The oxidation behavior of solid-solution nickel-aluminum alloys was studied at four levels of oxygen pressure ranging from a partial pressure of 10−4 atmosphere to a total pressure of 10 atmospheres. Three such alloys containing 1.04, 3.90, and 6.40 atomic percent (a/o) Al were oxidized at 1000 C for times of 6.25, 25, and 100 hours. Studies of subscale penetration, particle characteristics and hardness were made. External scale and total weight-gain measurements were also obtained. Prevailing rate laws were determined for subscale penetration and total weight-gain data.
The subscale penetration, total weight gain and external scaling processes were found to proceed at rates intermediate to the linear and parabolic rate laws. The extent of the subscale was observed to be nearly independent of oxygen pressure when considered on the basis of average values of penetration, except in the case of the Ni-6.40 a/o Al alloy which exhibited a pressure-dependent penetration maximum. Subscale particle characteristics and hardnesses were also observed to be nearly independent of oxygen pressure. It was found that alloys containing higher concentrations of aluminum exhibited a greater hardness in the subscale zone. All specimens showed a general trend of increased total weight gain as well as larger quantities of external scale as oxygen pressure was increased. 3.2.3, 3.5.7, 3.4.6, 6.3.10
