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.     

Rapid Crystallization of Levitated and Undercooled Semiconducting Material Melts

Using a CO₂ laser-equipped electromagnetic levitator, we carried out the containerless crystallization of Si and Ge. From the point of interface morphologies, the relation between growth velocities and undercoolings was classified into three regions. In regions I and II, although the morphologies of growing crystals are different: plate-like needle crystals in region I and facetted dendrite at region II, the growth velocities in these two regions are fundamentally scaled by the thermal diffusivities and the temperature increase caused by the release of the latent heat. This result means that the growth velocity can be expressed by the product of the thermal diffusivity and the growth kinetics. An analysis of the dendrite morphologies revealed that the kinetics of crystal growth in regions I and II represent two-dimensional nucleation at the reentrant corner formed at the edge of the two parallel twins. In region III, thermal diffusion-controlled interface attachment kinetics control as described by a modified Wilson?CFrenkel model.     

深过冷Fe-80at%Ni凝固组织

采用熔融玻璃与循环过热相结合方法使Fe-80at%Ni合金熔体获得了340K的大过冷,对Fe-80at%Ni过包晶合金在宽过冷范围内凝固组织进行研究。结果表明：在小过冷范围（ΔT〈28K）,凝固组织为普通树枝晶;当28K〈△T〈54K时,凝固组织为不规则粒状晶;当54K〈△T〈70K时,凝固组织为树枝晶;当70K〈△T〈210K时,凝固组织转变为细小的粒状晶;当△T〉210K时,凝固组织为粗大的晶粒。随着过冷度的增加,凝固组织发生了两次粒化和一次粗化过程,分别为由小过冷树枝晶向第一类粒状晶的转变,由大过冷树枝晶向第二类粒状晶的转变和由细小粒状晶向粗大晶粒转变。粒化机理分别是枝晶重熔,枝晶碎断＋再结晶和极大的表面能导致小晶粒合并。     

Solidification of Undercooled Melts of Al-Based Alloys on Earth and in Space

Containerless processing of droplets and drops by atomization and electromagnetic levitation are applied to undercool metallic melts and alloys prior to solidification. Heterogeneous nucleation on crucible walls is completely avoided giving access to large undercoolings. Experiments are performed both under terrestrial (1 g) conditions and in reduced gravity (µg) as well. Microgravity conditions are realized by the free fall of small droplets during atomization of a spray of droplets, individual drops in a drop tube and by electromagnetic levitation of drops during parabolic flights, sounding rocket missions, and using the electro-magnetic levitator multi-user facility on board the International Space Station. The comparison of both sets of experiments in 1 g and µg leads to an estimation of the influence of forced convection on dendrite growth kinetics and microstructure evolution.     

过冷Cu80Ni20合金熔体凝固组织的两次细化机制

在大气条件下,采用熔融玻璃净化与循环过热相结合的方法,在44K-176K过冷度范围内。研究了Cu80Ni20合金凝固组织的两次细化机制。第一类粒状晶的形成为熔断-再结晶机制．枝晶形成过程为：首先,快速凝固过程中的树枝晶发生严重重熔,形成树枝晶段;然后。树枝晶段通过外延生长后形成不稳定晶界,并在界面能驱动下与高温发生晶界移动和晶粒合并,形成再结晶晶粒。第二类粒状晶的形成为碎断-再结晶机制,在大过冷度下,快速凝固过程中液固相体积转变速率的提高,不仅使枝晶内部缺陷骤然增加,而且会导致固相内极高的应力和应变能。在应力作用下枝晶全面碎断,形成“网状枝晶块”,枝晶块通过内部缺陷和应变能的作用,发生界面的移动和合并即再结晶过程,形成第二类粒状晶。     

Ni_(80)B_(20)深过冷凝固中的相竞争机制研究

采用熔融玻璃净化配合循环过热法,研究了Ni80B20合金熔体深过冷快速凝固中的相竞争规律。结果表明,过冷度是决定Ni80B20合金熔体中Ni(α)与Ni3B析出的主要因素。当初始过冷度大于临界过冷度180 K时,Ni3B将作为初生相从熔体中析出,反之,Ni(α)将作为初生相从熔体中析出。综合考虑形核和生长因素,讨论了Ni80B20合金的形态选择及相竞争机制。     

低过冷Cu70Ni30合金熔体凝固组织粒化机制

采用熔融玻璃净化技术,使大体积Ｃｕ７０Ｎｉ３０合金获得２７０Ｋ深过冷,在宽过冷范围内合金不同过冷度区间的凝固组织演化表明,存在２类晶粒细化和２类不同的枝晶花样,其中,介于３８Ｋ－１２０Ｋ过冷区间,由于再辉过程中的化学过热,首先发生了枝晶熔断,熔断后的枝晶段在界面能驱动下,通过晶界移动形成了第一类晶粒状晶。     

