The Application Of Systematic Alloy Science In Au-Cu Alloy System

In the development history of alloying theory, Au-Cu system is always the classic subject investigated. The crystallogphies target it as an exemplification for studying alloy phase structure; The theoretical physicists choose it as an exemplification for studying electronic structure and transformation of order-disorder; The thermal chemists consider it as an exemplification for evaluating and calculating phase diagram.In this paper, the classic Au-Cu alloy system is chose as object. On the basis of studying pure metals Cu and Au, this alloy system is researched from the two respects of atomic structure level of alloy phase and electronic structure level of atom. Then the energetic properties, volumetric properties and electronic structures of alloys and components are obtained through systematic alloy science. This study produces umpty innovative results, enriches the contents for systematic alloy science and supplies fundamental datum for studying transformation of order-disorder, calculating phase diagram and designing new materials.The electronic structures, coefficients of heat expansion, single bond radii, lattice parameters, specific heats at constant volume, isopiestic specific heats, internal energies, enthalpies, entropies and Gibbs energies of pure metals Cu and Au are studied adopting one-atom theory within systematic alloy science. The calculated results are in good agreement with the experimental datum."Obtaining the whole from the part" is the most idiomatical method in systematic alloy science, the most employable technique and is the principal task of systematic alloy science for choosing the interaction function between energy and volume accurately. This paper obtains, creatively, two characteristic atom sequences, which contain the energetic properties, volumetric properties and state behaviors of characteristic atoms on the basis of experimental heat of formation and volume of formation of a few disordered alloys and experimental heat of formation and volume of formation of a few compounds respectively in Au-Cu system. Then, using the one-atom theory, we determine the information of valence electronic structures, cohesive energies, single bond radii, lattice parameters, etc for characteristic crystals, which are the premise of designing materials, calculating the properties of alloy phases and phase diagrams and studying transformations of order-disorder. On the basis of these, we adopt the method of bidirectional proof and obtain some valuable results:it is determined that the interaction function of energy is equation 5 and the interaction function of volume is equation 6; it is found that the disordered alloys measured by experiment is not full disordered, but have larger degree of short range ordering; it also interpret the question perplexing us chronically of voluminal expansion when disordering in Au-Cu alloy. The reason is that the volume of characteristic atom AiCU increases with increasing the number of nearest neighboring atom Au, essentially, due to both increase of covalent electrons changing smaller and increase of free electrons changing more markedly in valence electronic structure, which is attributed to increase of single bond radius and viCu". Then, it is proved that the partial molar property can't veritably describe the average properties of components.Using the additivity law of characteristic crystalline properties, the energetic properties, volumetric properties and electronic structures of disordered alloys, ordered alloys and compounds in Au-Cu alloy system are studied from the information of two group of characteristic crystal sequences definited by disordered alloys and compounds. The results of the two studying methods exist small differences, yet the whole conclusions are same:the formations of disordered alloys, ordered alloys and compounds from pure metals are exothermic and their volumes are expansive, which is positive deviation relative to Zen's Law and Vegard's Law, and that the transformation of disordered→ordered is exothermic reaction and its volume is contractible. Also, these prove that systematic alloy science can obtain the whole infromation from different parts.It is proposed a new description method of phase structure, i.e., the crystal characteristic atom arranging structure which not only reflects the arrangement of atoms in space, but also contains the information of energies, volumes and states. According to the J-L long period antiphase structure model proposed by Johannsson-Linde and G-F-L model proposed by Guymont-Feutelais-Legendre, we illustrate the corresponding crystal characteristic atom arranging structures respectively. Then the heats of formation, volumes of formation and ordering degree of AuCuⅠ, AuCuⅡand the region (plane) of antiphase, as well as the enthalpy of transition and volume of transition of AuCuⅠ→AuCuⅡare all calculated respectively. The results denote that the transition of AuCuⅠ→AuCuⅡcorresponding to J-L model is an exothermic and volume contractic reaction which is opposite from experimental phenomenon. Therefore, the J-L model can not be used to describe the structure of AuCuⅡ. However, the transition of AuCuⅠ→AuCuⅡcorresponding to G-F-L model is an endothermic and voluminal expansion reaction which is in agreement with the experimental phenomenon. Thus, the G-F-L model reflects the structure of AuCuⅡfactually.