Accelerating the isothermal forging process of titanium aluminides by microstructure adaptive speed control, MSE, Darmstadt, 2018

Titanium aluminides (TiAl) are attractive materials due to their low weight, high strength, high temperature- and corrosion resistance. Currently, TiAl turbine blades produced by isothermal forging are being used in commercial aircraft jet engines. However, low ram speeds, costly dies and a required protective atmosphere makes the process relatively expensive, restricting implementation into other areas. Reducing the processing time can cut costs and in turn lead to a much wider range of applications for TiAl forgings. This project focuses on the TiAl alloy TNM-B1. During preliminary testing, the material displayed a pronounced peak in flow stress followed by a strong softening response. If this behavior can be utilized by accelerating the ram during softening, the processing time can be significantly reduced. The impact on microstructure and limits of such an acceleration are important to consider. Compression tests at constant and variable speeds are to be performed to map the flow behavior, microstructure development and damage criteria. Based on the results, a material model will be developed and used in simulations. The aim is to establish a process design, which can adapt and optimize the forging speed to a given microstructure within the limits of the material. TNM-B1 is a complex multiphase alloy, with highly varied deformation and recrystallization behaviors across the different phases. This implies the importance of a suitable heat treatment strategy to achieve high deformability during forging, as well as the desired final microstructure. Heat treatment procedures will be investigated with the aim of generating highly deformable and damage resistant microstructures prior to forging, and application specific microstructures after forging.