Microstructure Refinement of Sn-Sb Peritectic Alloy under High-Intensity Ultrasound Treatment

In this paper the solidification behavior of Sn-Sb peritectic alloy and the mechanism of grain refinement in solidification process under high-intensity ultrasonic field are investigated. Three different powers of high-intensity ultrasound are introduced into molten Sn-Sb peritectic alloy to study the refining effectiveness. The results show that the application of high-intensity ultrasound during solidification process of Sn-Sb peritectic alloy can refine α phase and β phase and eliminate gravity segregation of the alloy. As acoustic intensity is increased from 400 W to 800 W, not only the homogenous fine structure can be obtained, but also the cubic β phase crystals tend to be spherical. Microstructure of the sample treated by 600 W high-intensity ultrasound demonstrates the best refining effect.

METASTABLE PHASE SEPARATION OF Fe_(50)Cu_(50) HYPOPERITECTIC ALLOY UNDER SPACE SIMULATION CONDITIONS

A 3m drop-tube was used to investigate the solidification of Fe50Cu50 hypoperitectic alloy. The falling droplets solidified as spheres and splats. The obtained particles range from 1000μm to 80μm in diameter. It was found that the phase separation occurred if the Fe-Cu liquid was undercooled to a certain extent before solidification.In the big particles macroscopic separation of Fe-rich phase always appeared in the cented of the particles, and in the small ones the Fe-rich phase usually solidified as little spheres. In the flakes the Fe-rich and Cu-rich layers alternatively displayed from top to bottom.

Macrosegregation and thermosolutal convection-related freckle formation in directionally solidified Sn−Ni peritectic alloy in crucibles with different diameters

Different from other alloys,the observation in this work on the dendritic mushy zone shows that the freckles are formed in two different regions before and after peritectic reaction in directional solidification of Sn−Ni peritectic alloys.In addition,the experimental results demonstrate that the dendritic morphology is influenced by the temperature gradient zone melting and Gibbs−Thomson effects.A new Rayleigh number(Ra_(P))is proposed in consideration of both effects and peritectic reaction.The prediction of Ra_(P) confirms the freckle formation in two regions during peritectic solidification.Besides,heavier thermosolutal convection in samples with larger diameter is also demonstrated.

Absolute stability of the solidification interface in a laser resolidified Zn-2wt.%Cu hypoperitectic alloy

This paper reports on laser surface remelting experiments performed on a Zn-2wt.%Cu hypoperitectic alloy by employing a 5kW CW CO2 laser at scanning velocities between 6 and 1207mm/s. The growth velocities of the mi- crostructures in the laser molten pool were accurately measured. The planar interface structure caused by the high velocity absolute stability was achieved at a growth velocity of 210 mm/s. An implicit expression of the critical solidification velocity for the cellular-planar transition was carried out by nonlinear stability analyses of the planar interface. The results showed a better agreement with the measured critical velocity than that predicted by M-S theory. Cell-free structures were observed throughout the whole molten pool at a scanning velocity of 652 mm/s and the calculated minimum temperature gradient in this molten pool was very close to the critical temperature gradient for high gradient absolute stability （HGAS） of the η phase. This indicates that HGAS was successfully achieved in the present experiments.

Microstructure refinement of Sn-Sb Peritectic alloy by power ultrasonic

Sn-Sb peritectic alloy was treated with 400 W, 600 W and 800 W ultrasonic, respectively, to study the effect of power ultrasonic on solidification microstructure. Results show that power ultrasonic can refine α phase and β phase of the alloy, as well as eliminate gravitational segregation. Moreover, 600 W ultrasonic demonstrated the best refining effect, not only homogenous and fine solidification microstructure can be obtained, the cubical β phase crystals can also be spheroidized.

Microstructure and Peritectic Reaction within As-solidified Mg-Zn-Y Alloy

An investigation on the microstructure and peritectic reaction involving icosahedra phase （I-phase） and crystalline phase （W-phase） within Mg-Zn-Y alloy during conventional solidification technology and rapid quenching was carried out, The solidification process of the peritectic reaction is discussed in details, It is shown that there is no obvious crystallographic relationship between the W-phase and I-phase during the solidification of Mg-Zn-Y alloy.

