Structural internal friction in CuAlNi crystals

Amplitude-dependent and amplitude-independent internal friction has been studied in martensite and during temperature induced martensitic transformation in CuAlNi single crystals after different heat treatments. The measurements of intrinsic damping were performed in ultrasonic and infrasonic frequency ranges. Low frequency measurements were combined with the direct observations of the stress-anelastic strain hysteretic loops. Observed regularities do not correspond to the breakaway model of amplitude-dependent internal friction both for quenched and aged samples. The conclusion is drawn, that during ageing in beta-phase the behaviour of the pinning obstacles changes from highly mobile at room temperature and forming atmospheres around the mobile defects, presumably dislocations, to rather immobile and homogeneously distributed in the bulk of the crystal. Amplitude dependent and amplitude independent internal friction components, measured at ultrasonic frequencies, exhibit different temperature dependences during direct martensitic transformation. A maximum of the non-linear anelasticity was observed near the M(s) temperature, implying a significant contribution of the premartensitic phenomena to the amplitude-dependent internal friction due to phase transition.