Effect of Heating Rates on Non-Isothermal and Isothermal Oxidation Behavior of Additive Friction Stir Deposited Nickel Base Superalloy IN625

Abstract

This study examined the effects of non-isothermal heating in air on formation of oxide layers on additive friction stir deposited (AFSD) IN625 as compared with the conventionally fabricated IN625 feed material. Oxidation kinetics and characteristics when heated to 1000 °C, at heating rates of 10, 100, and 1000 °C/min followed by isothermal holding at 1000 °C on the oxidation behavior and oxide species formation were evaluated in both feed and additive friction stir deposited IN625 alloy. The AFSD IN625 alloy experienced lower oxidation compared to the feed IN625 material under similar conditions due to the significantly smaller grains forming a uniform protective oxide layer during non-isothermal heating. Oxidation during isothermal heating followed a parabolic growth law in IN625 supporting Wagner’s oxidation theory. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy studies revealed oxidation of almost all major alloying elements, with chromia being the predominant species. Interestingly, the formation of a continuous layer of NiO on top of chromia at 10 °C/min and 100 °C/min was observed in feed IN625, while in additive friction stir deposited discrete islands of NiO was formed. The material condition influenced the oxidation behavior while the evolution of oxides was influenced by the combined effects of heating rate and thermal kinetics. This experimental approach was designed to evaluate the material response to rapid, short-duration, and high-temperature oxidation, offering insights into the dynamic oxidation behavior of AFSD IN625 under varying thermal conditions.