Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characteri...Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation展开更多
Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates (5.32-250.0μm/s) at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus.The values of eutectic spac...Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates (5.32-250.0μm/s) at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus.The values of eutectic spacing were measured from transverse sections of the samples.The dependences of the eutectic spacing and undercooling on growth rate are determined as λ=9.21V-0.53 and ΔT=0.0245V0.53,respectively.The results obtained in this work were compared with the Jackson-Hunt eutectic theory and the similar experimental results in the literature.Microhardness of directionally solidified samples was also measured by using a microhardness test device.The dependency of the microhardness on growth rate is found as Hv=115.64V0.13.Afterwards,the electrical resistivity (r) of the casting alloy changes from 40×10-9 to 108×10-9 Ω·m with the temperature rising in the range of 300-630 K.The enthalpy of fusion (ΔH) and specific heat (Cp) for the Zn-Al eutectic alloy are calculated to be 113.37 J/g and 0.309 J/(g·K),respectively by means of differential scanning calorimetry (DSC) from heating trace during the transformation from liquid to solid.展开更多
Tb0.3Dy0.TFe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The re...Tb0.3Dy0.TFe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the (Tb,Dy)Fe2 phase changed from (113) to (111) direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is remarkably improved. The change in magnetostriction of Tb0.3Dy0.TFe1.95 alloys is linked to the amount and the crystal orientation behavior of the (Tb,Dy)Fe2 phase.展开更多
Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the ...Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.展开更多
The effect of rare earth element on the solidification behavior of Al-Mg alloy was investigated in a directional solidification apparatus.It was found that during the solidification process.the rare earth element segr...The effect of rare earth element on the solidification behavior of Al-Mg alloy was investigated in a directional solidification apparatus.It was found that during the solidification process.the rare earth element segregated in the liquid at sold-liquid interface,changed the solidification morphology and reduced the secondary arm spacing markedly.展开更多
A cellular automaton-lattice Boltzmann coupled model is extended to study the dendritic growth with melt convection in the solidification of ternary alloys. With a CALPHAD-based phase equilibrium engine, the effects o...A cellular automaton-lattice Boltzmann coupled model is extended to study the dendritic growth with melt convection in the solidification of ternary alloys. With a CALPHAD-based phase equilibrium engine, the effects of melt convection, solutal diffusion, interface curvature and preferred growth orientation are incorporated into the coupled model. After model validation, the multi dendritic growth of the Al-4.0 wt%Cu-1.0 wt%Mg alloy is simulated under the conditions of pure diffusion and melt convection. The result shows that the dendritic growth behavior, the final microstructure and microsegregation are significantly influenced by melt convection in the solidification.展开更多
The effect of Ce, La and mischmetal on the solidification structure of Fe-36Ni invar alloy was investigated. The results show that great amounts of high-melting point compounds ( Ce2O3, La202S and ( Ce, La)2O2S ) ...The effect of Ce, La and mischmetal on the solidification structure of Fe-36Ni invar alloy was investigated. The results show that great amounts of high-melting point compounds ( Ce2O3, La202S and ( Ce, La)2O2S ) respectively formed in the alloy with the addition of Ce, La or mischmetal. Based on the theory of lattice misfit, the lattice misfit between the (0001) surfaces of Ce2O3,Ce2O2S and La2O2S and (100) surface of Fe-36Ni invar alloy were 6.21%, 5.77 % and 5.42 %, respectively, which are relatively low. Therefore, Ce2 O3, La2 O2 S and ( Ce, La) 2 O2 S could serve as the core of heterogeneous nucleation, improve the equiaxed grain ratio, reduce the equiaxed grain size and refine the solidification structure of alloy.展开更多
High strength, ductility, and superplasticity Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr(wt%) alloy was prepared by sequentially applying rapid solidification, extrusion, and reciprocating extrusion(REX). The microstructure of...High strength, ductility, and superplasticity Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr(wt%) alloy was prepared by sequentially applying rapid solidification, extrusion, and reciprocating extrusion(REX). The microstructure of the alloy after 2-pass REX consisted of fine grains smaller than 0.7 μm and nanometer strengthening particles. The refined grains resulted from recrystallization during which the nanometer particles played an important role in restrain grain growth. The mechanical properties of the material were investigated at room and elevated temperatures. High tensile yield strength of 336 MPa and elongation of 27% were obtained at room temperature. At elevated temperatures, the highest elongation of 270% was obtained at 250 ℃ and an initial strain rate of 3.3×10^-3 s^-1, and LTS and HSRS were achieved. The high strength, ductility, and superplasticity were attributed to the refined unique microstructure.展开更多
