Evading strength−ductility trade-off of GH605 alloy using magnetic field-assisted undercooling treatment

Undercooling solidification under a magnetic field(UMF)is an effective way to tailor the microstructure and properties of Co-based alloys.In this study,by attributing to the UMF treatment,the strength−ductility trade-off dilemma in GH605 superalloy is successfully overcome.The UMF treatment can effectively refine the grains and increase the solid solubility,leading to the high yield strength.The main deformation mechanism in the as-forged alloy is dislocation slipping.By contrast,multiple deformation mechanisms,including stacking faults,twining,dislocation slipping,and their strong interactions are activated in the UMF-treated sample during compression deformation,which enhances the strength and ductility simultaneously.In addition,the precipitation of hard Laves phases along the grain boundaries can be obtained after UMF treatment,hindering crack propagation during compression deformation.

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.

Undercooling and Solidification of Sn-Pb Alloy Droplets Prepared by Uniform Droplet Spray

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.

DENUCLEATION AND HIGH UNDERCOOLING OF Ni-32.5%Sn EUTECTIC ALLOY

Undercoolings up to 397 K(0.283 T_E)have been obtained for Ni-32.5% Sn eutectic alloy melted by superheating-cooling cycles and denucleating with inorganic glasses.The predomi- nant dissipation of heat for highly undercooled alloy melt is through radiation.An approxi- mate method is consequently derived to calculate its mean specific heat from measured cooling curves.With the aid of high speed cinematography,it is revealed that the surface or interface heterogeneous nucleation takes place in preference to homogeneous nucleation even though the undercooling has exceeded 0.2 T_E.

Vacuum Electromagnetic Levitation Melting and Undercooling of Peritectic Terfenol-D

For the first time, the undercooling of a magnetostrictive material a near peritectic Tb 0.27 Dy 0.73 Fe 1.90 alloy was realized by vacuum electromagnetic levitation melting and 60 K undercooling was obtained. There is one recalescence behavior during solidification of the undercooled melt,which can attribute to the priority precipitation of REFe 2 phase instead of REFe 3 phase, due to preferential nucleation and higher crystal growth rate of REFe 2 phase and the suppression of peritectic reaction. According to the crystal structural characteristics of REFe 2 and REFe 3, REFe 2 is a Laves phase intermetallics with MgCu 2 type structure, which has similar polytetrahedral structure with short range ordered structure in undercooled melt and has lower potential barrier for nucleation than that of REFe 3,which lead to the preferential nucleation of REFe 2 phase directly from the undercooled melt. Also, the similarity of structures between REFe 2 phase and undercooled melt leads to higher crystal growth rate of REFe 2 phase than that of REFe 3.

Effects of the fourth component and undercooling on morphology of primary Mg-Zn-Y icosahedral quasicrystal phase under normal casting conditions

The paper presents some results of the investigation on effects of the fourth component(Ti,C,Sb or Cu)and undercooling on the morphology,size and forming process of primary Mg-Zn-Y icosahedral quasicrystal phase(I-phase)under normal casting conditions.The result shows that the addition of certain amount of fourth component can transform I-phase morphology from petal-like to spherical.However,I-phase will grow up to petal-like if superfluous addition of the fourth component applied.It is also found that the solidified morphology of I-phase depends on the stability of spherical I-phase during the subsequent growth,and critical radius of maintaining the spherical I-phase interface relatively stable.Further,mini-sized spherical I-phase can be produced with high content of the fourth component by undercooling.Such findings are beneficial for industrializing Mgbased quasicrystals.

