The liquid state undercoolability and crystal growth kinetics of ternary Ni-5%Cu-5%Sn and Ni-10%Cu-10%Sn alloys are investigated by the glass fluxing method. In these two alloys, experimental maximum undercoolings of ...The liquid state undercoolability and crystal growth kinetics of ternary Ni-5%Cu-5%Sn and Ni-10%Cu-10%Sn alloys are investigated by the glass fluxing method. In these two alloys, experimental maximum undercoolings of 304 K （0.18TL ） and 286K （0.17TL ） are achieved and the dendritic growth velocities attain 39.8 and 25.1 m/s, respectively. The transition of morphology from coarse dendrite into equiaxed structure occurs and the grain size of the a （Ni） phase decreases remarkably when the undercooling increases. Both the lattice constant and microhardness increase obviously with the enhancement of undercooling. The enrichment of Cu and Sn solute contents reduces the dendritic growth velocity, while enhances the lattice constant and microhardness of a （Ni） phase.展开更多
A deep-undercooling rapid-solidification technique combining cyclic superheating and molten glass purification was employed to successfully prepare Cu60Ni40 and Cu65Ni35 alloys at various undercooling levels.Furthermo...A deep-undercooling rapid-solidification technique combining cyclic superheating and molten glass purification was employed to successfully prepare Cu60Ni40 and Cu65Ni35 alloys at various undercooling levels.Furthermore,through precise compositional regulation by adjusting the Cu content and introducing Co,the Cu60Ni35Co5 alloy was obtained.The morphological evolution of the solidification front and the variation in solidification rate with undercooling were systematically investigated.By combining metallographic analysis,the BCT model,electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM),the microstructural evolution and grain refinement mechanisms of the undercooled alloys were revealed.This work aims to establish the intrinsic relationship among undercooling,solidification behavior,and microstructure,thereby provides both experimental and theoretical foundations for a deeper understanding of the deep undercooling solidification mechanism and microstructural control.展开更多
The liquid Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys were undercooled to the maximum undercooling of 364 K(0.18 T_(L)),405 K(0.21 T_(L)),and 375 K(0.21 T_(L)),respectively,by using electrostatic levitation technique.The Zr...The liquid Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys were undercooled to the maximum undercooling of 364 K(0.18 T_(L)),405 K(0.21 T_(L)),and 375 K(0.21 T_(L)),respectively,by using electrostatic levitation technique.The Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys present only one recalescence during liquid/solid phase transition,while the Zr_(70)V_(30) alloy presents a transformation from two recalescence to one recalescence phenomenon with a critical undercooling of approximately 300 K.According to the LKT/BCT model,the calculated results of the primary β-Zr dendrite growth velocity in undercooled liquid Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys agree well with the experiments.The velocity inflection points at 119 K of Zr_(91.4)V_(8.6) alloy and 201 K of Zr_(83.5)V_(16.5) alloy could be explained by the competition between solutal undercooling control and thermal undercooling control modes.For Zr_(70)V_(30) alloy solidified in the P1 with twice recalescence,a critical second undercooling of 253 K and corresponding undercooling of 65 and 244 K are obtained.When the un-dercooling is in the range of 65-244 K,the second undercooling would be greater than 253 K,and the residual liquid phase would solidify into anomalous eutectic microstructure for Zr_(70)V_(30) alloy.The Vickers hardness of Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys all show a quadratic relationship with undercooling.Under electrostatic levitation condition,the mechanical property of Zr-V alloys could be significantly regulated through solidifying the alloys at different undercoolings.展开更多
The evolution of the microstructure and morphology of Cu55Ni45 and Cu60Ni40 alloys under varying degrees of undercooling was investigated through molten glass purification and cyclic superheating technology.By increas...The evolution of the microstructure and morphology of Cu55Ni45 and Cu60Ni40 alloys under varying degrees of undercooling was investigated through molten glass purification and cyclic superheating technology.By increasing the Cu content,the effect of Cu on the evolution of the microstructure and morphology of the Cu-Ni alloy during undercooling was studied.The mechanism of grain refinement at different degrees of undercooling and the effect of Cu content on its solidification behaviour were investigated.The solidification behaviour of Cu55Ni45 and Cu60Ni40 alloys was investigated using infrared thermometry and high-speed photography.The results indicate that both Cu55Ni45 and Cu60Ni40 alloy melts undergo only one recalescence during rapid solidification.The degree of recalescence increases approximately linearly with increasing undercooling.The solidification front of the alloy melts undergoes a transition process from a small-angle plane to a sharp front and then to a smooth arc.However,the growth of the subcooled melt is constrained to a narrow range,facilitating the formation of a coarse dendritic crystal morphology in the Cu-Ni alloy.At large undercooling,the stress breakdown of the directionally growing dendrites is primarily caused by thermal diffusion.The strain remaining in the dendritic fragments provides the driving force for recrystallisation of the tissue to occur,which in turn refines the tissue.展开更多
