Microstructure And Properties Of Laser Cladding Al_xCoCrFeMoVTi High Entropy Alloy Coating On TC4 Titanium Alloy

TC4 titanium alloy is widely used as an important structural material in aerospace,petrochemical,automobile and ship industries due to its light weight,low density,high specific strength and yield ratio,good corrosion resistance and excellent weldability.However,due to the inherent shortcomings of low hardness,poor friction,wear resistance and high temperature oxidation resistance,titanium alloys are limited to be widely used as structural materials in complex service environment.The high entropy alloy coating prepared by laser cladding on TC4 titanium alloy has high microhardness,excellent wear resistance and high temperature oxidation resistance,which has gradually become a new technology way of titanium alloy surface modification.In this paper,Al_xCoCrFeMoVTi high entropy alloy coatings were prepared on the surface of titanium alloy by laser cladding with Al,Mo,V and Ti,added to CoCrFe based high entropy alloy.XRD,OM,SEM and EDS were used to characterize the phase structure and micro morphology of the coating with different Al content.The effects of Al content on the microhardness,wear resistance,high temperature oxidation resistance and electrochemical performance of the coating were investigated,the wear mechanism,oxidation mechanism and corrosion resistance of the coating were analyzed,The results are as follows:The coatings had good metallurgical bonding with the substrate TC4 titanium alloy,and had no obvious defects such as pores and cracks.The phase structure of the coatings were binary eutectic phase of BCC+FCC.With the increase of Al content,FCC gradually transformed to BCC.The microstructure of the coatings from right down to top were columnar crystal,dendrite,petal equiaxed crystal and free dendrite like structure.Columnar crystal mainly existed in the heat affected zone,the structure of the bonding zone was epitaxial dendrite,and the structure of the cladding zone was affected by surface oxygen and temperature Under the influence of gradient,petal like equiaxed crystals were formed.Al_xCoCrFeMoVTi(x=0,0.5,1,1.5)the microhardness of the coatings were 2.64,2.81,3.44 and2.61 times higher than that of TC4,the average friction coefficient of the coatings were 0.43,0.37,0.31 and 0.45,the wear resistance of the coatings were 2.78,4.19,8.33 and 2.64 times higher than that of TC4,the friction mechanism of Al0 coatings were abrasive wear and adhesive wear,and the wear mechanism of Al0.5 coatings were abrasive wear,adhesive wear and oxidation wear The results showed that the wear mechanism of Al1 coatings were abrasive wear and oxidation wear;the wear mechanism of Al1.5 coatings were abrasive wear and adhesive wear;the wear mechanism of TC4 titanium alloy substrate was adhesive wear with a small amount of erosion wear;the oxidation weight gain of the coatings were 48%,42.2%,16.4%and 55.6%of that of the substrate respectively after 50 h cyclic oxidation at 800?,and the material had high wear resistance With the increase of Al content,the corrosion resistance of the coating decreases too.