A design of self-generated Ti–Al–Si gradient coatings on Ti–6Al–4V alloy based on silicon concentration gradient

Abstract A new method, referred to as Self-generated Gradient Hot-dipping Infiltration (SGHDI), was proposed to prepare Ti–Al–Si gradient coatings on Ti–6Al–4V alloy. The coating samples with different dipping time (20, 30, 40, 50 and 60 min) were prepared at the dipping temperature of 800 °C. The microstructure, phase structure and composition of the coating were observed by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results demonstrated that the silicon concentration gradient coatings were in the sequence of Ti(Al,Si)3 phase, τ2 (Ti(AlxSi1-x)2) phase + Liquid-(Al,Si) phase, and Liquid-(Al,Si) phase from the substrate. The high temperature oxidation kinetics data of samples with a hot-dipping time of 60 min showed that the coating exhibited good high temperature oxidation resistance. The main advantage of this design of coatings lies in that in addition to the dense Al2O3 layer formed at high temperature to block oxygen atoms, the newly formed dense alloy layers during high temperature oxidation would stop crack growth in the coatings, further preventing oxygen atoms from entering the substrate.