Up-scaling the size of TiAl components made via ingot metallurgy

Abstract

The quality of wrought discs made from large Ti-45Al-5Nb-0.2B-0.2C (at. %) ingots has been assessed at various stages of processing. Such components suffer from different types of defects that can usually be traced back to structural and chemical inhomogeneities that are present in the starting ingot. In conventional manufacturing routes the imparted mechanical strain is often insufficient for complete dynamic recrystallisation, particularly for large parts. In an attempt to overcome these problems, a new multi-stage method has been developed, which has the advantages that: i) the strain is significantly higher than that imparted using conventional routes, ii) the flow direction of the material is inverted between the first and second processing stages in the sense that the length of the ingot is first increased via extrusion, and then the resulting extruded bar is shortened via axial forging in the subsequent processing stages, and iii) the geometrical constraints associated with the production of large components from ingots can be overcome. The reliability of the method has been assessed by metallographic and mechanical characterisation. The challenges that have to be addressed for the new technique to be employed for the manufacture of large components are discussed.