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Tantalum Performance Significantly Pulled High
Jul 27, 2017

China developed the high temperature alloy K438 contains 1.5% to 2.0% Ta, K409 contains 4.0% to 4.5% Ta, K4002 contains 2.25% to 2.75% Ta. US-made nickel-based superalloys IN738LC, IN939, IN792, M22, MM-002, MM-005, MM-006 and MM-011 contain 1% to 4% Ta, PWA1480 contains 12% Ta. Tantalum is a strategic element that is expensive and should be used as little as possible. Tantalum in the nickel-based superalloy about 80% into the γ 'phase, enhanced γ' phase of the strengthening effect, about 10% to 15% of the formation of Ta-rich MC carbide, only about 5% to 10% into the γ solid solution, solid Solubilization effect. Like Nb, the atomic radius of Ta is also large, Tantalum 15% to 18% larger than Ni, Co and Fe atoms. Therefore, the addition of nickel-based solid solution, causing a greater increase in lattice constant. Therefore, the elastic stress field poses a greater resistance to the dislocation movement, and at the same time, Tantalum Ta also reduces the stacking fault of the γ solid solution, so that the instantaneous tensile strength and creep performance of the γ solid solution are obviously increased.

The results show that with the increase of the tantalum content in the alloy from 1% to 6.4%, the tensile strength increases at 760 ℃, the plasticity improves, the creep resistance is improved, Tantalum and the creep rupture time is higher than that of the K409 alloy. extend. The tantalum in the alloy enters the γ 'phase, increases the γ' phase, the number and the dissolution temperature of the γ 'phase, changes the composition of the γ' phase, the size of the γ 'phase, increases the γ' phase precipitation strengthening effect, Tantalum In order to distinguish the effect of solid solution strengthening and precipitation strengthening, the components containing Ta and Ta-free austenite without phase analysis were prepared by smelting Ta-containing and Ta-free Austenite matrix alloy, its content in the austenite, by the Cr + Co + Mo and the sum of 30%, Tantalum increased to 38.5%. K409 alloy matrix containing 1% Ta, Tantalum these large size of the Ta atoms, coupled with increased content of Cr, Co and Mo atoms, is bound to cause a large elastic stress field, while the γ austenite matrix layer error The creep life of the Ta-containing austenitic matrix alloy is greatly prolonged, and the creep plasticity is improved obviously, that is, Tantalum the solid solution strengthening of Ta and the increase of Cr, Tantalum Co and Mo contents caused by Ta. At the same time, Tantalum the instantaneous tensile strength and plasticity are also greatly improved. Ta also significantly improved the thermal corrosion resistance and hot and cold fatigue properties of the alloy. In the range studied, Tantalum the higher the Ta content, the better the thermal corrosion resistance and the cold and thermal fatigue resistance. In the cobalt-based sheet alloys MM-918 and S-57 used at high temperatures, Tantalum W has been successfully substituted for W, and the antioxidant performance is remarkably improved.

Tantalum also has a very good chemical properties, with high corrosion resistance, Tantalum whether in cold and hot conditions, hydrochloric acid, concentrated nitric acid and "aqua regia" do not respond. But tantalum in the hot concentrated sulfuric acid can be corrosive, below 150 ℃, tantalum will not be concentrated sulfuric acid corrosion, only in the temperature above this reaction will be in the 175 degrees of concentrated sulfuric acid in 1 year, the corrosion of the thickness 0.0004 mm, the tantalum into 200 ℃ sulfuric acid soak for one year, Tantalum the surface damage only 0.006 mm. At 250 degrees, the corrosion rate increased, the corrosion per year for the thickness of 0.116 mm, at 300 degrees, the corrosion rate is faster, soaking for 1 year, Tantalum the surface was corrosion 1.368 mm. The corrosion rate of fuming sulfuric acid (containing 15% SO3) is more severe than concentrated sulfuric acid, immersed in the solution at 130 degrees for 1 year, and the surface is etched with a thickness of 15.6 mm. Tantalum at high temperatures will be corrosion of phosphoric acid, but the reaction is generally more than 150 degrees occurred in the 250 degrees of 85% phosphoric acid, soak for 1 year, the surface was corrosion 20 mm, in addition, tantalum in hydrofluoric acid and nitric acid Of the mixed acid can quickly dissolve in hydrofluoric acid can also be dissolved. However, Tantalum tantalum is more afraid of strong alkali, in the 110 degrees 40% concentration of caustic soda solution, tantalum will be quickly dissolved in the same concentration of potassium hydroxide solution, Tantalum as long as 100 degrees will be quickly dissolved. In addition to the above-mentioned circumstances, Tantalum the general inorganic salt in the 150 degrees below the general can not corrosion tantalum. Experiments show that tantalum at room temperature, Tantalum the alkaline solution, chlorine, Tantalum bromine, dilute sulfuric acid and many other agents do not work, Tantalum only in the hydrofluoric acid and heat concentrated sulfuric acid under the reaction. This situation is relatively rare in the metal.

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