By applying the rapid solidification technique of deep undercooling,Cu65Ni35 and Cu60Ni40 alloys achieved maximum undercoolings of 284 and 222 K,respectively.Microstructural images captured reveal grain refinement in ...By applying the rapid solidification technique of deep undercooling,Cu65Ni35 and Cu60Ni40 alloys achieved maximum undercoolings of 284 and 222 K,respectively.Microstructural images captured reveal grain refinement in both alloys across both large and small undercooling ranges.High-speed photography was used to analyze the relationship between solidification front morphology and undercooling,showing that dendrite remelting and fragmentation caused grain refinement under small undercooling,while stress-induced recrystallization is responsible under large undercooling.Microhardness testing further demonstrates a sudden drop in microhardness near the critical undercooling point,providing evidence for grain refinement due to recrystallization in large undercooling tissues.展开更多
This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined wi...This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.展开更多
During the tungsten inert gas(TIG)welding process of Ti_(2)AlNb alloy,high heat input leads to the formation of coarse grains,which are detrimental to the mechanical properties of welded joints.To address this problem...During the tungsten inert gas(TIG)welding process of Ti_(2)AlNb alloy,high heat input leads to the formation of coarse grains,which are detrimental to the mechanical properties of welded joints.To address this problem,Ta microalloyed welding wires were developed to enhance the strength of the welded joints.The Ta-modifed fusion zone(FZ)exhibited a well-defned structure with a smooth,defect-free surface.Systematic analysis of the microstructure evolution and mechanical properties of the welded joints revealed that the Ta element completely dissolves into the FZ.During solidifcation,a signifcant constitutional undercooling efect occurs,promoting the columnar-to-equiaxed transition(CET)and reducing grain size from 187.42 to 133.49μm.Mechanical properties tests indicated that with increased Ta content,the strength of the welded joints initially increased and then decreased.When the Ta content in the welding wire was 1 wt%,the joints showed the best performance,with a tensile strength of 909.36 MPa and an elongation of 1.21%.Compared to the welded samples without Ta,the tensile strength and elongation increased by 153.01 MPa and 0.53%,respectively.Grain refnement and increased dislocation density were the main reasons for the improved mechanical properties.However,excessive Ta content led to signifcant the intragrain misorientation,increasing the joint’s anisotropy and causing uneven deformation during tensile testing.Therefore,further addition of Ta did not substantially enhance the tensile properties of the joint.Additionally,the paper provides a detailed analysis of the low elongation observed in the joint.After welding,dislocations were neatly arranged in the FZ,forming numerous parallel dislocation walls,leading to local stress concentration and accelerating crack initiation and propagation.Consequently,the elongation at the weld was lower than that of the base metal(BM).This research ofers a new approach to improve the mechanical properties of Ti2AlNb alloy during welding.展开更多
A series of Co-Sn alloys with Sn content ranging from 12% to 32%（mole fraction） were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by ...A series of Co-Sn alloys with Sn content ranging from 12% to 32%（mole fraction） were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification microstructures.A boundary clearly exists,which separates the coupled growth zone from the decoupled growth zone of eutectic phases for the alloys with Sn content ranging from 14% to 31%（mole fraction）.The other Co-Sn alloys out of this content range are hard to be undercooled into the coupled growth zone in the experiment.It is found that the so-called non-reciprocal nucleation phenomenon does not happen in the solidification of undercooled Co-Sn off-eutectic alloys.展开更多
Departing from the volume-averaging method,an overall solidification kinetic model for undercooled single-phase solid-solution alloys was developed to study the effect of back diffusion on the solidification kinetics....Departing from the volume-averaging method,an overall solidification kinetic model for undercooled single-phase solid-solution alloys was developed to study the effect of back diffusion on the solidification kinetics.Application to rapid solidification of undercooled Ni-15%Cu（mole fraction） alloy shows that back diffusion effect has significant influence on the solidification ending temperature but possesses almost no effect on the volume fraction solidified during recalescence.Inconsistent with the widely accepted viewpoint of Herlach,solidification ends at a temperature between the predictions of Lever rule and Scheil＇s equation,and the exact value is determined by the effect of back diffusion,the initial undercooling and the cooling rate.展开更多
Rapid solidification of undercooled Ni-15%Cu （mole fraction） alloy was studied using glass fluxing and cyclic superheating. To show the effect of cooling history on the microstrucyure and microtexture evolution, the...Rapid solidification of undercooled Ni-15%Cu （mole fraction） alloy was studied using glass fluxing and cyclic superheating. To show the effect of cooling history on the microstrucyure and microtexture evolution, the as-solidified samples were either cooled naturally or quenched into water after recalescence. At low undercooling, grain-refined microstructure has a random texture and a highly oriented texture without annealing twins for the case of naturally cooling and quenching, respectively. At high undercooling, a fully random texture as well as a number of annealing twins are observed, and recrystallization and grain growth independently happen on the cooling history. Fluid flow and recrystallization play an important role in the microtexture formation for grain refinement at both low and high undercooling.展开更多
