Abstract
Fracture toughness values and tensile properties were determined in the Fe-Ni-Co superalloy IN903* as a function of hydrogen concentration, loading rate, and grain size to define the effects of hydrogen on fracture toughness and failure modes. Tests using precracked, precharged three point bend samples showed that fracture toughness decreased from 90 to 50 MPa-m1/2 as hydrogen increased from zero to 5000 appm. The decrease in fracture toughness was accompanied by a fracture mode change from microvoid coalescence in the uncharged samples to principally slip band fracture with some twin band and ductile intergranular fracture in the hydrogen charged samples. Fractographic observations and application of ductile fracture toughness models showed that fracture initiated at matrix carbides in all samples. These carbides established the critical fracture distance for all fracture processes observed in the fracture toughness samples. Hydrogen promoted the secondary fracture processes of slip band, twin band, and ductile intergranular fractures which lowered both the critical fracture strain and the fracture toughness of IN903.
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