Formation mechanism of Hf-based ceramic particles in tungsten alloys

To meet the requirements of high strength of tungsten (W) based alloys at high temperature applied in the aerospace field, the preparation and formation of Hf-related ceramic particles in W were studied. It is found that the HfO 2 phase with a size of about 500 nm was observed at the grain boundary in both W-0.26 wt.% HfC and W-0.25 wt.% HfH 2 -0.125 wt.% C systems. Further study of phase stability and thermodynamic properties of Hf(W)-O(C) compounds reveals that the HfO 2 phase possesses the most stability of all the Hf-related compounds, and the oxidation of Hf is preferred to the carbonization. It is predicted that more stability of W base metal, higher temperature, and higher carbon concentration can reduce the formation of HfO 2 while promoting the formation of the HfC particle phase.