In non-equilibrium nonlinear region, the nonlinear equations of time dependence of perturbation amplitude at the solid/liquidinterface during solidification of a dilute binary alloy are established on the base of assu...In non-equilibrium nonlinear region, the nonlinear equations of time dependence of perturbation amplitude at the solid/liquidinterface during solidification of a dilute binary alloy are established on the base of assuming that there is local equilibrium at the solid/liquid interface and considering that curvature, temperature and composition at the solid/liquid interface which are related to the perturbation amplitude are nonlinear. As a result, patterns at the solid/liquid interface during solidification process, which is from nonsteadystate to steady state can be controlled by these nonlinear equations.展开更多
Directional solidification methods are being used f or in-situ production of metallic immiscible composites. A quantitative understa nding of the dynamic behavior and growth kinetics of the nucleated second phase duri...Directional solidification methods are being used f or in-situ production of metallic immiscible composites. A quantitative understa nding of the dynamic behavior and growth kinetics of the nucleated second phase during solidification is necessary to produce homogeneous dispersion in solidifi ed composites. This paper presents a mathematical model for describing the grow th of nucleated dispersed phase in the two-liquid phase region ahead of the sol idification front and the entrapment of these droplets by the moving solid-liqu id interface in vertical unidirectional solidification systems. The model has t wo components. A macro-heat transfer model for describing the temperature prof iles and the rate of advance of the solidification front. The dynamic behavior and coalescence and growth of nucleated droplets in the two-liquid phase region under the influence of effective gravity and thermocapillary forces were repres ented through the solution the droplet momentum and mass conservation equations in particle space. These two components of the models were coupled through a sp ecial algorithm for tracking the particle location and size with respect to movi ng solidification front in the solidification time scale. The model is used to study the particle size distribution in unidirectional solidified Zn-Bi hypermo notectic alloys at reduced gravity conditions. It has been found that the parti cle size and distribution in the solidified alloy depends on solidification rate and the ratio of effective gravity to thermocapillary forces. It was also foun d that uniform dispersion could only be obtained in a very narrow range of effec tive gravity values near zero gravity. The model predictions were compared agai nst experimental measurements obtained at different effective gravity conditions in a novel unidirectional solidification apparatus that uses electromagnetic fo rces to modulate gravitational forces. The model was found to reasonably predic t the experimentally measured particle size and distribution over the entire ran ge of effective gravity investigated as well as gravity conditions for settling and flotation of the second phase during solidification. The practical signific ance of these findings will be discussed.展开更多
A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures: gravity...A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures: gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples' mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness(Hv = 122 MPa), compressive yield strength(382 MPa), tensile yield strength(332 MPa), ultimate tensile strength(370 MPa), and elongation(9%). This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.展开更多
The fractal structures formed in rapidly quenched Al_(86)Mn_(14)alloy have been observed on SEM.Their fractal dimensions are from 1.46 to 1.97.The principal phase examined by TEM and X-ray diffractometer is icosahedra...The fractal structures formed in rapidly quenched Al_(86)Mn_(14)alloy have been observed on SEM.Their fractal dimensions are from 1.46 to 1.97.The principal phase examined by TEM and X-ray diffractometer is icosahedral quasicrystalline one with a small amount of Al phase. It is believed that these fractal structures are formed by many aggregated particles during the rapid-quenching process.展开更多
Bascd on serires authors study ofAl—Li alloys in recent years,the formation theory of powders,characteristics,powder compaction,the microstructures and the mechanical behaviors of RSP Al-Li based alloys analyzed and ...Bascd on serires authors study ofAl—Li alloys in recent years,the formation theory of powders,characteristics,powder compaction,the microstructures and the mechanical behaviors of RSP Al-Li based alloys analyzed and discussed in this paper.展开更多