Electrical resistivity and viscosity of Pb–Sb alloys are measured to investigate Peierls distortion behavior in the melts. In Pb30Sb70, Pb20Sb80, and Pb10Sb90 melts, temperature dependence of resistivity deviates fro...Electrical resistivity and viscosity of Pb–Sb alloys are measured to investigate Peierls distortion behavior in the melts. In Pb30Sb70, Pb20Sb80, and Pb10Sb90 melts, temperature dependence of resistivity deviates from linear dependence during cooling. At 663 °C, different trends in isothermal behavior between experimental and theoretical resistivities, are interpreted as the existence of Peierls distortion in Sb-rich melts. In Pb30Sb70 and Pb20Sb80 melts, abnormal viscosity results verify the existence of abnormal structure transition, which is attributed to the formation of large Sb clusters with Peierls distortion. In undercooled liquid Pb20Sb80, minute resistivity coefficient and quadratic resistivity behavior are interpreted as the rapid increase of cluster size of Sb clusters with Peierls distortion, which provides preferential nucleation sites for higher structure similarity to the crystalline and lower liquid–solid interfacial energy.展开更多
Various undercoolings 14-232 K of bulk K4169 superalloys were obtained by the method of molten glass fluxing combined with superheating cycling and the mechanical properties of undercooled K4169 with as-solidified sta...Various undercoolings 14-232 K of bulk K4169 superalloys were obtained by the method of molten glass fluxing combined with superheating cycling and the mechanical properties of undercooled K4169 with as-solidified state were tested. Microstructures and phases composition in undercooled bulk K4169 superalloy were identified by transmission electron microscope （TEM）, scanning electron microscope （SEM） and optical microscopy （OM）. The morphology of dendrites, grain size and intergranular phase all change with the increased undercooling. Meanwhile, the relationship between microstructure of undercooled K4169 superalloy and tensile properties was investigated. The experimental results show that the uniform distribution of Laves phase and the decrease of grain size and intergranular phase content are favorable for the improvement of mechanical properties. The maximum tensile strength and elongation obtained at undercooling of 232 K are 932.2 MPa and 6.5%, respectively.展开更多
Peritectic reaction was studied by directional solidification of Cu-Ge alloys.A larger triple junction region of peritectic reaction was used to analyze the interface stability of the triple junction region during per...Peritectic reaction was studied by directional solidification of Cu-Ge alloys.A larger triple junction region of peritectic reaction was used to analyze the interface stability of the triple junction region during peritectic reaction.Under different growth conditions and compositions,different growth morphologies of triple junction region are presented.For the hypoperitectic Cu-13.5%Ge alloy,as the pulling velocity（v） increases from 2 to 5 μm/s,the morphological instability of the peritectic phase occurs during the peritectic reaction and the remelting interface of the primary phase is relatively stable.However,for the hyperperitectic Cu-15.6%Ge alloy wim v=5 μm/s,the nonplanar remelting interface near the trijunction is presented.The morphological stabilities of the solidifying peritectic phase and the remelting primary phase are analyzed in terms of the constitutional undercooling criterion.展开更多
The homogeneous liquid was separated into two phases, （Fe, Co）-rich LI and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature Tsep. If the duration from Tsep to Tsl （solidificatio...The homogeneous liquid was separated into two phases, （Fe, Co）-rich LI and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature Tsep. If the duration from Tsep to Tsl （solidification temperature of LI phase）, termed the liquid-phase separation interval Δt, exceeded a critical value, an eggtype structure was observed. By utilizing differential thermal analyses （DTA）, the solidification process of the undercooled Fe-Co-Cu alloys was studied. Additionally, an immiscible boundary was obtained, which was a convex parabola with a symmetrical axis of XCu=0.52. Depending on the relative amounts of LI and L2, the minor phase was nucleated firstly to form liquid droplets and separated from the original liquids at the beginning of liquid-phase separation.展开更多
