Consideration of the influence of contamination from oxide crucibles on TiAl cast material, and the possibility of achieving low-purity TiAl precision cast turbine wheels

In order to promote the development of low-cost TiAl precision cast turbine wheels, consideration was given to the influence of reduced purity. In the research reported here, the contamination behavior of Ti–46 at%Al cast material from various oxide crucibles was examined, and the influence of impurities and inclusions on material properties of Ti–46 at%Al cast material was evaluated. As a result, it was found that oxygen concentration had the greatest effect on properties, although it was observed that a relatively high concentration of up to approx. 0.4 wt% did not reduce room temperature tensile strength. Next, upon attempting the precision casting of TiAl turbine wheels, it was confirmed that items produced from an yttria crucible and having oxygen concentration of 0.17 wt% had greater room temperature tensile strength than turbine wheels from a conventional water-cooled copper crucible, together with comparable toughness required in practical use. Accordingly, the upper limit for oxygen concentration in TiAl castings, formerly considered to be 0.1 wt%, can be revised upward, which is extremely beneficial from the standpoint of reducing production costs.