Al-3.8Li-0.8Mg-0.4Cu-0.13Zr alloy was prepared by a novel spray deposition technique,and its microstructure and tensile properties after various aging treatments have been investigated. The experimental results show t...Al-3.8Li-0.8Mg-0.4Cu-0.13Zr alloy was prepared by a novel spray deposition technique,and its microstructure and tensile properties after various aging treatments have been investigated. The experimental results show that the alloy,under study has very fine equiaxed grains about 5-20μm in diameter and a relative density of(94±3)% on average.Grains in the as-extruded alloy are'brick-like'in morphology,and few oxide particles have been found al the grain boundaries.δ' particles with irregular shape and'δ'-β''coprecipitates appear in the aged alloy.The coarsening of δ'particles is fast,and the distance between the particles does not widen so obviously as that of IM(ingot-casting method) alloys with increasing aging time.The spray deposited Al-Li alloy.reaches the peak-aged condition in a short time(10 h al 190℃) when the best properties(σb=534 MPa, σ0.2=480 MPa.δ=10%) are obtained.Compared with RSPM(rapid solidification processing method)Al-Li alloy,the ductility of the tested alloy has been obviously.enhanced while a comparable tensile strength is maintained.展开更多
Rapidly solidified Al 8Fe 4Ce alloy was prepared by melt spinning.As quenched and as annealed microstructures were studied by TEM and energy dispersive spectrum analysis.The microhardness of the alloy at different...Rapidly solidified Al 8Fe 4Ce alloy was prepared by melt spinning.As quenched and as annealed microstructures were studied by TEM and energy dispersive spectrum analysis.The microhardness of the alloy at different annealing temperature was measured.The results obtained indicated that as quenched microstructure varied with different cooling rates.The microstructure annealed at 300℃ was much the same as that of the as quenched.The dispersed phases at grain boundary of the microstructure annealed at 400℃ became coarsening.After annealing at 450℃ for 2 hours,the primary phase and the intercellular dispersed phases,metastable phase Al 6Fe and Al 20 Fe 5Ce respectively,coarsened further.The soften temperature was deduced at over 300℃ by measuring microhardness.展开更多
The phase constitution and solidification pathways of AZ91+xSb(x = 0, 0.1, 0.5, 1, in wt%) alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculat...The phase constitution and solidification pathways of AZ91+xSb(x = 0, 0.1, 0.5, 1, in wt%) alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91+xSb(x = 0.1, 0.5, 1) is composed of a-Mg matrix, b-Mg17Al12 phase, and intermetallic compound Mg3Sb2. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg3Sb2 phase forms after a-Mg nucleation, thus impossible acts as heterogeneous nucleus for a-Mg dendrite. Besides,the solid fraction at dendrite coherency point(fDCPs) determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.展开更多
The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction(...The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction(XRD) and Vickers-hardness testing. Under atmospheric-pressure solidification, Mg-6Zn-1Y consisted of α-Mg, Mg7Zn3 and Mg_3YZn_6; whilst Mg-6Zn-3Y consisted of α-Mg, Mg_3Y_2Zn_3 and Mg_3YZn_6. Under 6 GPa high-pressure solidification, both alloy consisted of α-Mg, MgZ n and Mg12 YZn. The shape of the main second phase changed from a lamellar structure formed for atmospheric-pressure solidification to small particles formed for solidification at 6 GPa pressure. The dendrite microstructure was refined and was more regular, and the length of the primary dendrite arm increased under 6 GPa high-pressure solidification, which was attributed to increasing thermal undercooling, compositional undercooling and kinetics undercooling. After solidification at 6 GPa pressure, the solid solubility of Y in the second phase and the Vickers-hardness increased from 15 wt.% and 69 MPa for Mg-6Zn-1Y to 49 wt.% and 97 MPa; and from 19 wt.% and 71 MPa for Mg-6Zn-3Y alloy to 20 wt.% and 92 MPa, respectively.展开更多
A model was developed to describe the microstracture evolution in a directionally solidified ternary monotectic alloy.The directional solidification experiments were carried out on Al-3Pb-lSn(wt%) alloys by using a ...A model was developed to describe the microstracture evolution in a directionally solidified ternary monotectic alloy.The directional solidification experiments were carried out on Al-3Pb-lSn(wt%) alloys by using a Bridgman apparatus.The microstracture evolution in the directionally solidified sample was calculated.The numerical results agree well with the experimental ones.It is demonstrated that the nucleation of the minority phase droplets occur at two different positions.One corresponds to the liquid-liquid decomposition,which occurs in front of the solidification interface.The other is at the liquid/solid interface.The nucleation rate of the minority phase droplets at the liquid/solid interface is significantly higher than at the position in front of the solidification interface.The characteristic of the nucleation process leads to a bimodal size distribution of the minority particles in the directionally solidified sample.展开更多
