The purpose of the Advanced Turbine Airfoil Manufacturing Technology Program is to develop single crystal and directionally solidified casting technologies to benefit Advanced Turbine Systems (ATS) industrial and utility gas turbine engines. The focus is on defining and implementing advanced Vacuum Induction Melting (VIM) furnace enhancements that provide precise control of mold temperatures during solidification. Emphasis was placed on increasing the total magnitude of thermal gradients while minimizing the difference in maximum and minimum gradients produced during the solidification process. Higher thermal gradients produce microstructural refinement and a reduction in grain defects and elemental segregation can be achieved. Reducing the difference in the maximum and minimum thermal gradients assists in maintaining a planar unidirectional solidification front for improved crystal quality. Advanced VIM casting techniques were applied to Solar Turbines Incorporated's Titan 130 First Stage High Pressure Turbine Blade under the ATS program. The advanced VIM techniques demonstrated an increase in maximum thermal gradients of 62% in the airfoil and 92% in the root over the conventional process. Microstructural refinements were obtained and benefited the homogenization behavior during solution heat treatment. Partitioning of heavy, slow diffusing elements, such as rhenium, tungsten, and tantalum, after heat treatment were significantly reduced in the airfoil and root sections of the blade. A comparison of the advanced VIM casting process to the conventional Bridgeman casting process will be presented as it pertains to the thermal gradients achieved during solidification, microstructure, elemental partitioning characterization, and solution heat treat response.
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