Preparation of Laser Cladding Coating Undercooling Cu-based Alloy and Co on Non-equilibrium Solidification Structure

The effect of the gradient content of Co element on the solidification process of Cu-based alloy under deep under cooling conditions was explored.The non-equilibrium solidification structure of the under cooled alloy samples were analyzed.It is found that the rapidly solidified alloy has undergone twice grain refinement during the undercooling process.Characterization and significance of the maximum undercooling refinement structure of Cu60Ni35Co5 at T=253 K were analyzed.High-density defects were observed,such as dislocations,stacking faults networks,and twinning structures.The standard FCC diffraction pattern represents that it is still a single-phase structure.Based on the metallographic diagram,EBSD and TEM data analysis,it is illustrated that the occurrence of grain refinement under high undercooling is due to stress induced recrystallization.In addition,the laser cladding technology is used to coat Co-based alloy(Stellite12) coating on 304 stainless steel substrate;the microstructure of the coating cross-section was analyzed.It was found that the microstructure of the cross-section is presented as columnar crystals,planar crystals,and disordered growth direction,so that the coating has better hardness and wear resistance.By electrochemical corrosion of the substrate and coating,it can be seen that the Co and Cr elements present in the coating are more likely to form a dense passivation film,which improved the corrosion resistance of the coating.

Construction and analysis of dynamic solidification curves for non-equilibrium solidification process in lost-foam casting hypoeutectic gray cast iron

Most lost-foam casting processes involve non-equilibrium solidification dominated by kinetic factors, while construction of a common dynamic solidification curve is based on pure thermodynamics, not applicable for analyses and research of non-equilibrium macro-solidification processes, and the construction mode can not be applied to nonequilibrium solidification process. In this study, the construction of the dynamic solidification curve(DSC) for the nonequilibrium macro-solidification process included: a modified method to determine the start temperature of primary austenite precipitation(T_(AL)) and the start temperature of eutectic solidification(T_(ES)); double curves method to determine the temperature of the dendrite coherency point of primary austenite(T-(AC)) and the temperature of eutectic cells collision point(T_(EC)); the "technical solidus" method to determine the end temperature of eutectic reaction(T_(EN)). For this purpose, a comparative testing of the non-equilibrium solidification temperature fields in lost-foam casting and green sand mold casting hypoeutectic gray iron was carried out. The thermal analysis results were used to construct the DSCs of both these casting methods under non-equilibrium solidification conditions. The results show that the transformation rate of non-equilibrium solidification in hypoeutectic gray cast iron is greater than that of equilibrium solidification. The eutectic solidification region presents a typical mushy solidification mode. The results also indicate that the primary austenite precipitation zone of lost-foam casting is slightly larger than that of green sand casting. At the same time, the solid fraction(f_s) of the dendrite coherency points in lost-foam casting is greater than that in the green sand casting. Therefore, from these two points, lost-foam casting is more preferable for reduction of shrinkage and mechanical burntin sand tendency of the hypoeutectic gray cast iron. Due to the fact that the solidification process(from the surface to center) at primary austenite growth area in the lost-foam cylinder sample lags behind that in the green sand casting, the mushy solidification tendency of lost-foam casting is greater and the solidification time is longer.

Metallurgical modeling of microcrack repairment during welding nonferrous materials: non-equilibrium solidification behavior of weld pool (Ⅰ)

Metallurgical modeling of synergistic microcrack self-repairmen during welding single crystal and polycrystalline superalloys of high-temperature aerospace materials has been properly established. The idea of improvement of nickel-based superalloys weldability through non-equilibrium solidification behavior of backfill to self-repair arterial crack network is usefully proposed. Crystallographic control strategy of crack self-repairmen of fusion zone interdendritic solidification cracking and heat-affected zone （HAZ） intergranular liquation cracking is technically achievable, indicating that optimal niobium alloying beneficially refines weld microstructure, stabilizes the primary solidification path, increases the solidification temperature and concomitantly decreases the weld pool geometry. High-carbon grain boundary is more thermal stable and less contributes to incipient intergranular liquid film than that of low-carbon grain boundary. The theoretical predictions of cracking susceptibility are indirectly verified in a rather satisfactory manner. Additionally, the metallurgical modeling enhances predicative capabilities and thereby is readily applicable for other alloy systems.