The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of t...The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of the commercial casting simulation package, ProCASTTM, were used to model the mold filling and solidification events employing a range of interfacial heat transfer coefficient values. The simulation results were used to estimate the centerline cooling curve at various locations through the casting. The centerline cooling curves, together with the die temperature and the thermodynamic properties of the alloy, were then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting, Finally, the local cooling rate was used to calculate the resulting grain size via previously established relationships. The effects of die temperature, filling time and heat transfer coefficient on the grain structure in skin region and core region were quantitatively characterized. It was observed that the grain size of skin region strongly depends on above three factors whereas the grain size of core region shows dependence on the interracial heat transfer coefficient and thickness of the samples. The grain size distribution from surface to center was estimated from the relationship between grain size and the predicted cooling rate. The prediction of grain size matches well with experimental results. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent interracial heat transfer coefficient for different locations.展开更多
Nd_9Fe_(85–x)Ti_4C_2B_x(x=10–15) magnetic alloys were investigated by differential thermal analysis and X-ray diffraction analysis. The results showed that with the B content increasing from 10 at.% to 15 at.%, ...Nd_9Fe_(85–x)Ti_4C_2B_x(x=10–15) magnetic alloys were investigated by differential thermal analysis and X-ray diffraction analysis. The results showed that with the B content increasing from 10 at.% to 15 at.%, the liquidus temperatures TL of the alloys decreased from 1498.5 to 1472.5 K; the solidus temperatures TS of them increased from 1353.2 to 1358.3 K; and the nucleation undercooling of the alloy melts cooled at the rate of 40 K/min decreased from 122.8 to 95.9 K, resulting in the solidification structures consisting of Nd_2Fe_(14)B, Fe_3B, α-Fe, Nd1.1Fe4B4 and TiC nanocrystallines. Furthermore, the Nd_9Fe_(85–x)Ti_4C_2B_x(x=11, 13, 15) bulk alloys in sheet form with the thickness of 0.7 mm were prepared by copper mold suction casting and their solidification characteristics and solidification structures under sub-rapidly cooling rate were investigated. The results showed that partially amorphous structures were obtained in the as-cast bulk alloys and the amount of amorphous decreased with the increase of the B content. By annealing the as-cast bulk alloys at 923 K for 10 min, the nanocomposite microstructures composed with Nd_2Fe_(14)B, Fe_3B and α-Fe nanocrystallines, which showed a single-phase hard magnetic behavior and enhanced magnetic properties, were achieved.展开更多
文摘Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation
基金supported by Erciyes University Scientific Research Project Unit (No.FBA-10-3376)
文摘Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates (5.32-250.0μm/s) at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus.The values of eutectic spacing were measured from transverse sections of the samples.The dependences of the eutectic spacing and undercooling on growth rate are determined as λ=9.21V-0.53 and ΔT=0.0245V0.53,respectively.The results obtained in this work were compared with the Jackson-Hunt eutectic theory and the similar experimental results in the literature.Microhardness of directionally solidified samples was also measured by using a microhardness test device.The dependency of the microhardness on growth rate is found as Hv=115.64V0.13.Afterwards,the electrical resistivity (r) of the casting alloy changes from 40×10-9 to 108×10-9 Ω·m with the temperature rising in the range of 300-630 K.The enthalpy of fusion (ΔH) and specific heat (Cp) for the Zn-Al eutectic alloy are calculated to be 113.37 J/g and 0.309 J/(g·K),respectively by means of differential scanning calorimetry (DSC) from heating trace during the transformation from liquid to solid.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51425401 and 51271056the Fundamental Research Funds for the Central Universities under Grant Nos N140901001 and N140902001the Doctoral Scientific Research Foundation of Liaoning Province under Grant No 20131034
文摘Tb0.3Dy0.TFe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the (Tb,Dy)Fe2 phase changed from (113) to (111) direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is remarkably improved. The change in magnetostriction of Tb0.3Dy0.TFe1.95 alloys is linked to the amount and the crystal orientation behavior of the (Tb,Dy)Fe2 phase.
文摘Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.
