Preparation Of TiMo/FeCrAl Based Composite Coating On The Surface Of Zirconium Alloy And Its High Temperature Oxidation Behavior

After the Fukushima nuclear accident,the safe operation of the reactor has become a hot topic for researchers of nuclear materials all over the world.It has become urgently necessary to find a solution in the existing cladding design and preparation for how to further safely and effectively increase the tolerance conditions of cladding materials under accident scenarios.The concept of Accident Tolerant Fuel(ATF)was proposed in time and received widespread attention.FeCrAl alloy coating has been widely concerned because of its excellent oxidation resistance at high temperature.However,the diffusion between the coating and substrate is still the biggest problem limiting its application at high temperature.In this research,TiMo,FeCrAl,FeCrAlSi,TiMo/FeCrAl,TiMo/FeCrAlSi and TiMo/(FeCrAlSi)N coatings were prepared on the surface of zirconium alloy by magnetron sputtering.Systematically investigated were the effects of adding a TiMo buffer layer and non-metallic components on the coating’s microstructure,hydrophilicity,hydrophobicity,adhesion,and high temperature oxidation resistance.The intact and continuous TiMo,FeCrAl and FeCrAlSi coatings were successfully prepared on zirconium alloy surface with the same process parameters.Through the test of coating contact angle and film-based adhesion,it was found that the water contact angle of FeCrAlSi coating was more than two times than that of TiMo and FeCrAl coatings,and the adhesion was stronger than that of TiMo and FeCrAl coatings.The surface of the single-layer FeCrAl coating remained intact and showing good high-temperature oxidation resistance after oxidation in air at 800℃for 60 min,with low oxidation weight gain(4.1 mg/cm~2).The damage of TiMo coating during high temperature steam oxidation at 1000℃could not protect the zirconium alloy substrate.The FeCrAl and FeCrAlSi coatings remained intact,but the coating cracks and warpage limit the protective effect of the coating.TiMo coating was used as buffer layer to improve the oxidation resistance of FeCrAl coating.It was found that the bias voltage had a great influence on the properties of the coating.The TiMo/FeCrAl composite coating prepared at 200 V bias voltage had better hydrophobicity(79.85°)and better bonding strength than bare zirconium alloy.The oxidation weight gain per unit area of TiMo/FeCrAl composite coating(2.97mg/cm~2)prepared by 0 V bias voltage at 800°C for 60 min was significantly better than that of bare sample(5.05 mg/cm~2).And the deposited phase structure was still retained,which can effectively protect the zirconium alloy substrate from oxidation.The TiMo/FeCrAl composite coating blistered obviously during high temperature steam oxidation at 1000℃.The internal stress generated during the preparation of the coating under a large bias voltage was the main cause of coating failure.The effect of doping elements on the oxidation resistance of TiMo/FeCrAl composite coating were further explored by doping Si and N on the surface of TiMo/FeCrAl composite coating.It was found that the weight gain per unit area(2.56mg/cm~2)of TiMo/(FeCrAlSi)N composite coating with smooth surface and excellent film-substrate bonding was significantly better than that of bare zirconium alloy after high temperature air oxidation at 800℃.Cracks appeared in the coating but did not damage the overall integrity of the coating.The surface of TiMo/FeCrAlSi composite coating and TiMo/(FeCrAlSi)N composite coating remained intact under oxidation at1000℃with steam.The addition of non-metallic elements Si and N can effectively improve the oxidation resistance of TiMo/FeCrAl composite coating.