Preliminary study of in situ transformed carbon fibers/Al_2O_3 ceramic matrix composites

摘要

The fabrication process, formation of carbon fibers and mechanical properties of in situ transformed carbon fibers/Al_2O_3 ceramic matrix composites prepared by hot-press sintering were investigated. In the sintering process, pre-oxidized polyacrylonitrile fibers (below named as pre-oxidized PAN fibers) were used as the precursors of the in situ transformed carbon fibers at the sintering temperature of 1700℃. Twice grade heating was employed respectively at 444℃ and 1070℃ for 10 min before reaching the sintering temperature in order to encourage the transformation of pre-oxidized PAN fibers into carbon fibers. XRD analysis shows that the composites present an apparent diffraction peak at 26.3°, which corresponds to (002) crystal face of carbon fibers. By EDX analysis the carbon content of the in situ transformed carbon fibers is 92.68%. These evidences certificate the PAN fibers have been in-situ transformed to carbon fibers during the sintering process. The fracture toughness of the composites with 20 vol. % pre-oxidized PAN fibers reaches 6.29 MPa m~(1/2). Compared with 4.75 Mpa m~(1/2) of alumina, it is clear that the in-situ transformed carbon fibers remarkably improve the fracture toughness of the composites and the toughening mechanisms contribute to fiber pull-out and crack bridging.