Study on Rare Earth-Containing Phases in TiAl Based Alloys Prepared by Non-Equilibrium Solidification Processing

Microstructure evolution of rare earth rich phase of rapidly-solidified (RS) TiAl based alloys was investigated. The two rapid-solidification techniques employed are melt-spinning technique (MS) and Hammer-and-Anvil technique (HB). MS ribbons and HA foils were obtained in the experiment. The results demonstrate that with the increasing of cooling rates of TiAl based alloys great changes are taken place in the microstructures of rare earth rich phase, from scattering mainly on grain boundaries of as-cast ingot to distributing homogeneously as very fine fibers or powders (nanometer grade) on the matrix. The fine paralleling second phase fibers in the HA foils are considered to be connected with gamma/alpha (2) lamellar colonies. Selected area electronic diffraction (SAED) patterns of the rare earth rich phase is in accordance with that of intermetallic AlCe.

Morphological Heredity of Intermetallic Nb_(5)Si_(3)Dendrites in Hypereutectic Nb-Si Based Alloys via Non-Equilibrium Solidification

For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,here we artificially manipulate the growth morphology of Nb_(5)Si_(3)using electron beam surface melting(EBSM)and subsequent annealing treatments.Results show that such a non-equilibrium solidification pathway enables the transition from faceted growth to non-faceted dendritic growth of Nb_(5)Si_(3),along with evident microstructure refinement,generation of metastableβ-Nb_(5)Si_(3)phases and elimination of chemical segregation.The transformation fromβ-Nb_(5)Si_(3)toα-Nb_(5)Si_(3)and Nb solid solution(Nbss)particles is triggered by the annealing treatment at 1450°C for 5 h.Also,we find the annealing-mediated formation of inherited Nb_(5)Si_(3)dendrites that maintain the dendritic morphology of the original as-solidifiedβ-Nb_(5)Si_(3)dendrites.This work thus provides a feasible routine to obtain thermally stable and refinedα-Nb_(5)Si_(3)dendrites in hypereutectic Nb-Si based alloys.

Effect of Co on Solidification Characteristics and Microstructural Transformation of Non-equilibrium Solidified Cu-Ni Alloys

Non-equilibrium solidification structures of Cu55Ni45 and Cu55Ni43Co2 alloys were prepared by the molten glass purification cycle superheating method.The variation of the recalescence phenomenon with the degree of undercooling in the rapid solidification process was investigated using an infrared thermometer.The addition of the Co element affected the evolution of the recalescence phenomenon in Cu-Ni alloys.The images of the solid-liquid interface migration during the rapid solidification of supercooled melts were captured by using a high-speed camera.The solidification rate of Cu-Ni alloys,with the addition of Co elements,was explored.Finally,the grain refinement structure with low supercooling was characterised using electron backscatter diffraction(EBSD).The effect of Co on the microstructural evolution during nonequilibrium solidification of Cu-Ni alloys under conditions of small supercooling is investigated by comparing the microstructures of Cu55Ni45 and Cu55Ni43Co2 alloys.The experimental results show that the addition of a small amount of Co weakens the recalescence behaviour of the Cu55Ni45 alloy and significantly reduces the thermal strain in the rapid solidification phase.In the rapid solidification phase,the thermal strain is greatly reduced,and there is a significant increase in the characteristic undercooling degree.Furthermore,the addition of Co and the reduction of Cu not only result in a lower solidification rate of the alloy,but also contribute to the homogenisation of the grain size.

