Determining the oxidation behavior of metal powders during heating through thermogravimetric and evolved gas analysis using a coupled thermogravimetry-gas chromatography-mass spectrometry technique

• Evolved gas analysis of superalloy powders using coupled TG-GCMS method.
• Develop techniques to study powder injection moulding (PIM) part processing.
• Determine oxidation of superalloy metal powders in industrially relevant processing conditions.

The oxidation behavior of a fine Ni superalloy (NiSA) powder, Inconel 625, within an alumina support powder during heating has been determined using combined thermogravimetry (TG) and evolved gas analysis (EGA). A gas chromatographic-mass spectrometer (GCMS) was used for EGA. The GCMS was able to semi-quantitatively measure the rate at which air was removed from the furnace due to a He purge, where no pre-evacuation was used. It also was able to measure the effectiveness of a three cycle evacuation and He purge in reducing the oxygen content in the furnace and identify an important alumina off-gassing process that exposed the NiSA powder to H2O and CO2. The parallel use of the TG signal was able to quantitatively determine the relationship between NiSA oxidation and relative concentrations of the oxidizing gases created by the differing furnace pre-conditions and the alumina powder off-gassing process. It was concluded that the developed TG-GCMS method can be widely applied to quantitatively study oxygen pick-up in metal powders under industrially relevant processing conditions.