Processing of β-solidifying and peritectic titanium aluminides by laser powder bed fusion

Kurzfassung

During the last years we investigated the processing of titanium aluminides with laser powder bed fusion (LPBF). In this presentation we address the challenges related to the required high pre-heat temperatures and discuss microstructure formation for different titanium aluminide types. On the one hand, high preheat temperatures are necessary to overcome the formation of critical macro cracks, while, at the same time, they can lead to unacceptable oxygen pick-up, unless very high purity Ar atmospheres are applied during LPBF, which is essential, as titanium aluminides are prone to oxygen embrittlement. A further challenge is to overcome the trade-off between porosity and Al evaporation by optimization of the energy density of the LPBF. Due to the fast cooling conditions during LPBF, as-built titanium aluminides are generally metastable, but the phase inventory and the degree of metastability strongly differs between the titanium aluminide types, the energy density of the LPBF process and pre-heat temperatures. We describe the microstructure formation for the whole process chain of β-solidifying and peritectic titanium aluminides beginning with the powder and the LPBF process and study phase transformations during heat treatments in situ by synchrotron high energy X-ray diffraction.