STRONG AND TOUGH HI-NICALON-FIBER-REINFORCED CELSIAN-MATRIX COMPOSITES

Strong, tough, and almost fully dense BN/SiC-coated Hi-Nicalon-fiber-r einforced celsian-matrix composites have been fabricated by impregnati on of the fiber tows with the matrix slurry, winding on a drum, stacki ng the prepreg tapes in the desired orientation, and hot pressing, The monoclinic celsian phase in the matrix was produced in situ, during h ot pressing, from a mixed oxide precursor, The unidirectional composit es having approximate to 42 vol% of fibers exhibited graceful failure with extensive fiber pullout in three-point bend tests at room tempera ture, Values of stress and strain at the proportional limit were 435 /- 35 MPa and 0.27 +/- 0.01%, respectively, and an apparent ultimate s trength of 900 +/- 60 MPa was observed, Young's modulus of the composi tes was 165 +/- 5 GPa.