EFFECT OF ORIGINAL GRAIN SIZE ON THE BOUNDARY NETWORK IN ALLOY 690 TREATED BY GRAIN BOUNDARY ENGINEERING

Abstract

Effect of original grain size on the grain boundary character distribution(GBCD) in alloy 690 after treatment by grain boundary engineering(GBE) was studied using electron backscatter diffraction(EBSD) and orientation image microscopy(OIM).The proportion of low-ΣCSL grain boundary and grain boundary network after GBE are obviously influenced by the original grain size. Optimized GBE grain boundary network after the same annealing process can be obtained by altering the cold work degree based on the original grain size.Thus the microstructure after GBE is influenced by the combined effect of original grain size and deformation amount before annealing.Mean strain of grain is used to express the combined effect.A proper value of mean strain of grain is necessary to achieve the desired GBE grain boundary network.