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Indexed by:期刊论文

Date of Publication:2021-02-01

Journal:Wuli Xuebao/Acta Physica Sinica

Volume:68

Issue:6

ISSN No.:10003290

Key Words:Alloying; Alloying elements; Atoms; Binary alloys; Chemical analysis; Cobalt alloys; Crystal atomic structure; Glues; Gluing; High temperature applications; Lattice constants; Lattice theory; Mechanical properties; Mixing; Molybdenum alloys; Nickel alloys; Single crystals; Superalloys; Ternary alloys; Ternary systems; Titanium alloys; Tungsten alloys, Chemical short range orderings; Cubic solid solutions; Glue atoms; High temperature structural material; Multi-element alloy; Ni-base single crystal superalloy; Partition behaviors; Pseudoternary system, Aluminum alloys

Abstract:Having a γ/γ' microstructure similar to Ni-base superalloys and also including various alloying elements such as Al and W, new Co-base superalloy, namely Co-Al-W-base alloy, has been widely studied as a kind of potential alternative of Ni-base superalloy, which is the most important high-temperature structural material in industrial applications. Besides, Co-Al-W-base alloy has also excellent mechanical properties, for example, creep properties comparable to those of the first-generation Ni-base single crystal superalloys. In our previous work, the ideal composition formula of Ni-base superalloy has been obtained by applying the cluster-plus-glue-atom structure model of faced centered cubic solid solution, which shows that the most stable chemical short-range-order unit is composed of a nearest-neighbor cluster and three next-neighbor glue atoms. In this paper, the ideal cluster formula of Co-Al-W-base superalloy is addressed by using the same approach. Based on cluster-plus-glue-atom model theory, according to lattice constants and atom radii, calculations are carried out. The results show that the atom radius of Al is equal to Covalent radius (0.126 nm) and for γ' phase the atom radius of W changes obviously (0.1316 nm). After analyzing atomic radii, the chemical formula for Co-Al-W ternary alloy is calculated to be [Al-Co12](Co, Al, W)3, which signifies an Al centered atom and twelve Co nearest-neighbored cluster atoms plus three glue atoms, which is in good consistence with that for Ni-base single crystal superalloy. For multi-element alloy, the alloying elements are classified, according to the heat of mixing between the alloying elements and Co as well as partition behavior of alloying elements, as solvent elements-Co-like elements Co(Co, Ni, Ir, Ru, Cr, Fe, and Re) and solute elements-Al-like elements Al(Al, W, Mo, Ta, Ti, Nb, V, etc.). The solvent elements can be divided into two kinds according to partition behaves: Coγ (Cr, Fe, and Re) and Coγ' (Ni, Ir, and Ru). The latter is further grouped into Al, W (W and Mo, which have weaker heat of mixing than Al-Co ) and Ta (Ta, Ti, Nb, V, etc., which have stronger heat of mixing than Al-Co). Then all chemically complex Co-Al-W-base superalloys are simplified into Co-Al pseudo-binary or Co-Al-(W, Ta) pseudo-ternary system. Within the framework of the cluster-plus-glue-atom formulism and by analyzing the compositions of alloy, it is shown that the Co-Al-W-base superalloy satisfies the ideal formula [Al-Co12] (Co1.0Al2.0). (or [Al-Co12]Co1.0Al0.5(W, Ta) 1.5 =Co81.250Al9.375(W, Ta)6.250 at.%) In the same way, those of γ and γ' phases are respectively [Al-Co12] (Co1.5Al1.5) (or [Al-Co12]Co1.5Al0.5(W, Ta) 1.0= Co84.375Al9.375(W, Ta)6.250 at.%) and [Al-Co12] (Co0.5Al2.5) (or [Al-Co12]Co0.5Al0.5(W, Ta) 2.0= Co78.125Al9.375(W, Ta)12.500 at.%). For example, alloy Co82Al9W9 and its γ and γ' phases are formulated respectively as [Al-Co12]Co1.1Al0.4W1.4 (～ [Al-Co12]Co1.0Al0.5W1.5), [Al-Co12]Co1.6Al0.4W1.0 (～ [Al-Co12]Co1.5Al0.5W1.0), and [Al-Co12]Co0.3Al0.5W2.2 (～[Al- Co12]Co0.5Al0.5W2.0). © 2019 Chinese Physical Society.