The eutectic Ag-Cu alloys exhibiting fine Ag-Cu lamellar eutectic structure formed upon rapid solidification have great potentials being used in various engineering fields.However,the desired fine primary lamellar eut...The eutectic Ag-Cu alloys exhibiting fine Ag-Cu lamellar eutectic structure formed upon rapid solidification have great potentials being used in various engineering fields.However,the desired fine primary lamellar eutectic structure(PLES)is usually replaced by a coarse anomalous eutectic structure(AES)when the undercooling prior to solidification exceeds a certain value.The forming mechanism of AES in the undercooled eutectic Ag-Cu alloy has been a controversial issue.In this work,the undercooled Ag-39.9 at.% Cu eutectic alloy is solidified under different cooling conditions by using techniques of melt fluxing and copper mold casting.The results show that the coupled eutectic growth of this alloy undergoes a transition from a slow eutectic-cellular growth(ECG)to a rapid eutectic-dendritic growth(EDG)above a undercooling of 72 K,accompanying with an abrupt change of the distribution and amount of AES in as-solidified microstructures.Two kinds of primary lamellar eutectic structures are formed by ECG and EDG during recalescence,respectively.The destabilization of PLES that causes the formation of AES is ascribed to two different mechanisms based on the microstructural examination and theoretical calculations.Below 72 K,the destabilization of PLES formed by slow ECG is caused by the mechanism of"termination migration"driven by interfacial energy.While above 72 K,the destabilization of PLES formed by rapid EDG is attributed to the unstable perturbation of interface driven by interfacial energy and solute supersaturation.展开更多
Bulk Fe-30Ni alloy melt was nudercooled up to 337K by combining the glass fluxing technique with superheating-cooling cycle. Grain refinement at low undercoolings was observed in the experiment in addition to that at ...Bulk Fe-30Ni alloy melt was nudercooled up to 337K by combining the glass fluxing technique with superheating-cooling cycle. Grain refinement at low undercoolings was observed in the experiment in addition to that at high undercoolings. The current grain refinement mechanisms were examined, and it is concluded that the refined gains are all developed from dendrites, however the grain refinement at low undercoolings is due to chemical superheating, while that at high undercoolings due to rapid solidification contruction.展开更多
The undercooling dependence of the solidification mechanism was systematically explored by the electrostatic levitation(ESL)facility.During the experiments,the maximum undercooling reached up to 406 K(0.26 T_L)and the...The undercooling dependence of the solidification mechanism was systematically explored by the electrostatic levitation(ESL)facility.During the experiments,the maximum undercooling reached up to 406 K(0.26 T_L)and the growth velocity of the primary TiNi phase was in-situ determined at various undercoolings.At the initial increase of alloy undercooling,the value of growth velocity sluggishly rose followed by a power function.In this case,the primary TiNi phase preferentially developed as the equiaxed dendrite,then the remnant liquid participated as Ti_(2)Ni andα-Ti phases on the grain boundary.Once the undercooling exceeded the critical value of 350 K,the growth velocity of the primary phase displayed a sharply increase tendency.Meanwhile,the TEM results demonstrated that the precipitation of the intermetallic Ti_(2)Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.展开更多
A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitut...A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitute for the stable Co3 B phase in the alloy melts undercooled above a critical undercooling value of -60 K.The Co23B6 and α-Co phases make up a metastable eutectic. The corresponding eutectic composition and temperature are Co80.4B19.6 and 1343 K, respectively. On exposure of the metastable Co23B6 phase at a given temperature above 1208 K, it does not decompose even after several hours. But it transforms by a eutectoid reaction to α-Co ＋ Co3 B at lower temperature.展开更多
The undercooling and solidification of 150 μm and 185 μm droplets of Sn 5%Pb alloy prepared by the uniform droplet spray (UDS) process have been investigated. The enthalpy of the droplet has been measured by non adi...The undercooling and solidification of 150 μm and 185 μm droplets of Sn 5%Pb alloy prepared by the uniform droplet spray (UDS) process have been investigated. The enthalpy of the droplet has been measured by non adiabatic calorimetric method as a function of the flight distance. A droplet solidification simulation model has been used to compare with the experimental data. The results show that the enthalpy released by the droplets in the calorimeter is 11.88 J/g and 22.29 J/g less than the simulated values up to a certain flight distance at 0.485 m and 0.460 m for 150 μm and 185 μm droplets respectively, but agrees with the expected values at larger distance. The nucleation of the droplets takes place at the distance where the experimental and simulated enthalpy values agree. The droplets quenched before nucleation solidify into metastable supersaturated solid solution and have large undercooling. The formation of the metastable structure in the droplets has been verified metallographically and by calculations based on a thermodynamic model.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 51327901 and 51301138the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No 20126102120064+1 种基金the Aviation Science Foundation of China under Grant No 2014ZF53069the Fundamental Research Funds for the Central Universities under Grant No3102014KYJD044
文摘The liquid state undercoolability and crystal growth kinetics of ternary Ni-5%Cu-5%Sn and Ni-10%Cu-10%Sn alloys are investigated by the glass fluxing method. In these two alloys, experimental maximum undercoolings of 304 K （0.18TL ） and 286K （0.17TL ） are achieved and the dendritic growth velocities attain 39.8 and 25.1 m/s, respectively. The transition of morphology from coarse dendrite into equiaxed structure occurs and the grain size of the a （Ni） phase decreases remarkably when the undercooling increases. Both the lattice constant and microhardness increase obviously with the enhancement of undercooling. The enrichment of Cu and Sn solute contents reduces the dendritic growth velocity, while enhances the lattice constant and microhardness of a （Ni） phase.
