Fatigue crack growth in a polycrystalline Ni/sub 3/Al+B alloy

Several accounts of the influence of boron on tensile ductility of polycrystalline Ni/sub 3/Al have been published. There is, as yet, no generally accepted mechanism for the boron ductilizing effect. Nevertheless, the ability to produce ductile Ni/sub 3/Al permits determination of other mechanical properties over a range of temperatures. With the exception of a brief report of cyclic life and crack growth behavior of Ni/sub 3/Al+B there are no published data on the resistance of boron-doped Ni/sub 3/Al to cyclic loading. In this paper the results of crack growth experiments on polycrystalline Ni/sub 3/Al prepared by ingot metallurgy are reported. Tests have been carried out at 250C in air and in vacuum at 5000C and 6000C. Crack growth thresholds are higher than in conventional alloys, perhaps because of difficulty in nucleating dislocation pairs at a crack tip. Crack growth rates increase with temperature between 250C and 6000C in spite of a rising yield stress and decreasing notch sensitivity over the same temperature range. Environmental effects due to absorbed oxygen appear to be the most likely factor influencing crack growth rates at elevated temperatures