Crystal viscoplasticity based Simulation of Ti-Al alloy under high-temperature condition

Since 1970s, phases in the Ti-Al alloy system have been widely recognized as a possible basis for the development of novel lightweight alloys for high temperature structural applications. These alloys exhibit impressive material properties such as high strength, fracture toughness, corrosive resistance, low density and high melting temperature. Because of these properties, Titanium alloys are widely used in numerous structural applications, particularly in aerospace application such as low pressure turbine blades, high pressure compressor blades, vanes, casings and tiles etc. From available different titanium alloys, gamma-TiAl type (with FCC structure) and alpha2-TiAl ( with CPH structure) alloys show superior properties. At the moment, the alloys with the best overall mechanical performance are based on the intermetallic, gamma-TiAl phase strengthened by minor fractions of the hexagonal αlpha2-TiAl phase and hence it is one of the most popular alloys used in aerospace application.

With the constraint of cost and time, modeling of alloys becomes priority to study the material response in extreme conditions of high stress and temperature, particularly in creep. Thermomechanical fatigue life prediction is also an important part in the design of high temperature materials and requires a stress-strain analysis for accurate results. The modern methods for life prediction in structures need inelastic analyses, which lead to much progress made in the development of constitutive equations to represent the mechanical response of materials under various loading conditions at high temperatures.

In short, the inelastic behavior like yielding, hardening, creep, relaxation etc. of mentioned Ti-based alloy will be investigated in detail by using the crystal viscoplasticity model and compared with experimental results. Representative Volume Element (RVE) is to be used with periodic boundary condition since plane and symmetric boundary conditions can not give the possibility to use complex loading condition experienced in practical application. Specific parameter determination protocols are will be established for crystal viscoplasticity model implemented in ABAQUS through a user material subroutine. This research will focus on the development, numerical implementation and application of two distinct versions of viscoplasticity, classical crystal plasticity and dislocation-based continuum dislocation theory in the context of Ti-Al alloy, the size-dependent deformation and temperature dependence are also to be studied via direct numerical simulation.