Evolution of the texture and microstructure in a nickel based superalloy during thermo-mechanical fatigue (TMF), using a modified integrated model and experimental results

Abstract

Microstructure & texture evolutions in Hastelloy X superalloy during thermo-mechanical fatigue (TMF) were investigated in this research. For this purpose TMF tests were performed in two different ways using linear elastic fracture mechanics (LEFM) and elastic plastic fracture mechanics (EPFM). These methods can produce small and large scale yielding in plane stress mode, respectively. On the base of data obtained in these tests a modified integrated model for prediction and simulation of texture evolution has been proposed. This model consists of a mechanical and a thermal part relating variations of stress and temperature occur during TMF tests. For the mechanical part of the model, a modified Taylor method based on strain partitioning in the grains orientations was used; and for the thermal part of the model, an integrated phased field and Monte Carlo models with harmonic Fourier approach for orientations distribution function (ODF) was used. The effects of Twin boundaries and dispersed secondary phase particles were also considered in the model. The validation tests show a good correlation between experimental results and the proposed model for texture development during TMF. To predict the initiation of unstable crack growth up to failure of the specimen during TMF, a new parameter in the form of reduced critical ODF value has also been introduced in this research.