The damping capacity of the shape memory alloy Cu–20.4Al–8.7Mn(at.%) at room temperature is investigated by an internal friction technique.Results indicate that the alloy exhibits higher damping capacity in the Martensitic condition than that in the austenitic condition due to the latter having lower intrinsic damping capacity and pinning effect coming from the precipitate particles.The maximum damping capacity is obtained in the coexistence condition of Martensite and austenite.The condition can be achieved when processing an isothermal ageing for the as-cast sample at temperatures of 100°C–150°C.Three possible mechanisms are considered to account for the maximum damping capacity.They are listed as much increased interfaces between twin boundaries,owing to the thinning of martensitic plates,martensitic transformation induced by the applied stress during internal friction measurements,phase transformation itself based on the coexistence of martensitic and austenitic phases with a macroscopic amount.However,the contribution of the first mechanism is predominant.
