Construction of suitable structural models in order to account for chemical short-range orders is the reason behind the difficult multi-scale computational simulation methods for solid solutions. Herein, using Ti–Mo alloys as representative, we used our cluster-plus-glue-atom model to address the chemical short-range orders for body-center cubic lattice. In accordance with the atomic interaction mode, an Mo solute atom would prefer 14 Ti solvent atoms as its nearest neighbors, forming a rhombic-dodecahedral cluster, and some next outer-shell Mo and Ti atoms would serve as the glue atoms, which is formulated as [Mo–Ti14](Mo,Ti)x. The number of glue atoms x corresponds to different spatial distribution of the clusters. One of the formula having good stability is [Mo–Ti14]Mo, i.e., with one Mo as the glue atom. To verify its stability, mechanical properties and electronic density of state are obtained using the first-principles calculations and the Young’s modulus agrees with the experimental values. Also the formulated structural unit [Mo–Ti14]Mo is indeed verified by the cluster expansion method. This work then confirms the existence of simple structural unit covering the nearest neighbors and a few next outer-shell atoms for the Ti–Mo alloy of high structural stability.

准晶材料兼具硬度高、摩擦系数小、耐磨损、耐腐蚀、表面能低等特性,有着十分广阔的应用前景.但受限于本征脆性,准晶材料不能作为结构件单独使用,涂层和薄膜形态成为研究热点.综述了准晶涂层和薄膜的几种制备工艺,主要介绍了热喷涂技术、激光熔覆技术、电子束沉积技术、真空蒸镀技术、磁控溅射技术,并对这几种镀膜技术的特点进行了归纳、对比、总结.详细概述了制备过程中涂层和薄膜的生长过程、生长机理,为之后相关研究工作奠定了良好的基础.对结构和性能的研究现状及在界面结合、组织转变、后续热处理工艺中面临的问题进行了讨论,性能方面主要包括准晶涂层和薄膜优良的抗氧化、耐腐蚀、耐磨损性能及其优异的不粘性,并对存在的相关问题提出了一些可能的解决方案.最后对准晶涂层和薄膜更先进的制备方法以及准晶材料在热障涂层、不粘涂层和固体润滑剂等方面的应用前景进行了展望.

It is expected that low-Sn Zr alloys are a good candidate to improve the corrosion resistance of Zr cladding alloys in nuclear reactors, presenting excellent corrosion resistance and high strength. The present work developed a new alloy series of Zr-0.25Sn-0.36Fe-0.11Cr-xNb (x = 0.4~1.2 wt %) to investigate the effect of Nb on autoclave corrosion resistance. Alloy ingots were prepared by non-consumable arc-melting, solid-solutioned, and then rolled into thin plates with a thickness of 0.7 mm. It was found that the designed low-Sn Zr alloys exhibit excellent corrosion resistances in three out of pile autoclave environments (distilled water at 633 K/18.6 MPa, 70 ppm LiOH solution at 633 K/18.6 MPa, and superheated water steam at 673 K/10.3 MPa), as demonstrated by the fact of the Zr-0.25Sn-0.36Fe-0.11Cr-0.6Nb alloy shows a corrosion weight gain ΔG = 46.3 mg/dm2 and a tensile strength of σUTS = 461 MPa following 100 days of exposure in water steam. The strength of the low-Sn Zr alloy with a higher Nb content (x = 1.2 wt %) is enhanced up to 499 MPa, comparable to that of the reference high-Sn N36 alloy (Zr-1.0Sn-1.0Nb-0.25Fe, wt %). Although the strength improvement is at a slight expense of corrosion resistance with the increase of Nb, the corrosion resistance of the high-Nb alloy with x = 1.2 (ΔG = 90.4 mg/dm2 for 100-day exposure in the water steam) is still better than that of N36 (ΔG = 103.4 mg/dm2).

A cluster formula of [M − V14]M1 was formed for vanadium alloys based on a cluster-plus-glue-atom model for BCC solid solutions, where the clusters [M − V14] were centered by one solute M and surrounded by fourteen solvent atoms V, and M could also be served as a glue atom to link clusters. The [M − V14]M1 formula with M = V1/3Cr1/3Ti1/3, an equal-molar combination of V, Cr and Ti, corresponded to the typical V–4Cr–4Ti alloy (wt.%). Based on this formula, a series of new alloys with Ta and Zr substitution for V and Ti respectively in M, were designed and molded into ϕ3 mm rods by copper-mold suction-cast method. These alloys were solid-solutioned at 1273 K for 2 h followed by water-quenching. For Zr-added alloys, the second phase V2Zr was prone to be precipitated, that made alloys much brittle and worse corrosion-resistant in Cl− solution. While Ta-alloyed alloys exhibited a single BCC structure, the Vickers hardness HV of alloys were enhanced obviously. Among them, the Ta-added alloy with M = Ta1/3Cr1/3Ti1/3 (V79.21Ta13.4Cr3.85Ti3.54 wt.%) displayed both higher microhardness and better corrosion-resistance in Cl− solution.

