PINNING POINTS ANCHORING ORDINARY AND SHOCKLEY DISLOCATIONS IN TIAL ALLOYS

Pinning points anchoring Shockley dislocations and ordinary dislocatio ns in the gamma phase of two TiAl alloys (a single-phase alloy and a l amellar two-phase alloy) are studied by in situ straining experiments performed inside a transmission electron microscope. The overcoming pr ocesses of these pinning points are observed. Their densities are meas ured and compared. The results indicate that the pinning points are ex trinsic to the dislocations. The measured densities do not correspond to a homogeneous distribution of the individual oxygen atoms present i n the crystal. It is proposed that they are due to the segregation of part of the interstitial oxygen atoms. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.