ATOMIC CONFIGURATION IN BAINITE OF A CU45ZN40AU15 ALLOY EXAMINED BY ALCHEMI

The atomic configuration in the bainite of a CU(45)Zn(40)Au(15)alloy w ith a L2(1) type ordered structure in parent phase has been studied by means of ALCHEMI. Thin bainite plates which are supposed to be at ear ly stages of formation possess the 18R type structure like the martens ite of the same alloy system formed at subzero temperature. As far as electron diffraction is concerned, it appears that they inherit the or dered configuration of atoms in the parent phase completely. However, when closely examined by ALCHEMI, the atomic configuration is found to differ slightly from that in the parent phase. A part of Cu and Zn at oms in the bainite interchange their sites with each other, which are in the first nearest neighbor relation in the parent phase. This type of disordering is different from that recently observed in the martens ite formed at subzero temperature and subsequently aged sufficiently a t room temperature. These facts suggest that the bainite is not the ma rtensite subjected to aging at temperature after its formation.