Effect of Composition on the Strength and Electrical Conductivity of Cu-Ti Binary Alloy Wires Fabricated by Aging and In
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INTRODUCTION
INDUSTRIAL age-hardenable Cu-Ti alloys, which usually contain 3 to 5 at. pct Ti, are attractive for use in advanced electrical devices, such as conductive lead wires and suspension guide springs; their strength, stiffness, and deformability are comparable to those of widely used Cu-Be alloys (containing 10 to 12 at. pct Be), although they have lower electrical conductivity.[1–7] Due to the current trend of downsizing and streamlining electrical devices, further enhancement of the mechanical and electrical properties of Cu-Ti alloys is required and numerous studies have been undertaken in this area.[8–18]
SATOSHI SEMBOSHI and NAOYA MASAHASHI are with the Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, Miyagi 980-8577, Japan and also with the Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, Osaka 599-8531, Japan. Contact e-mail: [email protected] YASUYUKI KANENO and TAKAYUKI TAKASUGI are with the Department of Materials Science, Osaka Prefecture University. SUENG ZEON HAN is with the Korea Institute of Materials Science, 797 Changwondaero, Seongsan-gu, Changwon, Gyeongnam, 51508, Republic of Korea. Manuscript submitted August 1, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
We recently reported that Cu-3.6 at. pct Ti alloy wires drawn from over-aged alloy sticks yielded an excellent combination of strength and electrical conductivity, superior to that of conventional wires drawn from peak-aged alloy sticks.[19] This enhancement of strength during drawing is thought to have originated from the microstructure of the over-aged parent alloy, which was dominated by coarse cellular components laminating the plates of a terminal Cu solid solution and a stable b-Cu4Ti intermetallic compound, which precipitated discontinuously by grain boundary reactions.[5,20–23] During drawing of the over-aged alloy sticks, all lamellae changed into fine fibers, resulting in significant strengthening. It is notable that the strengthening behavior and microstructural evolution during drawing the Cu-3.6 at. pct Ti alloy were similar to those of pearlitic steel wires with eutectoid or hypereutectoid compositions in the Fe-C system [24–29] and in-situ composite wires of Cu-Ag,[30,31] Cu-Fe,[32] and Cu-Cr[33] alloys. In addition, the electrical conductivity of overaged alloy sticks before drawing was much higher than that of peak-aged alloy sticks due to depletion of solute Ti in the Cu matrix, which was accompanied by precipitation of Ti-enriched stable b-Cu4Ti precipitates.[34–36] The electrical conductivity of over-aged and drawn alloy wires is always higher than that of
conventional peak-aged and drawn wires. Eventually, it was demonstrated that over-aged and intensely drawn Cu-3.6 at. pct alloy wires had a tensile strength of 1640 MPa and an electrical conductivity of > 20 pct IACS, which was much greater than that of 1440 MPa and 8 pct IACS for the same alloy composition fabricated by conventional peak-aging and intense drawing.[19] T
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