EFFECT OF 3RD ELEMENTS ON DAMPING CAPACITY OF MN-20CU ALLOY

An attempt has been made to develop the manganese-based and workable damping alloys containing 20 at% copper, together with 2 or 5 at% additive elements, such as nickel, iron, cobalt, vanadium, chromium, zirconium, titanium, aluminum, zinc and tin. Nickel was the most effective element for increasing damping capacity of a Mn-20Cu alloy. The second ranking elements were followed by iron, cobalt, aluminium, and zinc. A group of additive elements consisting of vanadium, zirconium, titanium, and chromium, showed some effect with the addition of 2%, but not with that of 5%. Tin was ineffective even with addition of 2% and 5%. We have discussed a correlation between additive elements and the effectiveness, on the basis of the following two viewpoints: (1) the solubility of additive elements in manganese or copper and (2) the possibility of the precipitation or the primary crystallization during solidification. We found that the damping capacity may increase proportionaly with the increased solubility of additive elements in manganese or copper. This effect of nickel addition may be related to formation of a complete solid solution for manganese and copper. Little effectiveness of the additive elements, such as chromium, titanium, zirconium, and tin, may be associated with little solubility for parent phase and with the possibility of the precipitation and the primary crystallization. The elements, showing a large solubility for one side and little for other side, such as iron, vanadium, cobalt, aluminum, and zinc, may yield the medium effect, depending on the additive quantity. We concluded that in manganese-based alloys the improvement of the damping characteristics may be obtained by the additive elements that have a large solubility without forming second phases during heat treatment or solidification. An alloy, Mn-20Cu-5Ni, showed a value of 0.28 in logarithmic decrement (a value of 43% in specific damping capacity), 370 MPa in tensile strength, and 27% elongation.