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Mechanical and thermal properties of light weight boron‐mullite Al 5 BO 9
Author(s) -
Ren Yixiao,
Dai FuZhi,
Xiang Huimin,
Wang Xiaohui,
Sun Luchao,
Zhou Yanchun
Publication year - 2020
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17313
Subject(s) - materials science , thermal expansion , mullite , flexural strength , composite material , spark plasma sintering , fracture toughness , vickers hardness test , thermal conductivity , boron , anisotropy , ceramic , microstructure , chemistry , physics , quantum mechanics , organic chemistry
Al 5 BO 9 is a promising thermal sealing material for hypersonic vehicles due to its low density, theoretically predicted low shear modulus, and low thermal conductivity. However, experimental investigations on the mechanical and thermal properties of bulk Al 5 BO 9 have not been carried out. Herein, we report the mechanical and thermal properties of bulk Al 5 BO 9 prepared by spark plasma sintering of solid‐state reaction synthesized Al 5 BO 9 powders. The bulk ( B ), shear ( G ), and Young's ( E ) moduli are 148 GPa, 85 GPa, and 214 GPa, respectively, which are close to the theoretical values. The Pugh's ratio G/B is 0.574, indicating its intrinsic damage tolerance, which is also revealed by Hertzian contact test. The Vickers hardness ( H v ) is 10.8 GPa, being lower than mullite. The flexural strength, compressive strength, and fracture toughness are, respectively, 277 ± 35 MPa, 814 ± 75 MPa, and 2.4 ± 0.3 MPa·m 1/2 , which are close to those of mullite. Al 5 BO 9 has anisotropic coefficient of thermal expansion (CTE) in three crystallographic directions, ie α a = (4.40 ± 0.21) × 10 −6 K −1 , α b = (7.11 ± 0.18) × 10 −6 K −1 , α c = (6.70 ± 0.29) × 10 −6 K −1 from Debye temperature to 1473 K, which are underpinned by its structural feature, ie lower α a is resulted from the edge‐shared AlO 6 octahedron chains along the [100] direction. The average CTE is (6.05 ± 0.06) × 10 −6 K −1 . The thermal conductivity declines with temperature as κ = 1336.39/T + 1.97, consisting with predicted trend from Slack's model. The low thermal conductivity and low density guarantee Al 5 BO 9 a promising candidate as ceramic wafer in the seal structure for hypersonic vehicles.