Cyclic Strain Amplitude and Heat Treatment Effects on the High Damping Behavior of INCRAMUTE Alloy under Random Vibration Loading in the 50-1000 Hz Frequency Range

The strain dependence of damping in the alloy INCRAMUTE (58 copper, 40 manganese, 2 aluminum) aged at 400 C for various times, was determined using a modified version of the resonant dwell technique. Cantilever beam specimens were vibrated at their first three resonant modes (50-1000 Hz) at room temperature. The highest specific damping capacity (SDC), 68%, was achieved with an average peak strain of 0.00227 in mode 1 at a resonant frequency of 49.2 Hz for the 16-hour aging condition. The INCRAMUTE alloy exhibited variations of Young's modulus, lattice parameter, hardness, tensile hysteresis, and SDC with aging, which typical of Cu-Mn binary alloys with greater than 50% Mn. However, no FCT transformation or microtwin banding was observed in the aged specimens under zero stress conditions, as verified by transmission electron microscopy (TEMO, X-ray diffraction (XRD) and optical microscopy. The characteristic microstructure observed at the TEM level was a mottled or a tweed pattern in both the as-quenched and the aged specimens. Neither (200) nor (220) peak splitting corresponding to tetragonality was detected from XRD traces of aged samples. Based on the results, an interpretation of the microstructural damping characteristics of INCRAMUTE is presented.