G.W. Qin

Ledge mechanism of primary α2/γ lamellae growing in the supersaturated α2 matrix for γ-TiAl-based (γα2) alloy

{gamma}-TiAl-based ({gamma}+{alpha}{sub 2}) two-phase alloys have been considered as potential structural materials for relatively high temperature use because of their good high-temperature properties. The service life of the alloy materials can be determined by the stability of the {alpha}{sub 2}/{gamma} lamellar structure at high temperature. This paper aims at examining the precipitation micromechanism of {gamma} lamella in supersaturated {alpha}{sub 2} matrix, including its nucleation and growth, by optical microscopy and transmission electron microscopy (TEM). The ledge mechanism of primary {alpha}{sub 2}/{gamma} lamellae growth has been proposed, and the {alpha}{sub 2}/{gamma} interfacial energy has been evaluated.

Discontinuous coarsening of primary α2γ lamellae in surface layer of the Ti58Al42 intermetallic alloy

Some experimental description of discontinuous coarsening (DC) reaction observed in various ({alpha}{sub 2} + {gamma}) two-phase TiAl-based alloys can be found in previous papers. This paper aims at examining the DC reaction in the surface layer of the alloy, and investigating the reaction by thermodynamic analysis. The cells in small size (about 30--50{micro}m) with coarse {alpha}{sub 2}/{gamma} lamellae due to the discontinuous coarsening nucleate randomly within the fine primary lamellae of the alloy surface and extend into a limited thickness of the surface layer for the Ti{sub 58}Al{sub 42} alloy ({alpha}{sub 2}{sup ss}) treated at 1,000 C. The elastic strain energy in the surface layer of the specimen has great effect on the discontinuous coarsening reaction. With the further prolonging of time, the extension of DC cellular microstructures with coarse {alpha}{sub 2}/{gamma} lamellae into the interior of the specimen becomes extremely difficult, and the discontinuous coarsening reaction nearly stops.

Strain analysis of misfit dislocations in α-Fe2O3/α-Al2O3 heterostructure interface by geometric phase analysis

The α-Fe2O3/α-Al2O3 heterostructure interfaces have been studied using transmission electron microscopy (TEM). The interface exhibited coherent regions separated by equally spaced misfit dislocations. The misfit dislocations were demonstrated to be edge dislocations with dislocation spacing of ∼4 nm. The strain fields around the misfit dislocation core were mapped using a combination of geometric phase analysis and high-resolution transmission electron microscopy images. The strain measurement results were compared with the Peierls-Nabarro dislocation model and the Foreman dislocation model. These comparisons show that the Foreman model (a=2) is the most appropriate theoretical model to describe the strain fields of the dislocation core.