Due to the significant differences in the formation temperature and crystal structure between the primaryα-Mg and eutecticβ-Mg_(17)Al_(12),it is a great challenge to achieve simultaneous refinement of the primary an...Due to the significant differences in the formation temperature and crystal structure between the primaryα-Mg and eutecticβ-Mg_(17)Al_(12),it is a great challenge to achieve simultaneous refinement of the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation.Surprisingly,we found that theα-Mg andβ-Mg_(17)Al_(12) in the AZ80 alloy can be simultaneously refined after 0.2 wt.%Sm addition,with the grain size decreasing from∼217±15μm to∼170±10μm and theβ-Mg_(17)Al_(12) morphology changing from a typical continuous network to a nod-like or spherical structure.The simultaneous refinement mechanism is investigated through solidification simulation,transmission electron microscopy(TEM),and differential thermal analysis(DTA).In the AZ80-0.2Sm alloy,many Al8Mn4Sm particles can be observed near the center of theα-Mg grains or inside theβ-Mg_(17)Al_(12).Crystallographic calculations further reveal that the Al8Mn4Sm has good crystallographic matching with both theα-Mg andβ-Mg_(17)Al_(12),so it possesses the potency to serve as heterogeneous nucleation sites for both phases.The promoted heterogeneous nucleation on the Al8Mn4Sm decreases the undercooling required by the nucleation of the primary and eutectic phases,which enhances the heterogeneous nucleation rate,thus causing the simultaneous refinement of theα-Mg andβ-Mg_(17)Al_(12).The orientation relationships between the Al8Mn4Sm and Mg/Mg_(17)Al_(12) are identified,which are[1210]_(Mg)//[010]_(Al8Mn4Sm),(1010)_(Mg)//(301)_(Al8Mn4Sm) and[112]_(Mg_(17)Al_(12))//[010]_(Al8Mn4Sm),(110)_(Mg_(17)Al_(12))//(301)_(Al8Mn4Sm),respectively.Furthermore,the refinement of theβ-Mg_(17)Al_(12) accelerates its dissolution during the solution treatment,which is beneficial for cost saving in industrial applications.Other Al8Mn4RE compounds such as Al8Mn4Y might have the same positive effect on the simultaneous refinement due to the similar physicochemical properties of rare earth elements.This work not only proves the possibility of simultaneously refining the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation,but also provides new insights into the development of refiners for cast Mg alloys.展开更多
The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucl...The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucleation sites and number of SiC present in the alloy.The aim of this paper was selection of parameters for the model describing the relationship between the grain density of primary phase and undercooling.This model in connection with model of crystallisation,which is based on chemical elements diffusion and grain interface kinetics,can be used to predict casting quality and its microstructure.Nucleation models have parameters,which exact values are usually not known and sometimes even their physical meaning is under discussion.Those parameters can be obtained after mathematical analysis of the experimental data.The composites with 0,1,2,3 and 4wt.% of SiC particles were prepared.The AZ91 alloy was a matrix of the composite reinforcement SiC particles.This composite was cast to prepare four different thickness plates.They were taken from the region near to the thermocouple,to analyze the undercooling for different composites and thickness plates and its influence on the grain size.The microstructure and thermal analysis gave set of values that connect mass fraction of SiC particles,and undercooling with grain size.These values were used to approximate nucleation model adjustment parameters.Obtained model can be very useful in modelling composites microstructure.展开更多
The heterogeneous nucleation process of NH4Cl crystals from a NH4Cl-70wt.%H2O solution on rough chilling substrates was considered in this paper. Scratched and etched substrates of aluminum were prepared with differen...The heterogeneous nucleation process of NH4Cl crystals from a NH4Cl-70wt.%H2O solution on rough chilling substrates was considered in this paper. Scratched and etched substrates of aluminum were prepared with different surface morphologies. It was concluded that for nucleation to occur on a rough substrate surface, the wettability or the generally said roughness are not the key factors affecting the heterogeneous nucleation process. Rather the surface morphologies on the nanometer scale, which is close to the scale of the critical nucleation radius, are more important.展开更多
Flaky graphite particles were coated by ZrOCl2 · 8H2O as precursors by heterogeneous nucleation process. The effects of factors such as pH values ( 2. 4 - 5. 1 ), concentration of the precursor solution ( 0. 0...Flaky graphite particles were coated by ZrOCl2 · 8H2O as precursors by heterogeneous nucleation process. The effects of factors such as pH values ( 2. 4 - 5. 1 ), concentration of the precursor solution ( 0. 005 - 0. 1 mol · L^-1) , mixing method of graphite and precursor solution on the surface modification of graphite were studied. Result shows that :1 ) the preferable technical process for heterogeneous nucleation modified graphite is to mix the graphite suspension and precursor solution with concentration 0. 025 mol ·L^-1 and then drip ammonia water to adjust the pH value to 3.6 ; 2 ) By surface modification, the ZrO2 particles are evenly coated on graphite surface and therefore improve oxidation resistance and dispersion ability of graphite.展开更多
Titanium diboride(TiB_(2))is an effective grain refiner of Al alloys in the industry that facilitates casting processes by forming uniformly refined microstructures.Although our understanding of the underlying refinem...Titanium diboride(TiB_(2))is an effective grain refiner of Al alloys in the industry that facilitates casting processes by forming uniformly refined microstructures.Although our understanding of the underlying refinement mechanisms has advanced,the atomic kinetics of heterogeneous nucleation of Al on TiB2 remains unknown.Here,we report atomic-scale observations of the heterogeneous nucleation and growth kinetics of Al on self-formed TiB_(2) particles by in situ heating of undercooled Al-5Ti-1B films.We demonstrate that an ordered Al monolayer forms on the Ti-terminated{0001}TiB_(2) surface;then,the surrounding Al atoms are initiated to form an island-shaped Al nucleus with face-centered cubic{111}stacking without the assistance of a Ti-rich buffer layer.The interfacial lattice mismatch between{111}Al and{0001}TiB_(2) causes remarkable out-of-plane strain that decreases gradually with Al nucleus layers increasing to 6 atomic layers.The elastic strain energy originating from this interfacial strain increases the free energy of the Al/TiB2 heterostructure,hence impeding the rapid growth of the Al nucleus.We found that TiB2 particles stabilize the Al nuclei rather than activating their free growth into grains when the experimental undercoolingΔT is lower than the onset undercoolingΔT fg in Greer's free growth model.Our findings provide an atomic-scale physical image of the heterogeneous nucleation and growth mechanisms of Al with inoculator participation and elucidate the strain-dependent growth kinetics of Al nuclei.展开更多
