TZM vs. Mo-La: Which Molybdenum Alloy Is Better?

In high-temperature engineering, few materials can match the performance of molybdenum-based alloys. Among these, TZM (Titanium-Zirconium-Molybdenum) and Mo-La (Lanthanum-doped Molybdenum) are two of the most widely used for demanding applications involving extreme heat, structural loads, and corrosive environments. But which alloy is better? The answer depends heavily on the specific requirements. Let’s have a clear comparison.

Understanding the Basics

--What is TZM?

TZM is a molybdenum alloy strengthened by small additions of titanium, zirconium, and carbon. The typical composition includes:

• ~0.5% Titanium
• ~0.08% Zirconium
• ~0.02% Carbon
• Balance: Molybdenum

These additives form stable carbides (TiC and ZrC) during processing, which are finely dispersed within the matrix and provide excellent high-temperature strength and creep resistance.

--What is Mo-La?

Mo-La is a molybdenum alloy doped with lanthanum oxide (La₂O₃), typically in amounts between 0.3% and 1.2% by weight. Unlike the precipitation-hardened TZM, Mo-La is a dispersion-strengthened alloy. Fine La₂O₃ particles inhibit grain growth, improving ductility and high-temperature stability, especially under cyclic thermal conditions.

Comparative Properties: TZM vs. Mo-La Alloy

To determine which alloy is better, let’s examine how TZM and Mo-La perform across key engineering metrics:

1. High-Temperature Strength and Creep Resistance

TZM clearly excels in terms of high-temperature strength and creep resistance. The presence of fine carbides strengthens the alloy and resists deformation under load at temperatures up to 1400–1600°C. This makes TZM ideal for static structural components in furnaces, aerospace, and die-casting environments.

Mo-La, while still strong, doesn't match TZM in load-bearing or long-duration high-temperature strength. However, its ability to retain form at high temperatures without grain growth gives it superior thermal cycling behavior.

Sum: TZM for strength; Mo-La for thermal stability under cycling.

2. Recrystallization Temperature

Recrystallization temperature indicates how well a material maintains its microstructure at elevated temperatures.

Mo-La has a slightly higher recrystallization temperature (~1500–1600°C), meaning it resists grain coarsening better during prolonged thermal exposure. This is particularly advantageous in applications where parts undergo repeated heating and cooling.

Winner: Mo-La (slightly)

3. Ductility and Formability

While TZM is strong, it is more brittle and less forgiving in forming operations, especially at room temperature. It is also more prone to cracking under impact or during cold working.

Mo-La is significantly more ductile, especially at elevated temperatures. It can be rolled, forged, and formed into complex shapes with less risk of cracking. This makes it better suited for thin-walled components and fine filaments.

Winner: Mo-La

4. Weldability and Fabrication

Mo-La is easier to weld and fabricate due to its higher ductility and reduced grain boundary embrittlement. TZM can be welded, but care must be taken to avoid cracking, and pre- and post-weld heat treatments are often necessary.

5. Thermal Shock Resistance

In environments with rapid temperature fluctuations (e.g., vacuum furnaces, electron emitters), Mo-La performs better due to its higher ductility and resistance to cracking under thermal stress.

6. Oxidation Resistance

Both TZM and Mo-La suffer from poor oxidation resistance above 400°C in air and must be used in vacuum or inert atmospheres. Surface coatings or protective environments are required for use in oxidizing conditions.

Application Suitability

TZM Alloy Is Ideal For:

• Hot tooling in die casting and extrusion
• Furnace components and heat shields
• Aerospace parts like rocket nozzles and combustion liners
• Nuclear structural components

Mo-La Alloy Is Ideal For:

• Vacuum furnace hardware
• X-ray tubes and thermionic emitters
• Ion thruster components
• Thin sheets and fine wires in electronics
• High-temperature, thermally cycled environments

Cost and Availability

Both alloys are commercially available and used globally, but Mo-La tends to be slightly more affordable and easier to process due to its simpler fabrication requirements. TZM, with its complex carbide strengthening, may incur higher production and machining costs.

Which Alloy Is Better?

There is no universal winner—“better” depends on the design priorities:

Table 1 TZM vs. Mo-La: Which Molybdenum Alloy Is Better

Table 2 TZM vs. Mo-La: Property Data Comparison

For more information and tech support, please check Advanced Refractory Metals (ARM).

Conclusion

If your application demands maximum strength under static high temperatures, TZM is your best choice. Its carbide-reinforced structure ensures long-term durability in aggressive thermal environments.

However, if your design calls for good ductility, weldability, and thermal shock resistance, especially in applications involving thermal cycling or complex forming, Mo-La provides better overall performance.