过偏晶Cu-40%Pb合金凝固组织的深过冷细化

利用电磁模拟微重力设备获得S(Pb)均匀分布的过偏晶Cu-40%Pb合金实验样品,然后用熔融玻璃净化与循环过热相结合获得熔体深过冷的方法,对上述获得的均质化实验样品进行深过冷快速凝固实验和凝固组织演化规律的研究.结果表明:经过深过冷技术进行二次处理试样的凝固组织中,随着过冷度的增加弥散的S(Pb)比模拟微重力环境下得到的S(Pb)明显细化.     

深过冷凝固Co80Pd20合金中的枝晶生长

采用玻璃熔体净化与循环过热相结合的深过冷凝固技术实现了Co80Pd20合金的深过冷,获得了高达415 K的最大过冷度.采用OM观察了不同过冷度下凝固合金的微观组织,分析了枝晶形成的过冷度区间及过冷度对枝晶形貌的影响.运用BCT模型对深过冷凝固Co80Pd20中的枝晶生长进行了理论分析,获得了深过冷凝固过程中的枝晶生长速...     

深过冷铁钴基块体合金的细晶化研究

采用熔融玻璃净化与循环过热相结合的深过冷技术,对比研究了深过冷凝固和过冷熔体Cu模激冷凝固Fe₄₄Co₄₄Nb₇-B₄Cu₁块体合金的组织特征.结果表明,随过冷度增大,深过冷和深过冷Cu模激冷凝固组织均由最初的发达树枝晶逐渐演变为细小的粒状晶,并且Cu模激冷可显著减小树枝晶向粒状晶转变的临界过冷度.在相同过冷度下,过冷熔体Cu模激冷凝固组织更加细小均匀,其根本原因在于Cu模激冷和熔体深过冷的双重作用不仅提高了熔体的形核率并抑制了晶粒长大,而合金化元素在晶界聚集并不是阻碍晶粒长大的主要原因.     

热分析在Fe-B合金深过冷凝固过程中的应用

采用熔融玻璃净化与循环过热相结合的深过冷技术,研究了Fe-B共晶合金熔体的深过冷及超过冷凝固组织与冷却曲线的关系.凝固过程的热分析表明,合金熔体冷却曲线的变化体现了熔体的过冷程度,即通过对冷却曲线特征参量的分析能够直接确定深过冷/超过冷凝固组织的获得,而且过冷度与初生相的形核、分布、晶粒大小及共晶组织形貌等凝固特征的对应关系也能够通过冷却曲线反映出来.     

微晶软磁合金生产工艺

微晶软磁合金生产工艺使软磁合金晶粒组织微细化是提高软磁合金软磁特性的重要途径。制造微晶软磁合金的通用方法，首先制成非晶合金，然后通过热处理品化使之析出微晶，但这类方法对于铁基合金的铁含量有一定限制，并且必须含有１８ａｔ％～２０ａｔ％左右的类金属元素，...     

快速定向凝固技术的研究及发展

综述了快速定向凝固技术的发展过程、原理及存在的问题。介绍了几种新发展起来的快速定向凝固技术，其中包括激光超高温度梯度快速定向凝固技术和深过冷熔体激发快速定向凝固技术。指出了发展的前景。     

过冷液态金属的研究进展

过冷是液态金属凝固过程中的一种现象.由于过冷对凝固后的组织结构和性能有重要影响,因此,研究液态-过冷液态-固态的结构、性能及其演变,对于控制液态金属的结构及其凝固过程,开发新型金属材料具有重要意义.本文综述了实现过冷的方法以及过冷液态金属的研究现状,同时介绍了通过测量电阻率研究过冷液态结构变化的新方法,并对深过冷技术的应用进行了展望.     

深过冷凝固TiAl基合金的研究进展

TiAl基合金由于诸多良好的性能而在许多领域广泛应用,而TiAl基合金非平衡凝固组织的多样性和复杂性往往影响其性能。电磁悬浮深过冷凝固技术作为一种分析和研究非平衡凝固行为的有效手段,可为研究非平衡凝固组织特征提供帮助。综述了深过冷凝固TiAl基合金近些年来的主要研究进展;从合金成分、相选择、组织演化以及相关理论等方面总结了TiAl基合金深过冷凝固研究的主要成果;提出了TiAl基合金深过冷凝固研究的研究方向和发展趋势,这对TiAl基合金成分设计和凝固组织控制具有重要意义。     

