HIGH-TEMPERATURE DAMPING IN DISPERSION-STRENGTHENED ALUMINUM-ALLOYS

Dispersion-strengthened alloys are promising candidates for applicatio n at high homologous temperatures. Mechanical loss measurements were c arried out on a dispersion-strengthened Al alloy with about 10 vol.% o f incoherent Al2O3 and Al4C3 particles. We observe a loss maximum at a bout 590 K for a frequency f=1 Hz which exhibits an exceptionally high activation enthalpy (H=2.2 eV) compared with that for self-diffusion (H-D=1.48 eV). The peak height increases with oscillation frequency. A dditionally, transmission electron microscopy studies were carried out for a correlation of the loss spectrum with the microstructure. To ex plain the experimental results, a relaxation model is proposed which c onsiders jog nucleation on climbing edge dislocations as the time-limi ting mechanism.