Morphologies of intermetallic compound phases in Sn-Cu and Sn-Co peritectic alloys during directional solidification

The morphologies of intermetallic phases(IMCs)during directional solidification of the Sn-Cu(L+Cu_(3)Sn→Cu_(6)Sn_(5))and Sn-Co(L+CoSn→CoSn_(2))peritectic systems were analyzed.The primary Cu_(3)Sn and peritectic Cu_(6)Sn_(5)phases in Sn-Cu alloy are IMCs whose solubility ranges are narrow,while both the primary CoSn and peritectic CoSn_(2)phases in Sn-Co alloy are IMCs whose solubility ranges are nil in equilibrium condition.The experimental results before acid corrosion shows that the dendritic morphology of both the Cu_(6)Sn_(5)and CoSn_(2)phases can be observed.The investigation on the local dendritic morphology after deep acid corrosion shows that these dendrites are composed of small sub-structures with faceted feature.Faceted growth of the primary Cu_(3)Sn and CoSn phases is also confirmed,and a faceted to non-faceted transition in their morphologies is observed with increasing growth velocities.Further analysis shows that the dendritic morphology is formed in the solidified phases whose solubility range is larger during peritectic solidification.

Solidification sequence and as-cast microstructure of a model Pb-Bi-Sn alloy with quasi-peritectic reaction

The Pb39 Bi25 Sn36 alloy was directionally solidified at varied withdrawal rates followed by quenching.From metallographic observation,composition analysis and differential scanning calorimetry(DSC)analysis,the solidification sequence of Pb39 Bi25 Sn36 alloy was characterized.The Sn-dendrite is observed as the primary phase during solidification,followed by theβ(Pb7 Bi3)/Sn divorced eutectic.At lower temperatures,theβ(Pb7 Bi3)/Sn binary eutectic is formed in the interdendritic region.However,the quasi-peritectic reaction[L+α-Pb→β(Pb7 Bi3)+Sn]does not occur as the prediction based on ternary phase diagram analysis,which can be attributed to the unequilibrium solidfication condition.Moreover,the as-cast microstructure is significantly refined with the increasing withdrawal rates.The quenched sample only exhibits the lamellar structure of Sn,β(Pb7 Bi3)and Bi phases.The results can provide instructions to optimize the as-cast microstructure of ternary alloys with quasi-peritectic reaction.

Laser resolidification of Zn-rich Zn-Ag peritectic alloys

Laser remelting experiments were performed by a 1.0?kW continuous CO 2 laser to investigate the rapid solidification behavior of Zn rich Zn Ag peritectic alloys. Three kinds of microstructures occurrs with the varying of laser scanning speed and Ag content in the alloys. It is mainly plate like single phase cellular η when the Ag content was lower than 1.8% (mole fraction). As the Ag content increased, instead of typical structure of primary dendrites of ε surrounded by peritectic η , a two phase plate like η+ε with primary dendrites of ε is found when the laser scanning speed was higher than a critical value. Intercellular spacing of cellular η or interphase spacing of two phase couple growth η+ε decreases with increasing laser scanning speed.

Microstructure of peritectic Tb-Dy-Fe alloys after electromagnetic levitation melting

The electromagnetic levitation melting of the rare earth giant magnetostrictive materials Tb 0.27 Dy 0.73 Fe 1.90 alloys is realized. The compound is difficult to realize levitation melting at terrestrial environment because of its high density and low electric conductivity. The microstructure of the sample near peritectic composition obtained by this process contains REFe 2 matrix phase, a large amount of rod like REFe 3 phase embedded in the matrix phase, rare earth rich phase enriching around the REFe 3 phase and a small amount of rare earth rich phase in the REFe 2 matrix phase far from the REFe 3 phase, which is significantly different from that of the sample obtained by general melting casting process with the same composition,which contains almost complete REFe 2 phase and a small amount of RE rich phase in the REFe 2 matrix phase. The formation of the microstructure can be attributed to the coupled growth of the peritectic phase—REFe 2 and the primary phase—REFe 3 , and the subsequent eutectic reaction under this experimental condition.

