Interpretation of the stress dependence of creep by a mixed climb mechanism in TiAl

Abstract

The behaviour of ordinary dislocations in TiAl alloy creep-deformed at 750°C has been investigated. Two alloys processed by the cast and powder metallurgy routes were crept under tensile stresses of 150 and 80 MPa, respectively. Transmission electron microscopy was performed on the crept samples to determine the characteristics of the dislocations. The stress dependence of the dislocation mechanisms was determined from stress jumps performed during creep deformation. Complementary in-situ heating experiments performed on previously crept samples are also presented. From these experimental investigations, it is shown that some ordinary dislocations move by a mixed climb mechanism for which the elementary process is the nucleation and the lateral propagation of a jog pair. The coherency between this mechanism and the determined activation parameters, as well as the driving force at its origin, are discussed.

Acknowledgements

This work forms part of the research contract Contrat de Programmation de Recherche CNRS: Intermétalliques base Titane involving the CNRS, Snecma moteurs—Groupe Snecma, Turboméca—Groupe Snecma and the Délégation Générale à l'Armement. The authors wish to thank all these partners for financial support and scientific discussions.