Effect of LaB6 addition on the microstructure and properties of (Ti3Al + TiB)/Ti composites by laser cladding

An amount of LaB6 was added into the (Ti3Al + TiB)/Ti composites prepared on Ti6Al4V by laser cladding. The results showed that nano-scale La2O3 particles were formed through the in-situ reaction between La and O elements in the material system. With appropriate LaB6 addition (3.0%), the microstructure was refined and the second phase reinforcements were distributed more homogeneously. In addition, the oxygen elements in the coating were bound through the formation of La2O3, and the residual stress concentration was obviously reduced compared with that in the coating without LaB6 addition. However, the beneficial effect would be disappeared because of the tendency to create clusters when the additive content of LaB6 was excessive. During the solidfication process, the first generated La2O3 particles had a significant hetregeneous nucleation effect especially on the TiB phase in the coating. The grain refinement effect played the equally and even higher important role as the dispersion strengthening in the system. The microhardness and wear resistance of the coating with 3.0% LaB6 addition were improved. In addition, its high temperature oxidation resistance was also obviously increased, and the related mechanisms were discussed. (C) 2019 The Authors. Published by Elsevier Ltd.