Microstructural characterisation of Al―Hf and Al―Li―Hf spray deposits

Microscopic examination of an Al—1.6 wt.%Hf and an Al—3.2 wt.%Li—1.6 wt.%Hf spray formed alloys revealed high density near the center axis with high porosity present at the edges of the spray deposits. Spherical particles with an apparent diameter of up to 140 μm were found near the center axis of the spray while larger particles were deformed upon impact on the substrate. The particle (drop) size as well as the grain size was found to decrease with distance from the center of the preforms. The intermetallic phases observed in the center of both deposits were filamentary L12―Al3Hf for the Al―Hf alloy and spherical/filamentary L12―Al3(Li,Hf) for the Al―Li―Hf alloy.

Research Highlights► The main mass in the spray was concentrated within an angle of 6° from the central axis. ► The gas jet angle downstream of the convergence region was approximately 25°. ► Spherical particles of up to 140 μm were observed near the perform centre axis. ► Al-1.6wt%Hf preform grain size decreased with distance from the spray symmetry axis. ► Filamentary L12-Al3Hf and L12-Al3(Li,Hf) precipitates were observed in both performs. ► δ′ precipitates were observed in the Al-1.6wt%Hf-3.2wt%Li preform.