The oxidation characteristics of the nickel-based superalloy, RR1000, at temperatures of 700 - 900°C

The oxidation kinetics are presented for a coarse-grained RR1000 alloy in the temperature range 700 - 900°C for times up to approximately 100 hours. The tests were undertaken in laboratory air in thermo-balances. The kinetics tended to sub-parabolic but were treated as parabolic to allow comparison with literature data. These parabolic rate constants were appreciably higher than expected for the growth of a protective oxide layer but were similar to those found previously on other Cr-rich Ni-based superalloys. SEM and confocal microscopy were used to show that the regions of emergent grain boundaries on the alloy surface oxidised faster than the grain centres. The surface oxide formed was Cr-rich with an enhancement of titanium in its outer regions. This is the situation at the grain boundaries and over the grain centres. Sub-surface oxidation of aluminium was observed, principally as intergranular fingers but also as intragranular particles. Ahead of this internal oxidation zone, at least for the specimen oxidised at 900°C, was a region containing titanium nitride particles, again principally as intergranular fingers.