Temperature induced porosity in hot isostatically pressed gamma titanium aluminide alloy powders

In this study the occurrence of temperature induced porosity (TIP) in hot isostatically pressed (HIP) compacts of different gamma Titanium aluminide alloys was investigated. Two gamma Titanium aluminide alloys Ti-48.9at.%Al and an advanced Niobium containing alloy Ti-46at.%Al-9at.%Nb have been atomized by gas atomization and by centrifugal atomization in an inert gas atmosphere. The alloy powders were studied regarding porosity and the content of inert gas entrapped in the powder particles. Selected powder batches were hot isostatically pressed at 1280 °C and were investigated with respect to TIP evolution after a high temperature exposure to 1390 °C for short and long time periods. It was found that gas atomized Titanium aluminide alloy powders contain a certain amount of atomization gas, the concentration of which increases with the powder particle size. The amount of inert gas entrapped in centrifugally atomized powders is higher as compared to powders produced by gas atomization. The occurrence of TIP after high temperature annealing of the HIP’ ed compacts depends on the grain size, the processing medium (Argon or Helium), the amount of entrapped inert gas and the annealing time. Guidelines are presented for minimizing or prevention of TIP in γ-TiAl alloys processed by powder metallurgy.