J. Gayda, T. Gabb, NASA Glenn Research Center, Cleveland, OH; P. Kantzos, Ohio Aerospace Institue, Cleveland, OH; B. Palsa, Ohio State University, Columbus, OH

Summary:

The dual microstructure heat treat (DMHT) process makes it possible to tailor the mechanical properties of the turbine disk to meet the location specific requirements of the gas turbine engine. The DMHT process produces a high strength, fine grain (subsolvus) microstructure in the bore region to meet the burst strength requirements; and a coarse grain (supersolvus) microstructure in the rim region, where higher disk temperatures require superior creep and dwell crack growth resistance.

A new low cost DMHT process has recently been developed at NASA GRC. The primary focus of this study was to establish the robustness of this process by characterizing the mechanical properties (strength, creep, and LCF) of the transition region between the coarse and fine grain microstructure. For any DMHT process this is a critical region which requires thorough evaluation to demonstrate microstructural soundness and the ability to meet acceptable mechanical property requirements.

Although the mechanical properties of most materials can be determined through mechanical testing using standard specimens such as tensile, creep, and fatigue crack growth bars; such test specimens don�t always represent the inherent full scale properties of the component. For example, due to the necessary sectioning required in producing such test specimens, they typically lack the inherent residual stress state present in the full scale component. The subscale nature of standard test specimens, may also fail to capture, or misrepresent, any long range mechanical property gradients due to microstructure, cooling rate, and segregation etc� For these reasons, in this study, the mechanical properties of the transition zone were evaluated through standard test specimens as well as spin pit testing using a full scale yet simple disk test specimen. The results of both the coupon level mechanical tests as well as the results of the full scale disk tests will be presented.