MECHANICAL-PROPERTIES OF MONOLITHIC ALN AND SICW ALN COMPOSITES/

Flexural, tensile, and high cycle fatigue test data are presented for pressureless sintered aluminium nitride (AlN) and hot-pressed aluminiu m nitride reinforced with silicon carbide whiskers (SiCW/AlN). Tests w ere conducted at ambient temperature. The SiCW/AlN composites consisti ng of 30 wt% SiCW produced significant increases in flexural strength, tensile strength, and tensile fatigue strength compared to monolithic AlN. Increases were nearly double in all cases. Corresponding strain- to-failures measured in tensile tests increased from similar to 0.04% in monolithic AlN to similar to 0.10% in the SiCW reinforced composite . Fracture surfaces showed evidence of whisker-toughening mechanisms d ue to additions of SiCW whiskers. High-cycle fatigue results indicated that both materials have the ability to sustain higher stress levels in the cyclic tests compared to the tensile experiments. The improved performance under cyclic testing is explained in terms of strain-rate effects. The times at or near peak stress are considerably less under high-cycle fatigue testing (20 Hz) compared to tensile tests (strain r ate = 0.5% min(-1)).