High temperature fracture of a SiC whisker-reinforced alumina in air and vacuum

• The fracture behaviour of a SiCw/alumina composite was studied between room temperature and 1320°C in vacuum by four-point bend testing of specimens pre-cracked by bridge indentation. The results are compared to those of earlier work on a similar material in air. In vacuum, the composite begins to exhibit stable crack growth (SCG) and increasing apparent toughness at about 1100°C. Between 1100 and 1320°C, the extent of SCG increases and the toughness rises to almost three times the room temperature fracture toughness. The toughness enhancement is due mainly to such processes as crack deflection, crack branching, microcrack zone formation and crack tip blunting rather than any temperature-related increase in intrinsic fracture resistance of the material. In air, the fracture processes are similar to those in vacuum but the toughness increase is delayed by about 100°C and the level of toughening is lower. These differences arise from the formation of a glass phase in air which delays microcrack formation but reduces the resistance to stable crack growth.

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TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Annan materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Other Materials Engineering (hsv//eng)

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