Coarsening Behavior of Co Precipitates in Cu-Co Alloys

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 39; no. 4; pp. 725 - 732
• Main Authors: Watanabe, D., Watanabe, C., Monzen, R.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.04.2008; Springer; Springer Nature B.V
• Subjects: Alloys; Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Equilibrium; Exact sciences and technology; Materials Science; Metallic Materials; Metallurgy; Metals. Metallurgy; Nanotechnology; Solid solutions; Structural Materials; Surfaces and Interfaces; Thin Films; Shape Transition; Electrical Resistivity Measurement; Elastic Strain Energy; Mixed Stage; Interface Energy; Precipitation; Precipitate; Microstructure; Grain coarsening
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-008-9472-y

The coarsening of Co precipitates in Cu alloys containing 1, 2, and 4 wt pct Co during aging at 873 to 973 K has been examined by transmission electron microscopy (TEM) and electrical resistivity. The precipitate shape transitions from a sphere to a {001}-faceted cuboid and from the cuboid to a {111}-faceted octahedron cause no change in the coarsening rate of Co precipitates. Application of the Lifshitz–Slyozov–Wagner (LSW) theory has enabled independent calculation of the Cu/Co interface energy, γ , and volume diffusion coefficient, D , of Co in Cu during the coarsening of precipitates. The value of γ is estimated as 0.15 J m −2 using data on coarsening alone. The pre-exponential factor and activation energy for diffusion of Co in Cu, experimentally corrected for the precipitate volume fraction, are determined as 1.2 × 10 −5  m 2  s −1 and 208 kJ mol −1 , which are in agreement with those for diffusion of Co in Cu obtained from tracer diffusion measurements. An analysis using the generalized Gibbs–Thomson equation has shown that the estimates of γ are 0.17, 0.18, and 0.11 J m −2 for the sphere, {001} and {111} interfaces. A free energy analysis for coarsening accounts for the lack of change in coarsening rate by the shape transitions.