Volume-averaged modeling of multiphase solidification with equiaxed crystal sedimentation in a steel ingot

Macrosegregation is a critical factor that limits the mechanical properties of materials.The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied,as it plays a significant role in determining the distribution of alloying elements and impurities within a material.To improve macrosegregation in steel connecting shafts,a multiphase solidification model that couples melt flow,heat transfer,microstructure evolution,and solute transport was established based on the volume-averaged Eulerian-Eulerian approach.In this model,the effects of liquid phase,equiaxed crystals,columnar dendrites,and columnar-to-equiaxed transition(CET)during solidification and evolution of microstructure can be considered simultaneously.The sedimentation of equiaxed crystals contributes to negative macrosegregation,where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET.Additionally,noticeable positive macrosegregation occurs in the area of final solidification in the ingot.The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts.To mitigate the thermal convection of molten steel resulting from excessive superheating,reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.

Advantages of rapid solidification over casting of Mg-0.4Zn-1Y alloy

The Mg-Y-Zn magnesium alloy system is commonly recognized for its remarkable combination of high strength and ductility,achieved even with minimal amounts of alloying elements.This exceptional performance is attributed to its unique microstructure,which includes Long-Period Stacking Ordered(LPSO)phases or the distinctive microstructure derived from the LPSO phase,referred to as the Mille-Feuille structure(MFS).This study systematically compares the traditional ingot metallurgy method with the rapid solidification technique,coupled with diverse heat treatments and extrusion processes.Microscopic analyses reveal variations in the presence of LPSO phases,Mille-Feuille structure,and grain size,leading to divergent mechanical and corrosion properties.The rapid solidification approach stands out,ensuring superior mechanical properties alongside a reasonable corrosion rate.

Solidification/Stabilization of Chromium in Red Mud-based Geopolymer

Up to 1.5wt%of Cr(Ⅲ)salts(CrCl_(3),and Cr_(2)O_(3))and Cr(Ⅵ)salts(Na_(2)CrO_(4),and CaCr_(2)O_(7))were incorporated into red mud-based geopolymers,respectively.The solidification/stabilization,compressive strength,and durability of the Cr-containing geopolymers were investigated.The experimental results indicate that the red mud-based geopolymer could effectively solidify/stabilize different types of Cr salts with solidification/stabilization rates of above 99.61%.Geopolymers are environmentally safe when the dosage of CaCr_(2)O_(7)is≤1.0wt%,or the dosage of CrCl_(3),Cr_(2)O_(3),and Na_(2)CrO_(4)is≤1.5wt%,respectively.The effects of Cr salts on the compressive strength varies with the type and content of Cr salts.The freeze-thaw cycle is more destructive to geopolymer properties than sulfate attack or acid rain erosion.The solidification/stabilization of Cr is mainly attributed to the following reasons:a)The chemical binding of Cr is related to the formation of Cr-containing hydrates(eg,magnesiochromite((Mg,Fe)(Cr,Al)_(2)O_(4)))and doping into N-A-S-H gel and C-A-S-H gel framework;b)The physical effect is related to the encapsulation by the hydration products(e g,N-A-S-H gel and C-A-S-H gel).This study provides a reference for the treatment of hazardous Cr-containing wastes by solid waste-based geopolymers.

Effect of solidification cooling rate on microstructure and tribology characteristics of Zn-4Si alloy

The main objective of this work was to modify the microstructure and enhance the tribological properties of a new Zn-4Si al-loy through a high solidification cooling rate(SCR).According to the results,by increasing the SCR from 2.0 to 59.5℃/s the average size of primary Si particles and that of the grains reduced from 76.1 and 3780μm to less than about 14.6 and 460μm,respectively.Augment-ing the SCR also enhanced the microstructural homogeneity,decreased the porosity content(by 50%),and increased the matrix hardness(by 36%).These microstructural changes enhanced the tribological behavior.For instance,under the applied pressure of 0.5 MPa,an in-crease in the SCR from 2.0 to 59.5℃/s decreased the wear rate and the average friction coefficient of the alloy by 57%and 23%,respect-ively.The wear mechanism was also changed from the severe delamination,adhesion,and abrasion in the slowly-cooled alloy to the mild tribolayer delamination/abrasion in the high-cooling-rate-solidified sample.