Undercooling heredity of Cu_(70)Ni_(30) melt solidified in non-catalytic nucleation coated mould

A new concept of undercooling heredity is developed to evaluate the undercooling ability in a non catalytic nucleation coated mould, where alloy melts were highly undercooled previously. Before the heredity experiment a non catalytic nucleation composite glass lined coating (B F) was prepared on the inner surface of mould and the Cu 70 Ni 30 alloy was selected to perform undercooling experiment in the B F non catalytic coating mould. Its ratio of undercooling heredity was 0.76. The results prove that the B F coating is an ideal non catalytic media for purified Cu 70 Ni 30 alloy melts due to its small contact angle between the melt and coating layer. Considering that various microstructures form under different undercoolings, two critical undercoolings, Δ T 1 and Δ T 2, and their corresponding microstructures of Cu 70 Ni 30 alloy are well defined. Moreover, it is found that the manned trigging solidification in the non catalytic coating mould could be used to get directional undercooling dendrite structure while the melt undercooling is larger than the critical undercooling Δ T 2.

RAPID QUENCHING AND LARGE UNDERCOOLING IN MULTISTAGE RAPID SOLIDIFICATION POWDER-MAKING PROCESS

The rapid quenching and large undercooling phenomena and device working principle in the rapid solidification process are analyzed, and the working characteristics are presented in detail. The results show that these multistage device are ideal for making amorphous, quasicrystalline, microcrystalline and fine metallic powders.

Are They Formed by Undercooling Crystallization or Devitrification？－On Origin of Various Textures inPlasticFragmentsofWeldedTuffs

A comprehensive petrographic observation contributes to classification of various textures in welded tuffs into two types, the textures in plastic fragments and the ones in rigid fragments. A detailed petrographic study of the textures in plastic fragments leads to suggestion that thesetextures are not a type of devitrification textures. and also that they were formed not by devitrification but by undercooling crystallization. This viewpoint is supported by results of undercooling crystallization experiments. The petrographic characteristics of these textures are satisfactorily demonstrated by the undercooling crystallization theory.

Isothermal Crystallization Behavior of Biodegradable Poly (butylene succinate-co-terephthalate) (PBST) Copolyesters at High Undercoolings

Poly （butylene succinatc-co-terephthalate） （PBST） copolycsters were prepared by polycondensation. The crystallization behavior of the as-prepared copolyesters was investigated by depolarized light intensity （DLI） at high undercoolings. According to Avrami equation, the exponent n, independent of the crystallization temperature, is at a range of 2. 5 to 3. 4, which probably corresponds to the heterogeneous mucleation and a 3-dimensional spherulitic growth. The maximum crystallization rate, very useful to polymer processing, was found at about 90℃ based on the half-crystallization time t1/2 analysis.

一个含Kinetic Undercooling的两相stefan问题

本文考虑了一个含KineticUndercooling的两相stefan问题并得到了这个问题关于时间的局部古典解存在唯一性

Effects of a high magnetic field on single-phase interface evolution,additional interfacial energy and nucleation undercooling in Al-based alloy

The effects of a high magnetic field on the evolution of the single-phase interface and the liquid-solid interface energy in Al-Cu alloy were investigated experimentally.It is found that the application of the magnetic field has a significant promotion effect on the migration of liquid droplets,accelerating the formation of the single-phase interface.This should be attributed to the thermoelectric(TE)magnetic convection in the droplets which has enhanced the diffusion and increased the migration speed of liquid droplets.Further,the effect of the high magnetic field on the solid-liquid interface energy is analyzed by an improved grain boundary groove(GBG)method.The average solid-liquid interface energy of theα-Al/Al-Cu and Al2Cu/Al-Cu systems increases and decreases with the increase of the magnetic field,respectively.The above experiment results are well explained based on the formation and interaction of the magnetic dipole at the solid-liquid interface.Moreover,experimental results reveal that the magnetic-field-induced interface energy increases and decreases the nucleation undercooling of the Al-30wt.%Cu alloy and Al-35wt.%Cu alloy,respectively.By studying the effect of the magnetic-field-induced interface energy on the nucleation undercooling,the understanding of the interface energy-induced nucleation undercooling deepens.