Plasma spray-physical vapor deposition(PS-PVD) as a novel coating process based on low-pressure plasma spray(LPPS) has been significantly used for thermal barrier coatings(TBCs).A coating can be deposited from l...Plasma spray-physical vapor deposition(PS-PVD) as a novel coating process based on low-pressure plasma spray(LPPS) has been significantly used for thermal barrier coatings(TBCs).A coating can be deposited from liquid splats, nano-sized clusters, and the vapor phase forming different structured coatings, which shows obvious advantages in contrast to conventional technologies like atmospheric plasma spray(APS) and electron beam-physical vapor deposition(EBPVD). In addition, it can be used to produce thin, dense, and porous ceramic coatings for special applications because of its special characteristics, such as high power, very low pressure, etc. These provide new opportunities to obtain different advanced microstructures, thus to meet the growing requirements of modern functional coatings. In this work, focusing on exploiting the potential of gas-phase deposition from PS-PVD, a series of 7 YSZ coating experiments with various process conditions was performed in order to better understand the deposition process in PS-PVD, where coatings were deposited on different substrates including graphite and zirconia. Meanwhile, various substrate temperatures were investigated for the same substrate. As a result, a deposition mechanism of heterogeneous nucleation has been presented showing that surface energy is an important influencing factor for coating structures. Besides, undercooling of the interface between substrate and vapor phase plays an important role in coating structures.展开更多
The segregation behavior of alloying elements X( X = Zr,V,Cr,Mn,Mo,W,Nb,Y) on the ferrite( 100) /TiC( 100) interface has been investigated using first principles method,and the work of separation and interface e...The segregation behavior of alloying elements X( X = Zr,V,Cr,Mn,Mo,W,Nb,Y) on the ferrite( 100) /TiC( 100) interface has been investigated using first principles method,and the work of separation and interface energy of ferrite / TiC interfaces alloyed by these elements were also analyzed. The results indicated that all these alloying additives except Y were thermodynamically favorable because of the negative segregation energy,showing that they have the tendency to segregate to the ferrite / TiC interface. When the Fe atom in the ferrite /TiC interface is replaced by Y,Zr,or Nb,the adhesive strength of the interface will be weakened due to the lower separation work,larger interfacial energy,and weaker electron effects. However,the introduction of Cr,Mo,W,Mn and V will improve the stability of the ferrite / TiC interface through strong interaction between these elements and C,and Cr-doped interface is the most stable structure. Therefore,the Cr,Mo,W,Mn and V in ferrite side of the interface can effectively promote ferrite heterogeneous nucleation on TiC surface to form fine ferrite grain.展开更多
Sodium/Potassium(Na/K)metal anodes have been considered as the promising anodes for next-generation Na/K secondary batteries owing to their ultrahigh specific capacity,low redox potential and low cost.However,their pr...Sodium/Potassium(Na/K)metal anodes have been considered as the promising anodes for next-generation Na/K secondary batteries owing to their ultrahigh specific capacity,low redox potential and low cost.However,their practical application is still hampered due to unstable solid electrolyte interphase,infinite volume change,and dendrite growth.Herein,we design a 3D-Na_(3)Bi/3D-K_(3)Bi alloy host which enables the homogeneous and heterogeneous nucleation growth of Na/K metal.The unique structure with periodic alternating of electron and ion conductivity improves the mass transfer kinetics and prevents the volume expansion during cycling.Meanwhile,the sodiophilicity of Na_(3)Bi/potassiophilicity of K_(3)Bi framework can avoid dendritic growth.Cycling lifespans over 700 h with 1 mAh cm^(−2)for 3D-Na_(3)Bi@Na electrode and about 450 h with 1 mAh cm^(−2)for 3D-K_(3)Bi@K electrode are achieved,respectively.3D-Na_(3)Bi@Na||Na_(3)V_(2)(PO_(4))3 full battery shows sustainable cycle performance over 400 cycles.This design provides a simple but effective approach for achieving safety of sodium/potassium metal anodes.展开更多
The development of rechargeable magnesium(Mg) batteries is of practical significance to upgrade the electric energy storage devices due to exceptional capacity and abundant resources of Mg-metal anode.However,the reve...The development of rechargeable magnesium(Mg) batteries is of practical significance to upgrade the electric energy storage devices due to exceptional capacity and abundant resources of Mg-metal anode.However,the reversible Mg electrochemistry suffers from unsatisfied rate capability and lifespan,mainly caused by non-uniform distribution of electrodeposits.In this work,a fresh design concept of threedimensional carbon cloths scaffolds is proposed to overcome the uncontrollable Mg growth via homogenizing electric field and improving magnesiophilicity.A microscopic smooth and nitrogen-containing defective carbonaceous layer is constructed through a facile pyrolysis of ZIF8 on carbon cloths.As revealed by finite element simulation and DFT calculation results,the smooth surface endows with uniform electric field distribution and simultaneously the nitrogen-doping species enable good magnesiophilicity of scaffolds.The fine and uniform Mg nucleus as well as the inner electrodeposit behavior are also disclosed.As a result,an exceptional cycle life of 500 cycles at 4.0 mA cm^(-2) and 4.0 mA h cm^(-2) is firstly realized to our best knowledge.Besides,the functional scaffolds can be cycled for over 2200 h at 2.0 mA cm^(-2) under a normalized capacity of 5.0 mA h cm^(-2),far exceeding previous results.This work offers an effective approach to enable the full potential of carbon cloths-based scaffolds towards metal storage for next generation battery applications.展开更多
