Scientists identify ways to decrease oxygen content during additive manufacturing

Titanium aluminides are lightweight structural materials used to manufacture turbine parts for the aeronautical industry. One such alloy, Ti-43.5Al-4Nb-1Mo-0.1B known commercially as TNM™, has characteristics which may allow weight reduction and increased performance of high temperature components. Unfortunately, titanium aluminides are prone to oxygen pickup during metallurgical processes which can lead to defects such as brittleness and decrease in ductility.

Previous attempts have been made to use laser metal deposition to repair defective and damaged turbine blades, but it can be difficult to minimize oxygen increase during these processes. Rittinghaus et al. identified causes of oxygen pickup during additive manufacturing and laser metal deposition, and developed ways to help control the negative effect.

The researchers discovered that the melt pool and powder particle size affect the final oxygen content in the alloy. They performed experiments with different process parameters and powder materials and learned that the usage of coarser powders can lead to decreased oxygen content.

“Larger powder particles contain less oxygen compared to small ones and additionally, processing large particles instead of small ones leads to a smaller oxygen content in the part,” Rittinghaus said.

Rittinghaus et al. hope future research will examine whether obtained results are valid for other titanium alloys and silicides and if similar effects can be observed in other additive manufacturing processes. They suggest that as a strategy to minimize oxygen content, large melt pools and coarse powders should be used.

Source: “Oxygen gain and aluminum loss during laser metal deposition of intermetallic TiAl,” by Silja-Katharina Rittinghaus, Veronica Rocio Molina Ramirez, Jonas Zielinski, and Ulrike Hecht, Journal of Laser Applications (2019). The article can be accessed at https://doi.org/10.2351/1.5096974 .