Cold gas spraying of Ti-48Al-2Cr-2Nb intermetallic for jet engine applications

The present article describes aspects of the cold gas spray processability of the intermetallic Ti-48Al-2Cr-2Nb (at. %) alloy, which is employed as a structural material in gas turbine engines. The effects of processing parameters, namely, gas pressure, gas temperature, spray distance, as well as the gas atomized feedstock particle size (d(50) = 30 and 42 mu m, respectively) and phase composition on deposition, were investigated. The results showed that when the highest available gas pressure (40 bar) and temperature (950 degrees C) were combined with a short spray distance (20 mm), well-adhering coatings could be deposited regardless of the investigated particle size. However, the maximum coating thickness could be achieved was about 30 mu m with a deposition efficiency of 1%. Phase composition of the gas atomized feedstock was investigated with HT-XRD and according to the findings, heat treatment of the feedstock under vacuum was carried out. With this treatment, non-equilibrium, disordered alpha phase of the atomized powder was transformed into an alpha, alpha(2) and gamma phase mixture. At the same time, an increase in the hardness and oxygen content of the powder was detected. Swipe test performed with the heat treated powder revealed no improvement in terms of deposition, in fact, the number of adhering particles on the substrate was decreased in comparison with that of the untreated powder.