文摘The effect of rare earth element on the solidification behavior of Al-Mg alloy was investigated in a directional solidification apparatus.It was found that during the solidification process.the rare earth element segregated in the liquid at sold-liquid interface,changed the solidification morphology and reduced the secondary arm spacing markedly.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51306037 and 51371051
文摘A cellular automaton-lattice Boltzmann coupled model is extended to study the dendritic growth with melt convection in the solidification of ternary alloys. With a CALPHAD-based phase equilibrium engine, the effects of melt convection, solutal diffusion, interface curvature and preferred growth orientation are incorporated into the coupled model. After model validation, the multi dendritic growth of the Al-4.0 wt%Cu-1.0 wt%Mg alloy is simulated under the conditions of pure diffusion and melt convection. The result shows that the dendritic growth behavior, the final microstructure and microsegregation are significantly influenced by melt convection in the solidification.
文摘The effect of Ce, La and mischmetal on the solidification structure of Fe-36Ni invar alloy was investigated. The results show that great amounts of high-melting point compounds ( Ce2O3, La202S and ( Ce, La)2O2S ) respectively formed in the alloy with the addition of Ce, La or mischmetal. Based on the theory of lattice misfit, the lattice misfit between the (0001) surfaces of Ce2O3,Ce2O2S and La2O2S and (100) surface of Fe-36Ni invar alloy were 6.21%, 5.77 % and 5.42 %, respectively, which are relatively low. Therefore, Ce2 O3, La2 O2 S and ( Ce, La) 2 O2 S could serve as the core of heterogeneous nucleation, improve the equiaxed grain ratio, reduce the equiaxed grain size and refine the solidification structure of alloy.
基金Funded by the National Natural Foundation of China(No.51571086)China Postdoctoral Science Foundation(No.2013M541973)The Research Fund for Doctoral Program of Henan Polytechnic University(No.B2015-14)
文摘High strength, ductility, and superplasticity Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr(wt%) alloy was prepared by sequentially applying rapid solidification, extrusion, and reciprocating extrusion(REX). The microstructure of the alloy after 2-pass REX consisted of fine grains smaller than 0.7 μm and nanometer strengthening particles. The refined grains resulted from recrystallization during which the nanometer particles played an important role in restrain grain growth. The mechanical properties of the material were investigated at room and elevated temperatures. High tensile yield strength of 336 MPa and elongation of 27% were obtained at room temperature. At elevated temperatures, the highest elongation of 270% was obtained at 250 ℃ and an initial strain rate of 3.3×10^-3 s^-1, and LTS and HSRS were achieved. The high strength, ductility, and superplasticity were attributed to the refined unique microstructure.
文摘In non-equilibrium nonlinear region, the nonlinear equations of time dependence of perturbation amplitude at the solid/liquidinterface during solidification of a dilute binary alloy are established on the base of assuming that there is local equilibrium at the solid/liquid interface and considering that curvature, temperature and composition at the solid/liquid interface which are related to the perturbation amplitude are nonlinear. As a result, patterns at the solid/liquid interface during solidification process, which is from nonsteadystate to steady state can be controlled by these nonlinear equations.
文摘Directional solidification methods are being used f or in-situ production of metallic immiscible composites. A quantitative understa nding of the dynamic behavior and growth kinetics of the nucleated second phase during solidification is necessary to produce homogeneous dispersion in solidifi ed composites. This paper presents a mathematical model for describing the grow th of nucleated dispersed phase in the two-liquid phase region ahead of the sol idification front and the entrapment of these droplets by the moving solid-liqu id interface in vertical unidirectional solidification systems. The model has t wo components. A macro-heat transfer model for describing the temperature prof iles and the rate of advance of the solidification front. The dynamic behavior and coalescence and growth of nucleated droplets in the two-liquid phase region under the influence of effective gravity and thermocapillary forces were repres ented through the solution the droplet momentum and mass conservation equations in particle space. These two components of the models were coupled through a sp ecial algorithm for tracking the particle location and size with respect to movi ng solidification front in the solidification time scale. The model is used to study the particle size distribution in unidirectional solidified Zn-Bi hypermo notectic alloys at reduced gravity conditions. It has been found that the parti cle size and distribution in the solidified alloy depends on solidification rate and the ratio of effective gravity to thermocapillary forces. It was also foun d that uniform dispersion could only be obtained in a very narrow range of effec tive gravity values near zero gravity. The model predictions were compared agai nst experimental measurements obtained at different effective gravity conditions in a novel unidirectional solidification apparatus that uses electromagnetic fo rces to modulate gravitational forces. The model was found to reasonably predic t the experimentally measured particle size and distribution over the entire ran ge of effective gravity investigated as well as gravity conditions for settling and flotation of the second phase during solidification. The practical signific ance of these findings will be discussed.
