Flow Stresses and Recrystallization Behaviors in Mo-La and TZM up to 1700 °C

Plastic flow and microstructure evolution are investigated at elevated temperatures in three Mo alloys, two containing La (Mo-0.6La and Mo-1.0La, by wt %) and one TZM alloy. Data are presented from static annealing experiments and tensile tests up to 1700 °C under constant true-strain rates from 3×10-5 to 10-3 s-1. TZM is the most used refractory alloy, but strengthening from its Ti and Zr additions is greatly diminished above 1500 °C. Strengthening from La in the Mo-La alloys is retained beyond 1500 °C. Stable, fine dispersoids pin dislocation structures, suppressing recrystallization and leading to small subgrain sizes during plastic flow. The La2O3 dispersoids in Mo-La alloys are very stable and produce higher flow stresses and recrystallization temperatures than observed in TZM. These results recommend the use of Mo-La alloys instead of TZM at temperatures beyond 1400 °C when strength and resistance to recrystallization are desired.