Influence of the coating brittleness on the thermomechanical fatigue behavior of a $\beta$-NiAl coated R125 Ni-based superalloy

TL;DR

This study examines how the brittleness of aluminide diffusion coatings affects the thermomechanical fatigue behavior of a Ni-based superalloy, revealing that oxidation processes can improve coating durability and fatigue life.

Contribution

It provides new insights into the impact of coating brittleness and oxidation on the fatigue performance of superalloys under thermal cycling conditions.

Findings

Oxidation improves strain-to-failure and fatigue life.

Damage initiation occurs within the coating during thermomechanical loading.

Advanced techniques detect coating cracking and damage evolution.

Abstract

The brittleness of an aluminide diffusion coating protecting a Ren\'e 125 Ni-based polycrystalline superalloy was investigated over a wide range of temperatures in its as-received and thermally aged form. Isothermal and thermal cycled aging were performed on the coated system at a maximum temperature of 1100 {\deg}C. Microstructure evolutions and damage initiation within the coating were characterized. Interrupted tensile tests and thermomechanical fatigue tests were conducted to document critical stress-strain conditions leading to the coating cracking and lifetime for the case of thermo-mechanical fatigue loading. Advanced digital image correlation and acoustic emission techniques were used to detect coating cracking. Isothermal oxidation or cyclic oxidation led to improved strain-to-failure due to metallurgical evolutions and also longer fatigue life under thermomechanical fatigue conditions.