Irregular initial solidification by mold thermal monitoring in the continuous casting of steels:A review

Occasional irregular initial solidification phenomena,including stickers,deep oscillation marks,depressions,and surface cracks of strand shells in continuous casting molds,are important limitations for developing the high-efficiency continuous casting of steels.The application of mold thermal monitoring(MTM) systems,which use thermocouples to detect and respond to temperature variations in molds,has become an effective method to address irregular initial solidification phenomena.Such systems are widely applied in numerous steel companies for sticker breakout prediction.However,monitoring the surface defects of strands remains immature.Hence,indepth research is necessary to utilize the potential advantages and comprehensive monitoring of MTM systems.This paper summarizes what is included in the irregular initial solidification phenomena and systematically reviews the current state of research on these phenomena by the MTM systems.Furthermore,the influences of mold slag behavior on monitoring these phenomena are analyzed.Finally,the remaining problems of the formation mechanisms and investigations of irregular initial solidification phenomena are discussed,and future research directions are proposed.

Numerical simulation on directional solidification and heat treatment processes of turbine blades

Study on turbine blades is crucial due to their critical role in ensuring the efficient and reliable operation of aircraft engines.Nickel-based single crystal superalloys are extensively used in the hot manufacturing of turbine blades due to their exceptional high-temperature mechanical properties.The hot manufacturing of single crystal blades involves directional solidification and heat treatment.Experimental manufacturing of these blades is time-consuming,capital-intensive,and often insufficient to meet industrial demands.Numerical simulation techniques have gained widespread acceptance in blade manufacturing research due to their low energy consumption,high efficiency,and rapid turnaround time.This article introduces the modeling and simulation of hot manufacturing in single crystal blades.The discussion outlines the prevalent mathematical models employed in numerical simulations related to blade hot manufacturing.It encapsulates the advancements in research concerning macro to micro-level numerical simulation techniques for directional solidification and heat treatment processes.Furthermore,potential future trajectories for the numerical simulation of single crystal blade hot manufacturing are also discussed.

Effect of TiB_(2)Nanoparticles on Microstructure and Mechanical Properties of Ni_(60)Cr_(21)Fe_(19)Alloy in Rapid Directional Solidification Process:Molecular Dynamics Study

Molecular dynamics(MD)simulations are employed to delve into the multifaceted effects of TiB2 nanoparticles on the intricate grain refinement mechanism,microstructural evolution,and tensile performance of Inconel 718 superalloys during the rapid directional solidification.Specifically,the study focuses on elucidating the role of TiB2 nanoparticles in augmenting the nucleation rate during the rapid directional solidification process of Ni60Cr21Fe19 alloy system.Furthermore,subsequent tensile simulations are conducted to comprehensively evaluate the anisotropic behavior of tensile properties within the solidified microstructures.The MD results reveal that the incorporation of TiB₂nanoparticles during the rapid directional solidification of the Ni_(60)Cr_(21)Fe_(19)significantly enhances the average nucleation rate,escalating it from 1.27×10^(34)m^(-3)·s^(-1)to 2.55×10^(34)m^(-3)·s^(-1).Notably,within the face centered cube(FCC)structure,Ni atoms exhibit pronounced compositional segregation,and the solidified alloy maintains an exceptionally high dislocation density reaching up to 10^(16)m^(-2).Crucially,the rapid directional solidification process imparts a distinct microstructural anisotropy,leading to a notable disparity in tensile strength.Specifically,the tensile strength along the solidification direction is markedly superior to that perpendicular to it.This disparity arises from different deformation mechanisms under varying loading orientations.Tensile stress perpendicular to the solidification direction encourages the formation of smooth and organized mechanical twins.These twins act as slip planes,enhancing dislocation mobility and thereby improving stress relaxation and dispersion.Moreover,the results underscore the profound strengthening effect of TiB2 nanoparticles,particularly in enhancing the tensile strength along the rapid directional solidification direction.

