Residual Stress of Individual Aluminum Grains from Three Dimensional X-Ray Diffraction

Abstract

Residual stress measurement by interpreting diffraction rings is well developed. The ring is produced by many grains contributing individual diffraction spots, each from their local stress environment. Local stresses limit the bulk strain resolution of X-ray stress methods. The local stresses can be so large, traditional methods fail to produce meaningful results. However, if the local stress environment could be understood, it provides additional value for measuring and predicting material behavior. Experimental determination of the internal stress for one grain from a ring has several challenges. In some special cases, these have been overcome using synchrotron radiation. Here, using a Bruker D8 laboratory X-ray diffractometer and a 2D Hi-star detector, a method of sensing and analyzing X-ray diffraction cones in three dimensions was introduced. After a certain sample detector distance, individual grains can be resolved in spots on the ring. The method requires collecting a sequence of 2D frames at increasing sample to detector distances. The entire three-dimensional X-ray diffraction pattern (XRD³) could be used to determine the average 2θ ring position. This allows new types of strain measurements. Other applications for tracking spots from grains are in development.