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.     

Cu原子簇触发形核下的深过冷Ag-Ge合金组织演变研究

采用玻璃包覆的方法获得具有较大过冷度的亚共晶、共晶以及过共晶Ag-Ge合金熔体，并通过高能离子束轰击Cu箔产生Cu原子团簇溅射到过冷合金熔体中来触发非均质形核过程。凝固后合金显微组织的分析结果表明：在深过冷合金熔体中引入Cu原子团簇，它对亚共晶、共晶以及过共晶Ag-Ge合金的显微组织演变有着不同的影响效果，分析了显微组织的演变规律与形成机制。     

金属熔体原子团簇的微观热收缩机制探讨

以多种纯金属及合金的X射线衍射实验结果为基础,结合理论分析,从自由体积的角度探讨金属熔体原子团簇的微观热收缩现象,进一步揭示微观热收缩的本质及机制:熔体中原子团簇的微观热收缩,是熔体中自由体积膨胀较之宏观体积膨胀更为严重的结果,团簇结构的变化是导致其出现热收缩的根本原因。     

金属过冷熔体等轴枝晶生长的相场方法研究

在纯物质相场模型中,采用计算效率较高的邻界面点相场大梯度计算域控制法,模拟了纯金属在无量纲过冷度为0．55熔体中等轴枝晶的生长演化过程,得到与实验观察相符合的等轴枝晶生长规律,通过加入形式较简单的热扰动,产生了明显的二次枝晶臂,有的二次枝晶臂上还出现了三次枝晶臂。同时计算了枝晶晶轴尖端的无量纲生长速度和曲率半径,并求出Peclet数。计算结果与微观可求解理论和Ivantsov理论吻合良好。     

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.     

掺杂Sn对V/UiO-66催化剂抗碱金属性能的影响

采用浸渍法,以UiO-66为载体,制备了V/UiO-66及改性Sn-V/UiO-66催化剂,并对催化剂的碱金属钾中毒进行了模拟,探讨了钒钛催化剂的反应机理和失活机理。结果表明,K负载后催化剂的晶型变化不大并且催化剂比表面积的变化呈现不规律波动。负载了碱金属以后,催化剂的金属氧化还原性能和表面酸量迅速降低,这是催化剂活性降低的主要原因。添加Sn能够增强VO_x与其他组分的相互作用,进而提高VO_x的可还原性及V⁵⁺的占比,使Sn-V/UiO-66催化剂表面的VO_x提供更多的酸性位点。中毒后的K-Sn-V/UiO-66催化剂仍然具有较高的总酸量和较强的氧化还原性,表明Sn-V/UiO-66催化剂具有优异的抗碱金属中毒能力。     

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.     

六方材料织构的近真ODF分析系统

采用熔融玻璃自分离净化工艺，可使液态（Ｎｉ０．５３Ｆｅ０．３３Ｃｏ０．１４）７３Ｂ１７Ｓｉ８Ｎｂ２合金稳定地获得０．３Ｔ１以上的过冷度。研究了电磁场在深过冷液态合金凝固过程中所起的作用。观察及分析结果表明，电磁场对于过冷度的影响甚微，但却对于形核及其生长产生明确的影响，使形核及生长表现出与自由凝固下完全不同的规律。电磁场对于进一步提高深过冷合金的热力学过冷度具有促进作用。     

等离子区域熔炼提纯金属Y过程中的杂质迁移规律

利用等离子体区域熔炼提纯金属钇,获得了区熔提纯过程中Al、Si、Fe、Ni、Cu和Mo等杂质的迁移规律。计算结果表明,金属钇中Al、Si、Fe、Ni、Cu和Mo等常见杂质的平衡分配系数分别是0.2173、0.2201、0.5065、0.1586、0.1742和0.8576。由于上述杂质平衡分配系数小于1,杂质在液相中的溶解度大于固相溶解度,所以从理论上可判断出Al、Si、Fe、Ni、Cu和Mo等杂质将随着熔区移动富集在金属钇锭的尾端,也就是最后凝固区。实验结果证明了该理论预判的准确性。此外,探究了区熔次数与杂质迁移的内在联系,结果表明：随着区熔次数由5次增加至10次,杂质在金属钇锭尾端富集程度增加,即去除率升高。10次区熔后,Al、Si、Fe、Ni、Cu和Mo等杂质的去除率分别为45.71%、61.54%、33.98%、64.15%、52.14%和46.28%。由于上述杂质饱和蒸气压与金属钇接近,所以很难通过常规方法予以去除。等离子体区域熔炼提纯金属钇的研究为制备高纯钇提供了一种新方向。     

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。