基金Funded by the Central Government-Guided Local Development Fund Project(No.YDZJSX2025D042)the Key R&D Program of Shanxi Province(No.202202150401018)+1 种基金the Basic Research Program of Shanxi Province(No.202503021211112)the State Key Laboratory of CAD/CG of Zhejiang University(No.A2325)。
文摘A deep-undercooling rapid-solidification technique combining cyclic superheating and molten glass purification was employed to successfully prepare Cu60Ni40 and Cu65Ni35 alloys at various undercooling levels.Furthermore,through precise compositional regulation by adjusting the Cu content and introducing Co,the Cu60Ni35Co5 alloy was obtained.The morphological evolution of the solidification front and the variation in solidification rate with undercooling were systematically investigated.By combining metallographic analysis,the BCT model,electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM),the microstructural evolution and grain refinement mechanisms of the undercooled alloys were revealed.This work aims to establish the intrinsic relationship among undercooling,solidification behavior,and microstructure,thereby provides both experimental and theoretical foundations for a deeper understanding of the deep undercooling solidification mechanism and microstructural control.
基金supported by the National Natural Science Foundation of China(Grant No.52088101)the Space Utilization System of China Manned Space Engineering(Grant No.KJZ-YY-NCL02)+1 种基金the National Key R&D Program of China(Grant No.2021YFA0716301)the Shannxi Key Science and Technology Program(Grant Nos.2023-ZDLGY-36,2024JC-ZDXM-24).
文摘The liquid Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys were undercooled to the maximum undercooling of 364 K(0.18 T_(L)),405 K(0.21 T_(L)),and 375 K(0.21 T_(L)),respectively,by using electrostatic levitation technique.The Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys present only one recalescence during liquid/solid phase transition,while the Zr_(70)V_(30) alloy presents a transformation from two recalescence to one recalescence phenomenon with a critical undercooling of approximately 300 K.According to the LKT/BCT model,the calculated results of the primary β-Zr dendrite growth velocity in undercooled liquid Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys agree well with the experiments.The velocity inflection points at 119 K of Zr_(91.4)V_(8.6) alloy and 201 K of Zr_(83.5)V_(16.5) alloy could be explained by the competition between solutal undercooling control and thermal undercooling control modes.For Zr_(70)V_(30) alloy solidified in the P1 with twice recalescence,a critical second undercooling of 253 K and corresponding undercooling of 65 and 244 K are obtained.When the un-dercooling is in the range of 65-244 K,the second undercooling would be greater than 253 K,and the residual liquid phase would solidify into anomalous eutectic microstructure for Zr_(70)V_(30) alloy.The Vickers hardness of Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys all show a quadratic relationship with undercooling.Under electrostatic levitation condition,the mechanical property of Zr-V alloys could be significantly regulated through solidifying the alloys at different undercoolings.
基金Funded by the Basic Research Project in Shanxi Province(No.202103021224183)the 2024 Science and Technology PlanProject of Jiaozuo City,Henan Province(No.2024410001)。
文摘The evolution of the microstructure and morphology of Cu55Ni45 and Cu60Ni40 alloys under varying degrees of undercooling was investigated through molten glass purification and cyclic superheating technology.By increasing the Cu content,the effect of Cu on the evolution of the microstructure and morphology of the Cu-Ni alloy during undercooling was studied.The mechanism of grain refinement at different degrees of undercooling and the effect of Cu content on its solidification behaviour were investigated.The solidification behaviour of Cu55Ni45 and Cu60Ni40 alloys was investigated using infrared thermometry and high-speed photography.The results indicate that both Cu55Ni45 and Cu60Ni40 alloy melts undergo only one recalescence during rapid solidification.The degree of recalescence increases approximately linearly with increasing undercooling.The solidification front of the alloy melts undergoes a transition process from a small-angle plane to a sharp front and then to a smooth arc.However,the growth of the subcooled melt is constrained to a narrow range,facilitating the formation of a coarse dendritic crystal morphology in the Cu-Ni alloy.At large undercooling,the stress breakdown of the directionally growing dendrites is primarily caused by thermal diffusion.The strain remaining in the dendritic fragments provides the driving force for recrystallisation of the tissue to occur,which in turn refines the tissue.
