Synthesis of Al-B4C composite coating on Ti-6Al-4V alloy substrate by mechanical alloying method

An Al-B4C coating was synthesized on Ti-6Al-4V alloy substrate with Al and B4C powder mixture by means of mechanical alloying. The coating had a B4Cp/Al metal matrix composite structure. The effects of the annealing treatment on the microstructure, the mechanical properties and the high-temperature oxidation resistance of the coating were investigated. The annealed coating had a bi-layer structure. The inner layer was an Al3Ti layer and the outer layer consisted of Al3BC, AlB2 and residual Al and B4C. The adhesion behavior of the coating decreased after annealing treatment. The microhardness of the coating was improved to > 4 times of the substrate hardness because of the formation of ceramic and intermetallic phases. The coatings could protect the substrate under dry sliding conditions. The oxidation resistance of the coating was improved after annealing. In the annealed coating, on the one hand, the B4C particles were surrounded by Al3BC, which could prevent the direct oxidation of B4C during oxidation; on the other hand, the thick Al3Ti layer could act as an oxygen barrier to retard the inward diffusion of oxygen. The annealing treatment could improve both the surface mechanical properties and the high-temperature oxidation resistance of the Al-B4C coating.