Exploration of the coupled lattice Boltzmann model based on a multiphase field model:A study of the solid-liquid-gas interaction mechanism in the solidification process

A multiphase field model coupled with a lattice Boltzmann(PF-LBM)model is proposed to simulate the distribution mechanism of bubbles and solutes at the solid-liquid interface,the interaction between dendrites and bubbles,and the effects of different temperatures,anisotropic strengths and tilting angles on the solidified organization of the SCN-0.24wt.%butanedinitrile alloy during the solidification process.The model adopts a multiphase field model to simulate the growth of dendrites,calculates the growth motions of dendrites based on the interfacial solute equilibrium;and adopts a lattice Boltzmann model(LBM)based on the Shan-Chen multiphase flow to simulate the growth and motions of bubbles in the liquid phase,which includes the interaction between solid-liquid-gas phases.The simulation results show that during the directional growth of columnar dendrites,bubbles first precipitate out slowly at the very bottom of the dendrites,and then rise up due to the different solid-liquid densities and pressure differences.The bubbles will interact with the dendrite in the process of flow migration,such as extrusion,overflow,fusion and disappearance.In the case of wide gaps in the dendrite channels,bubbles will fuse to form larger irregular bubbles,and in the case of dense channels,bubbles will deform due to the extrusion of dendrites.In the simulated region,as the dendrites converge and diverge,the bubbles precipitate out of the dendrites by compression and diffusion,which also causes physical phenomena such as fusion and spillage of the bubbles.These results reveal the physical mechanisms of bubble nucleation,growth and kinematic evolution during solidification and interaction with dendrite growth.

Lunar In Situ Large-Scale Construction:Quantitative Evaluation of Regolith Solidification Techniques

Lunar habitat construction is crucial for successful lunar exploration missions.Due to the limitations of transportation conditions,extensive global research has been conducted on lunar in situ material processing techniques in recent years.The aim of this paper is to provide a comprehensive review,precise classification,and quantitative evaluation of these approaches,focusing specifically on four main approaches:reaction solidification(RS),sintering/melting(SM),bonding solidification(BS),and confinement formation(CF).Eight key indicators have been identified for the construction of low-cost and highperformance systems to assess the feasibility of these methods:in situ material ratio,curing temperature,curing time,implementation conditions,compressive strength,tensile strength,curing dimensions,and environmental adaptability.The scoring thresholds are determined by comparing the construction requirements with the actual capabilities.Among the evaluated methods,regolith bagging has emerged as a promising option due to its high in situ material ratio,low time requirement,lack of hightemperature requirements,and minimal shortcomings,with only the compressive strength falling below the neutral score.The compressive strength still maintains a value of 2–3 MPa.The proposed construction scheme utilizing regolith bags offers numerous advantages,including rapid and large-scale construction,ensured tensile strength,and reduced reliance on equipment and energy.In this study,guidelines for evaluating regolith solidification techniques are provided,and directions for improvement are offered.The proposed lunar habitat design based on regolith bags is a practical reference for future research.

Recent research progress on the phase-field model of microstructural evolution during metal solidification

Solidification structure is a key aspect for understanding the mechanical performance of metal alloys,wherein composition and casting parameters considerably influence solidification and determine the unique microstructure of the alloys.By following the principle of free energy minimization,the phase-field method eliminates the need for tracking the solid/liquid phase interface and has greatly accelerated the research and development efforts geared toward optimizing metal solidification microstructures.The recent progress in the application of phasefield simulation to investigate the effect of alloy composition and casting process parameters on the solidification structure of metals is summarized in this review.The effects of several typical elements and process parameters,including carbon,boron,silicon,cooling rate,pulling speed,scanning speed,anisotropy,and gravity,on the solidification structure are discussed.The present work also addresses the future prospects of phase-field simulation and aims to facilitate the widespread applications of phase-field approaches in the simulation of microstructures during solidification.

