Elastic and anelastic behaviour of Ti6Al4V-SiCf composites produced by HIP and RDB

The Ti6Al4V-SiCf composite is a promising material for applications in aeronautical engines including turbine components. Sheets of Ti6Al4V-SiCf have been produced by two different routes: Hot Isostatic Pressing (HIP) and Roll Diffusion Bonding (RDB), a new process developed at C.S.M. This work reports the elastic and anelastic characterization of the materials carried out by internal friction (IF) and dynamic modulus experiments. IF spectra of HIP and RDB composites are similar. They exhibit a relaxation peak superimposed to an exponentially increasing background. The peak is due to C-Al and C-V pairs re-orientation in the  phase  matrix around the fibres. The background, is higher for the RDB composite owing to its higher dislocation density and smaller grain size. Long-term isothermal tests performed at different temperatures evidenced a progressive increase of the dynamic modulus E and decrease of the damping factor Q-1: higher the temperature greater the variation. According to the Granato-Lücke dislocation string model the phenomenon has been explained by considering the interstitial atoms diffusion to dislocations which progressively reduces the mean distance between pinning points.