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TZM Alloy Thermodynamic Analysis

In TZM alloy, strengthening elements titanium (Ti), zirconium (Zr) and carbon (C) will produce second phase strengthening and solid solution strengthening in the alloy. TZM alloy during sintering, the oxygen (O) in molybdenum powder will react with C to generate CO, and in this process C acts as a deoxidizer. In addition, C works together H₂ protective gas to reduce oxygen content of the alloy.

Using thermodynamic calculation found, TZM alloy during the sintering process, Ti, Zr and O reaction’s Gibbs energy is much lower than the binding energy of C and O, so Ti and Zr priority react with O to form TiO₂ and ZrO₂, reducing C’s deoxidize effect greatly. Further, since the strengthening elements Ti and Zr reacts with oxygen or nitrogen adsorbed in the compacted material, which also reduces the deoxygenation of C, so that the C content in TZM alloy is difficult to control.

After thermodynamic analysis, Ti, Zr, Mo reacts with C to generate TiC, ZrC, Mo2C decomposed at elevated temperatures, dissolved into the molybdenum substrate. If the alloy O content is higher, there may occur the following reaction: Ti (Zr) C + [O] → Ti (Zr) _nO_2n-1 + CO₂ or Mo₂C + [O] → Mo + CO₂. And this is the reason TZM alloy after high temperature treatment the second phases are all Ti and Zr oxides.

If TZM alloy oxygen content is too high, the oxygen will react with Ti, Zr to form the corresponding oxide, so a large number of second phase produce at grain boundaries and make mechanical properties of the alloy deterioration. Thereby controlling the oxygen content in TZM alloy has an important influence on the mechanical properties of the material guarantee. During the alloy production, to reduce the oxygen content of the TZM alloy, the most effective measure is to reduce the oxygen content of the raw material and production process oxygen content. So the manufacturers can use hypoxia molybdenum powder and vacuum mixing powder measure.

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