The structures of solid solution alloys are characterized by chemical short-range orders that determine largely the alloy performance. In the present work, the cluster-plus-glue-atom model, which suits for the description of chemical short-range orders in solid solutions, is introduced in the structural description of BCC solid solutions. In this model, solute atoms form 1st-neighbor clusters in the solvent matrix, so that a stable solid solution is represented by a specific local unit containing the characteristic cluster plus certain number of outer-shell 2nd neighbor glue atoms, or expressed in cluster formula [cluster](glue atom)(x). The cluster packing geometry is then analyzed and their structural stability is discussed in terms of cluster packing density. The cluster packing density reaches the maximum when x = 1, signifying that these alloys might possess special stabilities and henceforth good properties. Commonly-used BCC alloys in Zr-, Ti-, V-, Nb-, Ta-, Mo-, W-, and U-based systems are found to conform to the as-mentioned composition formulas, and in particular to that with x = 1, thus unveiling universal composition rules for BCC metals. (C) 2015 Elsevier B.V. All rights reserved.

The multi-element Zr-based bio-alloys are optimized for reaching lower Young׳s modulus and magnetic susceptibility by introducing the cluster-plus-glue-atom model to realize the composition design. A general cluster formulas of [(Mo,Sn)–(Zr,Ti)14]Nbx (x=1, 3) was obtained from the model and alloy rods with a diameter of 3mm were prepared by copper-mold suction-casting processing. The β structural stabilities of the designed alloys were studied by the valence electron concentration (VEC). Among the β-Zr alloys, the [(Mo0.5Sn0.5)–Zr14]Nb1 (Zr87.5Nb6.25Mo3.13Sn3.13 at%) and [(Mo0.5Sn0.5)–(Zr13Ti)]Nb1 (Zr81.25Nb6.25Ti6.25Mo3.13Sn3.13 at%) alloys, corresponding to the lower β stability limit, display lower Young׳s moduli (77–79GPa), lowest magnetic susceptibilities (2.12×10−6–2.13×10−6cm3g−1), as well as higher Vickers hardness (288–311HV).

Ni-Hf binary alloys are merely known as a category of marginal glass formers. In this system, the assessment of glass-forming abilities has not been made and the optimal glass-forming composition remains unclear. In the present work, Ni-Hf glass-forming compositions are explored using the atomic cluster plus glue atom model. Ni-Hf phase diagram shows a deep eutectic point at Ni65Hf35 which is associated two intermetallic phases, namely, Ni7Hf3 and Ni10Hf7. A predominant atomic cluster was first derived from the crystalline structures of the deep eutectic related phases, and several glass-forming compositions were determined considering the one or three glue atoms constraint condition. Rapid quenching results show that Ni71.43Hf28.57 and Ni68.75Hf31.25 metallic glasses can be made fully glassy. The latter can be well described with the model composition formula as [Ni-Ni7Hf5]Ni3. Among the melt-spun alloys, the Ni68.75Hf31.25 glass which locates in between the deep eutectic point and the Ni7Hf3 phase in the phase diagram, exhibited a highest crystallization temperature of 877 K and a lowest liquidus of 1482 K, and hence is suggested to be the optimal Ni-Hf glass former by the high reduced glass temperature criterion.

A cluster-plus-glue atom model was employed to design Ni-Nb based ternary bulk metallic glasses. The binary eutectic point Ni59.5Nb40.5 was first interpreted by the model in form of a cluster formula [(Ni0.5Nb0.5)-Ni6Nb6]Ni-3, where the cluster is (Ni0.5Nb0.5)-centered icosahedron derived from a eutectic phase Ni6Nb7 (Fe7W6 type). It was then pointed out that the best binary glass former Ni62Nb38 could be interpreted based on the eutectic cluster formula by replacing the cluster center Nb-0.5 with Ni-0.5 namely [Ni-Ni6Nb6]Ni-3=Ni62.5Nb37.5. To further improve the glass-forming ability, Zr, Ta and Ag are selected as alloying additions to partially replace Nb in the [Ni-Ni6Nb6]Ni-3 cluster formula, and glassy rods with a critical size of 3 mm are achieved at appropriate ternary compositions by copper-mould suction-casting. DTA measurements indicate these bulk metallic glasses exhibit high thermal stabilities, among which the [Ni-Ni6Nb5Ta]Ni-3 alloy has the highest T-g (glass transition temperature)of 935 K and T-x (crystallization temperature) of 952 K. Room-temperature compressive curves of [Ni-Ni6Nb5Zr]Ni-3 and [Ni-Ni6Nb5Ta]Ni-3 alloys show they have limited plasticity with a elongation of about 0.3%, fracture strength of the [Ni-Ni6Nb5Zr]Ni-3 and [Ni-Ni6Nb5Ta]Ni-3 BMGs are about 3.2 GPa and 3.4 GPa, respectively.

The Ni–Nb–Zr bulk metallic glass composition was analyzed by our cluster-plus-glue-atom model using a eutectic-related binary cluster M-Ni6Nb6, M = 0.5Ni + 0.5Nb, which was derived from a eutectic phase Ni7Nb6 (Fe7W6 type). A composition formula [M-Ni6Nb4MZr]Ni3 was then proposed, where the combination of one M and one Zr atom had an almost equal atomic size as a Nb atom to be substituted for. Alloy rods with 3 mm in diameter were obtained using copper mould suction casting. XRD results showed that compositions [M-Ni6Nb5-xMZrx]Ni3, x = 0.76, 0.84, 0.92, 1, 1.08, 1.16 formed single glassy phases, conforming to the proposed formula.