Directionally solidified microstructures and peritectic phase growth of Cu-75%Sn peritectic alloy

Directionally solidified microstructures of Cu-75%Sn peritectic alloy were investigated at the growth rate ranging from 1 to 300 μm/s. With the growth rate increasing, directionally solidified plate-like microstructures in Cu-75%Sn peritectic alloy are refined by the increase of nucleation quantities of primary ε phases and cooling rate. Peritectic η phase can grow by the peritectic transformation and direct solidification from the liquid. At the low growth rate varying from 5 to 10 μm/s, the width of ε phase increases due to the effect of the peritectic transformation; however, at higher growth rate, the deviation between the width of ε phase and the whole plate-like microstructure increases resulting from direct solidification of η phase from the undercooled melt. The regressed data show that the relationship between the width of the whole plate-like microstructure （W） and the growth rate （v） satisfies as Wv0.27=117 μm1.27·s-0.27 and the primary dendritic arm spacing （λ） with the growth rate has a relation of λv0.208=153.8 μm1.208·s-0.208 as the growth rate increases from 3 to 300 μm/s.

Stability of remelting and solidification interfaces of triple-phase region during peritectic reaction at lower speed

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.

Solidification characteristics of Fe-Ni peritectic al oy thin strips under a near-rapid solidification condition

This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of δ-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe-7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the microsegregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.

Multi-phase field simulation of multi-grain peritectic transition in multiple phase transformation

Taking Fe-C binary alloy as an example,based on the multi-phase field model,the nucleation and growth ofδphase,peritectic reaction,peritectic transformation,and the growth of subsequent austenite are simulated.Effects of the nucleation site of austenite on the peritectic reaction rate and the starting time of the peritectic transformation were studied.The simulation results show that theγphase,as a shell,surrounds theδphase and grows rapidly when the peritectic reaction occurs between the dendriticδgrains,and a layer ofγphase shell is formed aroundδphase after the peritectic reaction.After theδphase is surrounded byγphase completely,the membrane shell separates the L phase from theδphase,so that the phase transfers from peritectic reaction to peritectic transformation.During the peritectic transformation,since the solute diffusion coefficient of the liquid phase is much greater than that of the solid phase,the average growth rate of austenite in the liquid phase is visibly higher than that of theδphase.The peritectic reaction rate is related to the curvature of the nucleation site of theγphase on theδphase grains.The peritectic reaction rate at the large curvatures is faster than that at small curvatures.

Multi-phase-field simulation of austenite peritectic solidification based on a ferrite grain

A multi-phase-field model is implemented to investigate the peritectic solidification of Fe-C alloy. The nucleation mode of austenite is based on the local driving force, and two different thicknesses of the primary austenite on the surface of the ferrite equiaxed crystal grain are used as the initial conditions. The simulation shows the multiple interactions of ferrite, austenite, and liquid phases, and the effects of carbon diffusion, which presents the non-equilibrium dynamic process during Fe-C peritectic solidification at the mesoscopic scale. This work not only reveals the influence of the austenite nucleation position, but also clarifies the formation mechanism of liquid phase channels and molten pools. Therefore, the present study contributes to the understanding of the micro-morphology and micro-segregation evolution mechanisms of Fe-C alloy during peritectic solidification.

