Unveiling the Coupled effects of La/Gd substitution on phase transition, lattice defects, and growth mechanism in (La1-xGdx)2Zr2O7 TBCs by EB-PVD

This study systematically investigates the effects of La/Gd substitution ratio on the crystal structure, microstructural evolution, and elemental distribution of (La 1-x Gd x ) 2 Zr 2 O 7 (LGZ) thermal barrier coatings fabricated via three-step EB-PVD. Five kinds of duplex LGZ/YSZ coatings (x = 0.1, 0.3, 0.5, 0.7, and 0.9) were deposited on (Ni,Pt)Al bond-coated superalloy substrates. The coatings reveal a composition-driven structural transition from ordered pyrochlore to disordered defect-fluorite phase with increasing Gd, alongside lattice contraction and dislocation density variation. Columnar grain size increases monotonically with Gd content, evolving from fine columns with lamellar tips in La-rich compositions (x < 0.5) to coarse columns with pyramid tips in Gd-rich compositions (x > 0.5). This growth behavior results from La 3+ surface segregation and pinning that inhibit lateral growth, whereas Gd-rich compositions lack this effect, allowing normal diffusion and competitive growth. Furthermore, elemental mapping reveals pronounced hierarchical segregation of La perpendicular to the growth in La-rich coatings, due to the higher vapor pressure of lanthanum oxide and stronger La 3+ segregation tendency, while Gd remains relatively uniformly distributed due to its moderate volatility. These findings establish comprehensive processing-structure-composition relationships, providing fundamental guidance for tailoring microstructures and elemental distributions via compositional design in rare-earth zirconate TBCs.