Aluminum-niobium alloys produced by laser surface alloying: their structure and properties

Aluminum-niobium alloys present considerable strength and hardness, being promising materials for structural applications and as coatings. This paper reports results of a study on the structure and properties of Al-Nb coatings produced by laser alloying. Sound, defect-free coatings are produced, provided that proper surface treatment techniques are used. The composition of the surface layers was Al-37.6 (+/-3) wt.% Nb and their microstructure is formed of dendrites of Al3Nb and a small volume fraction of interdendritic alpha-Al. The Vickers microhardness of the surface alloys is high, owing to the large amount and fineness of Al3Nb intermetallic compound. It varies from 480 to 650 HV, depending on the volume fraction and dendrite arm spacing of Al3Nb dendrites. Despite the brittleness of Al3Nb the coatings did not show any tendency to crack, probably because of the presence of the thin interdendritic film of ductile alpha-Al, which allows for a better accommodation of the generated stresses, and stops the propagation of microcracks that may develop in the intermetallic compound particles.