|About this Abstract
||2017 TMS Annual Meeting & Exhibition
||Solid State Precipitation
||Formation of Complex Intermetallic Phases from Supersaturated Co Solid Solution in a Co-3.9Nb Alloy
||Toshiaki Horiuchi, Frank Stein, Kohei Abe, Shunsuke Taniguchi
|On-Site Speaker (Planned)
The present study aimed at an investigation of the precipitation behaviour of complex monoclinic intermetallic phase Nb<SUB>2</SUB>Co<SUB>7</SUB> from supersaturated Co solid solution in order to understand its formation process and morphology. The Co-3.9 at.%Nb alloy was solution heat treated at 1240<SUP>o</SUP>C resulting in a single-phase fcc-Co solid solution and was subsequently cooled to various temperatures for isothermal heat treatments.
A distinct Widmannstätten-like discontinuous precipitation microstructure was observed after isothermal heat treatment at 900<SUP>o</SUP>C, and the underlying Co matrix was found to have an hcp structure in contrast to the expectations from the equilibrium phase diagram. On the other hand, the Co matrix after direct cooling from 1240<SUP>o</SUP>C to room temperature has an fcc structure and contains finely dispersed L1<SUB>2</SUB> ordered regions with a significantly increased Nb content, what indicates the occurrence of a metastable intermediate phase during this solid state reaction in the Co-Nb system.
||Planned: Supplemental Proceedings volume