A variety of elemental additives, in particular titanium (Ti), zirconium (Zr), and carbon (C), significantly enhance the strength and performance characteristics of titanium, zirconium, molybdenum alloy (TZM) over pure molybdenum. These additives support the three principal strengthening mechanisms involved in TZM alloy processes: dispersion, solid solution, and deformation strengthening.
Additional additives that enhance TZM’s strength at both room and high temperatures include titanium carbide (TiC), zirconium carbide (ZiC), rhenium (Re), and lanthanum oxide (La2O3).
Zirconium and Titanium Carbides in Dispersion Strengthening
The addition of trace amounts of zirconium carbide (ZrC) or titanium carbide (TiC) to the TZM alloy enhances its density and strength at both room and high temperatures. The optimal room temperature strength of TZM is achieved when the weight percentage of both ZrC and TiC is maintained at 0.4%.
Within the molybdenum matrix, interactions between ZrC or TiC and oxygen lead to the formation of dispersed and second-phase particles, with two principal effects. First, the porosity of TZM is reduced, increasing its density and markedly improving the alloy’s high-temperature strength. Second, the dispersed and second-phase particles shift the fracture mode of TZM from a trans-granular/dimple fracture mode to a predominantly dimple type, further strengthening the alloy and enhancing its overall performance.
Molybdenum-Rhenium in Solid Solution Strengthening
Molybdenum-rhenium (MoRe) solid solution grains, well known for their high strength and dense structures, are crucial in maintaining TZM’s stability. Optimal amounts of MoRe additives absorb much of the energy generated when TZM undergoes bending and trans-granular fractures, enhancing the alloy’s strength. However, overly high levels of MoRe can lead to the accumulation of second-phase particles and gaseous pores along the TZM grain boundaries, reducing strength.
Lanthanum Oxide in Boosting Strengthening Effect
The refining effect of lanthanum oxide (La2O3) on TZM is evident in the size reduction and uniform distribution of particles within the TZM matrix. When a precise amount of La2O3 is dissolved into the particles and dispersed along their boundaries, the resulting TZM-La demonstrates increased strength and density compared to standard TZM.