基金financially supported by the Czech Science Foundation(No.P108/12/G043)
文摘A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures: gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples' mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness(Hv = 122 MPa), compressive yield strength(382 MPa), tensile yield strength(332 MPa), ultimate tensile strength(370 MPa), and elongation(9%). This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.
文摘The fractal structures formed in rapidly quenched Al_(86)Mn_(14)alloy have been observed on SEM.Their fractal dimensions are from 1.46 to 1.97.The principal phase examined by TEM and X-ray diffractometer is icosahedral quasicrystalline one with a small amount of Al phase. It is believed that these fractal structures are formed by many aggregated particles during the rapid-quenching process.
文摘Bascd on serires authors study ofAl—Li alloys in recent years,the formation theory of powders,characteristics,powder compaction,the microstructures and the mechanical behaviors of RSP Al-Li based alloys analyzed and discussed in this paper.
文摘Al-3.8Li-0.8Mg-0.4Cu-0.13Zr alloy was prepared by a novel spray deposition technique,and its microstructure and tensile properties after various aging treatments have been investigated. The experimental results show that the alloy,under study has very fine equiaxed grains about 5-20μm in diameter and a relative density of(94±3)% on average.Grains in the as-extruded alloy are'brick-like'in morphology,and few oxide particles have been found al the grain boundaries.δ' particles with irregular shape and'δ'-β''coprecipitates appear in the aged alloy.The coarsening of δ'particles is fast,and the distance between the particles does not widen so obviously as that of IM(ingot-casting method) alloys with increasing aging time.The spray deposited Al-Li alloy.reaches the peak-aged condition in a short time(10 h al 190℃) when the best properties(σb=534 MPa, σ0.2=480 MPa.δ=10%) are obtained.Compared with RSPM(rapid solidification processing method)Al-Li alloy,the ductility of the tested alloy has been obviously.enhanced while a comparable tensile strength is maintained.
文摘Rapidly solidified Al 8Fe 4Ce alloy was prepared by melt spinning.As quenched and as annealed microstructures were studied by TEM and energy dispersive spectrum analysis.The microhardness of the alloy at different annealing temperature was measured.The results obtained indicated that as quenched microstructure varied with different cooling rates.The microstructure annealed at 300℃ was much the same as that of the as quenched.The dispersed phases at grain boundary of the microstructure annealed at 400℃ became coarsening.After annealing at 450℃ for 2 hours,the primary phase and the intercellular dispersed phases,metastable phase Al 6Fe and Al 20 Fe 5Ce respectively,coarsened further.The soften temperature was deduced at over 300℃ by measuring microhardness.
基金financially supported by the National Basic Research Program of China (No. 2013CB632202)the National Natural Science Foundation of China (Nos. 51105350 and 51301173)
文摘The phase constitution and solidification pathways of AZ91+xSb(x = 0, 0.1, 0.5, 1, in wt%) alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91+xSb(x = 0.1, 0.5, 1) is composed of a-Mg matrix, b-Mg17Al12 phase, and intermetallic compound Mg3Sb2. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg3Sb2 phase forms after a-Mg nucleation, thus impossible acts as heterogeneous nucleus for a-Mg dendrite. Besides,the solid fraction at dendrite coherency point(fDCPs) determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.
