Investigation of Precipitation Behavior in Age-Hardenable Cu-Ti Alloys by an Extraction-Based Approach
- PDF / 2,283,309 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 2 Downloads / 142 Views
ON
AGE-HARDENABLE Cu-Ti alloys are important industrial materials that are widely used for electric connectors and lead frames owing to their excellent strengths and good electric conductivities. Figure 1 shows the Cu-rich portion of the phase diagram of a recently reported Cu-Ti binary system.[1] Cu-Ti alloys containing approximately from 3 to 6 mol pct Ti can be manufactured commercially by performing solution treatment of these alloys in the Cu solid-solution phase at temperatures >1123 K (>850 C) and then aging process at temperatures between 623 K to 773 K (350 C to 500 C). Optimal thermomechanical processing in combination with cold working and precipitation hardening can produce tensile strengths in excess of SATOSHI SEMBOSHI, Associate Professor, is with the Kansai Center, Institute for Materials Research, Tohoku University, Gakuencho 1-1, Naka-ku, Sakai, Osaka 599-8531, Japan, and also with the Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, Miyagi 980-8577, Japan. Contact e-mail: [email protected] SHIGEO SATO, Associate Professor, MIKIO ISHIKURO, Senior Engineer, and KAZUAKI WAGATSUMA, Professor, are with the Institute for Materials Research, Tohoku University. AKIHIRO IWASE and TAKAYUKI TAKASUGI, Professors, are with the Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, Osaka 599-8531, Japan. Manuscript submitted August 5, 2013. Article published online April 8, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
1200 MPa;[2,3] this value is competitive with the strengths of the widely used Cu-Be alloy series. Hence, many researchers are attempting to develop Cu-Ti systems that exhibit high strengths and electric conductivities for use in practical applications.[4–11] The high strengths of Cu-Ti alloys can be attributed to their relatively complex precipitation behavior, which has been recognized to progress in the following sequence. In the initial stage of the aging process, the supersaturated solid solution of copper, which has a face-centered cubic (fcc) structure, begins to decompose spinodally into two disordered fcc phases, forming a Ti-depleted a region and a Ti-rich a¢ region.[12–17] The disordered a¢ region then becomes ordered, and a fine needle-shaped, metastable, and coherent precipitate, which is denoted as b¢-Cu4Ti and has a tetragonal structure (prototype, Ni4Mo; space group: I4/m), forms continuously in the matrix phase.[12,14–18] During prolonged aging, coarse cellular components composed of the stable intermetallic phase and the terminal copper solid solution nucleate and grow discontinuously in the grain boundaries, consuming the finely dispersed b¢-Cu4Ti particles.[13,14,17,19–21] The stable phase has been generally reported to be b-Cu4Ti with an ordered orthorhombic structure (prototype, Au4Zr; space group; Pnma); however, its precise structure and composition are yet to be determined.[17,19–23] The development and natures of these precipitates are of importance since their microstructures have a
Data Loading...
