Martensitic Transformation in a Cast Co-Cr-Mo-C Alloy
Abstract
The face-centered-cubic (fcc) to hexagonal close-packed (hcp) martensitic transformation exhibited by an as-cast Co-Cr-Mo-C alloy was investigated in this work. The alloy was annealed at 1150 °C, water quenched, and then isothermally aged at 700 °C to 900 °C. Quantitative measurements of transformed hcp martensite (also known as ɛ-martensite) as a function of time and temperature were used in plotting C curves describing the transformation kinetics. Moreover, microstructural characterization indicated that the transformation exhibited two distinctive ɛ-martensite morphologies. In the neighborhood of coarse carbides, multiple nucleation events were linked to the formation of ɛ-martensite, while in the bulk of the dendrite matrix, the dominant morphology was as straight plates. Kinetic determinations of activation energies, Q, in either region indicated that in platelike ɛ-martensite, Q = 57.24 kcal/mol, but in “pearlite”-like morphologies, Q = 37.88 kcal/mol. Apparently, as the activation energy was reduced, multiple nucleation events were favored leading to the “pearlitic” appearance.
- Publication:
-
Metallurgical and Materials Transactions A
- Pub Date:
- January 2008
- DOI:
- 10.1007/s11661-007-9370-8
- Bibcode:
- 2008MMTA...39....8L