Effect of mixing temperature on microstructure of an Al-Si alloy prepared by controlled diffusion solidification

The effects of mixing temperature,i.e.,the temperatures of two precursor melts(pure Al and Al-12Si),on the temperature and solute fields of resultant mixture,the nucleation and growth,and the size and morphology of primary grains during controlled diffusion solidification(CDS) of Al-8Si alloy were investigated by using simulation and calculation.The results indicate that a lower mixing temperature is helpful for achieving more supercooled microscale Al-rich pockets in the mixture,and increasing the width and supercooling degree of supercooling zone in the Al-rich pockets,and thus,the nucleation rate.The nuclei grow up in nondendritic mode,resulting in spheroidal,at least,nondendritic grains.In a successful CDS,the superheat degrees of the two precursor melts should be limited within several degrees,and it is not necessary to extra stipulate the superheat degree of target alloy melt(Al-8Si) when the requirement about Gibbs energies of the three melts is matched.Subsequent observation on casting microstructures shows that the employed simulation and calculation processes are reasonable and the achieved results are reliable.

Effects of mechanical vibration on filling and solidification behavior, microstructure and performance of Al/Mg bimetal by lost foam compound casting

Al/Mg bimetal was prepared by lost foam solid-liquid compound casting,and the effects of mechanical vibration on the filling and solidification behavior,microstructure and performance of the bimetal were investigated.Results show that the mechanical vibration has a remarkable influence on the filling and solidification processes.It is found that after mechanical vibration,the filling rate increases and the filling rate at different times is more uniform than that without vibration.In addition,the mechanical vibration also increases the wettability between liquid AZ91D and A356 inlays.The mechanical vibration reduces the horizontal and vertical temperature gradient of the casting and makes the temperature distribution of the whole casting more uniform.Compared to the Al/Mg bimetal without vibration,the shear strength is improved by 39.76%after the mechanical vibration is applied,due to the decrease of the inclusions and Al_(12)Mg_(17) dendrites,and the refinement and uniform distribution of the Mg_(2)Si particles in the interface of the Al/Mg bimetal.

High-Performance Quasi-Solid-State Pouch Cells Enabled by in situ Solidification of a Novel Polymer Electrolyte

Conventional lithium-ion batteries(LIBs)with liquid electrolytes are challenged by their big safety concerns,particularly used in electric vehicles.All-solid-state batteries using solid-state electrolytes have been proposed to significantly improve safety yet are impeded by poor interfacial solid–solid contact and fast interface degradation.As a compromising strategy,in situ solidification has been proposed in recent years to fabricate quasi-solid-state batteries,which have great advantages in constructing intimate interfaces and cost-effective mass manufacturing.In this work,quasi-solid-state pouch cells with high loading electrodes(≥3 m Ah cm^(-2))were fabricated via in situ solidification of poly(ethylene glycol)diacrylate-based polymer electrolytes(PEGDA-PEs).Both single-layer and multilayer quasi-solid-state pouch cells(2.0 Ah)have demonstrated stable electrochemical performance over500 cycles.The superb electrochemical stability is closely related to the formation of robust and compatible interphase,which successfully inhibits interfacial side reactions and prevents interfacial structural degradation.This work demonstrates that in situ solidification is a facile and cost-effective approach to fabricate quasi-solid-state pouch cells with both excellent electrochemical performance and safety.

Non-equilibrium microstructure and the metastable phase of Al-9.6wt%Mg Alloy solidification under high pressure

The non-equilibrium microstructure and a new metastable phase of Al-9.6wt%Mg alloy solidified at 6 GPa were studied by optical microscope,differential scanning calorimetry,X-ray diffraction and transmission electron microscope.The results showed that dendrite microstructure was refined,and the solid solubility of Mg in α-Al phase increased greatly.Correspondingly,the lattice parameter of α-Al phase increased.Al3Mg2 phases disappeared under high pressure solidification.In particular,a metastable phase with small size(20 nm or so) was produced in the alloy,its melting temperature range was 464～518.2 ℃,which was higher than that of Al3Mg2 phase(453～465 ℃) under normal pressure.These metastable phases located in the interdendritic position.It was the first time that the metastable phase was found in Al-Mg alloy at a high pressure of 6 GPa.The formation mechanism of the metastable phases was discussed.