Strengthening Mechanism of TZM Alloy

The strengthening mechanism of TZM alloy is divided into: solid solution strengthening, second phase strengthening and deformation strengthening.

1. Solid solution strengthening

Solid solution strengthening is caused by the solute atoms incorporated into the solid solution causing lattice distortion. The lattice distortion increases the resistance to dislocation motion, making slippage difficult, thereby increasing the strength and hardness of the alloy solid solution. This phenomenon of strengthening a metal by incorporating a certain solute element to form a solid solution is called solid solution strengthening. The solid solution strengthening of TZM is the addition of Ti, Zr and other alloying elements dissolved in the Mo matrix. Among them, the strengthening effect of Zr is the most obvious, followed by Hf. This is because the Mo lattice 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 at a temperature above 1000°C is very obvious, but it is not as good as deformation strengthening, but in reality, the amount of addition is not very large due to the limitation of solubility.

Second, the second phase of strengthening

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

3. Deformation strengthening

Deformation strengthening, that is, work hardening, is one of the four typical metal strengthening methods. It means that when the external force exceeds the yield strength during the entire deformation process of the metal, the external force must be continuously increased to continue the plastic deformation, so that the true stress-strain curve shows that the stress continues to rise. The 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 grains of the TZM alloy are elongated along the processing direction, and the dislocation density increases, and the grains are generated, which increases the strength of the alloy. The strength of the alloy after annealing can be significantly reduced. If the alloy is nitrided during annealing, nitrided particles are produced in the matrix after nitriding, and the hardness and tensile strength of the alloy can be further improved.