Conventional aluminum nitride (AlN) ceramics exhibited insufficient mechanical properties expected from their potential applications in the presence of dynamic loads and intensive stresses caused by thermal shock. In this study, the mechanical properties of AlN ceramics were enhanced by toughening them using AlN whiskers (AlN w ) via gel casting followed by low-temperature sintering at 1650°C. The addition of AlN w simultaneously increased the bending strength, toughness and thermal conductivity of the AlN ceramics. The maximum values of the bending strength, toughness, and thermal conductivity of 9.0 wt% AlN w /AlN were 303.92 MPa, 3.92 MPa·m 1/2 and 186.53 W·m −1 ·K −1 , respectively, which were higher than those of the AlN ceramics by 39.93%, 61.31% and, 15.61%, respectively. The AlN w in AlN w /AlN ceramics tightly bonded with the ceramic matrix, leading to two characteristic toughening mechanisms in the ceramics: crack pinning and deflection at irregular grain boundaries caused by doped whiskers, as well as bridging and stress relaxation caused by whiskers incorporated with the grains. Moreover, the one-dimensional morphology of AlN w can provide a channel for quick photon transport, thereby enhancing the thermal conductivity of AlN w /AlN.
Tiange Xue,Xinqing Su,Shixiang Yu,Meng Meng,Xinya Xu,Jinqi Xin,Jinjin Ran
In this work, a small amount of AlN whiskers (ranging from 2 wt.% to 8 wt.%) was incorporated into CaO-MgO-ZnO-B2O3-SiO2(CMZBS)–glass/Al2O3composites so as to obtain glass-ceramics with a thermally conductive network through sintering between 700 °C and 1000 °C. Special attention was given to the densification behavior, dielectric properties, and thermal conductivity of CMZBS/Al2O3/AlN–glass–ceramic composites with varying AlN whisker contents. According to the results, composites with desirable thermal, mechanical, and dielectrical properties were successfully fabricated. Notably, the composites containing 6 wt.% AlN whiskers, sintered at 800 °C, exhibited the most optimal comprehensive properties (dielectric constant of 7.06, dielectric loss of 383 × 10−5, thermal expansion coefficient of 6.40·10−6/K, flexural strength of 180 MPa, and thermal conductivity of 5.17 W/(m·K)). Given these attributes, this CMZBS/Al2O3/AlN composite holds great potential for applications in LTCC (low-temperature co-fired ceramic).
In this work, AlN whisker-reinforced (Zr, Hf)O 2 coating was prepared on SiC coated carbon/carbon composites by sol-gel and plasma spraying methods. Its cyclic ablation resistance was evaluated using an oxyacetylene torch with a heat flux of 2.38 MW/m 2 . After ablation, the coating showed apparently decreased crack sizes and quantity as compared with the one without AlN whisker addition, pointing out its better crack tolerance. Moreover, the coating had a thinner oxidized region based on the linear ablation rate (−0.042 µm/s), greatly lower than that of pure oxide coating (−0.922 µm/s). After detailed observation and characterization, probable protection mechanism was proposed.
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