Effect of silicide coating on mechanical properties of Nb‒Ti‒Al alloys

he low-density Nb‒Ti‒Al alloy ingots were prepared by vacuum arc furnace smelting method in this paper, the Si‒Cr‒Ti composite silicide coatings were deposited on the surface of Nb‒Ti‒Al alloys by the slurry sintering method, and the universal electronic tensile testing machine was used to study the effect of silicide coating on the mechanical properties of the uncoated and coated alloys. The results show that, the mechanical properties (tensile strength, yield strength, and elongation) at room temperature of the coated low-density niobium alloys are significantly reduced, comparing with the uncoated alloys. To investigate the reasons for the decrease in the mechanical properties of the uncoated alloys, the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to observe the microstructure, analyze the composition of interface between coating and substrate, and test the C content (mass fraction) of the uncoated and coated alloys. In the results, the main reasons for the decrease in the mechanical properties of the coated niobium alloys are the significant growth of the alloy grains, the outward diffusion of the strengthening element Al, the formation of the brittle phase Nb₃Al, and the “seepage effect” of the alloy due to the Si‒Cr‒Ti coating.