In situ observations of unusual dislocation mechanisms in the intermetallic alloy Ti3Al

In situ straining experiments in a transmission electron microscope have be en carried out on a Ti3Al intermetallic alloy, with the aim of determining the microscopic mechanisms controlling glide in prism, basal and pyramidal planes. Five different antiphase boundary energies have been measured and c ompared with the corresponding densities of incorrect first nearest neighbo ur atoms. The determination of a tension-compression asymmetry in pyramidal slip, and the detailed analysis of the complex microscopic mechanisms invo lved illustrate the efficiency of in situ experiments to solve complex prob lems in plasticity. A comparison between the properties of the different sl ip systems shows that they are controlled by different microscopic mechanis ms, none of them being of covalent origin.