TZM Alloy TIG Welding

TZM alloy susceptible to oxidation, even very little oxygen atoms in the molybdenum can be formed MoO2 and segregation at the grain boundaries by monolayer, thereby reducing the binding strength of molybdenum at grain boundaries, leading to TZM alloy intergranular brittle failure. In order to prevent the alloy oxidation or inhaled nitrogen and other impurities in the welding process, welding method is generally used TIG welding (TIG Promise).

TIG welding will produce arc to welding between the non-consumable electrode and the workpiece. During the welding process, the heating area tungsten electrode, furnace hearth, arc and TZM alloy will protect by gas protective layer to isolate the air. And the protective layer is formed by an inert gas provide full protection during welding.

During the test, the welding rod should use the same material of TZM alloy and the diameter of it is ≤3mm. On the other hand, before welding TZM alloy and welding bar should be washed 10% of nitric acid and hydrofluoric acid alcohol 3% for 1-3min, remove scale and stains. Then after cleaning put the alloy in the welding workbench and use DC to welding. The joint gap is 1mm.

Analysis the Room Temperature Mechanical Properties of TZM Alloy After Rolling Deformation

TZM alloy after appropriately rolling deformation become tight and room temperature mechanical properties of alloy has been greatly improved. The tensile strength of TZM alloy is more than 840Mpa and the elongation is more than 4%. Besides, the gain is finer. What’s more, its tensile properties are better than un-rolling deformation TZM alloy. Since un-rolling deformation alloy’s Mo grains have weak combine and grain boundaries is weaker, so in lesser strain and lower energy it is easy to become the source of cracks. The rolled alloy, the grain after pressure processing stretched into a fibrous distribution and interplay with Mo grains so the greatly reduced susceptibility of alloy to crack.

At the same time, due to the fine grain size, in the same amount of deformation the deformation dispersed in more crystal grains to operate. The difference of strain ratio in grains and the grain boundary is difference and deformation is more uniform so stress concentration reduces. Alloy can withstand large amount of deformation before breaking. And because fine grain size, grain boundaries zigzags, is not conducive to the spread of crack resulting in the fracture process can absorb more energy, resulting in a relatively large elongation, performance good room temperature toughness.

Different annealing temperatures influence TZM Alloy’s fracture morphology

Different annealing temperatures, tensile fracture morphology of TZM alloy is not the same. When annealing temperature is 850 ℃, the tensile fracture of TZM alloy is mainly transgranular fracture. There is a significant cleavage step on the fracture. And there are a lot of holes in fracture grain boundary. Besides, these holes are formed crack sources in the stretching process which causes alloy break by interconnected. Annealed at 1000 ℃, the fracture has obvious river-like pattern and cleavage step. When the cracks expansion will connect with dislocation and therefore will generate cleavage step. Meanwhile, the alloy before breaking through a lot of strain, so there has been a lot of tearing ridge on cleavage surface. When the annealing temperature is 1150 ℃, the fracture characteristics is similar to 1000 ℃ fracture characteristics, but the degree of cleavage fracture has improved, so the breaking plastic of alloy also increased.

Recrystallization temperature of TZM alloy is about 1200 ℃, when the annealing temperature exceeds the recrystallization temperature, the alloy has coarse grains, the fracture surface is relatively flat. The fracture is mainly transgranular fracture and ductile fracture which is mean plastic of alloy has been further increase. But there have been many irregularities particles and pits in the alloy and there are enhanced phase precipitate in local area. This shows the high annealing temperature weakened dispersion strengthen and have a certain influence on the mechanical properties of the alloys. Therefore, the annealing temperature should be controlled below the recrystallization temperature of TZM alloy.

Deformation Degree Influence Titanium Zirconium Molybdenum Alloy’s Organization Structure

By observing different deformation degrees’ low magnification and high-powered microstructure photograph of titanium zirconium molybdenum (TZM) alloys was found, low-temperature sintering alloy billet has grain fine and uniform structure. After rolling, with deformation degree increases, the original equiaxed grain components along the deformation direction extending and carbide phase dispersed evenly, so the dispersion strengthening effect is more pronounced. When the deformation degree increases, the organization structure of grains becomes blurred, but the grain size and form are consistency good, a fiber distribution. And Mo grains coexist with each other so the intergranular binding force strong and TZM alloy susceptibility to crack greatly reduced. Meanwhile, the alloy grain boundary inside impurity segregation decreased, tensile strength and toughness has been greatly improved. As the deformation increases, the overall variation of the alloy structure is as follows: a large amount of deformation of TZM alloys occur carbide phase dispersed uniformly, high dispersion, fibrous tissue increased and more refined, the final alloy room temperature mechanical properties significantly improved.