Study On Microstructure And Properties Of Laser Cladding FeCrAl Coating On Zr702 Surface

Zirconium alloys have excellent thermal conductivity,low thermal neutron absorption cross section coefficient,and excellent nuclear performance.They are currently widely used as cladding materials for light water nuclear reactors.However,the safety issues exposed by existing zirconium alloys under accident conditions pose higher requirements for the performance of cladding materials.Surface modification technology can solve the problems of high temperature oxidation rate and poor wear resistance of zirconium alloys during service under harsh conditions while maintaining their original advantages.It is one of the important ways to further improve the properties of zirconium alloy materials.Based on this,FeCrAl coating manufactured by laser cladding technology on the surface of Zr702 in this article.The effects of process parameters on the microstructure,microhardness,wear resistance,and high-temperature air oxidation performance of the FeCrAl coating were studied.Aiming at the cracking problem of the FeCrAl coating and oxide layer exposed during high-temperature oxidation,the rare earth element Y was introduced to improve it,and the effect of the addition of Y element on the microstructure and properties of FeCrAl coating was investigated,and the influence of the amount of Y element on the microstructure and properties of FeCrAl coating was revealed.The main research contents and conclusions are as follows:（1）The effects of laser power and scanning speed on the microstructure,microhardness,and wear resistance of FeCrAl coatings were studied.The results show that when the laser power is 1600 W and 1800 W,the surface structure of the costing is dense,without obvious defects,the interface between the coating and the substrate is fully fused,and the molding quality is good.With the increase of scanning speed,the grain size of the coating decreases,and the cracking tendency decreases.When the laser power is 1600 W or above,the microhardness of the coating tends to decrease with the increase of laser power and scanning speed.When the laser power is 1600 W and the scanning speed is 8 mm/s,the average microhardness of the coating is the highest,698.75HV0.2.When the laser power is 1600 W and the scanning speed is 9 mm/s,the coating has the lowest wear amount and the best wear resistance.（2）The oxidation behavior of FeCrAl coatings in air at 800℃and 1000℃was studied.The results show that when oxidized in air at 800℃,the laser power is 1600 W,and the scanning speed is 9 mm/s,the oxide layer of the prepared coating remains intact after 120minutes and 24 hours of oxidation,without cracking and peeling off.During oxidation for 120min,the oxidation products on the surface of FeCrAl coating are mainly mixed oxides of Fe,Cr,Al,and Zr.A small amount of Zr O₂can improve the adhesion of the oxide layer.According to oxidation thermodynamics and kinetics,the oxidation process of the coating is relatively slow and the high-temperature oxidation resistance is good.At 24 h,Al is consumed,and the oxidation products are mainly oxides of Fe and Cr.At this time,the oxide layer formed has a certain thickness,which can protect the Zr702 substrate.When oxidized in air at1000℃,the surface of the coating prepared at a laser power of 1600 W and a scanning speed of 9 mm/s remained intact after 120 minutes of exposure to air at 1000℃,and the oxide layer did not crack or fall off.At this time,the oxidation product is mainly Fe Cr₂O₄spinel oxide layer with Fe-rich agglomerated oxides distributed on it,and the thickness of the coating oxide layer is far lower than that of the substrate.However,due to cracks in the coating/bonding interface,the oxidation weight gain per unit area of the coating sample is slightly higher than that of the substrate.（3）The effect of the amount of Y element added on the microstructure,microhardness,and wear resistance of the coating was studied.The results show that adding Y element can inhibit the diffusion of Zr element towards the coating direction,increase the phase of Fe-Cr solid solution,and eliminate the segregation phenomenon of Cr element,making the structure more uniform.When the addition amount of Y is 0.5 wt.%,the content of Zr element in the coating is the lowest,and the microhardness is the highest.The friction and wear test results show that the addition of Y element can lead to a decrease in the wear performance of the coating.（4）The effect of the amount of Y element added on the oxidation behavior of the coating in air at 1000℃was studied.The results show that the addition of Y can reduce the cracking phenomenon of the coating and oxide layer,thereby improving the high-temperature oxidation resistance of the coating.When the addition of Y is 0.5 wt.%,the oxidation weight gain per unit area is the lowest.