| Titanium alloy has many characteristics,such as light weight,high strength,heat resistance,good high temperature mechanical properties and hot workability,and it is widely used in aviation,aerospace,engine and other fields,however,the poor oxidation resistance at high temperature limits its further application in high temperature and complex service environment.It is an ideal method to solve the problem that clad a protective coating with high temperature oxidation resistance on the surface of titanium alloy.Ti-Si and Ti-Al compounds have the characteristics of low density,high melting point and hardness,good temperature stability and oxidation resistance,and they get more and more people's favor in the new generation of high temperature structural parts.Therefore,it is an effective way to improve the high temperature oxidation resistance of titanium alloy by preparing Ti-Al-Si composite coating with the advantages of Ti-Si and Ti-Al compounds.In this paper,the Ti-Al-Si coating with good macroscopic quality,no pores and cracks was fabricated by laser cladding on the surface of TC4 titanium alloy,with the combustion reaction of Ti,Al,Si mixed elemental powders by high energy laser beam.The microstructure and phase composition of the coatings were characterized by X ray diffraction?XRD?and scanning electron microscopy?SEM?.The microhardness and the corrosion resistance in artificial seawater of the coatings were investigated by means of microhardness tester and electrochemical workstation.The oxidation resistance and antioxidation mechanism of the coating at 800 ?×24 h×5 cyclic oxidation were analyzed by the oxidation weight gain and oxidation kinetics curves.The results of XRD and SEM show that the Ti-Al-Si coating and titanium alloy substrate have good metallurgical bonding,and the coating is composed of Ti5Si3,Ti7Al5Si12,Ti3Al,TiAl and TiA13.According to the results of microhardness test,the microhardness of the coating increased significantly compared with the substrate,and the maximum average microhardness was 853.3 HV0.2,which was 2.37 times of the substrate.And according to the oxidation kinetics curve under the condition of 800 ?×24 h×5 cyclic oxidation,the best oxidation resistance of the coating was 12.5 times higher than that of the substrate under the condition of 800?×24 h×5 cyclic oxidation.In the artificial seawater corrosion environment,the polarization curves show that the corrosion potential increases and the corrosion current density decreases obviously compared with the titanium alloy substrate.The main reason for the high temperature oxidation resistance of laser cladding Ti-Al-Si coating is reflected in two aspects:one is the surface of the coating obtained a continuous dense oxide layer,hindered the diffusion of oxygen;two is to improve the adhesion of the oxide layer,so that the oxide layer is not easy to peel off the surface of the coating.When the laser power is 3.5 kW,the scanning speed is 350 mm·min-1,the defocusing amount is 45 mm,the circular spot diameter is 3 mm,and the Ar protection gas flow rate is 25 L·min-1,the ideal Ti-Al-Si coating can be obtained. |
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