Control of multiphase evolution and Al-deficiency in reactive-sintered MoAlB ceramics with excessive Al |
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| Affiliation: | 1. School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China;2. State Key Laboratory of Science and Technology on Advanced Composites in Special Environments, Center for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150001, China;3. School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China;1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China;2. School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China;3. Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-2), 52425 Jülich, Germany;4. Center for Adaptive System Engineering, School of Creativity and Art, ShanghaiTech University, 201210 Shanghai, China;1. Department of Mechanical Engineering, the University of Alberta, Edmonton, AB T6G 2R3, Canada;2. Weapons and Materials Research Directorate, Combat Capabilities Development Command Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA;1. Shaanxi Key Laboratory of Fiber Reinforced Light Composite Materials, State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, PR China;2. Key Laboratory of High Performance Ceramic Fibers (Xiamen University), Ministry of Education, Xiamen, PR China;1. School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China;2. State Key Laboratory of High Performance Ceramics and Super?ne Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, China;1. Université de Bordeaux, CNRS, Laboratoire des Composites ThermoStructuraux, UMR 5801, 33600 Pessac, France;2. Université de Bordeaux, CNRS, PLACAMAT UMS 3626, 33600 Pessac, France |
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| Abstract: | MoAlB is a ternary boride of MAB phases with strong resistance to oxidation and ablation at service temperature, thanks to preferential Al diffusion to form a protective oxide scale. However, excessive Al were often necessary in sintering of MoAlB ceramics, suggesting that a liquid-phase densification might occur thus leading to complex microstructures. By quantitative SEM analysis, ~17 mol.% Al2O3 phase was found common in MoAlB ceramics. The liquid-phase of Al-Mo-B-O facilitates the direct conversion from MoB to MoAlB before in situ formation of Al2O3. An intermediate Mo3Al8 phase competes with layered conversion, which limits the insertion rate of Al into B-B layers of MoB to form abundant Al-deficient stacking-faults. Intermetallic Mo3Al8 phase precipitates further in the intergranular regions parallel to the crystallization of Al2O3, leaving the reprecipitation of remaining Al. Both layered-conversion and intergranular oxides can improve ablation behavior for MoAlB ceramics, as well as fracture toughness and compressive strength. |
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| Keywords: | MoAlB ceramics Multiphase evolution Liquid-phase sintering Ablation resistance |
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