This study revealed the nucleation event and grain refinement mechanism of Mg-Al alloy induced by Fe impurity.The following orientation relationship was observed between Al-Fe particle andα-Mg matrix in the Mg-3Al al...This study revealed the nucleation event and grain refinement mechanism of Mg-Al alloy induced by Fe impurity.The following orientation relationship was observed between Al-Fe particle andα-Mg matrix in the Mg-3Al alloy containing Fe impurity using a focused ion beam aided transmission electron microscope technique:(1^(-)011)[011^(-)1]_(Mg)//(011^(-))[011]_(Al_(2)Fe).Mg-3Al alloy was inoculated by adding 0.02wt%Fe to verify the nucleating potency of the Al_(2)Fe phase forα-Mg grain.The results indicated that Mg-3Al alloy was effectively refined with an average grain size declining from 1135 to 540μm.Among the potential Al-Fe phases of Mg-3Al-0.02Fe alloy,only the precipitation of the Al_(2)Fe phase occurs earlier than that ofα-Mg grain,and the Al_(2)Fe phase is stable in the nucleation stage ofα-Mg grain.Therefore,the Al_(2)Fe particle is the only available nucleating site for Mg-Al alloy with Fe impurity.The heterogeneous nucleation event ofα-Mg grain on the Al_(2)Fe particle is responsible for the grain refinement of Mg-3Al alloy inoculated by Fe.展开更多
The precipitation behavior of V(C, N) in steels microalloyed with vanadium was researched using a thermal simulator during single-pass deformation at 800-750 ℃. The V(C, N) precipitates and its nucleation effect ...The precipitation behavior of V(C, N) in steels microalloyed with vanadium was researched using a thermal simulator during single-pass deformation at 800-750 ℃. The V(C, N) precipitates and its nucleation effect on ferrite were investigated by TEM and EDS. The experimental results show that there are two remarkable heterogeneous nucleation effects of V(C, N) particles precipitated before γ →/ α phase change: primary reason is that high coherency between V(C, N) and ferrite promotes V(C, N) to become a nucleating center of intragranular ferrite; secondary reason is that the coarsening of V(C, N) causes locally solute-poor region in austenite, thus expedites the nucleation of intragranular ferrites further. Furthermore, the relationship between the size and shape of V(C, N) was studied, and identification method was provided for distinguishing interphase precipitation and general precipitation to avoid erroneous judgment and misguide.展开更多
A thermodynamic approach at the nanometer scale was performed for the heterogeneous nucleation inside nanocavity, and an analytical expression of the critical energy of nucleation was evaluated considering a rough bal...A thermodynamic approach at the nanometer scale was performed for the heterogeneous nucleation inside nanocavity, and an analytical expression of the critical energy of nucleation was evaluated considering a rough ball nucleus nucleating inside nanocavity. Compared with the case of the nucleation locating on planar or convex substrate, the critical energy of nucleation inside the concave substrate is the smallest. Based on the thermodynamic and kinetic analyses, at low supersaturation, the smaller the curvature radius of cavity and/or the smaller the contact angle, the smaller the critical energy of nucleation, and the larger the nucleation rate. At high supersaturation, the nucleation rate increases with increasing the contact angle and/or increasing the curvature radius of cavity. In this way, at the low supersaturation, the heterogeneous nucleation rate is larger than the homogeneous one, as the nucleation rate is mainly determined by the heterogeneous nucleation. At the high supersaturation, the heterogeneous nucleation rate is smaller than the homogeneous one, as the nucleation rate is mainly determined by the homogeneous nucleation.展开更多
The effect of Ce content(0–1.6 wt.%)on the modification of Mg_(2)Si phase in the as-cast Mg-5Al-2Si alloy was investigated.The original Chinese script type Mg_(2)Si phase was refined distinctly and transformed to dis...The effect of Ce content(0–1.6 wt.%)on the modification of Mg_(2)Si phase in the as-cast Mg-5Al-2Si alloy was investigated.The original Chinese script type Mg_(2)Si phase was refined distinctly and transformed to dispersive block shape gradually by adding Ce element.The length of Chinese script type Mg_(2)Si phase was reduced from 110 to 50μm with increasing Ce content to 1.6 wt.%.The results calculated by Pandat software indicated that the added Ce element first combined with Si to form CeSi_(2)phase,which could serve as the heterogeneous nucleation of Mg_(2)Si phase due to the small lattice mismatch of 7.97%.The modification of Mg_(2)Si phase was mainly attributed to the facts that Ce changed the growth steps of Mg_(2)Si phase and CeSi_(2)promoted the nucleation of Mg_(2)Si phase.With increasing Ce content from 0 wt.%to 1.6 wt.%,the YS,UTS and EL at 150℃were improved from 67.7 MPa,91.2 MPa and 1.6%to 84.2 MPa,128 MPa and 7.5%,respectively.展开更多
As a potent nucleating substrate forα-Mg grain,MgAl_(2)O_(4) powder was used to inoculate the Mg-Al melt in this study.The effects of MgAl_(2)O_(4)amount,holding time and Al content on the grain size and grain refini...As a potent nucleating substrate forα-Mg grain,MgAl_(2)O_(4) powder was used to inoculate the Mg-Al melt in this study.The effects of MgAl_(2)O_(4)amount,holding time and Al content on the grain size and grain refining ratio of the inoculated Mg-Al alloys are systematically investigated.The results show that the minimum grain size of Mg-3Al alloy is achieved by adding 2wt.%MgAl_(2)O_(4)powder and this alloy exhibits higher grain refining ratio than Mg-5Al and Mg-8Al alloys.The crystallographic misfit calculation indicates the wellmatching and possible orientation relationships(ORs)betweenα-Mg and MgAl_(2)O_(4).Among these predicted ORs,[10–10]α−Mg//[110]MgAl2O4 in(0002)α−Mg//(1–13)MgAl2O4 possesses the smallest misfit,i.e.,2.34%(fr).Both results of the experiment and crystallographic calculation demonstrate that the grain refinement of Mg-Al alloys is attributed to the MgAl_(2)O_(4)particles acting as the heterogeneous nucleation substrates forα-Mg grains.展开更多
