GRAIN BOUNDARY CHEMICAL ANALYSIS BY SIMS

Abstract
Al-Li alloys are prone to severe intergranular fracture if certain metallurgical parameters are not controlled. The concentration level of trace elements, notably Na which is likely to segregate at grain boundaries, may well be of critical importance. To investigate the possible role of Na a novel approach to grain boundary chemical analysis using SIMS has been developed. This general method, based on depth profiles performed on controlled bevelled sections, is demonstrated for an Al-Li alloy containing 40 µg/g of Na. It would appear that Na does not form a continuous grain boundary film, but may be found in small nodules within the grain boundary regions. The intergranular fracture mode observed for this specimen cannot therefore be directly attributed to the abnormal Na concentration.