Effect of Sn Micro-alloying on Recrystallization Nucleation and Growth Processes of Ferritic Stainless Steels

We investigated the effect of Sn micro-alloying on recrystallization nucleation and growth processes of ferritic stainless steels. The as-received hot rolled sheets were cold rolled up to 80% reduction and then annealed at 740–880 °C for 5 min. The cold rolling and recrystallization microstructures and micro-textures of Sn-containing and Sn-free ferritic stainless steels were all determined by electron backscatter diffraction. Our Results show that Sn micro-alloying has important effects on recrystallization nucleation and growth processes of ferritic stainless steels. Sn micro-alloying conduces to grain fragmentation in the deformation band, more fragmented grains are existed in Sn-containing cold rolled sheets, which provides more sites for recrystallization nucleation. Sn micro-alloying also promotes recrystallization process and inhibits the growth of recrystallized grains. The recrystallization nucleation and growth mechanism of Sn-containing and Sn-free ferritic stainless steels are both characterized by orientation nucleation and selective growth, but Sn micro-alloying promotes the formation of γ-oriented grains. Furthermore, Sn micro-alloying contributes to the formation of Σ13b CSL boundaries and homogeneous γ-fiber texture. Combining the results of microstructure and micro-texture, the formability of Sn-containing ferritic stainless steels will be improved to some extent.     

过冷金属熔体中枝晶生长的相场法模拟

采用相场模型和有限差分法，模拟了过冷金属熔体的枝晶生长，系统研究相场模型中相场和温度场耦合系数（λ）、热扩散系数（DT）以及界面原子运动时间参数（T0）对枝晶形貌的影响。模拟结果表明，随着相场和温度场耦合系数的增大，晶粒形貌由紧实枝晶向海藻态转变；随着热扩散系数和界面原子运动时间参数的增大．晶粒形貌由光滑枝晶向紧实枝晶转变。     

Controlled Nucleation Method:A New Process for Semisolid Metal Forming

Semisolid metal forming requires special feedstock material with a fine-grained and globular structure to achieve thixotropic properties. A number of methods have been developed to produce such feedstock materials. Controlled Nucleation Method (CNM) is a new and simple, cost effective method that has been developed by the University of Queensland. The CNM process does not use the conventional stirring process, instead, it uses solidification conditions to control nucleation, nuclei survival and grain growth, thereby produce fine and globular structures suitable for semisolid forming. No specialised equipment is required. The method can produce both semisolid slurry for rheocasting and semisolid billet for thixocasting. It can be applied to a wide range of alloys and can easily be incorporated into existing metal forming installation. Semisolid slurries/billets of hypoeutectic and hypereutectic aluminium-silicon casting alloys, aluminium wrought alloys and a magnesium alloys have been successfully produced.     

Size Characteristics of the Surface Tension of One- and Two-Component Metal Melts

A molecular theory based on the lattice gas model is employed to describe the surface tension of the vapor–liquid interfaces of one- and two-component metal melts. The surface tension of the melts are calculated in the quasi-chemical approximation of taking into account intermolecular interactions of the nearest neighbors. Parameters of the model are found from the experimental data for the bulk surface tension of the melts, which enables the calculation of the surface tensions of vapor–liquid interfaces of one- and two-component droplets with different sizes as a function of their radii. Estimates for the minimum size of small droplets of melts having the properties of a homogeneous phase inside them, which correspond to their thermodynamic stability, are obtained.     

Determination of Residues and Safety Analysis of Metal Impurities in Platinum-based Antitumor Drugs

The residual metal impurities in cisplatin, carboplatin and oxaliplatin were determined by ICP-AES. The samples were ignited and dissolved with HCl:HNO 3 (3:1). The method is simple and accurate. By the determination of the metal residues in the samples, the calculated actual daily exposure and concentration of the metal Pd, Ir, Rh, Ru, Mo, Ni, Cr, V, Cu, Mn, Fe and Zn that were less than the permitted daily exposures (PDE) and the limited concentration permitted in the EMEA guideline on the specification limits for residues of metal catalysts or metal reagents [1] . The metal residues can de adequately removed from the active pharmaceutical ingredients and the corresponding drugs. The trace metal residues will not affect human health and lead to the safety hazard by the intravenous injection.     