The grain refining process of an AZ91D Mg alloy by Sr addition was studied and the heterogeneous nucleating particles of α-Mg were investigated by electron probe microanalysis (EPMA). With 0.6 wt% Sr addition, the ...The grain refining process of an AZ91D Mg alloy by Sr addition was studied and the heterogeneous nucleating particles of α-Mg were investigated by electron probe microanalysis (EPMA). With 0.6 wt% Sr addition, the mean grain size of AZ91D alloy was refined from 235.4μm to 52.5 μm at the one-half radius of the ingot. The morphology of primary crystal changed from a sixford symmetrical shape to a petallike shape, Mg-Sr-Al-Fe-Mn heterogeneous nucleating particles were observed at the grain centers and Sr solute atoms presented segregation along the grain boundaries. Grain refinement was facilitated by both the Mg-Sr-Al- Fe-Mn nucleating particles and the Sr solute atoms, and the former played a dominate role in the process.展开更多
SiC-YAG(Y3Al5O12) ceramic composite powders were prepared by co-precipitation coating method. Mechanism of co-precipitation coating of SiC powders with Y3+ and Al3+ precursors was investigated. If the concentration of...SiC-YAG(Y3Al5O12) ceramic composite powders were prepared by co-precipitation coating method. Mechanism of co-precipitation coating of SiC powders with Y3+ and Al3+ precursors was investigated. If the concentration of [OH-] ion in the solution is controlled within the range between critical values for heterogeneous nucleation and homogeneous nucleation, Y3+ and Al3+ precipitation precursors can be coated on the surface of SiC particles. Y3+ and Al3+ precipitation precursors transform into YAG phase after calcining at 1000 ℃ without the formation of YAM and YAP phases. The formation temperature of YAG phase is about 600 ℃ lower than that of conventional powder mixing method. The effect of pH value of the solution and precipitant titration rate on coating quality of SiC-YAG composite powders was also studied. The results show that co-precipitation coating can be realized at a final pH of 9 and a precipitant titration rate of 5 ml·min-1.展开更多
Tramp elements such as tin are considered harmful to steel because of hot brittleness they induce at high temperatures. Because tramp elements retained in steel scrap will be enriched in new steel due to the difficult...Tramp elements such as tin are considered harmful to steel because of hot brittleness they induce at high temperatures. Because tramp elements retained in steel scrap will be enriched in new steel due to the difficultly of their removal, studies on the precipitation behavior of tin are essential. In this study, the effects of different inclusions on the precipitation behavior of tin in steel were studied. The results show that the tin-rich phase precipitates at austenite grain boundaries in an Fe-5%Sn alloy without MnS precipitates, whereas Sn precipitates at the boundaries of MnS inclusions in steel that contains MnS precipitates. MnS is more effective than silicon dioxide or aluminum oxide as a nucleation site for the precipitation of the tin phase, which is consistent with the disregistry between the lattice parameters of the tin phase and those of the inclusions.展开更多
To improve the thermal properties of aluminum(Al)in the energetic system,a coated structure with ammonium perchlorate(AP)was prepared by a facile approach.And N,N-Dimethylformamide(DMF)was chosen as an ideal solvent b...To improve the thermal properties of aluminum(Al)in the energetic system,a coated structure with ammonium perchlorate(AP)was prepared by a facile approach.And N,N-Dimethylformamide(DMF)was chosen as an ideal solvent based on heterogeneous nucleation theory and molecular dynamics simulation.This coated structure could enlarge the contact area and improve the reaction environment to enhance the thermal properties.The addition of AP could accelerate oxidation temperature of Al with around 17.5°C.And the heat release of 85@15 composition rises to 26.13 k J/g and the reaction degree is97.6%with higher peak pressure(254.6 k Pa)and rise rate(1.397 MPa/s).An ideal ratio with 15 wt%AP was probed primarily.The high energy laser-induced shockwave experiment was utilized to simulate the reaction behavior in hot field.And the larger activated mixture of coated powder could release more energy to promote the growth of shockwave with higher speed up to 518.7±55.9 m/s.In conclusion,85@15 composition is expected to be applied in energetic system as a novel metal fuel.展开更多
The grain refi nement limits of commercial pure Al inoculated by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master alloys were studied, and the infl uence of melting temperature on the grain refi ning performance of...The grain refi nement limits of commercial pure Al inoculated by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master alloys were studied, and the infl uence of melting temperature on the grain refi ning performance of these three master alloys was investigated using a high scope video microscope(HSVM), a fi eld-emission scanning electron microscope(FESEM), an electron probe micro-analyzer(EPMA) and X–ray diffraction(XRD) method. Results show that there is a grain refi nement limit of commercial pure Al refi ned by these three master alloys; with the same addition level of 1.5% under the present experimental conditions, the grain refi nement limits(smallest average grain size) of commercial pure Al refi ned by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master alloys are 50 μm, 80 μm and 80 μm, respectively. In addition, with an increase in the melting temperature of the pure Al, the grain refi ning performance of Al-5Ti-1B and Al-5Ti-0.25C master alloys decreases, but the grain refi ning performance of Al-5Ti-0.3C-0.2B changes little.展开更多
The effect of vanadium carbide(VC) on the grain size of commercial pure aluminum was experimentally investigated by varying the content of VC, the holding time, and casting temperature. The refining efficiencies of ...The effect of vanadium carbide(VC) on the grain size of commercial pure aluminum was experimentally investigated by varying the content of VC, the holding time, and casting temperature. The refining efficiencies of VC and Al5Ti1 B were also compared. The refined samples of commercial pure aluminum were examined using optical microscopy, scanning electron microscopy(SEM) and energy-dispersive spectroscopy(EDS). The results suggest that VC is a good refiner of commercial pure aluminum. The addition of only 0.3wt% VC can decrease the grain size of aluminum to 102 μm, whereas the casting temperature and holding time have little effect on the grain size. The refining efficiency of VC is better than that of Al5Ti1 B. The VC particles in molten aluminum act as nuclei and the grain refinement of aluminum alloys by VC particles is achieved via heterogeneous nucleation.展开更多
