Fabrication and Properties of Magnetoplumbite-type Rare-earth Hexaaluminate Thermal Barrier Coating Materials

doi:10.15541/jim20250386

Abstract

Abstract:

Magnetoplumbite-type rare-earth hexaaluminates RMgAl₁₁O₁₉ (RMA, R=La, Pr, Nd, Sm, Gd) emerged as promising candidates for next-generation thermal barrier coatings (TBCs) capable of operating at temperatures exceeding 1300 ℃, owing to their high melting points, low thermal conductivity, and remarkable sintering resistance. To elucidate the influence of rare-earth ion substitution on the structural and functional properties, a series of single rare-earth cation substituted RMA ceramics were synthesized via a solid-state reaction route and densified using spark plasma sintering. Their phase composition, microstructure, thermophysical, and infrared radiative properties were systematically characterized by different measurements. All samples crystallize in a hexagonal magnetoplumbite-type structure, with both lattice parameters and unit cell volumes exhibiting a gradual contraction as the rare-earth ionic radius decreases. The grain growth rate generally increases with a reduction in ionic radius. The thermal diffusivity and conductivity of RMA ceramics decrease with increasing temperature, reaching a minimum of 2.86-3.19 W/(m·K) in the temperature range of 25-1000 ℃. The average thermal expansion coefficients vary from 8.22×10^-6 to 8.70×10^-6 K^-1 between 200 and 1300 ℃, indicating comparable thermo-physical properties across different compositions. In contrast, notable differences appear in the 3-5 μm infrared band, where PrMA exhibits the highest average emissivity (0.746) and LaMA exhibits the lowest (0.493), reflecting the critical role of rare-earth cation electronic structure in radiative behavior. This work elucidates the coupled thermal-radiative modulation mechanism induced by rare-earth ion substitution in magnetoplumbite-type hexaaluminates, offering valuable insights for the design of high-temperature TBC materials that combine low thermal conductivity with high infrared radiative performance.

Key words: thermal barrier coating, RMgAl₁₁O₁₉, grain growth rate, thermo-physical property, infrared radiation property

CLC Number:

TB306

XU Mingyi, XIONG Ying, WANG Bo, ZHANG Yixin, CHEN Wenbo, CAO Xueqiang. Fabrication and Properties of Magnetoplumbite-type Rare-earth Hexaaluminate Thermal Barrier Coating Materials[J]. Journal of Inorganic Materials, 2026, 41(8): 1103-1109.

Figures/Tables 9

Fig. 1 (a) XRD patterns and (b) lattice parameters of RMA ceramic bulks

Table 1 Density and relative density of RMA ceramic bulks

Sample	Theoretical density/(g·cm^-3)	Archimedes’ density/(g·cm^-3)	Relative density/%	Sample	Theoretical density/(g·cm^-3)	Archimedes’ density/(g·cm^-3)	Relative density/%
LaMA	4.268	4.063	95.20	SmMA	4.371	4.039	92.40
PrMA	4.300	4.295	99.88	GdMA	4.418	4.106	92.94
NdMA	4.326	4.183	96.69

Fig. 2 Surface morphologies of (a) LaMA, (b) PrMA, (c) NdMA, (d) SmMA, (e) GdMA ceramics and corresponding (f) average width of grains after thermal etching

Fig. 3 Sm3d XPS spectra of SmMA ceramic

Fig. 4 (a) Temperature-dependent thermal expansion coefficients and (b) average thermal expansion coefficients of RMA ceramics

Fig. 5 Temperature-dependent (a) heat capacity, (b) thermal diffusivity and (c) thermal conductivity of RMA ceramics

Fig. 6 (a) Temperature-dependent infrared emissivity and (b) average emissivity in the range of 8-14 μm of RMA ceramics

Fig. 7 (a) Temperature-dependent infrared emissivity and (b) average emissivity in the range of 3-5 μm of RMA ceramics

Fig. 8 (a) Temperature-dependent infrared emissivity and (b) average emissivity in the range of 3-5 μm of rare-earth oxides

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