SCANNING-TUNNELING-MICROSCOPY AND TRANSMISSION ELECTRON-MICROSCOPY STUDY OF ULTRAFINE STRUCTURE AND SURFACE-RELIEF OF BAINITE IN A CU-ZN-ALALLOY

The fine structure of bainite (alpha(1) plate) in a Cu-25.9 wt% Zn-4.0 wt% Al-0.1 wt% Re alloy has been studied by scanning tunnelling micro scopy (STM) and transmission electron microscopy (TEM). The experiment al results demonstrated that bainite plates are composed of subplates, and the subplates are composed of subunits. STM investigation shows t hat the surface relief with a bainite plate is composed of groups of s mall reliefs which correspond to subplates and subunits. The relief ar ising from the formation of bainite is tent like, which is different f rom that with martensite. Ledges exist on the broad faces of the subun it, 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 concernin g the ultrafine structure and surface relief accompanying bainite, the sympathetic nucleation-ledgewise growth mechanism of bainite is propo sed.