Scanning tunnelling microscopy and transmission electron microscopy study of ultrafine structure and surface relief of bainite in a Cu–Zn–Al alloy

Abstract

The fine structure of bainite (α1 plate) in a Cu–25.9 wt% Zn–4.0 wt% Al–0.1 wt% Re alloy has been studied by scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). The experimental results demonstrated that bainite plates are composed of subplates, and the subplates are composed of subunits. STM investigation shows that the surface relief with a bainite plate is composed of groups of small reliefs which correspond to subplates and subunits. The relief arising from the formation of bainite is tent like, which is different from that with martensite. Ledges exist on the broad faces of the subunit, indicating that it grows by a ledgewise mechanism. Three types of nucleation of the subunits were observed under TEM: face to face, edge to edge and edge to face. Based on the experimental results concerning the ultrafine structure and surface relief accompanying bainite, the sympathetic nucleation–ledgewise growth mechanism of bainite is proposed.