Speaker
Steven Zinkle
(University of Tennessee)
Description
Although high room temperature strength (300-1000 MPa) and conductivity (200-360 W/m-K) have been achieved in Cu alloys, these alloys suffer significant thermal creep deformation at temperatures above 300-400oC. Deformation analysis indicates dislocation creep and grain boundary sliding are occurring. Design requirements for improved high-performance copper alloys are: 1) thermally stable microstructure up to high temperatures; 2) precipitates to inhibit creep deformation (grain boundary sliding) that are stable under neutron irradiation; and 3) sufficient sink strength to enable suitable radiation resistance. Creep resistance can be improved by using relatively large particles along grain boundaries to inhibit grain boundary movement, along with a high density of fine-scale matrix precipitates to suppress dislocation motion. The fine-scale matrix particles also provide beneficial radiation resistance. For high creep strength, high thermal conductivity and radiation resistance, the optimized matrix precipitates should have a volume concentration near f~1-5% with an average particle diameter near 10 nm. The matrix and grain boundary particles must be resistant to thermal and radiation-enhanced coarsening during extended times (>1 year) at operating temperatures. These particles should also be thermally stable during short-term exposure to joining-relevant temperatures (brazing, HIP, etc.).
Computational thermodynamic calculations of Cu-Cr-Zr-based quarternary alloys have identified several promising compositions using conventional metallurgy processing to produce a bimodal distribution of large grain boundary particles (Cu5Zr and laves phase) and a high density of matrix precipitate particles (e.g. Cr precipitates) that can be aged to provide good matrix strengthening up to 400-500oC. Small research heats of these newly designed high conductivity creep-resistant Cu alloys have been fabricated. Microstructural characterization is being performed on the as-fabricated alloys and after several heat treatments to examine the overall distribution and thermal stability of the precipitates. The results of elevated temperature tensile and thermal creep tests to quantify the mechanical properties will be summarized.
Co-authors
Lance L. Snead
(Massachusetts Institute of Technology, NW-12, Rm 212, Cambridge, MA 02139, United States)
Steven Zinkle
(University of Tennessee, Knoxville, TN, United States;Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, United States)
Ying Yang
(Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, United States)