基金Funded by the Basic Research Project in Shanxi Province(No.202103021224183)the 2024 Science and Technology Plan Project of Jiaozuo City,Henan Province(No.2024410001)。
文摘By applying the rapid solidification technique of deep undercooling,Cu65Ni35 and Cu60Ni40 alloys achieved maximum undercoolings of 284 and 222 K,respectively.Microstructural images captured reveal grain refinement in both alloys across both large and small undercooling ranges.High-speed photography was used to analyze the relationship between solidification front morphology and undercooling,showing that dendrite remelting and fragmentation caused grain refinement under small undercooling,while stress-induced recrystallization is responsible under large undercooling.Microhardness testing further demonstrates a sudden drop in microhardness near the critical undercooling point,providing evidence for grain refinement due to recrystallization in large undercooling tissues.
基金Funded by the Central Government-Guided Local Development Fund Project(No.YDZJSX2025D042)the Key R&D Program of Shanxi Province(No.202202150401018)+1 种基金the Basic Research Program of Shanxi Province(No.20210302124220)the State Key Laboratory of CAD/CG of Zhejiang University(No.A2325)。
文摘This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.
基金supported by the National Natural Science Foundation of China(No.52171041)the Science and Technology Special Project(K19168).
文摘During the tungsten inert gas(TIG)welding process of Ti_(2)AlNb alloy,high heat input leads to the formation of coarse grains,which are detrimental to the mechanical properties of welded joints.To address this problem,Ta microalloyed welding wires were developed to enhance the strength of the welded joints.The Ta-modifed fusion zone(FZ)exhibited a well-defned structure with a smooth,defect-free surface.Systematic analysis of the microstructure evolution and mechanical properties of the welded joints revealed that the Ta element completely dissolves into the FZ.During solidifcation,a signifcant constitutional undercooling efect occurs,promoting the columnar-to-equiaxed transition(CET)and reducing grain size from 187.42 to 133.49μm.Mechanical properties tests indicated that with increased Ta content,the strength of the welded joints initially increased and then decreased.When the Ta content in the welding wire was 1 wt%,the joints showed the best performance,with a tensile strength of 909.36 MPa and an elongation of 1.21%.Compared to the welded samples without Ta,the tensile strength and elongation increased by 153.01 MPa and 0.53%,respectively.Grain refnement and increased dislocation density were the main reasons for the improved mechanical properties.However,excessive Ta content led to signifcant the intragrain misorientation,increasing the joint’s anisotropy and causing uneven deformation during tensile testing.Therefore,further addition of Ta did not substantially enhance the tensile properties of the joint.Additionally,the paper provides a detailed analysis of the low elongation observed in the joint.After welding,dislocations were neatly arranged in the FZ,forming numerous parallel dislocation walls,leading to local stress concentration and accelerating crack initiation and propagation.Consequently,the elongation at the weld was lower than that of the base metal(BM).This research ofers a new approach to improve the mechanical properties of Ti2AlNb alloy during welding.
基金Project(50874073) supported by the National Natural Science Foundation of ChinaProject(2011CB610405) supported by the National Basic Research Program of ChinaProject(2011M500074) supported by China Postdoctoral Science Foundation
文摘A series of Co-Sn alloys with Sn content ranging from 12% to 32%（mole fraction） were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification microstructures.A boundary clearly exists,which separates the coupled growth zone from the decoupled growth zone of eutectic phases for the alloys with Sn content ranging from 14% to 31%（mole fraction）.The other Co-Sn alloys out of this content range are hard to be undercooled into the coupled growth zone in the experiment.It is found that the so-called non-reciprocal nucleation phenomenon does not happen in the solidification of undercooled Co-Sn off-eutectic alloys.
基金Project(2011CB610403) supported by the National Basic Research Program of ChinaProject(51125002) supported by the National Science Fund for Distinguished Young Scholars of China+4 种基金Projects(51101122,51071127,50901059) supported by the National Natural Science Foundation of ChinaProject(111502) supported by the Huo Yingdong Young Teacher Fund,ChinaProjects(66-QP-2010, 24-TZ-2009) supported by the Free Research Fund of State Key Laboratory of Solidification Processing,ChinaProjects(JC201008, JC200801) supported by the Fundamental Research Fund of Northwestern Polytechnical University,ChinaProject(B08040) supported by the Program of Introducing Talents of Discipline to Universities,China
文摘Departing from the volume-averaging method,an overall solidification kinetic model for undercooled single-phase solid-solution alloys was developed to study the effect of back diffusion on the solidification kinetics.Application to rapid solidification of undercooled Ni-15%Cu（mole fraction） alloy shows that back diffusion effect has significant influence on the solidification ending temperature but possesses almost no effect on the volume fraction solidified during recalescence.Inconsistent with the widely accepted viewpoint of Herlach,solidification ends at a temperature between the predictions of Lever rule and Scheil＇s equation,and the exact value is determined by the effect of back diffusion,the initial undercooling and the cooling rate.
