Surface alloying of titanium with aluminium by non-vacuum electron beam cladding of powder mixtures

Titanium aluminides are promising materials for structural and high temperature applications. They possess low density and a high strength level which are very important properties for the aircraft. However, they have a range of disadvantages. Among them, there are low plasticity and crack growth resistance. One of the solutions which allow making use of beneficial properties of intermetallics consists in the formation of intermetallic layers on the surface of metallic samples. In this study the method of non-vacuum electron beam cladding of powder mixtures consisted of aluminium and titanium was used to obtain the surface layers reinforced with intermetallics on cp-titanium workpieces. Microstructure, microhardness and tribological properties of surface alloyed materials were investigated. An average thickness of coatings was about 2 mm. The microstructure of coatings was characterized mainly by formation of lamellar crystals. The maximum microhardness level of the coatings was about 600 HV. The reasons of microhardness increase consisted in the formation of titanium aluminides and action of the solid solution hardening mechanism. Phase composition of different clads varied from γ-TiAl to α-Ti according to Al percentage in the powder mixture. In comparison with cp-titanium the obtained materials possessed a lower level of a friction coefficient and a lower tendency to adhesion at a contact with a steel indenter. The best results obtained in the process of a sliding friction test were obtained for the Ti-Al(10/35) sample. It possessed 3-4-fold decrease of a friction coefficient compared to pure titanium. Relative wear resistance values obtained during interaction of samples with fixed abrasive particles correlated with their microhardness.

titanium aluminides, electron beam cladding, structure, properties