Editors: | Kongoli F, Kobe S, Calin M, Dong C |
Publisher: | Flogen Star OUTREACH |
Publication Year: | 2016 |
Pages: | 130 pages |
ISBN: | 978-1-987820-38-6 |
ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
Metallic alloys show complex chemistry that is not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn a-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn1,6 and [Zn-Cu12](Zn,Cu)6, which explain the a-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1st-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formalism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistry of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys.