Internal strain evolution during heating of Ti-6Al-4V/SCS-6 composite

Abstract

The characteristics of the residual stresses and their effects on the properties in continuous SiC fiber reinforced Ti-6Al-4V matrix composites (TMCs) have been extensively studied. However, to date, few experimental studies (e.g. Ti-14Al-21Nb/SCS-6) have characterized the thermal residual strain in TMCs at elevated temperatures. Therefore, the authors investigated the evolution of the thermal residual strain during heating of Ti-6Al-4V/35vol% SiC composite. In this study the authors used in situ high temperature neutron diffraction to measure strains: (1) in the matrix ({alpha} and {beta} phases) and in the fiber, (2) for several lattice reflections in each phase and (3) from both axial and the transverse directions. One distinguishing feature is the wide temperature range (from room temperature up to 1,170K) over which the study was performed. Although the proposed application temperature is typically less than 800K, TMCs are subject to higher temperatures during fabrication and may experience high temperature excursions while in service. Therefore, the authors extended the study to the high temperature regime where the matrix starts to undergo a phase transformation between {alpha}{minus} and {beta}{minus}Ti. Measurements from this regime (800{approximately}1,170K) provide insights on; (1) the inelastic relaxation of the residual strains through matrix yielding and creep, (2) the effectmore » of the phase transformation on the residual strains and (3) the effect of the presence of SiC on the matrix phase evolution.« less