Modelling Creep Controlled by the Glide of Jogged Screw Dislocations in TiAl and Ti-Based Alloys

Abstract

Crept microstructures in g-TiAl based alloys reveal a preponderance of 1/2[110]-type jogged-screw dislocations, suggesting that the rate of creep deformation is controlled by the glide of such dislocations. A creep model based on these microstructural observations has been recently developed. This leads to an excellent prediction of creep rates and stress exponents. In this paper, the framework of this model including the verification and validation of the functional dependencies of various microstructural model parameters is reviewed. It has also been observed that creep phenomenology is extremely sensitive to microstructure – fully lamellar g-based alloys exhibit lower creep rates and higher stress exponents even though the deformation microstructure is similar to that in equiaxed alloys. The modifications made to the model that account for the constrained nature of deformation in lamellar alloys are discussed. The applicability of the model is explored in materials systems, including a-Ti and a+b Ti alloys where similar creep exponents and deformation structures have been observed. Finally, the relevance, applicability and shortcomings of the model are critically analyzed.