TaC Precipitation Kinetics During Cooling of Co−Re-Based Alloys

Abstract

Cobalt−rhenium (Co−Re) alloys are developed for high-temperature applications at ≈1200 °C and are strengthened by dispersion of nanosized tantalum carbide (TaC) precipitates. Herein, the precipitation behavior during cooling from supersolution depending on the cooling rate and the addition of chromium is presented. The phase composition (matrix phases and TaC) is analyzed from the wide-angle neutron diffraction patterns measured in situ during temperature cycling. The precipitation of nanosized TaC particles is measured by in situ and ex situ neutron and X-ray small-angle scattering. The in situ measurements are used to extract the temperature-dependent volume fraction of the precipitates; the final size distribution after cooling is extracted from the ex situ measurements. A Kampmann−Wagner's numerical (KWN) model is adapted to isochronal cooling processes. The in situ measurements give the unique possibility to calibrate the model parameters, whereas the ex situ measurements are used to assess the model predictions.