TZM Alloy Deformation Resistance Affected By Deformation Rate

TZM alloy deformation resistance is affected by deformation temperature, deformation degree and deformation rate, and the impact of deformation temperature on deformation resistance are more obvious. When deformation rate is certain, deformation resistance increases with deformation temperature rises. The following mainly analyzes the influence of deformation rate on the deformation resistance of the alloy.

When the deformation temperature is certain, TZM alloy deformation resistance increases with deformation rate increases. As shown below, when the strain rate is small, the slope of the curve is large, showing that the deformation resistance increasing faster in this time, and then with strain rate increasing the deformation resistance is tend to flat. In the initial stage, with deformation rate increasing, the deformation resistance increases faster, and the dislocation density increases as well. Because the deformation rate is not great, the strain stress caused by dislocations strain has certain time to pass to other grain. When the dislocation density increase to a certain extent, Zr, Ti and other trace elements in TZM alloy will cause solid solution strengthening, increasing the lattice distortion, resulting in deformation strengthening, increasing work hardening, so at the initial stages the deformation resistance increased rapidly.

In initial stage, the deformation resistance increases rapidly, but with deformation rate further increases the deformation resistance increases stabilized. Because with deformation rate increasing, unit time deformation amount increases and dislocations tangles in motion, so that the energy of plastic deformation has no chance to pass to other grains, resulting in strain energy increase and deformation temperature increase, so the deformation metal to some extent occurs  dynamic recovery and dynamic recrystallization. Dynamic recovery and dynamic recrystallization softening effect can offset partially work hardening, so that the deformation resistance tend to stabilized with deformation rate further increase.

In general, the deformation resistance increases with deformation degree increases. When deformation rate is certain, the deformation resistance decreases with deformation temperature increases. When deformation temperature is certain, deformation resistance increases with strain rate increases.

TZM Alloy Deformation Resistance Affected By Deformation Temperature

TZM alloy has good mechanical property and high temperature performance, in industry, metallurgical industry, aerospace and other fields has been widely used. But TZM alloy has high deformation temperature, high deformation resistance, and poor low temperature ductility, so during rolling process it is difficult, limiting its application and development in the relevant field. In the rolling process, the deformation resistance is an important criterion to determine the rolling process, and different rolling process the deformation resistance and morphology of alloy is different, so understanding the effects of different rolling parameters on deformation resistance can optimize rolling process, improve the mechanical properties and the application of TZM alloys.

Using powder metallurgy m to produce TZM alloy billet obtained by mixing, pressing and sintering. Putting the billets at -1500 thermal simulator in a vacuum state process rolling thermal simulation test of the alloy billet. The deformation was 50% and the experimental temperature was 1150 ℃, 1200 ℃, 1250 ℃ and 1300 ℃. Besides, the deformation rate is 1s-1, 3s-1 and 5s-1. TZM alloy deformation resistance is related to deformation temperature and deformation rate, and the following will main analyze the relationship between the deformation resistance and deformation temperature.

Under certain deformation rate, deformation resistance increase with the rolling deformation temperature rises. This is because when the deformation temperature increases, metal atoms’ kinetic energy in the alloy increases as well, which decreased the dislocation resistance. In the other hand, space, interstitial atoms and other disadvantages defects also more active, resulting in dynamic softening to reduce flow stress. What’s more, when the deformation temperature increases, there will have a new sliding system which produces on the internal original sliding systems of alloy, to enhance the interoperability of the alloy, reducing the dislocation density, improving alloy’s plastic deformation.

TZM Alloy and Molybdenum Performance Comparison

Observing sintered TZM alloy and molybdenum microstructure found, TZM alloy sintered grains is about 30um, while pure molybdenum sintered grains is about 40um. This is because Ti and Zr and other the trace element in TZM alloy are conducive to refine the grain, so TZM alloy grains compare to molybdenum’s is smaller.

TZM alloy room temperature property is significantly higher than molybdenum’s, but not as good as its elongation. At 1200 ℃ high temperature, the tensile strength of molybdenum has dropped significantly, while the tensile strength of the TZM alloy remained at a high level. This is mainly because TZM alloy second phase impede dislocation movement, resulting in a significant second phase strengthening and solid solution strengthening, improved strength of the alloy. Meanwhile, dispersed second phase having pinning effect on dislocation will reduce the deformation resistance of the alloy, resulting in ductility property significantly reduced. The molybdenum at 1200 ℃ high temperature occurs recrystallization, so the strength of it is not as good as TZM alloy, while plastic is better than TZM alloy.

Observing tensile fracture morphology of TZM alloy and molybdenum at room temperature and 1200℃ high temperatures found, at room temperature, TZM alloy fracture morphology is cleavage fracture, so the elongation is poor. At 1200 ℃ high temperature, TZM alloy fracture morphology has changed. There are has many dimples, and the fracture morphology is dimples-cleavage fracture, so the elongation get some improvement, higher than the room temperature elongation. Molybdenum high-temperature tensile fracture morphology shows ridge pattern humanoid, with a clear dimples, so it has good elongation.

TZM alloy starting recrystallization temperature is about 1350 ℃, the end recrystallization temperature is about 1700 ℃. Molybdenum starting recrystallization temperature is about 850 ℃, and the end recrystallization temperature is about 1250 ℃.

High Performance TZM Alloy Rod Production

TZM alloy rod can be used to produce the casting mold, rocket nozzle throat liner, nozzle, effuser and gas conduits and so on. High performance TZM alloy rod not only has long life, but also can produce high performance products, thus to development high-performance TZM alloy rod is conducive to expanding its application range.

TZM alloy rods usually produce by powder metallurgy method. Doped with 0.55% (wt) titanium hydride powder (TiH2), 0.12% (wt) zirconium hydride powder (ZrH2) and 0.05% (wt) carbon powder (C) into molybdenum powder, was placed in a V-type blender mixing tub for 24 hours, making powder well mixed. And the TiH2, ZrH2 and C powder’s purity is higher than 99.5%. Under the pressure of 196MPa pressed the mixed powder by isostatic pressing method and the material density is 7.2g/cm3. Through hydrogen the material sintered at induction heating sintered, and after sintering the blank density is more than 9.5g / cm3.

In TZM alloy related products, TZM alloy rod deformation processing is more difficult. If TZM alloy rod direct hot forge without extrusion, the alloy has low yield. Therefore, after sintered alloy rod should process hot extrusion to cogging and then forged. In the hot extrusion cogging and forging process, if you can control the heating temperature and the deformation quantity, the mechanical properties of alloy rods can be improved. However, due to the lack of technology, it is difficult to control the process parameters, so processing as this way will reduce the mechanical properties of the alloy. TZM alloy is kind of brittle material, during forging it is prone to cracking, and thus alloy rods should work with large deformation and quickly forged during forging. After extrusion cogging and forged molding TZM alloy rod has poor mechanical properties, but compared to other materials, TZM alloy can meet products’ performance requirement and has high yield.