A high damping Cu-Mn alloy with a nominal composition of 48Cu-48Mn-1.5Al-0.27Si-0.072Sn-0.028C-0.05Er (all compositions in wt pct) was studied to determine the mechanism of the loss of damping capacity during room-temperature storage. In this study, it was found that an Er-modified alloy sample that was artificially aged for 16 hours at 400 ЊC was stable even after 68 weeks of room-temperature storage. However, a loss of damping capacity was exhibited in the same material when aged to produce an underaged or peakaged condition. The decrease in damping capacity was found to be thermally activated with at least three relaxation processes. Each of the three relaxation processes appear to be related to the diffusion of carbon within the Mn-rich regions and a single activation energy of 0.970 ‫ע‬ 0.05 eV was used to model these processes. Rapid loss of damping capacity was observed in the same alloy when doped with excess carbon. After 3 weeks of storage at room temperature, the damping of the carbon-doped material, artificially aged at 400 ЊC for 4 hours, was reduced to one-third of its initial damping capacity.

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This paper reviews the physical metallurgy and damping characteristics of copper-manganese (Cu-Mn) alloys. Many of the examples given in this paper are based upon the authors' experimental investigations of an alloy with nominal composition (composition in weight percent) of 48Cu-48Mn-1.5Al-0.27 Si-0.072Sn-0.028C-0.05Er. The results for this material were obtained in a bending mode, and the reported strain amplitudes represent the maximum surface strain imposed. Damping in these materials is very sensitive to heat treatment and carbon content. Recent work has shown that carbon in solid solution is detrimental to the damping capacity and results in a strain aging behavior and subsequent loss of damping capacity when stored at room temperature. Copper-manganese alloys can lose more than 50% of their damping capacity during room temperature storage. The role of erbium in the stabilization of the damping capacity is explained in the context of the physical metallurgy of the Cu-Mn system.