Powder Metallurgy Method
TZM is produced by either of two methods—powder sintering or arc casting metallurgy.
In powder sintering metallurgy, pure powder forms of molybdenum, titanium, zirconium, and carbon powders are mixed in a precise ratio: 0.5% Ti, 0.08% Zi, 0.03% C. Subsequent hot and cold isothermal pressing forms high density billets.
The billets are sintered for hours in a high temperature vacuum or inert gas atmosphere. The resulting TZM “blanks” undergo a series of deformations which may include hot/cold rolling or forging; and surface heat treatments such as medium and hot temperature annealing. These processes impart unique physical and mechanical properties to the finished TZM product.
Vacuum Arc-casting Method
Arc casting metallurgy for TZM production uses consumable electrodes made of preformed TZM billet. The preformed TZM electrode is arc-melted to the desired ingot by direct current in a vacuum environment and solidifies in a water-cooled mold on the bottom of the arc-casting furnace. Arc-casting process largely reduces the gas impurity contents in TZM such as oxygen and nitrogen. It also efficiently limits the possibility of presenting centerline porosity and segregation so to assure the material’s homogeneity state and ductility.
Arc-casted TZM exhibit several distinguishable attributes compared with powder-sintered TZM.
- Arc casted TZM extensively assures that TZM material’s density, homogeneity, and porosity can reach or even beyond desired requirements. Therefore, arc-casted TZM exhibits stable machinable properties and weldability.
- Arc casted TZM contains less percentage of oxygen content than powder metalized (P/M) TZM. The oxygen content of arc-casted TZM is 0.03%. The oxygen content of P/M TZM is 0.003%. When oxygen content in molybdenum alloy is higher than 0.002%, it is easy to cause hot brittleness
- When arc-casting furnace is equipped with devices having strong electric current and vacuum ability, to yield a high melting rate, arc-casting metallurgy can theoretically produce large bulk TZM materials beyond the size limitations of TZM materials made through powder-sintering metallurgy.
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