基金Financial supports from The National Natural Science Foundation of China(Nos.52104376,U19A2084,52074132,and 52004100)China Postdoctoral Science Foundation(2021T140250 and 2021M701376)+1 种基金Partial financial support came from The Science and Technology Development Program of Jilin Province(Nos.20200401025GX and 20200201002JC)Program for JLU Science and Technology Innovative Research Team(JLUSTIRT,2017TD-09)。
文摘Due to the significant differences in the formation temperature and crystal structure between the primaryα-Mg and eutecticβ-Mg_(17)Al_(12),it is a great challenge to achieve simultaneous refinement of the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation.Surprisingly,we found that theα-Mg andβ-Mg_(17)Al_(12) in the AZ80 alloy can be simultaneously refined after 0.2 wt.%Sm addition,with the grain size decreasing from∼217±15μm to∼170±10μm and theβ-Mg_(17)Al_(12) morphology changing from a typical continuous network to a nod-like or spherical structure.The simultaneous refinement mechanism is investigated through solidification simulation,transmission electron microscopy(TEM),and differential thermal analysis(DTA).In the AZ80-0.2Sm alloy,many Al8Mn4Sm particles can be observed near the center of theα-Mg grains or inside theβ-Mg_(17)Al_(12).Crystallographic calculations further reveal that the Al8Mn4Sm has good crystallographic matching with both theα-Mg andβ-Mg_(17)Al_(12),so it possesses the potency to serve as heterogeneous nucleation sites for both phases.The promoted heterogeneous nucleation on the Al8Mn4Sm decreases the undercooling required by the nucleation of the primary and eutectic phases,which enhances the heterogeneous nucleation rate,thus causing the simultaneous refinement of theα-Mg andβ-Mg_(17)Al_(12).The orientation relationships between the Al8Mn4Sm and Mg/Mg_(17)Al_(12) are identified,which are[1210]_(Mg)//[010]_(Al8Mn4Sm),(1010)_(Mg)//(301)_(Al8Mn4Sm) and[112]_(Mg_(17)Al_(12))//[010]_(Al8Mn4Sm),(110)_(Mg_(17)Al_(12))//(301)_(Al8Mn4Sm),respectively.Furthermore,the refinement of theβ-Mg_(17)Al_(12) accelerates its dissolution during the solution treatment,which is beneficial for cost saving in industrial applications.Other Al8Mn4RE compounds such as Al8Mn4Y might have the same positive effect on the simultaneous refinement due to the similar physicochemical properties of rare earth elements.This work not only proves the possibility of simultaneously refining the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation,but also provides new insights into the development of refiners for cast Mg alloys.
基金supported financially by the European Community under Marie Curie Transfer of Knowledge grant No. MTKD-CT-2006-042468 (AGH No.27.27.170.304)Polish Ministry of Science and Higher Education for financial support under grant No. N507-44-66-34 (AGH No.18.18.170.325)
文摘The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucleation sites and number of SiC present in the alloy.The aim of this paper was selection of parameters for the model describing the relationship between the grain density of primary phase and undercooling.This model in connection with model of crystallisation,which is based on chemical elements diffusion and grain interface kinetics,can be used to predict casting quality and its microstructure.Nucleation models have parameters,which exact values are usually not known and sometimes even their physical meaning is under discussion.Those parameters can be obtained after mathematical analysis of the experimental data.The composites with 0,1,2,3 and 4wt.% of SiC particles were prepared.The AZ91 alloy was a matrix of the composite reinforcement SiC particles.This composite was cast to prepare four different thickness plates.They were taken from the region near to the thermocouple,to analyze the undercooling for different composites and thickness plates and its influence on the grain size.The microstructure and thermal analysis gave set of values that connect mass fraction of SiC particles,and undercooling with grain size.These values were used to approximate nucleation model adjustment parameters.Obtained model can be very useful in modelling composites microstructure.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50901061 and 50971102)the National Key Basic Research Project of China (Grant No. 2011CB610402)the Fundamental Research Funds of the State Key Laboratory of Solidification Processing (NWPU), China (Grant Nos. 02-TZ-2008 and 36-TP-2009)
文摘The heterogeneous nucleation process of NH4Cl crystals from a NH4Cl-70wt.%H2O solution on rough chilling substrates was considered in this paper. Scratched and etched substrates of aluminum were prepared with different surface morphologies. It was concluded that for nucleation to occur on a rough substrate surface, the wettability or the generally said roughness are not the key factors affecting the heterogeneous nucleation process. Rather the surface morphologies on the nanometer scale, which is close to the scale of the critical nucleation radius, are more important.
文摘Flaky graphite particles were coated by ZrOCl2 · 8H2O as precursors by heterogeneous nucleation process. The effects of factors such as pH values ( 2. 4 - 5. 1 ), concentration of the precursor solution ( 0. 005 - 0. 1 mol · L^-1) , mixing method of graphite and precursor solution on the surface modification of graphite were studied. Result shows that :1 ) the preferable technical process for heterogeneous nucleation modified graphite is to mix the graphite suspension and precursor solution with concentration 0. 025 mol ·L^-1 and then drip ammonia water to adjust the pH value to 3.6 ; 2 ) By surface modification, the ZrO2 particles are evenly coated on graphite surface and therefore improve oxidation resistance and dispersion ability of graphite.
基金financially supported by the National Natural Science Foundation of China(Nos.52173224,51821001,52130105,and 52273230)the Natural Science Foundation of Shanghai(No.21ZR1431200)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning.
