Characterization of Laser Additive Manufacturing-Fabricated Porous Superalloys for Turbine Components

Abstract

The limits of gas turbine technology are heavily influenced by materials and manufacturing capabilities. Lately, incremental performance gains responsible for increasing the allowable turbine inlet temperature (TIT) have been made mainly through innovations in cooling technology, specifically convective cooling schemes. Laser additive manufacturing (LAM) is a promising manufacturing technology that uses lasers to selectively melt powders of metal in a layer-by-layer process to directly manufacture components, paving the way to manufacture designs that are not possible with conventional casting methods. This study investigates manufacturing qualities seen in LAM methods and its ability to successfully produce complex features found in turbine blades. A leading edge segment of a turbine blade, containing both internal and external cooling features, along with an engineered-porous structure is fabricated by laser additive manufacturing of superalloy powders. Through a nondestructive approach, the presented geometry is analyzed against the departure of the design by utilizing X-ray computed tomography (CT). Variance distribution between the design and manufactured leading edge segment are carried out for both internal impingement and external transpiration hole diameters. Flow testing is performed in order to characterize the uniformity of porous regions and flow characteristics across the entire article for various pressure ratios (PR). Discharge coefficients of internal impingement arrays and engineered-porous structures are quantified. The analysis yields quantitative data on the build quality of the LAM process, providing insight as to whether or not it is a viable option for direct manufacture of microfeatures in current turbine blade production.