The effect of carbon on the loss of room-temperature damping capacity in copper-manganese alloys
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I.
INTRODUCTION
CU-MN alloys exhibit a loss of damping capacity when stored at room temperature[1–5] and it has been proposed that the room-temperature aging is associated with the pinning of antiferromagnetic domain boundaries by impurity atoms.[6] A similar time-dependent decrease in the damping capacity has also been observed in ferromagnetic materials[7,8,9] and antiferromagnetic chromium[10] and has been explained on the basis of directional ordering of interstitial atoms that oppose the motion of domain walls. This phenomenon has been referred to as the ‘‘magnetoelastic after-effect’’ and is a mechanical equivalent of the magnetic after-effect in permeability.[7] A detailed theory of the interaction of point defects with magnetic domain walls in ferromagnetic materials is given by Rathenau[11] and Klein.[12] In a previous study,[13] it was found that the addition of 0.1 wt pct Er to an INCRAMUTE* alloy reduced the loss *INCRAMUTE is a trademark of International Copper Research Association, Inc., New York, NY.
in damping capacity on storage at room temperature. Preliminary analytical transmission electron microscopy (TEM) of the Er-modified alloy revealed a Mn-rich second phase containing silicon and erbium. Based on these studies, Ross and Van Aken[13] concluded the loss in damping capacity of INCRAMUTE was a strain-aging phenomenon, with the tetragonal Mn-rich regions acting as solute traps and the beneficial effect of erbium was to remove (‘‘getter’’) impurity atoms from the solid solution. However, these conclusions were based on a limited period of storage at room temperature; also, the exact nature of the impurities was not
SHASHI LADDHA, Materials Engineer, is with Varity/Kelsey-Hayes, Ann Arbor, MI 48104. DAVID C. VAN AKEN, Associate Professor, and HUH-TSWEN LIN, Graduate Student, are with the Department of Metallurgical Engineering, University of Missouri–Rolla, Rolla, MO 65401-0249. Manuscript submitted August 7, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS A
identified. This report presents a more detailed investigation of the room-temperature aging characteristics of an Ermodified INCRAMUTE alloy and the same alloy intentionally doped with excess carbon. II.
EXPERIMENTAL PROCEDURE
The INCRAMUTE alloy used in this study was produced at Olin Brass Co. (New Haven, CT) by induction melting copper and manganese under an argon atmosphere. Based on the study by Ross and Van Aken,[13] 0.1 wt pct erbium was added to the initial charge itself. Chemical analysis of the ingot showed that half of the added Er was lost to the slag and Table I shows the final composition obtained. The alloy was supplied in the form of a plate with a nominal thickness of 8 mm. It was hot-rolled at 800 7C to a thickness of 3 mm, homogenized at 820 7C for 7 days, and air cooled. Damping specimens were cut perpendicular to the rolling direction and machined to a thickness of 1.3 mm. A Cameca MBX (Cameca Instruments, Inc. Stamford, CT) electron microprobe analyzer was used to identify the chemical nature of various inclusions
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