Structure Fluctuation Model of Melting and Polymorphic Transformations in Metals

Resumo

Relationships of volumes during thermal expansion of metals are analyzed. It is demonstrated that metals with BCC structure undergo two-step structural change at the melting point: at the beginning the BCC structure is transformed into FCC structure and then clusters are formed with K = 12 and statistical packing of atoms of the liquid phase. Before melting, hexagonal layer-by-layer (6 + 6) packed Cd and Zn change their structure from K = 6 to K = 8. Metals with FCC structure do not change the number of neighbors before melting, forming clusters with K = 12. It is shown that conditions of pre-melting and polymorphic FCC (HDP) → BCC transformations are reached for the critical volume of thermal expansion caused by leveling of fluctuations of atom and electron densities.