深过冷条件下Fe-Ni-P-B合金的纳米晶凝固组织与液相Spinodal分解

采用玻璃融覆法（fluxing）提纯技术能显著提高Fe40Ni40P14B6合金的过冷度,并可获得深过冷条件下的凝固组织．研究结果表明,不同过冷度下Fe40Ni40P14B6的凝固组织存在显著差异,增加过冷度能大幅细化凝固组织．在深过冷条件下,能获得纳米晶凝固组织;当过冷度为360K时,所制备的Fe40Ni40P14B6块体纳米晶合金的平均晶粒尺寸约为40nm;当过冷度足够大时,获得的凝固组织具有液相Spinodal分解导致的网状组织特征．热力学分析结果表明,Spinodal分解所形成的网状组织的特征尺寸与熔体过冷度有关,过冷度越大,尺寸越小．     

大体积深过冷Co-Sn合金的凝固过程与组织演化

将含12％-32％Sn(摩尔分数)的系列Co-Sn合金熔体过冷至平衡液相线以下不同温度进行凝固实验,通过监测快速凝固过程中的温度再辉与凝固组织分析不同过冷度下各合金的凝固行为进行研究.确定了Sn含量从14％到31％范围内Co-Sn合金凝固时共晶两相进行耦合生长和非耦合生长的分界线,在此成分范围之外的Co-Sn合金则很难被过冷至共晶共生区.在非共晶成分Co-Sn合金的深过冷凝固过程中不存在非互惠形核现象.     

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.     

Rapid solidification and liquid-phase separation of undercooled CoCrCuFexNi high-entropy alloys

Fluxing and cyclic superheating technique was used to investigate the rapid solidification behavior of CoCrCuFe_xNi (x = 1.0, 1.5, 2.0, molar concentration) high-entropy alloys in this study. The microstructures of CoCrCuFe_xNi (x = 1.0, 1.5, 2.0) high-entropy alloys solidified at different undercoolings (ΔT) were investigated. Liquid-phase separation leading to Cu-rich and Cu-depleted regions, were obtained in the solidified microstructure from highly undercooled melt. This occurs when the melt undercooling exceeds a critical undercooling (ΔT_crit) of 160 K for CoCrCuFeNi, 190 K for CoCrCuFe_1.5Ni and 293 K for CoCrCuFe₂Ni alloy. However, typical dendrites and interdendritic regions were observed in rapid-solidified CoCrCuFe_xNi alloys prepared from melts with a small undercooling (ΔT < ΔT_crit). Conversely, a large amount of Cu-rich spheres and even egg-type structures were observed in alloys solidified from melts with large degree of undercooling, ΔT in excess of the critical value, ΔT_crit. A large amount of Cu-rich nano-phases were found in the matrix, possibly, due to the precipitation of Cu-rich phase from the supersaturated solid solution obtained during solidification. The positive enthalpies of mixing between Cu and the other elements in the multi-component alloys resulted in the occurrence of liquid-phase separation prior to the liquid–solid transformation starts. The sluggish diffusion effect of high-entropy alloys and rapid solidification play an important part in the precipitation of nanophase during the solid-state transformation in the Cu-based matrix. Similar to other immiscible alloys, liquid-phase separation occurred when a critical undercooling was exceeded. Differently, nanophases were found in the microstructures of multi-component CoCrCuFe_xNi (x = 1.0, 1.5, 2.0) alloys.     

Modeling the formation of twins and stacking faults in the ag-cu system

In forming new grains, both in solid state reactions and in solidification, the formation of twins or stacking-faults is of considerable interest. In the present work, a terrace/ledge nucleation model is used to explore the relationship between the degree of undercooling and the probability of forming twins or stacking-faults, and compared with experimental results for rapid solidification of several alloys in the two-phase Ag-Cu system. The model is consistent with the experimental results and indicates that at an undercooling between 37 K and 55 K, twins or stacking-faults form first in the Ag-rich solid solution. Larger undercooling brings about the formation of twins or stacking-faults in the Cu-rich solid solution. The degree of undercooling required for defect formation can be related to the stacking fault or twin boundary energies of the materials.     

Effect of high undercooling on Co-Ni-Ga ferromagnetic shape memory alloys

Co₄₅Ni₂₅Ga₃₀ ferromagnetic shape memory alloys were treated by glass fluxing combined with superheating cycling. The effect of high undercooling on solidified microstructure and transformation temperatures was investigated. The martensite lath is obviously refined and a mass of sub-grains are produced with the increase of undercooling. Undercooling rapid solidification introduces a number of dislocations and large internal stress, which give rise to the production of sub-grains in recovery. During the following annealing process, these sub-grains can gradually recrystallize and grow up with an amount of γ′ phase precipitated. Meanwhile, transformation temperatures of undercooled alloys are greatly elevated compared with those of as cast, which results from the large internal stress, and gradually reduce with the heating time.     

