Research At The Hot Corrosion Resistance Properties Of The Aluminized Layer On Thesurface Of Ti₂AlNb Alloy

Ti2Al Nb alloy, Compared with other high temperature alloys, has its own unique advantages, like high tensile strength and fatigue strength, good crack propagation resistance and fracture toughness at room temperature, good creep resistance and low thermal expansion coefficient, has potential to become a new generation of aero-industries materials. However, insufficient hot corrosion resistance is the main drawback which restricts the actual application of this alloy in many circumstances. By using the arc-added glow discharge plasma surface alloying technique, Aluminized layer is formed on the surface of Ti2 Al Nb to improve its high temperature hot corrosion resistance.The optimum process parameters of arc-added glow discharge plasma aluminizing on Ti2 Al Nb alloy are listed as follows: work-piece bias is 800 V, distance between target and work-piece is 80 mm, time is 35 min, temperature is 750 ℃, working pressure is 6.69 Pa. SEM was used to detect the morphology of the oxidation film, EDS was used to detect the element distribution and XRD was used to identify the phase. It turns out that the aluminized layer is compact and homogeneous, The mainly surface phase structure is Al. The aluminized layer is about 20 μm thick and metallurgy combined with the substrate, the bonding force is 43.5 N.Hot corrosion studies are conducted in Na2SO4 environment at 650℃, 700℃, 750℃, 800℃, 850℃ for 100 h. The results show that the weight gains of the aluminized samples are much less than the substrates, and both of them show hot corrosion resistance below 800℃. After hot corrosion for 50 h at 800℃, the surface of substrate has peeled seriously. After 850℃ corrosion, the surface of aluminized layer has peeled lightly, due to its high content of Al, it still can form a protective Al2O3 scale and protect the substrate.Hot corrosion studies are conducted in Na2SO4 at different times. The results indicate that the substrates and aluminized samples show hot corrosion resistance. The Na2SO4 salt can make the Al2O3 oxide film loose and accelerated the oxidation process of the specimens, the oxidation reaction and the vulcanization reaction between the Na2SO4 salt and the specimens were occurred.Hot corrosion studies are conducted in 75%Na2SO4+25%Na Cl environment at different times. It turned out that the hot corrosion resistance of the substrates declined sharply in the mixed salt environment, yet the aluminized layer shows a certain hot corrosion resistance. The oxidation film destroyed by the chloridion and stripped from the surface of the substrate. The chloridion can also react with alloying elements and oxides. Therefore, the process of hot corrosion in mixed salts is a combination of oxide, sulfide and chlorination.