Abstract: Nickel base superalloy articles, especially gas turbine disks, are provided with substantially enhanced resistance to crack growth through a specific heat treatment. The heat treatment employs a true solution treatment step followed by a subsolvus solution treatment step, followed by at least one aging step. The effect of this series of heat treatment steps is to provide a microstructure having an optimum arrangement of gamma prime particles, with respect to both size and location. Reductions in crack growth rates of several hundred percent relative to prior art heat treatments are achieved.