On the Application of Magnetomechanical Models to Explain Damping in an Antiferromagnetic Copper-manganese Alloy

The Smith-Birchak model for magnetoelastic damping was successfully applied to model the damping observed in an antiferromagnetic Cu-48Mn-1.5Al (wt pct) alloy. Antiferromagnetic domains were developed by solution treatment at 820 ‡C and subsequent aging at 400 ‡C for 4, 10, and 16 hours. Damping capacity and dynamic elastic modulus were measured as a function of strain amplitude and temperature. A maximum in the strain-amplitude-dependent damping was obtained for the 4-hour-aged sample for which a magnetostriction constant, λ, equal to 4.65 × 10 -4, was derived. An exact fit for the Smith-Birchak model was obtained at low strains, whereas the model predicted lower damping than was observed for strains greater than 1.1 × 10 -3. This discrepancy was attributed to an additional damping mechanism at high strain amplitudes, i.e., dislocation damping. A magnetostriction constant equal to 3.23 × 10 -4 was also calculated based upon the Néel temperature and the observed microstructure. © 1995 The Minerals, Metals & Material Society

The Effect of Carbon on the Loss of Room-temperature Damping Capacity in Copper-manganese Alloys

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 °C 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 ± 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 °C for 4 hours, was reduced to one-third of its initial damping capacity