Partial oxidation of Ni-based alloy powder and oxidation resistance following a TIG cladding of heat treatment

Although oxidation is a primary challenge in the industrial high-temperature sector, the formation of oxidation-resistant surfaces via low-cost routes has been progressing. In this study, partially oxidized alloy powders were developed by a controlled heat-treatment process as a low-cost alternative to conventionally gas-atomized oxide-containing powders. The heat-treated powders of the three nickel-based alloys, AMDRY 962 (NiCrAlY), METCO 15E (NiCrBSiCFe), and PRAXAIR (NiCr), were subjected to cooling under various conditions to produce partial oxidation. Optical and scanning electron microscopies were used to identify the microstructural features of treated powders; these observations indicated a modified surface layer on the treated particles, consistent with partial surface oxidation. X-ray diffraction (XRD) showed treatment-induced changes in the metallic phases but no crystalline oxide, indicating that any surface oxide is thin or amorphous. TIG cladding was performed directly on SS321 stainless-steel substrates with partially oxidized powders deposited without the application of a bond coat. Cyclic oxidation tests were performed at 700 °C for 25 cycles, and the oxidation resistance was evaluated from mass-gain measurements. Under the present test conditions, all coated specimens showed a lower mass gain than the uncoated substrate. The coating layered with METCO 15E exhibited the best oxidation resistance of all layered coatings.