Mechanism in Solidification of a Ternary Nickel Based Alloy

The experiment employed the use of melt purification and cyclic superheating technique to achieve maximum undercooling of Ni65Cu31Co4 alloy at 300K.Simultaneously,high-speed photography techniques were used to capture the process of alloy liquid phase interface migration,and analyzed the relationship between the shape characteristics of the front end of alloy solidification and undercooling.The microstructure of the alloy was observed through metallographic microscopy,and the micro-morphological characteristics and evolution of the rapidly solidified microstructure were systematically studied.It is found that the grain refinement mechanism of Ni-Cu-Co ternary alloy is similar to that of Ni-Cu binary alloy.Grain refinement at low undercooling is caused by intense dendritic remelting,while grain refinement at high undercooling is attributed to recrystallization,driven by the stress and plastic strain accumulated from the interaction of liquid flow and primary dendrites caused by rapid solidification.It also shows that the addition of the third element Co plays a significant role in solidification rate and re-ignition effect.

Refinement Mechanism of Microstructure of Undercooled Nickel Based Alloys

Through the use of purification and recirculation superheating techniques on molten glass,the Ni65Cu33Co2 alloy was successfully undercooled to a maximum temperature of 292 K.High-speed photography was employed to capture the process of interface migration of the alloy liquid,allowing for an analysis of the relationship between the morphological characteristics of the alloy liquid solidification front and the degree of undercooling.Additionally,the microstructure of the alloy was examined using metallographic microscopy,leading to a systematic study of the microscopic morphological characteristics and evolution laws of the refined structure during rapid solidification.The research reveals that the grain refining mechanism of the Ni-Cu-Co ternary alloy is consistent with that of the binary alloy(Ni-Cu).Specifically,under low undercooling conditions,intense dendritic remelting was found to cause grain refinement,while under high undercooling conditions,recrystallization driven by accumulated stress and plastic strain resulting from the interaction between the liquid flow and the primary dendrites caused by rapid solidification was identified as the main factor contributing to grain refinement.Furthermore,the study highlights the significant role of the Co element in influencing the solidification rate and reheat effect of the alloy.The addition of Co was also found to facilitate the formation of non-segregated solidification structure,indicating its importance in the overall solidification process.

Peritectic solidification under high undercooling conditions

The solidification characteristics of highly undercooled Cu-7.77% Co peritectic alloy has been examined by glass fluxing technique. The obtained undercoolings vary from 93 to 203 K(0.14 T_L). It is found that the a(Co) phase always nucleates and grows preferentially, which is followed by peritectic transformation. This means that the peritectic phase cannot form directly, even though the alloy melt is undercooled to a temperature far below its peritectic point. The maximum recalescence temperature measured experimentally decreases as undercooling increases, which is lower than the thermodynamic calculation result owing to the actual non-adiabatic nature of recalescence process. The dendritic fragmentation of primary α(Co) phase induced by high undercooling is found to enhance the completion of peritectic transformation. In addition, the LKT/BCT dendrite growth model is modified in order to make it applicable to those binary alloy systems with seriously curved liquidus and solidus lines. The dendrite

Rapid growth of ternary eutectic un der high undercooling conditions

Rapid solidification of bulk Ag42.4Cu21.6Sb36 ternary eutectic alloy is accomplished by glass fluxing method,during which the maximum undercooling attains 114 K (0.16 TE). Under high undercooling conditions,the ternary eutectic consists ofε (Ag3Sb),(Sb)and θ(Cu2Sb)phases,instead of (Ag),(Sb)and θphases as predicted by the phase diagram.In the sample of small undercooling,the alloy microstructure is characterized by the mixture of primary θ(Cu2Sb),(ε+θ) and (ε+Sb) pseudobinary eutectics,and regular (ε+θ+Sb) ternary eutectic.With the increase of undercooling, θ (Cu2Sb) primary phase and pseudobinary eutectics disappear gradually,and ternary eutectic transfers from regular to anomalous structure.When undercooling exceeds 102 K,anomalous (ε+θ+Sb) ternary eutectic is the unique microstructure.Competitive nucleation and growth of these three eutectic phases is the main cause for the formation of complex growth morphologies.Based on the current experiments and theoretical calculations,it can be concluded that the intermetallic compound phaseθ(Cu2Sb) is the leading nucleating phase.

