Atomic configuration model with emitting dislocations in the ${α_2}$ /γ by ${α_2}$ to γ phase transformation during creep deformation in the lamellar TiAl alloy

Abstract

TiAl alloys are high temperature structural advanced materials and are expected to be utilized under the environment of sustained stress or cyclic stress at high temperature such as turbine blades of jet engine and valves of automobile engine. It is reported recently that the ${α_2}$/γ lath boundary gives a significant effect on the deformation characteristics when the TiAl alloys are deformed at high temperature. However, it is very important for developing creep and fatigue resistance material to reveal the microscopic mechanism related with lamellar interface for the creep deformation and damage accumulation by fatigue. Throughout this investigation, we expect the mechanism of creep deformation in the TiAl alloy. New dislocations can be emitted from ${α_2}$ to γ interface during the creep deformation especially, after 0.4% crept strains. As a result of dislocation emitting, new ledge is formed from an original flat interface, so the morphology of ${α_2}$/γ interface is changed to have rough interface again while mostly the morphology of ${α_2}$ to γ interface is changed to flat interface with absorbing dislocations at early primary stage less than 0.4% crept strains. In addition, during creep deformation, ${α_2}$ phase is transformed to γ phase through the formation of the transition phase of $Ti_2Al$ phase, which acts as an intermediate phase. Like 0.05% crept strain, $Ti_2Al$ diffraction pattern is detected at the range of 0.4% crept strains. That is, transition phase is detected not only the beginning of primary stage but the mid-primary stage. Considering this result, $Ti_2Al$ phase can be observed throughout all strain ranges during the creep deformation. So, finally using atomic configuration models in 2 and 3 dimensional with emitting edge dislocations by ${α_2}$ to γ phase transformation and schematic diagram to show changing morphology with ${α_2}$ to $Ti_2Al$ to phase transformation are suggested. And, the side of Chinese, they gain...