that lacustrine deposits came primarily from widespread volcanic rocks at the peninsula. Under cold and dry condition in Antarctica, the weathering process of the parent rocks in some area is mainly physical weathering with a weak chemical one. The relation curves of abundance of kaolinite and calcite against deposition age change steeply at the boundary between lacustrine and glacial deposits, indicating that the corresponding environment changes are abrupt, which may be related to different transportation fashion of both different deposits and the protection of glacial deposits.展开更多
An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents ...An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents and the microstructure of the composites and the particle size of the reinforcement were analysed using X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results have shown that TiCp/Al composite with 40～70 vol. pct TiC particle reinforcement and high relative density can be directly obtained by TE/QP. TiC is the only reaction product when Al content in Al-Ti-C system is no more than 60 vol. pct, but Al3Ti phase will also form when Al content is more than 60 vol. pct. Increasing Al content prolongs the initial reaction time, reduces the highest reaction temperature and the reaction rate, and decreases the size of TiC particles. In addition, the microstructure of TiCp/Al composite and the structure of interface between TiCp and Al are studied using SEM and transmission electron microscopy （TEM）. The results show that the in-situ synthesized TiC particle has fcc cubic structure. The orientation between TiC particles and Al matrix can be described as （220）Al//（022）TiC and [112]Al//[011]TiC. Results of the mechanical property tests reveal that the ultimate strength （σ） and modulus （E） are 687 MPa and 142 GPa respectively when the Al content is 40 vol. pct. On contrary, 6 elongation increases by 3.2% with increasing Al content.展开更多
Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance a...Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.展开更多
High-entropy alloys （HEAs） usually contain more than five alloying elements. The ductility of a body-centered cubic （bcc）- type HEA typically is lower than that of their face-centered cubic （fcc） counterpart. An...High-entropy alloys （HEAs） usually contain more than five alloying elements. The ductility of a body-centered cubic （bcc）- type HEA typically is lower than that of their face-centered cubic （fcc） counterpart. And low ductility restricts engineering applications of the bcc-structured HEAs. In engineering materials, improvement in ductility usually results in deduction of mechanical strength. A method to improve both mechanical strength and ductility in a bcc-structured HEA was proposed by adding interstitial carbon. Experimental results showed that replacement of 5 at.% Cr with 5 at.% C in a bcc-structured Fe35Mn25Al15Cr10Ni15 HEA resulted in an increase in fcc phase from 0.3 to 93.7 vol.%. Strength and ductility increased at the same time. The transition of bcc-structure to fcc-structure along with a remaining small amount of bcc phase improved mechanical properties. This work indicates that interstitial carbon can be employed to modulate the fraction of constituent phases in a bcc-structured HEA to enhance engineering mechanical properties.展开更多
Nb-Ti-Si-based alloy powders were prepared by mechanical alloying （MA） of elemental particles.The evolutions of morphology,size,phase constituents,crystallite size,lattice strain,composition and internal microstruct...Nb-Ti-Si-based alloy powders were prepared by mechanical alloying （MA） of elemental particles.The evolutions of morphology,size,phase constituents,crystallite size,lattice strain,composition and internal microstructure,etc.,of the alloy powders were analyzed by X-ray diffraction （XRD）,scanning electron microscopy （SEM）,energy-dispersive spectroscopy （EDS）,laser particle size analyzer and transmission electron microscope （TEM） analyses.The alloy particles are gradually refined and their shapes become globular with the increase in milling time.The diffraction peaks of Nb solid solution （Nbss） phase shift toward lower 2θ angles during ball milling from 2 to 5 h,and after that Nbss diffraction peaks shift toward higher 2θ angles with the increase in milling time from 5 to 70 h,which is mainly attributed to the alteration of the lattice parameter of Nbss powders due to the solution of the alloying element atoms into Nb lattice to form Nbss.During ball milling process,the decrease in crystallite size and increase in lattice strain of Nbss powders lead to continuous broadening of their diffraction peaks.A typical lamellar microstructure is formed inside the powder particles after ball milling for 5 h and becomes more refined and homogenized with the increase in milling time.After 40-h-ball milling,the typical lamellar microstructure disappears and a very homogeneous microstructure is formed instead.This homogeneous microstmcture is proved to be composed of only supersaturated Nbss phase.展开更多
基金Project supported by Natural Science Foundation of Shanxi Province (2007011067)
文摘Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. The experimental results show that the addition of 1.0% Y is beneficial to the formation of TiC particles; Al-Ti-C-1.0Y consists of rod-like and blocky TiAl3, TiC, Al3Y and α-Al matrix. Y is found around TiC particles in Al-Ti-C-0.5Y master alloy while blocky (AlTiY) phase appears in Al-Ti-C-1.0Y master alloy. Al3Y with dendritic morphology and small blocky Al2Y except for TiC are found in Al-Ti-C-2-0Y master alloy.
文摘X-ray microanalysis,convergent beam electron diffraction(CBD)and selected area electron diffraction(SAD)studies on the structures and compositions of the constituent phases in 2024 series Al alloys have been conducted.Partial substitution of alloying elements is found to occur in all the constituent phases,which cause small deviations from the stoichiometric com- positions reported in these ternary compounds.The dominant phase is α-Al_(12)(FeMn)_3Si which has a body center cubic crystal structure with the Im■ space group and a=1.25 nm.The next dominant phase is Cu_2FeAl_7 which has a primitive tetragonal crystal structure with the P4/mnc space group and a=0.6336 nm,c=1.487 nm.The minor phase is α'-Al_(12)Fe_3Si hav- ing α primitive cubic crystal structure with the Pm■ space group and α=1.27 nm.
