Solid-Phase Low-Temperature Evolution of the Binary Pb–Au System: Via Contact Interactions to Intermetallic Compounds, through the Destructurization to a New Multielemental State

Abstract

The paper presents the results of the long-term experiment on the solid-phase transformation of the Au–Pb metallic system which takes place at room and cryogenic temperatures. It is found that the solid-phase contact interactions between lead and gold lead to the formation of the Pb + AuPb₃ eutectoid. The mass transfer and the phase formation are due to the lead extrusion along the percolation channels that form as a result of the substructural destruction of gold. No reaction layer forms at the boundary of the contacting metals. The decomposition of the solid solutions based on intermetallics AuPb₃ occurs through the process of the destructurization of the material into nanoparticles, the displacement of impurity atoms from the bulk to the boundaries, the integration and ordering of separated components of the solid solution. The decomposition of the AuPb₃ intermetallic compound leads to the formation of AuPb₂ and the phases of variable compositions, and, then, pure components Au + Pb. The decomposition occurs through the stage of fast growth of lead crystals accompanying by the formation of loose gold nanoparticles that gradually take a faceting. The results of these studies can be useful for solution of problems of designing multicomponent metallic materials with an evolution prediction of their structure–phase transformations under the service conditions.