Molecule-like chemical units in metallic alloys
Research output: Journal Publications and Reviews (RGC: 21, 22, 62) › 21_Publication in refereed journal › peer-review
Related Research Unit(s)
|Number of pages||9|
|Journal / Publication||Science China Materials|
|Online published||28 May 2021|
|Publication status||Published - Oct 2021|
|Link to Scopus||https://www.scopus.com/record/display.uri?eid=2-s2.0-85107305921&origin=recordpage|
Each conventional alloy has its own specific compositions but the compositional origin is largely unknown due to our insufficient understanding about chemical short-range ordering in the alloy, in particular, in the solid-solution state. In the present paper, the compositions of metallic alloys are discussed and formulated, by unveiling the basic moleculelike structural units in solid solutions. Friedel oscillation theory, which describes the partial charge screening behavior in solid solutions, and henceforth the origin of short-range ordering, is applied to pin down the ideal chemical compositions of conventional metallic alloys. We propose that, at a specific composition, atoms self-assemble into an ideally ordered structure consisting of atoms residing in the nearest-neighbor shell (denoted as cluster) plus those in the next outer shell (denoted as glue atoms), which can be formulated as [cluster](glue atoms). This simplified version of short-range-order structure represents the smallest charge-neutral and mean-density zone (termed as “chemical units”) and can be regarded as the ‘molecules’ of solid solutions. Accordingly, the chemical units and the corresponding molecule-like formulas for face-centered-cubic (FCC), hexagonal close-packed (HCP), and body-centered cubic (BCC) structures are analyzed and equations are obtained to identify the chemical formulas for FCC solid solutions. For instance, well-known α-brass Cu-30Zn alloy is formulated as [Zn-Cu12]Zn4. Examples of aluminum alloys, superalloys and stainless steels are also illustrated, demonstrating the versatility of the present model to interpret chemically complex alloys.
本文引入Friedel振盪理論, 揭示固溶體合金中存在類似分子式的結構單元, 指出在特定的成分下, 合金中的原子在近程式上傾向於聚集為理想的有序結構, 這個結構包括最近鄰殼層原子(記作團簇)和次近鄰殼層原子(記作連接原子), 用團簇式: [團簇](連接原子)來表示. 這種近程式結構被稱為化學結構單元, 類似於固溶體中的“分子”. 本文給出了FCC結構固溶體合金中化學結構單元的計算公式, 通過計算得到Cu基二元體系的理想化學結構單元, 包括CuZn、Cu-Al、Cu-Ni、Cu-Be和Cu-Sn, 均為工業中最常用的合金成分. 此外, 工業上常用的多元合金, 如Al合金5083和7075、高溫合金 TMS-196和TMS-82、馬氏體時效不銹鋼Cutom-465和奧氏體不鏽 鋼310s, 其成分均滿足模型的預測, 表明本模型可以為FCC結構複雜固溶體合金的成分設計提供理論指導.
- chemical unit, cluster-plus-glue-atom model, metallic alloys, short-range order, solid solution