Investigation Of Phase Precipitation Sequence Calculation And Formation Mechanism At Interface In Oxidation Resistant Coating On Titanium Surface

Titanium and titanium alloys are widely used in aerospace,chemical,shipbuilding and other fields.However,when served in a high-temperature environment,titanium and titanium alloys are easily oxidized and produce oxide scales on the metal surface,resulting in a decrease in the overall mechanical properties of the components.Depositing high-temperature oxidation-resistant coatings on the surface of titanium and titanium alloys is an effective measure to improve the oxidation resistance of titanium and titanium alloys.Exploring the formation order and mechanism of the anti-oxidation phase in the coating will help to understand the anti-oxidation mechanism of the coating.The formation sequence and formation mechanism of intermetallic compounds in pure Al,Al/Ni and Al/Cu coatings on Ti surface were systematically studied by calculation prediction and experimental observation in this paper.The calculation of the phase formation sequence in the coating was carried out by using the effective heat of formation model(EHF),and the first-principles calculation method was used to obtain the thermodynamic data required in the calculation.Afterwards,pure Al,Al/Ni and Al/Cu coatings were prepared on the Ti surface by arc spraying and plasma spraying techniques.Put the coating in a resistance furnace for different heat treatment at 800?.Use scanning electron microscope(SEM),energy dispersive spectrometer(EDS),X-ray diffractometer(XRD)and other methods to analyze the generation rules of phases in each coating.Finally,the preferential adsorption positions of oxygen atoms on the low index surfaces of Ti Al₃,Ni Al and Al₂Cu were calculated.The research results show that the order of phase formation in pure Al coating is Ti Al₃?Ti Al₂?Ti Al?Ti₃Al,the order of phase formation in Al/Ni coating is Ni Al₃?Ni₂Al₃?Ni Al?Ni₃Al,and the order of phase formation in Al/Cu coating is Al₂Cu?Al Cu?Al₄Cu₉.The Ti-Al compounds generated at the Al/Ti interface do not show preferential grain orientation.As the heat treatment time increases,after the phases in the pure Al and Al/Cu coatings are sequentially formed,the types of phases no longer change,but the phases in the Al/Ni coating have evolved.The presence of intermetallic compounds in the three coatings has a pinning effect on the diffusion of oxygen,so that oxygen atoms can only diffuse from the gaps between the compounds.The oxygen adsorption calculation results show that the Al-Al bridge is the preferential adsorption site on the(110)low index surface of Ti Al₃,Ni Al and Al₂Cu.O-Al is more likely to bond on the surface of the compound to form Al₂O₃ film that hinders oxygen diffusion.