Fundamental Concepts Relating Local Atomic Arrangement Deformation and Fracture of Intermetallic Alloys

Abstract

Abstract : The creep resistance of a TiAl/Ti3Al alloy with a lamellar microstructure has been previously found to be superior to the creep resistance of single-phase TiAl and Ti3Al alloys with compositions close to the compositions of the individual phases in the lamellar alloy. The objectives of the present research project were to identify the origin of the enhanced creep resistance of the TiAl/Ti3Al lamellar alloy, to formulate a model capable of predicting the creep strength of the TiAl/Ti3Al lamellar alloy, and to evaluate the effect of thermal exposure on the creep strength of the TiAl/Ti3Al lamellar alloy. The results, analyses and interpretations described in this report show that the enhanced creep resistance of the TiAl/Ti3Al lamellar alloy arises from the lamellar morphology of the TiAl and Ti3Al phases. The lamellar morphology provides a large interphase interfacial area per unit volume, which is proposed to introduce a high density of dislocation sources. The high density of dislocation sources is thought to increase the work hardening rate of the lamellar alloy relative to the individual single phase alloys; an effect which contributes the small primary creep strain and low secondary creep rate exhibited by the lamellar alloy. When the increased work hardening rate is accounted for in the constitutive equations for creep of the individual TiAl and Ti3Al phases, an analytical model formulated for creep of discontinuous, lamellar-reinforced composites can be used to predict the creep strength of the TiAl/Ti3Al lamellar alloy from the creep properties of the single phase alloys. TiAl, Ti3Al, Intermetallic, Creep, Lamellar composite, Constitute model, Coarsening.