Cyclic Oxidation Behavior of Conventional and Niobium-Modified MAR-M246 Superalloy at 900 and 1000 °C

Abstract

Nickel-based superalloys have excellent properties at high temperatures, which makes them appropriate for applications such as turbocharges and aeronautic gas turbines. MAR-M246 is a superalloy developed for these kinds of applications. The objective of this work was to study the total replacement of Ta by Nb in atomic percentage for this superalloy, regarding the oxidation resistance. Although both elements have the same role (form the γ’ precipitates) in nickel-based superalloys, Ta is more expensive than Nb. Thus, this replacement leads to the possibility of a price reduction. This work studied both conventional MAR-M246(Ta) and experimental MAR-M246(Nb) on cyclic oxidation tests at 900 and 1000 °C for up to 180 cycles. The oxide products were characterized by SEM/EDS and XRD analysis. The products of oxidation were mainly TiO2, Al2O3, Cr2O3, NiO, and Ni(Co)Cr2O4. Mass gain variation per unit area was stable for both materials and temperatures. However, spalled areas were detected for tests performed at 1000 °C. The results obtained here suggest that use of Nb instead of Ta can be considered regarding high temperature oxidation for MAR-M246 superalloy.

A Comparative Study on Characterization and High-Temperature Wear Behaviors of Thermochemical Coatings Applied to Cobalt-Based Haynes 25 Superalloys

“…Consequently, these alloys display flatter stress-rupture curves, which in turn grant them enhanced stress and tensile capacities in high-temperature applications [1]. As with other superalloys, there are two types of Co-based superalloys used in industrial applications: cast (e.g., X40 or MAR-M-302) and wrought (e.g., Haynes 25; Haynes 188, S-816) alloys [2,3].…”

“…Cobalt-based superalloys, similar to other superalloys, feature microstructures comprising an FCC γ matrix along with several strengthening phases. However, when compared to nickel-iron or nickel-based superalloys, the precipitation hardening in cobalt-based superalloys is not as effective as in the nickel-based superalloys [3][4][5]. This necessitates strengthening cobalt-based superalloys primarily through carbide formation and/or solidsolution strengthening [6].…”

Advanced Corrosion and High-Temperature Protection through Surface Modification and Coatings

“…A stable, dense and defect-free surface oxide layer may yield protection even against high temperature corrosion, acting as a diffusion barrier and therefore hindering the degradation progress. In this sense, minor additions of reactive elements, i.e., Hf, Ta, Nb, Ce, Y and others, may further improve the high-temperature response of an alloy [4][5][6].…”