定向凝固Cu-50%Sn包晶合金显微组织演变

随着科学技术的进步,越来越多的包晶合金因其优良性能广泛应用于工业生产领域,比如Fe-Cr-Ni、Ti-Al、Nd-Fe-B合金以及应用于电子封装领域的Cu-Sn合金等。随着电子信息产业向微型化和多功能化方向发展,对集成电路的机械、电子和热性能提出了更高的要求。本文以Cu-50%Sn(原子分数)包晶合金(L+Cu^(3)Sn→Cu6Sn5)作为研究对象,通过布里奇曼定向凝固法,在显微镜下对组织进行观察和测量,研究淬火固液界面的凝固组织随凝固条件改变而产生的变化。生长距离、温度梯度一定时,随着生长速度的增大,初生相Cu^(3)Sn经历了胞状→胞/枝状→枝晶状组织转变,Cu^(3)Sn相的尺寸与间距均随生长速度的增大而减小;生长速度、生长距离一定时,随着温度梯度的增大,初生相Cu^(3)Sn相由块状与枝晶状转变为胞状组织;生长速度、温度梯度一定时,随着生长距离的增大,初生相Cu^(3)Sn由块状与胞/枝状转变为胞状组织,且Cu^(3)Sn相尺寸发生小幅细化。基于上述实验结果,绘制了关于生长速度、温度梯度及生长距离条件下的显微组织选择图,进一步阐明了凝固条件的改变对Cu-50%Sn(原子分数)包晶合金显微组织的影响。

钛铝合金包晶相变的多相场模拟研究

包晶相变使传统钛铝合金在铸造过程中极易出现成分偏析、显微组织粗大等现象,导致塑性较差且各向异性明显,显著影响了钛铝合金的使役性能。为深入理解包晶相变过程并进一步合理调控微观组织,本文建立了适用于可描述钛铝合金包晶相变的多相场模型,基于定量化多相自由能输入、多相界面处理、考虑反溶质截流及相界面处虚拟相成分的简化计算策略,针对Ti-45Al(原子分数)合金的包晶相变过程,主要研究了过冷度对包晶相变时微观组织演变的影响规律。研究发现,发生包晶反应(β+L→α)时,α相沿着β/L界面快速增长。考虑到α向L与β相的生长速度存在差异,使得α相片层生长时表现出非对称性。包晶转变过程由扩散控制,α/L、α/β相界面的迁移满足xij=Aijt1/2规律。随着过冷度增大,两种相界面迁移速率均增大,且α/L界面迁移速率的增幅较为显著;较低过冷度下,在α片层前端可见β相的重熔现象。增大过冷度后,其重熔现象逐渐消失,但L/β/α三相区的形状保持不变。三相交界区域形状主要由界面能(界面张力)之间的平衡决定,而与界面迁移速率的差异无关。

Al-Y包晶合金非平衡凝固过程及组织特征

包晶凝固过程中小平面-小平面两相复相生长方式是凝固领域研究的一个热点。以初生相和包晶相都是严格计量比金属间化合物的Al-Y包晶合金作为研究对象,利用DSC热分析技术,严格控制冷却速度,获得不同凝固条件的非平衡凝固试样,研究了两相为小平面相的Al-Y包晶合金的凝固行为。发现小平面-小平面包晶系合金包晶凝固过程中,非平衡凝固特性及宏观偏析特点比非小平面包晶系更加明显。凝固特征温度与平衡相图偏差明显,包晶反应温度和包晶相直接凝固温度都远高于平衡相图给定的值,相对于相图是在"过热"条件下发生的,而固溶体型包晶合金一般是在"过冷"条件下发生的。包晶转变过程非常微弱,致使初生相残留量远高于平衡相图。即使对于过包晶成分的合金,其凝固组织中仍存在大量的共晶凝固组织,最终得到的凝固组织与平衡相图存在显著差异。

旋转与脉冲磁场对Zn-2.75%Cu包晶合金凝固组织的影响

研究了旋转磁场和脉冲磁场对Zn-2.75%Cu包晶合金凝固组织的影响。结果表明:Zn-2.75%Cu合金凝固组织是由初生树枝状和球状ε-CuZn5相和基体η相组成,其靠近试样边部的树枝晶更为粗大。施加旋转磁场和脉冲磁场后,Zn-2.75%Cu包晶合金组织中粗大发达树枝晶逐渐细化,转变为细小均匀的球状和蔷薇状组织;ε相变得细小圆整,尺寸减小,向等轴晶转变,分布更为均匀,且数量明显减少;中心处的初生ε相较于边缘处皆更为细小,数量更少。施加旋转磁场细化作用效果更为明显,树枝晶完全转变。