Influence of Ln~(3+) and B~(3+) Ions Co-Substitution on Thermophysical Properties of LnMB_(11)O_(19)-type Magnetoplumbite LaMgAl_(11O_(19) for Advanced Thermal Barrier Coatings

摘要

Lanthanum hexaaluminate is a promising competitor to establish yttria partially stabilized zirconia as a thermal barrier coating material for Ni-based superalloy due to its relative low intrinsic thermal conductivity and low sinterability at temperatures exceeding 1100℃. Sr~(2+) and Ti~(4+) were selected as two dopants to partially substitute the La~(3+) and Al~(3+) in LaMgAl_(11)O_(19), respectively. The variation in thermal conductivity with Sr~(2+) and Ti~(4+) fractions was analyzed based on structure information provided by X-ray diffraction and Raman spectroscopy. The average crystal size of LaMgAl_(11)O_(19) sintered at 1600℃ for 10 min by spark plasma sintering is in nanoscale. The fully dense La_(1-x)Sr_xMgAl_(11-x)Ti_xO_(19) solution showed a minimum thermal conductivity value (λ. = 1.12 W/(m K)~(-1),T = 1273 K) at the composition of La_(0.5)Sr_(0.5)MgAl_(10.5)Ti_(0.5)O_(19),which possibly reduces from the enhanced phonon scattering due to mass and strain fluctuations at the Ln~(3+) and B~(3+) sites.