High temperature damping behaviour of Ti6Al4V-SiCf composite

The Ti6Al4V–SiCf composite, reinforced by unidirectional SiC fibres (SCS-6), has been investigated by internal friction (IF) and dynamic modulus measurements in the temperature range 300–1173K. Experiments have been carried out by using a vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations in the frequency range from 600 to 1800 Hz. For comparison the monolithic Ti6Al4V alloy has been submitted to the same experiments. The IF spectrum of the composite exhibits a relaxation peak at about 870K superimposed to an exponentially increasing background. The peak, not present in the spectrum of matrix alloy, has activation energy H= 186 kJ mol−1 and relaxation time tau0 = 2.3×10−15 s. The peak has been explained by an interstitial-substitutional pair reorientation mechanism in the phase of Ti6Al4V matrix around the fibres.