基金Project(2011CB610403)supported by the National Basic Research Program of ChinaProject(51125002)supported by the National Natural Science Fund for Distinguished Young Scholars of China+3 种基金Projects(51101122,51071127,50901059)supported by the National Natural Science Foundation of ChinaProject(1110502)supported by the Fok Ying Tong Education Foundation,ChinaProjects(66-QP-2010,24-TZ-2009)supported by the Free Research Fund of State Key Laboratory of Solidification Processing,ChinaProject(B08040)supported by the Program of Introducing Talents of Discipline to Universities,China
文摘Rapid solidification of undercooled Ni-15%Cu （mole fraction） alloy was studied using glass fluxing and cyclic superheating. To show the effect of cooling history on the microstrucyure and microtexture evolution, the as-solidified samples were either cooled naturally or quenched into water after recalescence. At low undercooling, grain-refined microstructure has a random texture and a highly oriented texture without annealing twins for the case of naturally cooling and quenching, respectively. At high undercooling, a fully random texture as well as a number of annealing twins are observed, and recrystallization and grain growth independently happen on the cooling history. Fluid flow and recrystallization play an important role in the microtexture formation for grain refinement at both low and high undercooling.
基金Project (50971083) supported by the National Natural Science Foundation of China
文摘Electrical resistivity and viscosity of Pb–Sb alloys are measured to investigate Peierls distortion behavior in the melts. In Pb30Sb70, Pb20Sb80, and Pb10Sb90 melts, temperature dependence of resistivity deviates from linear dependence during cooling. At 663 °C, different trends in isothermal behavior between experimental and theoretical resistivities, are interpreted as the existence of Peierls distortion in Sb-rich melts. In Pb30Sb70 and Pb20Sb80 melts, abnormal viscosity results verify the existence of abnormal structure transition, which is attributed to the formation of large Sb clusters with Peierls distortion. In undercooled liquid Pb20Sb80, minute resistivity coefficient and quadratic resistivity behavior are interpreted as the rapid increase of cluster size of Sb clusters with Peierls distortion, which provides preferential nucleation sites for higher structure similarity to the crystalline and lower liquid–solid interfacial energy.
基金Project(2011CB610406)supported by the National Basic Research Program of China
文摘Various undercoolings 14-232 K of bulk K4169 superalloys were obtained by the method of molten glass fluxing combined with superheating cycling and the mechanical properties of undercooled K4169 with as-solidified state were tested. Microstructures and phases composition in undercooled bulk K4169 superalloy were identified by transmission electron microscope （TEM）, scanning electron microscope （SEM） and optical microscopy （OM）. The morphology of dendrites, grain size and intergranular phase all change with the increased undercooling. Meanwhile, the relationship between microstructure of undercooled K4169 superalloy and tensile properties was investigated. The experimental results show that the uniform distribution of Laves phase and the decrease of grain size and intergranular phase content are favorable for the improvement of mechanical properties. The maximum tensile strength and elongation obtained at undercooling of 232 K are 932.2 MPa and 6.5%, respectively.
基金Projects (50901025,50975060,51331005) supported by the National Natural Science Foundation of ChinaProject (2011CB610406) supported by the National Basic Research Program of China+2 种基金Projects (201104420,20090450840) supported by China Postdoctoral Science FoundationProject (JC201209) supported by Outstanding Young Scientist Foundation of Heilongjiang Province,ChinaProject (HIT.BRET1.20100008) supported by the Fundamental Research Funds for Central Universities,China
文摘Peritectic reaction was studied by directional solidification of Cu-Ge alloys.A larger triple junction region of peritectic reaction was used to analyze the interface stability of the triple junction region during peritectic reaction.Under different growth conditions and compositions,different growth morphologies of triple junction region are presented.For the hypoperitectic Cu-13.5%Ge alloy,as the pulling velocity（v） increases from 2 to 5 μm/s,the morphological instability of the peritectic phase occurs during the peritectic reaction and the remelting interface of the primary phase is relatively stable.However,for the hyperperitectic Cu-15.6%Ge alloy wim v=5 μm/s,the nonplanar remelting interface near the trijunction is presented.The morphological stabilities of the solidifying peritectic phase and the remelting primary phase are analyzed in terms of the constitutional undercooling criterion.
基金supported by the Natural Science Foundation of China (Grant No.50771084)the Natural Science Foundation of the Education Department of Jiangsu province,China (Grant No.09KJB430004)
文摘The homogeneous liquid was separated into two phases, （Fe, Co）-rich LI and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature Tsep. If the duration from Tsep to Tsl （solidification temperature of LI phase）, termed the liquid-phase separation interval Δt, exceeded a critical value, an eggtype structure was observed. By utilizing differential thermal analyses （DTA）, the solidification process of the undercooled Fe-Co-Cu alloys was studied. Additionally, an immiscible boundary was obtained, which was a convex parabola with a symmetrical axis of XCu=0.52. Depending on the relative amounts of LI and L2, the minor phase was nucleated firstly to form liquid droplets and separated from the original liquids at the beginning of liquid-phase separation.
