摘要
原子簇在熔体晶体生长中的作用蔡英文，范新会，李建国，傅恒志原子簇是指由原子群体所构成的相对稳定的集团，也称团簇［１］。它的存在构成了凝固形核理论的核心，但在生长动力学理论中却从未有人对原子簇的作用加以思考。事实上，从高温过热工艺（ＢＴＯＰ，俄）［２］...
We, at Northwestern. Polytechnical University, after m4ny yealrs Of solidincation research, came to realize that cluster, long recognized as the core of nucleation theory but never given thinking in growth kinetics, needs to be carefully studied in order to obtain better materials. For instance, we have found that such carefUl study explains why just an increase in pouring temperature can improve the phase morphology and distribution of the final microstructures in Al-Si eutectic system, Cu-Ni single phase system,superalloys,etc. We deem that the cluster size distribution (CSD) is not a constant as usually assumed but a function of temperatute, solvent-solute type, their interactions, heat preservationtime, alloy composition, etc.Let Ti denote the solid/liquid interface temperature and TL, the temperature of bulk liquid. The thermal history peliod τλfor TL to drop to Ti can be determined by Fodrler's law of heat conduction. If CL and Ci represent the alloy compositions of bulk liqluid and interface respectively, then we can calculate the relaxation time τr required for the equilibrium CSD that corresponds,to CL to reach the equilibrium CSD that corresponds to Ci, If τλ≥τr, then the system can reach the eqluilibrium CSD that corresponds to Ci and Ti; if τλ<τr, then, CSD in the melt will be the equilibrium one eorresponding to Ti only.The above highly condensed sketch of our new viewpoint together With Principles already known appear to enable us to explain semi-quantitatively the effect of overheat treatment on crystalline microstructures.As the size of clusters decreases with increasing temperature, thera exists a transition stage of melt structure between short range ordered crystalline-like one in the neighborhood of the melting point and gaseous-like one in the neighborhood of the boiling temperature. When the melt temperature is raised, clusters of Si-Si in Al- Si alloy or carbonides in superalloys decrease in size and tend to disappear. If the cooling is comparatively rapid, growth of clusters wil
出处
《西北工业大学学报》
EI
CAS
CSCD
北大核心
1996年第2期323-324,共2页
Journal of Northwestern Polytechnical University
