X-RAY MICROBEAM MAPPING OF MICROTEXTURE RELATED TO FATIGUE-CRACK ASPERITIES IN AL-LI-2090

In certain orientations, AI-Li 2090 T8E41 cracks more slowly in fatigu e than other aluminum alloys due to roughness-induced closure linked t o the average texture or macrotexture. For this application, three-dim ensional, non-destructive measurement of microtexture and strain evolu tion within samples was developed using synchrotron polychromatic X-ra y microbeam diffraction; its use in mapping the microtexture of fatigu e crack asperities in AI-LI 2090 are reported. Groups of adjacent grai ns with nearly identical orientations were found at numerous locations in the plate centers, and this type of ''mesotexture'' appeared close ly tied to asperity formation. Changing arrangements of 111 diffractio n spots relative to the samples' rolling and crack propagation directi ons are found to correspond to the transitions between a relatively pl anar section of the crack and an adjacent asperity. (C) 1998 Acta Meta llurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.