基金Project supported by the China Scholarship Council(2011836024)the International Science and Technology Cooperation Project of Jiangxi Province(20151BDH80006)+5 种基金the Prior Science and Technology Program led by the Returned Overseas Chinese Talents(RSTH[2015]192-GRSZ[2015]273)the Key Program of Natural Science Foundation of Jiangxi Province(20133BAB2000820144ACB20013)the Science and Technology Innovation Project of Jiangxi Academy of Sciences(2013-YYB-12013-XTPH1-192015XTTD04)
文摘The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction(XRD) and Vickers-hardness testing. Under atmospheric-pressure solidification, Mg-6Zn-1Y consisted of α-Mg, Mg7Zn3 and Mg_3YZn_6; whilst Mg-6Zn-3Y consisted of α-Mg, Mg_3Y_2Zn_3 and Mg_3YZn_6. Under 6 GPa high-pressure solidification, both alloy consisted of α-Mg, MgZ n and Mg12 YZn. The shape of the main second phase changed from a lamellar structure formed for atmospheric-pressure solidification to small particles formed for solidification at 6 GPa pressure. The dendrite microstructure was refined and was more regular, and the length of the primary dendrite arm increased under 6 GPa high-pressure solidification, which was attributed to increasing thermal undercooling, compositional undercooling and kinetics undercooling. After solidification at 6 GPa pressure, the solid solubility of Y in the second phase and the Vickers-hardness increased from 15 wt.% and 69 MPa for Mg-6Zn-1Y to 49 wt.% and 97 MPa; and from 19 wt.% and 71 MPa for Mg-6Zn-3Y alloy to 20 wt.% and 92 MPa, respectively.
基金supported by the National Natural Science Foundation of China(Nos.51471173,51271185 and 51031003)China Manned Space Engineering
文摘A model was developed to describe the microstracture evolution in a directionally solidified ternary monotectic alloy.The directional solidification experiments were carried out on Al-3Pb-lSn(wt%) alloys by using a Bridgman apparatus.The microstracture evolution in the directionally solidified sample was calculated.The numerical results agree well with the experimental ones.It is demonstrated that the nucleation of the minority phase droplets occur at two different positions.One corresponds to the liquid-liquid decomposition,which occurs in front of the solidification interface.The other is at the liquid/solid interface.The nucleation rate of the minority phase droplets at the liquid/solid interface is significantly higher than at the position in front of the solidification interface.The characteristic of the nucleation process leads to a bimodal size distribution of the minority particles in the directionally solidified sample.
基金jointly supported by Canadian Network for Research and Innovation in Machining TechnologyNatural Sciences and Engineering Research Council of Canada-Automotive Partnership Canada programNRCan’s Office of Energy R&D through the Program on Energy R&D
文摘The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of the commercial casting simulation package, ProCASTTM, were used to model the mold filling and solidification events employing a range of interfacial heat transfer coefficient values. The simulation results were used to estimate the centerline cooling curve at various locations through the casting. The centerline cooling curves, together with the die temperature and the thermodynamic properties of the alloy, were then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting, Finally, the local cooling rate was used to calculate the resulting grain size via previously established relationships. The effects of die temperature, filling time and heat transfer coefficient on the grain structure in skin region and core region were quantitatively characterized. It was observed that the grain size of skin region strongly depends on above three factors whereas the grain size of core region shows dependence on the interracial heat transfer coefficient and thickness of the samples. The grain size distribution from surface to center was estimated from the relationship between grain size and the predicted cooling rate. The prediction of grain size matches well with experimental results. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent interracial heat transfer coefficient for different locations.
基金Project supported by National Natural Science Foundation of China(51174121,51274125)Zhejiang Province Science and Technology Innovation Team of Key Projects(2010R50016-30)
文摘Nd_9Fe_(85–x)Ti_4C_2B_x(x=10–15) magnetic alloys were investigated by differential thermal analysis and X-ray diffraction analysis. The results showed that with the B content increasing from 10 at.% to 15 at.%, the liquidus temperatures TL of the alloys decreased from 1498.5 to 1472.5 K; the solidus temperatures TS of them increased from 1353.2 to 1358.3 K; and the nucleation undercooling of the alloy melts cooled at the rate of 40 K/min decreased from 122.8 to 95.9 K, resulting in the solidification structures consisting of Nd_2Fe_(14)B, Fe_3B, α-Fe, Nd1.1Fe4B4 and TiC nanocrystallines. Furthermore, the Nd_9Fe_(85–x)Ti_4C_2B_x(x=11, 13, 15) bulk alloys in sheet form with the thickness of 0.7 mm were prepared by copper mold suction casting and their solidification characteristics and solidification structures under sub-rapidly cooling rate were investigated. The results showed that partially amorphous structures were obtained in the as-cast bulk alloys and the amount of amorphous decreased with the increase of the B content. By annealing the as-cast bulk alloys at 923 K for 10 min, the nanocomposite microstructures composed with Nd_2Fe_(14)B, Fe_3B and α-Fe nanocrystallines, which showed a single-phase hard magnetic behavior and enhanced magnetic properties, were achieved.