Deformation Strengthening of Titanium Zirconium Molybdenum Alloy

Deformation strengthening for molybdenum and titanium zirconium molybdenum (TZM) alloy is an important enhancement means. The object of deformation strengthening is making alloy crystal lattice distortion, dislocation density increases, as well as produce secondary grains and so on, so that the alloy mechanical is changed, thereby changing its performance. Deformation strengthening has many ways, such as forging, extrusion, hot-rolled etc.. So when selecting deformation strengthening means should follow product different shape and requirements. After a series of research data found that TZM alloy after deformation strengthening not only improve strength and ductility, but also ductile - brittle transition degree reduces and the tensile strength significantly increased.

When produce TZM bars, the usual deformation strengthening method is hot extrusion. After extrusion, alloy along with extrusion axis direction and perpendicular extrusion direction performance will vary. Alloy along with extrusion axis direction show ductility and along with perpendicular extrusion direction showing brittleness.

Annealing Temperature Influence Titanium Zirconium Molybdenum Alloy Properties

Titanium zirconium molybdenum (TZM) alloy after deformation strengthening typically generate residue stress. In order to eliminate residue stress, while changing the properties of the alloy, are generally required to anneal.

After studies found that TZM alloy process vacuum annealing after extrusion after, in which the annealing temperature increased from 950℃ to 1050℃, the strength and the elongation of TZM alloy changed little, but when the annealing temperature increased from 1050℃ to 1600℃, TZM alloy significantly improved elongation, and tensile strength decreased.

In addition, as the annealing temperature increase, the hardness of the TZM alloy is lowered, especially when in 1400~1500 ℃. So we can see, with the annealing temperature increase the hardness of the alloy is lowered very obvious. Therefore, it is considered that grains group up with annealing temperature increases, but can quickly eliminate dislocation, lattice distortion and other defects, so that the ductility of the alloy increases, stretching decreased.

Annealing temperature also make titanium zirconium molybdenum alloy dislocation density changes, TZM alloy annealed at 1450 ℃ for 15 minutes, the dislocation density decreased from the original 3 × 1010cm-2 to 7 × 109cm-2, and the higher the annealing temperature, the shorter the time to reduce the dislocation density.

Titanium Zirconium Molybdenum Alloys Annealing Treatment

When produce the titanium zirconium molybdenum (TZM) alloys, the last step generally required extrusion, forging or pressing, so to improve shaping and processing performance. But TZM alloy after extrusion, forging or pressing will produce residual stress. In order to eliminate residual stress and change the brittleness of the alloy, therefore need to do some annealing treatment. Because the Ti, Zr and C in TZM alloy will cause carbide precipitation and Ti, Zr solid solution so that TZM alloy recrystallization temperature will improve, and the annealing temperature of TZM alloy is generally above 1150 ℃. On the other hand, select the annealing temperature annealing is crucial. Because the annealing temperature can affect not only impact the hardness, but also tensile properties of the alloy can be greater.

Annealing is generally happen in a vacuum or protection of hydrogen, but after some recent studies have found that nitrogen use as a protected gas during annealing, that is making nitriding alloy to alloy during annealing. TZM alloy after nitriding, the base body to produce titanium nitride particle and it can improve the hardness and tensile strength of the alloy.

Using Powder Metallurgy Method Produce Titanium Zirconium Molybdenum Alloy

Using powder metallurgy method produce titanium zirconium titanium zirconium molybdenum (TZM) alloy and the alloy will has solid solution strengthening and second phase strengthening. Besides, its high-temperature strength higher than conventional high-temperature alloys, deformation by appropriate treatment can greatly enhance its shaping, which makes the TZM alloy become an very important high temperature structure materials in civil industry and defense industry.

After the study found that using powder metallurgy method to produce titanium zirconium molybdenum alloy not only smelting process is complicated and also costly. So in recent years some researcher using thermite reaction method to produce TZM alloy, which directly use oxides as raw material and can not only reduce costs, but also can produce high-hardness alloy. What’s more it after hot rolling with good workability.

Using powder metallurgy method to produce titanium-zirconium-molybdenum alloy there produce processes are as follows:

1. Making high-purity molybdenum powder, TiH2 powder, ZrH2 powder and spray carbon black powder mixed evenly in accordance with a certain proportion and then cool molding.

2. Then at 1900 ~ 2100 ℃ high temperature sintering in a hydrogen atmosphere to give the TZM blanks.

3.TZM blank and then hot-roll at 1250~1350 ℃ high temperature, at 600~750 ℃ temperature warm rolling and at 200 ~ 300 ℃cold rolling.

4 Finally, after stress annealing get TZM finished materials.