文摘Titanium diboride(TiB_(2))is an effective grain refiner of Al alloys in the industry that facilitates casting processes by forming uniformly refined microstructures.Although our understanding of the underlying refinement mechanisms has advanced,the atomic kinetics of heterogeneous nucleation of Al on TiB2 remains unknown.Here,we report atomic-scale observations of the heterogeneous nucleation and growth kinetics of Al on self-formed TiB_(2) particles by in situ heating of undercooled Al-5Ti-1B films.We demonstrate that an ordered Al monolayer forms on the Ti-terminated{0001}TiB_(2) surface;then,the surrounding Al atoms are initiated to form an island-shaped Al nucleus with face-centered cubic{111}stacking without the assistance of a Ti-rich buffer layer.The interfacial lattice mismatch between{111}Al and{0001}TiB_(2) causes remarkable out-of-plane strain that decreases gradually with Al nucleus layers increasing to 6 atomic layers.The elastic strain energy originating from this interfacial strain increases the free energy of the Al/TiB2 heterostructure,hence impeding the rapid growth of the Al nucleus.We found that TiB2 particles stabilize the Al nuclei rather than activating their free growth into grains when the experimental undercoolingΔT is lower than the onset undercoolingΔT fg in Greer's free growth model.Our findings provide an atomic-scale physical image of the heterogeneous nucleation and growth mechanisms of Al with inoculator participation and elucidate the strain-dependent growth kinetics of Al nuclei.
基金financial supports from National Key Research Program (2017YFB0306100)Guangdong Academy of Sciences (No. 2017GDASCX-0843)+3 种基金Guangdong Technical Research Program (Nos. 201707010385, 2014B070706026, 2013B061800053)Guangdong Natural Science Foundation (No. 2016A030312015)National Natural Science Foundation of China (No. 51501044)Guangzhou Technical Research Program (No. 201707010385)
文摘Plasma spray-physical vapor deposition(PS-PVD) as a novel coating process based on low-pressure plasma spray(LPPS) has been significantly used for thermal barrier coatings(TBCs).A coating can be deposited from liquid splats, nano-sized clusters, and the vapor phase forming different structured coatings, which shows obvious advantages in contrast to conventional technologies like atmospheric plasma spray(APS) and electron beam-physical vapor deposition(EBPVD). In addition, it can be used to produce thin, dense, and porous ceramic coatings for special applications because of its special characteristics, such as high power, very low pressure, etc. These provide new opportunities to obtain different advanced microstructures, thus to meet the growing requirements of modern functional coatings. In this work, focusing on exploiting the potential of gas-phase deposition from PS-PVD, a series of 7 YSZ coating experiments with various process conditions was performed in order to better understand the deposition process in PS-PVD, where coatings were deposited on different substrates including graphite and zirconia. Meanwhile, various substrate temperatures were investigated for the same substrate. As a result, a deposition mechanism of heterogeneous nucleation has been presented showing that surface energy is an important influencing factor for coating structures. Besides, undercooling of the interface between substrate and vapor phase plays an important role in coating structures.
基金financially sponsored by National Natural Science Foundation of China(51304053)
文摘The segregation behavior of alloying elements X( X = Zr,V,Cr,Mn,Mo,W,Nb,Y) on the ferrite( 100) /TiC( 100) interface has been investigated using first principles method,and the work of separation and interface energy of ferrite / TiC interfaces alloyed by these elements were also analyzed. The results indicated that all these alloying additives except Y were thermodynamically favorable because of the negative segregation energy,showing that they have the tendency to segregate to the ferrite / TiC interface. When the Fe atom in the ferrite /TiC interface is replaced by Y,Zr,or Nb,the adhesive strength of the interface will be weakened due to the lower separation work,larger interfacial energy,and weaker electron effects. However,the introduction of Cr,Mo,W,Mn and V will improve the stability of the ferrite / TiC interface through strong interaction between these elements and C,and Cr-doped interface is the most stable structure. Therefore,the Cr,Mo,W,Mn and V in ferrite side of the interface can effectively promote ferrite heterogeneous nucleation on TiC surface to form fine ferrite grain.
基金This work was supported by the National Natural Science Foundation of China(Nos.51925207,U1910210,51872277,22005292,52002083)the National Synchrotron Radiation Laboratory(KY2060000173)+1 种基金the Joint Fund of the Yulin University and the Dalian National Laboratory for Clean Energy(Grant.YLU-DNL Fund 2021002)the Fundamental Research Funds for the Central Universities(WK2060140026).
文摘Sodium/Potassium(Na/K)metal anodes have been considered as the promising anodes for next-generation Na/K secondary batteries owing to their ultrahigh specific capacity,low redox potential and low cost.However,their practical application is still hampered due to unstable solid electrolyte interphase,infinite volume change,and dendrite growth.Herein,we design a 3D-Na_(3)Bi/3D-K_(3)Bi alloy host which enables the homogeneous and heterogeneous nucleation growth of Na/K metal.The unique structure with periodic alternating of electron and ion conductivity improves the mass transfer kinetics and prevents the volume expansion during cycling.Meanwhile,the sodiophilicity of Na_(3)Bi/potassiophilicity of K_(3)Bi framework can avoid dendritic growth.Cycling lifespans over 700 h with 1 mAh cm^(−2)for 3D-Na_(3)Bi@Na electrode and about 450 h with 1 mAh cm^(−2)for 3D-K_(3)Bi@K electrode are achieved,respectively.3D-Na_(3)Bi@Na||Na_(3)V_(2)(PO_(4))3 full battery shows sustainable cycle performance over 400 cycles.This design provides a simple but effective approach for achieving safety of sodium/potassium metal anodes.
基金supported by the National Natural Science Foundation of China(51972187,22279068,52374306)the Natural Science Foundation of Shandong Province(ZR2021QE166)Qingdao New Energy Shandong Laboratory Open Project(QNESL OP202312)。
文摘The development of rechargeable magnesium(Mg) batteries is of practical significance to upgrade the electric energy storage devices due to exceptional capacity and abundant resources of Mg-metal anode.However,the reversible Mg electrochemistry suffers from unsatisfied rate capability and lifespan,mainly caused by non-uniform distribution of electrodeposits.In this work,a fresh design concept of threedimensional carbon cloths scaffolds is proposed to overcome the uncontrollable Mg growth via homogenizing electric field and improving magnesiophilicity.A microscopic smooth and nitrogen-containing defective carbonaceous layer is constructed through a facile pyrolysis of ZIF8 on carbon cloths.As revealed by finite element simulation and DFT calculation results,the smooth surface endows with uniform electric field distribution and simultaneously the nitrogen-doping species enable good magnesiophilicity of scaffolds.The fine and uniform Mg nucleus as well as the inner electrodeposit behavior are also disclosed.As a result,an exceptional cycle life of 500 cycles at 4.0 mA cm^(-2) and 4.0 mA h cm^(-2) is firstly realized to our best knowledge.Besides,the functional scaffolds can be cycled for over 2200 h at 2.0 mA cm^(-2) under a normalized capacity of 5.0 mA h cm^(-2),far exceeding previous results.This work offers an effective approach to enable the full potential of carbon cloths-based scaffolds towards metal storage for next generation battery applications.