文摘Through microstructure observation and X-ray diffraction analysis, the equilibrium phase constituents of Al-Zn alloy that contains 2 at. pct Cu at room temperature have been determined as Al-based solid solution (α), Zn-based solid solution and AI4Cu3Zn phase (T'-phase), which are different from a phase, Zn phase and CuZn4 phase originally believed. It is determined that the products of discontinuous precipitation transformation below 277℃ are not the equilibrium phase constituents, but the metastable phases made up of a phase, Zn phase and CuZn4 phase. The phase constituents after discontinuous precipitation of AIZn-2Cu alloy would transform to the ones in equilibrium status: Al-based solid solution (α) in fcc structure, Zn-based solid solution in hcp structure and AI4Cu3Zn phase (T'-phase) ultimately through plastic deformation at room temperature and re-heating treatment below 277℃.
文摘Based on analytical data of mineral phase constituents at three sections from Tern Lake, West Lake and Kitezh Lake in the Fildes Peninsula of King George Island, Antarctica, the characteristics of mineral phase constituents, material source and their environmental implication have been discussed. Research results indicate that lacustrine deposits came primarily from widespread volcanic rocks at the peninsula. Under cold and dry condition in Antarctica, the weathering process of the parent rocks in some area is mainly physical weathering with a weak chemical one. The relation curves of abundance of kaolinite and calcite against deposition age change steeply at the boundary between lacustrine and glacial deposits, indicating that the corresponding environment changes are abrupt, which may be related to different transportation fashion of both different deposits and the protection of glacial deposits.
文摘An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents and the microstructure of the composites and the particle size of the reinforcement were analysed using X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results have shown that TiCp/Al composite with 40～70 vol. pct TiC particle reinforcement and high relative density can be directly obtained by TE/QP. TiC is the only reaction product when Al content in Al-Ti-C system is no more than 60 vol. pct, but Al3Ti phase will also form when Al content is more than 60 vol. pct. Increasing Al content prolongs the initial reaction time, reduces the highest reaction temperature and the reaction rate, and decreases the size of TiC particles. In addition, the microstructure of TiCp/Al composite and the structure of interface between TiCp and Al are studied using SEM and transmission electron microscopy （TEM）. The results show that the in-situ synthesized TiC particle has fcc cubic structure. The orientation between TiC particles and Al matrix can be described as （220）Al//（022）TiC and [112]Al//[011]TiC. Results of the mechanical property tests reveal that the ultimate strength （σ） and modulus （E） are 687 MPa and 142 GPa respectively when the Al content is 40 vol. pct. On contrary, 6 elongation increases by 3.2% with increasing Al content.
基金Foundation item： National Natural Science Foundation of China （50671081）
文摘Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.
基金Acknowledgements This work was financially supported by the Joint Fund of Iron and Steel Research （No.U1660103） and National Natural Science Foundation of China （No. 51574162）. XRD, SEM and EBSD tests were conducted in the Instrumental Analysis ＆ Research Center at Shanghai University. The authors would like to express sincere thanks to the staff support at the Center. We thank Dr. Tyler for editing. Part of the work was undertaken in the US National High Magnetic Field Laboratory, which is supported by NSF DMR- 1157490, the State of Florida, and DOE.
文摘High-entropy alloys （HEAs） usually contain more than five alloying elements. The ductility of a body-centered cubic （bcc）- type HEA typically is lower than that of their face-centered cubic （fcc） counterpart. And low ductility restricts engineering applications of the bcc-structured HEAs. In engineering materials, improvement in ductility usually results in deduction of mechanical strength. A method to improve both mechanical strength and ductility in a bcc-structured HEA was proposed by adding interstitial carbon. Experimental results showed that replacement of 5 at.% Cr with 5 at.% C in a bcc-structured Fe35Mn25Al15Cr10Ni15 HEA resulted in an increase in fcc phase from 0.3 to 93.7 vol.%. Strength and ductility increased at the same time. The transition of bcc-structure to fcc-structure along with a remaining small amount of bcc phase improved mechanical properties. This work indicates that interstitial carbon can be employed to modulate the fraction of constituent phases in a bcc-structured HEA to enhance engineering mechanical properties.
基金financially supported by the National Natural Science Foundation of China(Nos.51371145,51431003,U1435201)the Research Fund of the State Key Laboratory of Solidification Processing,China(No.143-TZ-2016)the Doctorate Foundation of Northwestern Polytechnical University(No.CX201229)
文摘Nb-Ti-Si-based alloy powders were prepared by mechanical alloying （MA） of elemental particles.The evolutions of morphology,size,phase constituents,crystallite size,lattice strain,composition and internal microstructure,etc.,of the alloy powders were analyzed by X-ray diffraction （XRD）,scanning electron microscopy （SEM）,energy-dispersive spectroscopy （EDS）,laser particle size analyzer and transmission electron microscope （TEM） analyses.The alloy particles are gradually refined and their shapes become globular with the increase in milling time.The diffraction peaks of Nb solid solution （Nbss） phase shift toward lower 2θ angles during ball milling from 2 to 5 h,and after that Nbss diffraction peaks shift toward higher 2θ angles with the increase in milling time from 5 to 70 h,which is mainly attributed to the alteration of the lattice parameter of Nbss powders due to the solution of the alloying element atoms into Nb lattice to form Nbss.During ball milling process,the decrease in crystallite size and increase in lattice strain of Nbss powders lead to continuous broadening of their diffraction peaks.A typical lamellar microstructure is formed inside the powder particles after ball milling for 5 h and becomes more refined and homogenized with the increase in milling time.After 40-h-ball milling,the typical lamellar microstructure disappears and a very homogeneous microstructure is formed instead.This homogeneous microstmcture is proved to be composed of only supersaturated Nbss phase.
