Effect of Al Addition in Cast Nickel Base Superalloys, Inconel-738 on Microstructures and Oxidation Behaviors at 900°C and 1000°C

Abstract

The objective of this research work is to investigate the effect of Aluminum addition in cast nickel base superalloy grade Inconel-738 by vacuum arc melting process on microstructural modification and oxidation behavior at elevated temperatures of 900°C and 1000°C. The Al element, basically, could be added in cast nickel base superalloys in proper amount to form precipitated intermetallic phase with nickel atoms as gamma prime phase (γ’, Ni3Al) to increase mechanical properties by blocking dislocation movements at elevated temperatures. Furthermore, Al can assist nickel base superalloy to form protective oxide film, Al2O3 for better oxidation resistance at very high temperatures (over 980°C). In this research, all casted samples of Inconel-738 with various Al additions for 1, 2 and 3 percent by weight were standard heat treated consisting of solution treating at 1125°C for 6 hours and following with precipitate aging at 845°C for 24 hours. The oxidation tests were carried out at temperatures of 900°C and 1000°C up to 110 hours. From all obtained results, it was found that the sample that has the most microstructural stability after long-term heating as simulated working conditions is Inconel-738 sample with 2%wt. Al addition. Furthermore, more Al addition had resulted in higher oxidation resistances for both testing temperatures.