基金financially supported by the National Natural Science Foundation of China(No.51871100)。
文摘This study revealed the nucleation event and grain refinement mechanism of Mg-Al alloy induced by Fe impurity.The following orientation relationship was observed between Al-Fe particle andα-Mg matrix in the Mg-3Al alloy containing Fe impurity using a focused ion beam aided transmission electron microscope technique:(1^(-)011)[011^(-)1]_(Mg)//(011^(-))[011]_(Al_(2)Fe).Mg-3Al alloy was inoculated by adding 0.02wt%Fe to verify the nucleating potency of the Al_(2)Fe phase forα-Mg grain.The results indicated that Mg-3Al alloy was effectively refined with an average grain size declining from 1135 to 540μm.Among the potential Al-Fe phases of Mg-3Al-0.02Fe alloy,only the precipitation of the Al_(2)Fe phase occurs earlier than that ofα-Mg grain,and the Al_(2)Fe phase is stable in the nucleation stage ofα-Mg grain.Therefore,the Al_(2)Fe particle is the only available nucleating site for Mg-Al alloy with Fe impurity.The heterogeneous nucleation event ofα-Mg grain on the Al_(2)Fe particle is responsible for the grain refinement of Mg-3Al alloy inoculated by Fe.
基金Funded by the National Natural Science Foundation of China (50775102)the Universities Natural Science Fund Key Project of Jiangsu Province (04KJA430021)
文摘The precipitation behavior of V(C, N) in steels microalloyed with vanadium was researched using a thermal simulator during single-pass deformation at 800-750 ℃. The V(C, N) precipitates and its nucleation effect on ferrite were investigated by TEM and EDS. The experimental results show that there are two remarkable heterogeneous nucleation effects of V(C, N) particles precipitated before γ →/ α phase change: primary reason is that high coherency between V(C, N) and ferrite promotes V(C, N) to become a nucleating center of intragranular ferrite; secondary reason is that the coarsening of V(C, N) causes locally solute-poor region in austenite, thus expedites the nucleation of intragranular ferrites further. Furthermore, the relationship between the size and shape of V(C, N) was studied, and identification method was provided for distinguishing interphase precipitation and general precipitation to avoid erroneous judgment and misguide.
基金supported by the Natural Science Foundation of Guangdong Province under Grant Nos.04300168 and 04009487Doctor Fund of Guangdong University of Technology.
文摘A thermodynamic approach at the nanometer scale was performed for the heterogeneous nucleation inside nanocavity, and an analytical expression of the critical energy of nucleation was evaluated considering a rough ball nucleus nucleating inside nanocavity. Compared with the case of the nucleation locating on planar or convex substrate, the critical energy of nucleation inside the concave substrate is the smallest. Based on the thermodynamic and kinetic analyses, at low supersaturation, the smaller the curvature radius of cavity and/or the smaller the contact angle, the smaller the critical energy of nucleation, and the larger the nucleation rate. At high supersaturation, the nucleation rate increases with increasing the contact angle and/or increasing the curvature radius of cavity. In this way, at the low supersaturation, the heterogeneous nucleation rate is larger than the homogeneous one, as the nucleation rate is mainly determined by the heterogeneous nucleation. At the high supersaturation, the heterogeneous nucleation rate is smaller than the homogeneous one, as the nucleation rate is mainly determined by the homogeneous nucleation.
基金supported by the Major Science and Technology projects in Qinghai province (2018-GX-A1)Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (Grant No. 2013M3A6B1078874)+1 种基金funded by Shanghai Science and Technology Committee (Grant No. 18511109302)the National Natural Science Foundation of China (Grant No. 51825101)
文摘The effect of Ce content(0–1.6 wt.%)on the modification of Mg_(2)Si phase in the as-cast Mg-5Al-2Si alloy was investigated.The original Chinese script type Mg_(2)Si phase was refined distinctly and transformed to dispersive block shape gradually by adding Ce element.The length of Chinese script type Mg_(2)Si phase was reduced from 110 to 50μm with increasing Ce content to 1.6 wt.%.The results calculated by Pandat software indicated that the added Ce element first combined with Si to form CeSi_(2)phase,which could serve as the heterogeneous nucleation of Mg_(2)Si phase due to the small lattice mismatch of 7.97%.The modification of Mg_(2)Si phase was mainly attributed to the facts that Ce changed the growth steps of Mg_(2)Si phase and CeSi_(2)promoted the nucleation of Mg_(2)Si phase.With increasing Ce content from 0 wt.%to 1.6 wt.%,the YS,UTS and EL at 150℃were improved from 67.7 MPa,91.2 MPa and 1.6%to 84.2 MPa,128 MPa and 7.5%,respectively.
基金This work was supported by the National Natural Science Foundation of China(51871100).
文摘As a potent nucleating substrate forα-Mg grain,MgAl_(2)O_(4) powder was used to inoculate the Mg-Al melt in this study.The effects of MgAl_(2)O_(4)amount,holding time and Al content on the grain size and grain refining ratio of the inoculated Mg-Al alloys are systematically investigated.The results show that the minimum grain size of Mg-3Al alloy is achieved by adding 2wt.%MgAl_(2)O_(4)powder and this alloy exhibits higher grain refining ratio than Mg-5Al and Mg-8Al alloys.The crystallographic misfit calculation indicates the wellmatching and possible orientation relationships(ORs)betweenα-Mg and MgAl_(2)O_(4).Among these predicted ORs,[10–10]α−Mg//[110]MgAl2O4 in(0002)α−Mg//(1–13)MgAl2O4 possesses the smallest misfit,i.e.,2.34%(fr).Both results of the experiment and crystallographic calculation demonstrate that the grain refinement of Mg-Al alloys is attributed to the MgAl_(2)O_(4)particles acting as the heterogeneous nucleation substrates forα-Mg grains.
