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Novel Csf/SiBCN composites prepared by densifying Csf/MA-SiBCN with the PIP process: Oxidation behavior and damage mechanism
Journal of Advanced Ceramics
Published: 21 May 2024
Downloads:68

To improve the oxidation resistance of short carbon fiber (Csf)-reinforced mechanically alloyed SiBCN (MA-SiBCN) (Csf/MA-SiBCN) composites, dense amorphous Csf/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN (PDCs-SiBCN) were prepared by repeated polymer infiltration and pyrolysis (PIP) of layered Csf/MA-SiBCN composites at 1100 °C, and the oxidation behavior and damage mechanism of the as-prepared Csf/SiBCN at 1300–1600 °C were compared and discussed with those of Csf/MA-SiBCN. The Csf/MA-SiBCN composites resist oxidation attack up to 1400 °C but fail at 1500 °C due to the collapse of the porous framework, while the PIP-densified Csf/SiBCN composites are resistant to static air up to 1600 °C. During oxidation, oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon (PyC) to the interior of the matrix. Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices, a relatively continuous and dense oxide layer is formed on the sample surface, and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix, which is primarily responsible for improving the oxidation resistance.

Open Access Research Article Issue
Microstructural evolution and mechanical properties of in situ nano Ta4HfC5 reinforced SiBCN composite ceramics
Journal of Advanced Ceramics 2020, 9 (6): 739-748
Published: 27 November 2020
Downloads:314

The in situ nano Ta4HfC5 reinforced SiBCN-Ta4HfC5 composite ceramics were prepared by a combination of two-step mechanical alloying and reactive hot-pressing sintering. The microstructural evolution and mechanical properties of the resulting SiBCN-Ta4HfC5 were studied. After the first-step milling of 30 h, the raw materials of TaC and HfC underwent crushing, cold sintering, and short-range interdiffusion to finally obtain the high pure nano Ta4HfC5. A hybrid structure of amorphous SiBCN and nano Ta4HfC5 was obtained by adopting a second-step ball-milling. After reactive hot-pressing sintering, amorphous SiBCN has crystallized to 3C-SiC, 6H-SiC, and turbostratic BN(C) phases and Ta4HfC5 retained the form of the nanostructure. With the in situ generations of 2.5 wt% Ta4HfC5, Ta4HfC5 is preferentially distributed within the turbostratic BN(C); however, as Ta4HfC5 content further raised to 10 wt%, it mainly distributed in the grain-boundary of BN(C) and SiC. The introduction of Ta4HfC5 nanocrystals can effectively improve the flexural strength and fracture toughness of SiBCN ceramics, reaching to 344.1 MPa and 4.52 MPa·m1/2, respectively. This work has solved the problems of uneven distribution of ultra-high temperature phases in the ceramic matrix, which is beneficial to the real applications of SiBCN ceramics.

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