A Micro—Macro Structural Approach of the Cyclic Behaviour of a Two—Phase Alloy

Abstract

In the past, much work has been carried out on titanium two-phase ductile alloys under tensile loading [1–3], whereas the cyclic behaviour of these alloys has been less comprehensively studied [4, 5], More recently, in previous investigations [6, 7] our work has focussed on the cyclic behaviour of an α/β titanium alloy (Ti-6246) under proportional and non-proportional loading paths. In particular, the plastic behaviour of the α-phase (h.c.p.) has been studied in detail using transmission electronic microscopy (TEM) and correlated with the cyclic macroscopic behaviour of the alloy. Although the two phases have different elastoplastic behaviours, the internal inhomo-geneities of stress and strain which result from this difference have not yet been investigated. Also, the crystallographic α-texture is significant in our alloy and induces slip anisotropy. The internal stresses which result from this anisotropy have been previously discussed qualitatively [7], but the importance of this phenomenon is not available using TEM observations. The purpose of this work is to evaluate the effect of the different microstructure levels on the development of internal stresses under complex loadings. The bridge between the micro-macro gap was built up using two different approaches: a quantitative TEM method [7] and a micro-macro modelling. The micromechanical model is a deductive process which takes into account MET observations [6, 7] in each phase, as well as the macroscopic behaviour.