基金Funded by the National Natural Science Foundation of China (No. 50171037) Key Project of Science and Technology Research of Ministry of Education of China (No. 01105)
文摘The grain refining process of an AZ91D Mg alloy by Sr addition was studied and the heterogeneous nucleating particles of α-Mg were investigated by electron probe microanalysis (EPMA). With 0.6 wt% Sr addition, the mean grain size of AZ91D alloy was refined from 235.4μm to 52.5 μm at the one-half radius of the ingot. The morphology of primary crystal changed from a sixford symmetrical shape to a petallike shape, Mg-Sr-Al-Fe-Mn heterogeneous nucleating particles were observed at the grain centers and Sr solute atoms presented segregation along the grain boundaries. Grain refinement was facilitated by both the Mg-Sr-Al- Fe-Mn nucleating particles and the Sr solute atoms, and the former played a dominate role in the process.
文摘SiC-YAG(Y3Al5O12) ceramic composite powders were prepared by co-precipitation coating method. Mechanism of co-precipitation coating of SiC powders with Y3+ and Al3+ precursors was investigated. If the concentration of [OH-] ion in the solution is controlled within the range between critical values for heterogeneous nucleation and homogeneous nucleation, Y3+ and Al3+ precipitation precursors can be coated on the surface of SiC particles. Y3+ and Al3+ precipitation precursors transform into YAG phase after calcining at 1000 ℃ without the formation of YAM and YAP phases. The formation temperature of YAG phase is about 600 ℃ lower than that of conventional powder mixing method. The effect of pH value of the solution and precipitant titration rate on coating quality of SiC-YAG composite powders was also studied. The results show that co-precipitation coating can be realized at a final pH of 9 and a precipitant titration rate of 5 ml·min-1.
基金financial support from the National Natural Science Foundation of China(Nos. 51174019 and 51274269)the Fundamental Research Funds for the Central Universities(FRF-SD-12-010A and FRF-SD-12-002B)
文摘Tramp elements such as tin are considered harmful to steel because of hot brittleness they induce at high temperatures. Because tramp elements retained in steel scrap will be enriched in new steel due to the difficultly of their removal, studies on the precipitation behavior of tin are essential. In this study, the effects of different inclusions on the precipitation behavior of tin in steel were studied. The results show that the tin-rich phase precipitates at austenite grain boundaries in an Fe-5%Sn alloy without MnS precipitates, whereas Sn precipitates at the boundaries of MnS inclusions in steel that contains MnS precipitates. MnS is more effective than silicon dioxide or aluminum oxide as a nucleation site for the precipitation of the tin phase, which is consistent with the disregistry between the lattice parameters of the tin phase and those of the inclusions.
基金supported by National Natural Science Foundation of China[No.21975024]。
文摘To improve the thermal properties of aluminum(Al)in the energetic system,a coated structure with ammonium perchlorate(AP)was prepared by a facile approach.And N,N-Dimethylformamide(DMF)was chosen as an ideal solvent based on heterogeneous nucleation theory and molecular dynamics simulation.This coated structure could enlarge the contact area and improve the reaction environment to enhance the thermal properties.The addition of AP could accelerate oxidation temperature of Al with around 17.5°C.And the heat release of 85@15 composition rises to 26.13 k J/g and the reaction degree is97.6%with higher peak pressure(254.6 k Pa)and rise rate(1.397 MPa/s).An ideal ratio with 15 wt%AP was probed primarily.The high energy laser-induced shockwave experiment was utilized to simulate the reaction behavior in hot field.And the larger activated mixture of coated powder could release more energy to promote the growth of shockwave with higher speed up to 518.7±55.9 m/s.In conclusion,85@15 composition is expected to be applied in energetic system as a novel metal fuel.
基金financially supported by the National Natural Science Foundation of China(No.51071097)
文摘The grain refi nement limits of commercial pure Al inoculated by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master alloys were studied, and the infl uence of melting temperature on the grain refi ning performance of these three master alloys was investigated using a high scope video microscope(HSVM), a fi eld-emission scanning electron microscope(FESEM), an electron probe micro-analyzer(EPMA) and X–ray diffraction(XRD) method. Results show that there is a grain refi nement limit of commercial pure Al refi ned by these three master alloys; with the same addition level of 1.5% under the present experimental conditions, the grain refi nement limits(smallest average grain size) of commercial pure Al refi ned by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master alloys are 50 μm, 80 μm and 80 μm, respectively. In addition, with an increase in the melting temperature of the pure Al, the grain refi ning performance of Al-5Ti-1B and Al-5Ti-0.25C master alloys decreases, but the grain refi ning performance of Al-5Ti-0.3C-0.2B changes little.
基金financially supported by the Department of Science and Technology of Sichuan Province (Nos. 2015KJT0081-2015G, 2015GZ0052, and 13CGZH0200)
文摘The effect of vanadium carbide(VC) on the grain size of commercial pure aluminum was experimentally investigated by varying the content of VC, the holding time, and casting temperature. The refining efficiencies of VC and Al5Ti1 B were also compared. The refined samples of commercial pure aluminum were examined using optical microscopy, scanning electron microscopy(SEM) and energy-dispersive spectroscopy(EDS). The results suggest that VC is a good refiner of commercial pure aluminum. The addition of only 0.3wt% VC can decrease the grain size of aluminum to 102 μm, whereas the casting temperature and holding time have little effect on the grain size. The refining efficiency of VC is better than that of Al5Ti1 B. The VC particles in molten aluminum act as nuclei and the grain refinement of aluminum alloys by VC particles is achieved via heterogeneous nucleation.