| Popis: |
High-cycle fatigue tests were performed on aligned CoTaC (Co, 10Cr, 10Ni-15TaC) at room temperature. In addition, tests were performed on related alloys in order to determine the effect of various metallurgical variables on fatigue life: non-alignment of the structure, elimination of the fiber reinforcement and prior fiber fragmentation all resulted in decreased fatigue resistance, while increasing growth rate and the precipitation of matrix carbides resulted in significant improvements. Crack initiation was observed in several samples using optical replicas. Fractographs revealed that fatigue crack growth in the aligned materials proceeded in a stage I mode. Transmission electron microscopic (TEM) investigation of CoTaC revealed no buildup of dislocation substructures during fatigue. Precipitate size and distribution for the heat treated materials also was investigated with TEM. |