基金the National Natural Science Foundation of China(Nos.51771153,51371147,51790481 and 51431008)the Innovation Guidance Support Project for Taicang Top Research Institutes(No.TC2018DYDS20)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX201825)。
文摘The eutectic Ag-Cu alloys exhibiting fine Ag-Cu lamellar eutectic structure formed upon rapid solidification have great potentials being used in various engineering fields.However,the desired fine primary lamellar eutectic structure(PLES)is usually replaced by a coarse anomalous eutectic structure(AES)when the undercooling prior to solidification exceeds a certain value.The forming mechanism of AES in the undercooled eutectic Ag-Cu alloy has been a controversial issue.In this work,the undercooled Ag-39.9 at.% Cu eutectic alloy is solidified under different cooling conditions by using techniques of melt fluxing and copper mold casting.The results show that the coupled eutectic growth of this alloy undergoes a transition from a slow eutectic-cellular growth(ECG)to a rapid eutectic-dendritic growth(EDG)above a undercooling of 72 K,accompanying with an abrupt change of the distribution and amount of AES in as-solidified microstructures.Two kinds of primary lamellar eutectic structures are formed by ECG and EDG during recalescence,respectively.The destabilization of PLES that causes the formation of AES is ascribed to two different mechanisms based on the microstructural examination and theoretical calculations.Below 72 K,the destabilization of PLES formed by slow ECG is caused by the mechanism of"termination migration"driven by interfacial energy.While above 72 K,the destabilization of PLES formed by rapid EDG is attributed to the unstable perturbation of interface driven by interfacial energy and solute supersaturation.
文摘Bulk Fe-30Ni alloy melt was nudercooled up to 337K by combining the glass fluxing technique with superheating-cooling cycle. Grain refinement at low undercoolings was observed in the experiment in addition to that at high undercoolings. The current grain refinement mechanisms were examined, and it is concluded that the refined gains are all developed from dendrites, however the grain refinement at low undercoolings is due to chemical superheating, while that at high undercoolings due to rapid solidification contruction.
基金the National Natural Science Foundation of China(Grant Nos.51734008,51522102 and 51327901)the National Key R&D Program of China(Grant No.2018YFB2001800)the Shannxi Key Industry Chain Program(Grant No.2019ZDLGY05-10)。
文摘The undercooling dependence of the solidification mechanism was systematically explored by the electrostatic levitation(ESL)facility.During the experiments,the maximum undercooling reached up to 406 K(0.26 T_L)and the growth velocity of the primary TiNi phase was in-situ determined at various undercoolings.At the initial increase of alloy undercooling,the value of growth velocity sluggishly rose followed by a power function.In this case,the primary TiNi phase preferentially developed as the equiaxed dendrite,then the remnant liquid participated as Ti_(2)Ni andα-Ti phases on the grain boundary.Once the undercooling exceeded the critical value of 350 K,the growth velocity of the primary phase displayed a sharply increase tendency.Meanwhile,the TEM results demonstrated that the precipitation of the intermetallic Ti_(2)Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.
基金supported by the National Natural Science Foundation of China(Grant Nos.51227001 and 51471108)the SJTU-UNSW Cooperative Research Fund(16X120030005)
文摘A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitute for the stable Co3 B phase in the alloy melts undercooled above a critical undercooling value of -60 K.The Co23B6 and α-Co phases make up a metastable eutectic. The corresponding eutectic composition and temperature are Co80.4B19.6 and 1343 K, respectively. On exposure of the metastable Co23B6 phase at a given temperature above 1208 K, it does not decompose even after several hours. But it transforms by a eutectoid reaction to α-Co ＋ Co3 B at lower temperature.
文摘The undercooling and solidification of 150 μm and 185 μm droplets of Sn 5%Pb alloy prepared by the uniform droplet spray (UDS) process have been investigated. The enthalpy of the droplet has been measured by non adiabatic calorimetric method as a function of the flight distance. A droplet solidification simulation model has been used to compare with the experimental data. The results show that the enthalpy released by the droplets in the calorimeter is 11.88 J/g and 22.29 J/g less than the simulated values up to a certain flight distance at 0.485 m and 0.460 m for 150 μm and 185 μm droplets respectively, but agrees with the expected values at larger distance. The nucleation of the droplets takes place at the distance where the experimental and simulated enthalpy values agree. The droplets quenched before nucleation solidify into metastable supersaturated solid solution and have large undercooling. The formation of the metastable structure in the droplets has been verified metallographically and by calculations based on a thermodynamic model.
