Recrystallization, Tensile Ductility, and Flow Stress of TZM and Mo-La Alloys at 1500 and 1700 Degrees C
Monica Martinez Henriquez, University of Texas at Austin
Molybdenum (Mo) is a refractory metal used in high temperature applications because of its strength at elevated temperatures and its high melting point. To increase the strength of Mo at elevated temperatures, dispersion strengthening mechanisms have been used to develop stronger alloys, such as Titanium-Zirconium-Molybdenum (TZM) and Lanthanated Molybdenum (Mo-La) alloys. TZM is the most used refractory metal alloy, and Mo-La alloys demonstrate a potential for even higher strengths at high temperatures. However, little is known about the mechanistic sources of strength in these Mo alloys at elevated temperatures. A primary reason for this gap in knowledge is a lack of mechanical test data for temperatures above 1400 °C. In this study, I present new data for the mechanical properties of TZM and Mo-La alloys at 1500 and 1700 °C. Static recrystallization behaviors, tensile ductilities, and flow stresses were measured for commercially-pure Mo, two Mo-La alloys (1.0% and 0.6% La, by weight), and two TZM alloys (one manufactured using powder metallurgy and the other using arc casting) at 1500 and 1700 °C under constant true-strain rates of 10-3, 10-4 and 3×10-5 s-1. Both La additions and Ti-Zr additions effectively suppress dynamic abnormal grain growth, which was only observed in unalloyed Mo. La additions inhibit recovery and recrystallization. Tensile ductility varied significantly among the alloyed materials but was generally lower than for unalloyed Mo. The flow stresses in the Mo-1.0La alloys were the highest at both test temperatures. Flow stresses in the Mo-0.6La material were comparable to those of the TZM alloys at 1500 °C but superior at 1700 °C.