反向扩散效应对过冷单相固溶体合金凝固动力学的影响(英文)

基于平均体积方法建立过冷单相固溶体合金的凝固动力学模型并研究反向扩散在凝固动力学过程中的作用。模型在过冷Ni-15%Cu(摩尔分数)合金快速凝固中的应用表明:反向扩散显著影响凝固结束温度但对再辉阶段凝固的固相体积分数影响不明显。与Herlach观点相反,凝固结束温度介于杠杆定律和Scheil方程的预测值之间,且其具体值由反向扩散、初始过冷度和冷却速率决定。     

过偏晶合金Ni-40%Pb深过冷凝固组织

采用熔融玻璃净化与循环过热相结合的方法研究过冷Ni-40%Pb(质量分数)过偏晶合金的组织演化规律. 结果发现 过偏晶合金在快速凝固阶段本质上是以枝晶方式生长; 当ΔT《50K时, 合金组织为粗大枝晶+枝晶间Pb相+团块状Pb相; 当100《ΔT《198K时, 合金组织宏观偏析严重; 当ΔT＝292K时, 合金组织呈粒状晶, 第二相均匀弥散分布. 分析表明凝固组织宏观偏析与快速凝固阶段固液相变速率和体系残余液相分数有关; 粒状晶粒化机制属于枝晶碎断再结晶机制.     

Rapidly directional solidification of highly undercooled Ni-Fe-Ga shape memory alloy melts

In the present work, high undercooling rapid solidification technique is applied to the directional crystal growth of ternary Ni-Fe-Ga shape memory alloys (SMAs). Experimental results show that the phase selection of undercooled melts strongly depends on the triggering mode and nucleation undercooling. With the planar triggering nucleation at the undercooling of 160 K from the bottom of alloy melt, a directionally solidified sample with a preferred (2 0 0) orientation of γ phase is obtained. When the point triggering mode is employed at 180 K, γ phase is suppressed completely and the directionally solidified sample demonstrates almost identical phase transformation temperatures.     

Roles of dendrite tip undercooling and solid state diffusion in microsegregation of Fe–Nb welds

Abstract

The contributions of dendrite tip undercooling and solid state diffusion to the final degree of microsegregation of gas tungsten arc welds in Fe–Nb alloys were experimentally determined. With a partitioning coefficient of ～0·28, niobium is expected to highly segregate to the liquid during solidification. However, weld microsegregation modelling using afinite difference technique indicated that almost complete homogenisation occurs as a result of solid state diffusion during solidification and cooling. The final degree of microsegregation could be accounted for considering only solid state diffusion. Examination of specimens that had been liquid tin quenched during welding showed that a significant amount of tip undercooling occurred during solidification. The degree of undercooling and amount of solid state diffusion measured were compared with predicted values using solidification models. It was found that although tip undercooling resulted in a higher niobium concentration during initial solidification, its impact on the final degree of microsegregation was small because of the overwhelming effect of solid state diffusion.     

镁合金快速凝固技术的研究现状及进展

快速凝固技术是改善镁合金组织结构、提高镁合金各项性能的重要技术。本文综述了快速凝固镁合金的制备方法,描述了镁合金各种快速凝固特征,旨在为今后高性能镁合金的研究提供方向和途径。     

Microstructures and evolution mechanism of highly undercooled Ni-Pb hypermonotectic alloy

The microstructures and evolution mechanism of the undercooled Ni-20%Pb(molar fraction) alloy were investigated systematically by high undercooling solidification technique. The experiment results indicate that the morphology of α-Ni phase and the distribution of Pb element in undercooled Ni-20% Pb alloys change with the in-crease of undercooling. The main evolution mechanisms of α-Ni are dendrite remelting and recrystallization. Pb phase in the microstructure of Ni-20% Pb hypermonotectic alloy originates from L2 phase separated from the parent melt during the cooling process through immiscible gap and L2 phase formed at the temperature of monotectic trans-formation. The solubility of Ph element in α-Ni phase under high undercooling condition is up to 5.83% which is ob-viously higher than that under equilibrium solidification condition. The real reason that causes the solubility difference is distinct solute trapping.