Microstructure and properties of in-situ synthesized (Ti3Al + TiB)/Ti composites by laser cladding

Abstract

(Ti3Al + TiB)/Ti composites were fabricated on Ti6Al4V substrates by laser cladding (LC) to improve the wear and high temperature oxidation resistance simultaneously. The microstructures of the coatings were analyzed; the strengthening mechanisms of the coatings were studied; the wear and high temperature oxidation resistance of the coatings were investigated and compared with those of the substrates. The results showed that the mixed Ti and AlB2 powder with 4:1 weight ratio was optimized as the best material system for the process. During cladding, AlB2 fully reacted with Ti in the molten pool to in-situ form Ti3Al and TiB particles in the α-Ti matrix. Dispersion strengthening provided the most significant effect to improve the hardness of the coating. The wear resistance of the coating was obviously improved compared with that of the substrate because of the high hardness of the coating produced by the reinforcements as well as the maintained good toughness due to a sufficient amount of soft matrix. The friction coefficient decreased from 0.65 of the substrate to 0.29 of the coating and the average wear loss of the coating was 12.5% that of the substrate. The weight gains of the coatings were obviously lower than those of the substrates under each oxidation condition, indicating a significant improvement of the high temperature oxidation resistance of the coatings. A mixed oxidation layer of TiO2 and Al2O3 was generated on the coated sample. Compared with the TiO2 layer on the substrate, the existence of Al2O3 made the layer structure denser and the adhesion with the coating more excellent, effectively hindering the diffusion of oxygen atoms.