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.