Investigation of Precipitates in Two Carbon-Containing Columbium-Base Alloys
AIR FORCE MATERIALS LAB WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
Pagination or Media Count:
The precipitates in the commercial columbium alloys D-31 and D-43 were investigated after various heat treatments. The titanium-rich and zirconium-rich monocarbides are the only stable precipitate phases in alloys D-31 and D-43, respectively. The temperatures for complete solid solution are 1600 deg C for alloy D-31 and 1700 deg C for alloy D-43 corresponding to a carbon content of about 0.09 wt.-. Non-equilibrium columbium carbides precipitate even during quenching from solid solution, so that no appreciable carbon supersaturation can be achieved in columbium alloys. During aging, the stable monocarbides form at the expense of the non-equilibrium columbium carbides but not from solid solution. Therefore, age-hardening caused by stable MC-phase precipitation does not occur. The effect of oxygen on carbide precipitates was investigated by increasing the oxygen concentration of the alloys on purpose. Oxygen behaved differently in both alloys with respect to precipitate phases. A columbium carbide phase with unknown lattice structure but a composition corresponding approximately to Cb3C2 was found in both alloys after suitable heat treatments.