How to Choose Sintering Methods for Titanium-Zirconium-Molybdenum (TZM) Alloy?

The earliest produced in the industry is titanium-zirconium-molybdenum (TZM) alloy, which is a molybdenum alloy containing 0.4%-0.55% titanium, 0.06%-0.12% zirconium and 0.01%-0.04% carbon. The total amount of alloying element does not exceed 1%. 

There are two main sintering methods for titanium-zirconium-molybdenum alloy: hydrogen protection sintering and vacuum sintering as following: 

1.Hydrogen protection sintering: the product is sintered under the protection of hydrogen. 

During the process, due to the reduction effect of hydrogen, the oxides in the molybdenum powder will be replaced by hydrogen, reducing the oxygen content in the material to below tens of ug/g. For molybdenum alloys with active elements such as titanium and zirconium, due to the high activity of alloying elements, they will react with impurity gases in hydrogen to form oxides, nitrides, hydrides, etc., resulting in high impurity content in TZM alloy. It seriously affected its mechanical properties. Therefore, vacuum sintering is more popular with most factories.

In the process, generally a slight excess of carbon element (relative to the predetermined composition) is added to deoxidize the metal oxide through the reduction of carbon element. Among them, there are two main types of deoxidation mechanisms: metal oxides in the carbon reduction system produce metal carbides and CO, and MoO2 undergo disproportionation reactions under vacuum and high temperature to produce metal Mo and MoO3 gases which are extracted.

In the disproportionation reaction of metal oxides and MoO2 in the carbon reduction system, the temperature at which the two reactions start is related to the partial pressure of the product gas in the furnace. As the partial pressure of the product in the furnace decreases, the reaction start temperature gradually decreases. Therefore, increasing the vacuum degree in the furnace and reducing the partial pressure of the product gas can lower the temperature at which the deoxygenation reaction proceeds, which is beneficial to the deoxygenation.

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What Are Strengthening Mechanisms of TZM Alloy

TZM is molybdenum’s prime alloy and is an alloy of titanium, zirconium and carbon. This alloy is the most popular materials among various kinds of molybdenum metal and molybdenum alloys. 

With better high temperature resistance, greater strength, it can be used as a mold for high-temperature heat processing of metals. In addition, to be applied in the hot runner system as nuzzle tip, it can maintain the plastic melting state and helps the formation of plastic products. 

For the strengthening mechanisms of TZM alloy, the types are as following: 

1. Solid solution strengthening

The solid solution strengthening of TZM is to add Ti, Zr and other alloying elements to dissolve in the Mo matrix. Among them, the strengthening effect of Zr is the most obvious, followed by Hf. This is because the base lattice of Mo is distorted. The larger the difference in the size of the solute and solvent atoms during solid solution, the better. The effect of solid solution strengthening is relatively stable above 1000 ℃, but it is not as good as deformation strengthening, but in practice, due to the limitation of solubility, the addition amount is not very large.

2. Second phase strengthening

When the second phase is uniformly distributed in the matrix phase with fine dispersed particles, it will have a significant strengthening effect, which is called the second phase strengthening. The strengthening of the second phase in TZM is due to the addition of Ti, Zr and C in Mo to form fine carbide particles. Their existence can effectively hinder the movement of dislocations and produce the strengthening of the second phase.

3. Deformation strengthening

TZM alloy is required to be below the recrystallization temperature, and the effect of deformation strengthening increases as the amount of deformation increases. In the process of deformation, the crystal grains of the alloy elongated along the processing direction, the crystal lattice is raised, the dislocation density increases, and the grains are produced, which increases the strength of the alloy. The strength of the annealed alloy can be significantly reduced. If the alloy is nitridated while annealing, nitriding points are generated in the matrix after nitriding, and the hardness and tensile strength of the alloy can be further improved.

If you have any inquiry of molybdenum alloy products, please feel free to contact us:

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