Evolution of beta grain size during beta phase processing of Ti-6A1-4V

Thermo-mechanical processing of Ti-6A1-4V above beta-transus temperature is currently rarely used for the production of structural components in aircrafts. A better forgeability and therefore a reduction of forging steps and material input would result in a significant cost reduction. The high temperature strongly influences the final microstructure. To reduce the risk of non conforming parts the limits of process variations must be well defined upfront. For that reason, the simulation of microstructure and in particular beta-grain size during closed die forging processes offers the possibility to predict the evolution of the microstructure and thus to optimize the whole thermo-mechanical process. The microstructure models discussed in this paper are capable to describe physical processes like grain growth and recrystallization of Ti-6A1-4V in beta phase field. Therefore the prediction of beta grain size in dependence of process parameters is possible. All models are calibrated with experimental as well as published data, thus their validity is given in the range of typical beta-processing temperatures, strains and strain rates. The semi-empirical models are linked to special purpose FE-code DEFORM™ in order to predict the evolution of beta grain size during thermo mechanical processing of critical aircraft components. Examples of simulation results as well as microstructural investigations are discussed in this paper.