Analysis of crystallographic high temperature fatigue crack growth in a nickel base alloy

Crack growth behavior of a nickel-base alloy, Udimet 700, was studied at room temperature and 850 °C in air and vacuum. Crack growth rates were higher in air than in vacuum but this increase in growth rates was nearly the same at both temperatures. In contrast to the effect of environment, an increase of temperature from 25 to 850 °C has a much larger effect on growth rates although the mode of crack growth did not change with temperature or with environment. A detailed analysis of the fracture surfaces indicated that the growth rates under all of the above experimental conditions occurs by a crystallographic faceted mode with the plane of the facet identified to be the {100} cleavage plane rather than a slip plane. Also the increase in growth rates with temperature appears not to be directly related to an environmental effect, creep effect or variation of elastic modulus with temperature.