Predicting the Self-Healing Potential of MAX Phase Metallo-Ceramics under Turbine Engine Relevant Conditions

Ceramics are increasingly being considered for aerospace engine applications due to their high temperature strength, fracture toughness and hardness. M_n+1AX_n-phase ceramics are a group of ternary carbides and nitrides that offer the same advantages as classic ceramics but also have an easier machinability and some of them even have the ability to self-heal crack damage by high temperature oxidation.  This makes them excellent candidate materials for use in turbine engine environments.

Autonomous self-healing in MAX phase ceramics is due to the formation of a stable, well adhering oxide with a high relative volume expansion and mechanical properties close to those of the matrix. The present work utilizes reported thermodynamic, thermo-kinetic and mechanical properties of MAX phases to predict potential self-healing compounds among the more than 75 known MAX phases. Six criteria are postulated to simplify the screening of materials according to the specific requirements of autonomous self-healing. Of the 312 and 211 MAX phase ceramics, two known self-healing compounds, Ti₂AlC and Ti₃AlC₂,  were correctly identified, along with two other ternary carbides, whose self-healing behaviour has hitherto not yet been investigated.  The concepts to predict intrinsic self-healing potential as presented are generic and can be used to other material systems as well.