A TEMPERATURE SENSITIVE CRYSTAL PLASTICITY MODEL FOR THE PREDICTION OF HIGH TEMPERATURE MECHANICAL BEHAVIOUR OF MULTI-PHASE TIAL ALLOY

Abstract

Intermetallic TiAl alloys for aero-engine turbine blade applications show good thermomechanical properties and excellent creep resistance. These alloys consist of multi-phase intermetallic constituents, mainly of Gamma-TiAl and Alpha2-Ti3Al intermetallic phases, which are arranged in the form of lamellar colonies and globular grains. Characterizing these alloys for room and high temperature behaviour is an ongoing issue that needs to be solved by using a synergic approach of experimental and numerical methods. In the recent progress of numerical approaches for the analysis of TiAl alloys, physically motivated crystal plasticity finite element models (CPFEM) have been successfully used to describe room temperature mechanical behaviour and to predict microstructure-property correlations [1]. Unfortunately, not much progress in numerical modelling that is able to characterize this alloy with respect to high temperature mechanical behaviour has been reported. To overcome this lacking, in the present work we propose a temperature sensitive CPFEM model based on a previous work of Kothari et. al [2]. As an alternative to Ref [2] our model describes the temperature-dependent slip rates of the crystallographic deformation modes as a function of history variable and physical material parameters. This model has been verified and validated for multi-phase TiAl lamellar microstructure using the experimental results of fully lamellar PST-TiAl single crystal as published in the literature [3,4]. For the computational analysis, unit cell based FE models are constructed with representative lamellar microstructure consisting of Gamma-TiAl and Alpha2-Ti3Al lamellar plates. Constitutive behaviour of the phases is described by the proposed crystal plasticity model. A multiscale local-global FE approach has been used to obtain macro-scale homogenized mechanical behaviour of the local microstructure. In this presentation, we will show that our model is able to predict high temperature deformation behaviour of TiAl alloy as observed in the PST-TiAl experiments quite satisfactory. The model successfully captures the temperature sensitive yield behaviour, anisotropic response due to morphological and crystallographic orientation, and rate sensitivity of the slip deformation. Further, we will demonstrate the activity of crystallographic slip systems to explain the local plasticity in both room and high temperature. References [1] M.R. Kabir, L. Chernova, M. Bartsch. Numerical investigation of room-temperature deformation behavior of a duplex type gammaTiAl alloy using a multi-scale modeling approach, Acta Mat 58 (2010) 5834–5847. [2]. M. Kothari, L. Anand. Elasto-viscoplastic constitutive equations for polycrystalline metals: application to tantalum, J.Mech. Phys. Solids. 46 (1998) 51–83. [3]. R. Lebensohn, H. Uhlenhut, C. Hartig, H. Mecking. Plastic flow of Gamma-TiAl-based polysynthetically twinned crystals: Micromechanical modeling and experimental validation, Acta Mat 46 (1998) 4701-4709. [4].H. Inui, M. Matsumuro, D.-H. Wu, M. Yamaguchi (1997) Temperature dependence of yield stress, deformation mode and deformation structure in single crystals of TiAl (Ti-56 at.% Al), Phil Mag A, 75:2, 395-423.