Ab initio simulations of M2AX (M = lanthanides, A = Al or Si, X = C or N) phases as bond coats for thermal barrier coatings

MAX phases such as Ti₂AlC and Cr₂AlC are attracting attention due to their oxides (Al₂O₃ or Cr₂O₃). However, little research has considered MAX phases incorporating rare earth elements at the M sites. This study used ab initio calculations to explore the temperature dependence of the Young's modulus and coefficient of thermal expansion (CTE) of MAX phases with M = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. MAX phases with M = Er, Lu, and Tm are particularly suitable for use as a bond coat (BC) layer between a thermally grown oxide (TGO) and substrate, given the compatibility of thermal expansion. The low CTE difference between a MAX phase and the TGOs or substrate can effectively relieve thermal stresses. These findings provide valuable insights into the development of MAX phase BCs.