Nucleation and undercooling of metal melt

The effects of thermodynamic and dynamic factors on nucleation process have been integrated in a theoretical formula representing the dependence of undercooling on parameters concerned. Moreover, a method to determine the kind and amount of the most effective catalyst in an undercooled melt has been acquired. The results show that the undercooling increases with the decreasing surface area of the most effective catalyst and the increasing cooling rate as the kind of the most effective catalyst is constant. It increases to a maximum value when the ratio of the surface area of catalyst (S v V) to the cooling rate of melt (R c ) decreases to a critical value. The maximum undecooling not only depends on the ratio of non-dimensional factor of activation energy for an atom to diffuse (?) to non-dimensional factor of driving force for nucleus to form (ψ), but also depends on the contact angle of the most effective catalyst; the smaller the ratio of ? to ψ, the higher the maximum undercooling, but it does not exceed the value of 2/3 melting point; the smaller the contact angle of the most effective catalyst, the lower the maximum undercooling, and the smaller the requisite value ofS v V/R c for the maximum undercooling also.

High undercooling and rapid dendritic growth of Cu-Sb alloy in drop tube

Droplets of Cu-20%Sb hypoeutectic alloy has been rapidly solidified in drop tube within the containerless condition. With the decrease of droplet diameter, undercooling increases and the microstructures of primary copper dendrite refines. Undercooling up to 207 K (0.17 TL) is obtained in experiment. Theoretic analysis indicated that, because of the broad temperature range of solidification, the rapid growth of primary copper dendrite is controlled by the solutal diffusion. Judging from the calculation of T0 curve in the phase diagram, it is shown that the critical undercooling of segregationless solidification is △T0=474 K. At the maximum undercooling of 207 K, the growth velocity of primary copper phase exceeds to 37 mm/s, and the distinct solute trapping occurs.

Study on undercooling of metal droplet in rapid solidification

A mathematical model for the undercooling of the metal droplet during the rapid solidification is established, by which the factors that influence the undercooling of the metal droplet during the rapid solidification are analyzed, and the parameter $\zeta = \sigma _{SL} ^3 /\left( {T_L \Delta H^2 } \right)$ is defined as the impact factor of the undercooling for the droplet solidification. Different undercoolings of droplets induced by various rapid solidification conditions are mainly ascribed to the change of the impact factor. Moreover, it is shown that the larger of ζ, the higher the relative undercooling can be gained. Meanwhile, the parameters such as solid-liquid interfacial energy σ SL and latent heat of solidification ΔH also vary with the rapid solidification conditions of droplets.

High undercooling of bulk water during acoustic levitation

The experiments on undercooling of acoustically levitated water drops with the radius of 5-8 mm are carried out, and the maximum undercooling of 24 K is obtained in such a containerless state. Various factors influencing the undercoolability of water under acoustic levitation are synthetically analyzed. The experimental results indicate that impurities tend to decrease the undercooling level, whereas the dominant factor is the effect of ultrasound. The stirring and cavitation effects of ultrasound tend to stimulate the nucleation of water and prevent further bulk undercooling in experiments. The stirring effect provides some extra energy fluctuation to overcome the thermodynamic barrier for nucleation. The local high pressure caused by cavitation effect increases the local undercooling in water and stimulates nucleation before the achievement of a large bulk undercooling. According to the cooling curves, the dendrite growth velocity of ice is estimated, which is in good agreement with the theoretical prediction at the lower undercooling. The theoretical calculation predicts a dendrite growth velocity of 0.23 m/s corresponding to the maximum undercooling of 24 K, at which the rapid solidification of ice occurs.