各向异性对过冷熔体中枝晶生长影响的相场法模拟

文中采用二元合金的等温相场模型，通过在相场参数中引入界面能各向异性强度参数，以A1-4．5％Cu合金为例模拟了各向异性强度对二元合金凝固过程的枝晶生长的影响。结果表明：各向异性强度小时，枝晶形貌呈海藻态，随着各向异性强度的增大，枝晶形貌从海藻态向枝晶态转变，主枝不再分叉，成为光滑枝晶，枝晶尖端生长速度增大，曲率半径减小并逐渐趋于定值，同时模拟的结果与经典枝晶生长理论相吻合。     

Hall Effect in Germanium Doped with Different Impurities

The influence of different impurities on the kinetics of electronic processes in n-Ge<Sb> single crystals is investigated. A substantial decrease in the charge carrier mobility in the region of predominantly impurity scattering (at 77 K) in n-Ge<Sb + Si> crystals, as well as in germanium crystals doped with the rareearth elements, is detected, and this effect is explained.     

玻璃组分与Cu—Ni熔体过冷稳定性

在高真空下,研究了５０ ％ （７９ ％ Ｓｉ Ｏ２ ＋ １２ ．５ ％ Ｂ２ Ｏ３ ＋ ２ ．２ ％ Ａｌ２ Ｏ３ ＋ ０ ．６ ％ Ｃａ Ｏ ＋ ５ ．７ ％ Ｎａ２ Ｏ） （ 简写为 Ｎａ Ｃａ Ａｌ Ｂ Ｓｉ） ＋ ５０ ％ （ Ｎａ２ Ｂ７ Ｏ４） 对 Ｃｕ５０ Ｎｉ５０ 和 Ｃｕ７０ Ｎｉ３０ 合金熔体循环过热过程中过冷度稳定性的影响。结果表明,５０ ％（ Ｎａ Ｃａ Ａｌ Ｂ Ｓｉ） ＋ ５０ ％ （ Ｎａ２ Ｂ７ Ｏ４） 玻璃对合金熔体的净化过程为物理—化学复合净化, 且在（ Ｎａ Ｃａ Ａｌ Ｂ Ｓｉ） 净化剂中加入（ Ｎａ２ Ｂ７ Ｏ４） 玻璃形成的净化剂粘度适中,因此合金熔体在２ ～５ 次循环过热过程中可以获得稳定深过冷。     

The Electropolishing of Nickel in Urea-Ammonium Chloride Melts

Nickel may be electropolished in melts based on urea containing 5–20% w/w of ammonium chloride and 0–3·5% w/w of anhydrous nickel chloride, held at 120–135°C. The optimum applied potential difference across a cell with a vertical anode spaced 1 cm. from the cathode is 2·5–3 v., and the optimum current density is 0·15—0·4 amp./cm.². Considerably higher current densities also give polishing but lead to much gas evolution and increase the tendency to pitting; still higher current densities produce a grey film on the metal surface. The melts age with time, so that the optimum current density falls, and become useless after about three days at temperature; they are partially restored by the addition of fresh urea.

There is an induction period before polishing begins (shorter the higher the current density) during which the metal dissolves normally; the onset of polishing is determined by a rise of anode potential (1·5–1·8 v.) similar to that found in anodic passivation. The evidence suggests that the rise is due, as in passivation, to the formation on the anode surface of a compact film, which during the polishing process, however, dissolves at its outer surface as fast as it is formed. It is suggested that this mechanism is general in electro-polishing, and it is shown that it can account for the avoidance of etching characteristic of the process.     

玻璃组分对Fe-Ga合金熔体净化效果的影响

研究了在循环过热过程中不同组分玻璃净化剂对Fe81Ga19和Fe72.5Ga27.5合金熔体获得的过冷度及其稳定性的影响。结果表明,通过物理-化学复合净化作用,90%Na-Si-Ca+10%B2O3(记作Na-Si-Ca-B玻璃)可使Fe81Ga19合金熔体在循环过热过程中获得250K的稳定深过冷。但是,由于高温(1273K)下Na-Si-Ca-B玻璃粘度过大,在循环过热过程中会大量吸附液态Ga,会使Fe72.5Ga27.5合金发生严重的Ga元素损耗。9.4%SiO2+84.6%Na2B4O7+6%CaO(记作Na-B-Si玻璃)的净化机理与Na-Si-Ca-B玻璃相似,它能使Fe72.5Ga27.5合金获得高达325K的深过冷,且由于其适中的高温粘性可有效避免Ga元素损失的发生。     

晶粒生长拓扑学的相场法模拟

基于金兹堡-朗道理论,采用连续相场模型,研究了晶粒生长的拓扑学。结果表明,晶粒生长过程中存在两种拓扑转变机制,即近邻切换机制和晶粒消失机制;发现三边晶粒、四边晶粒、五边晶粒直接消失以及晶粒近邻切换现象,符合经典拓扑公式和欧拉公式,模拟结果与实验结果吻合。研究还发现了新的拓扑转变机制,四叉点直接分离,这种拓扑转变与经典欧拉公式存在差异。