Preliminary study of in situ transformed carbon fibers/Al2O3 ceramic matrix composites

The fabrication process, formation of carbon fibers and mechanical properties of in situ transformed carbon fibers/Al2O3 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 degrees C. Twice grade heating was employed respectively at 444 degrees C and 1070 degrees C 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. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.