| Nuclear fusion reactions can release enormous energy and thus may satisfy the human sustainable demand for energy.Preventing the leakage of tritium fuel has become one of the key engineering problems in the thermonuclear fusion reactor.The main method to solve this problem is to prepare the tritium permeation barrier on the surface of reactor structural materials.As reported in the literature,ceramics are the most ideal material as tritium permeation barrier.Therefore,the study on ceramic tritium permeation barrier is of great importance for the application of nuclear fusion energy.In this paper,the alpha-Al2O3/AlPO4 composite ceramic coating was successfully prepared on 316L stainless steel by the thermal chemical reaction method.The sealing effect of alpha-Al2O3/AlPO4 colloid slurry on plasma sprayed coatings as well as on the coating performance was further studied.The main results are as follows:Firstly,the preparation process and composition of the coating slurry were studied.The results showed that when the Al/P ratio was 1:3.18,the bonding phase of the prefabricated coating was Al（H2PO4）3,which was beneficial to improve the adhesion of the coating.Alpha-Al2O3 can promote the transformation of AlPO4 into the cube phase.When the relative content of alpha-Al2O3 was about 72%,the coating was rather compact.The heat treatment process of the coating showed that the sintering process could be divided into three stages:loss of crystalline water,chemical reaction and phase transition.The sintering temperature and heating rate had great influence on the solidification of the coating.The curing extent of the coating was different with varying sintering temperatures.The curing effect was the best when the sintering temperature was about 500℃,and the bonding strength of the coating can reach up to 14.6 MPa.The optimal heating rate was3-5℃/min.The study on the structure and properties of alpha-Al2O3/AlPO4 coating showed that the coating was uniform,dense and smooth with good adhesion,excellent corrosion resistance and hydrogen permeation resistance.The hydrogen permeability of the alpha-Al2O3/AlPO4coating was only 1/29 of the substrate,and 1/7 of the plasma sprayed coating.The results showed that decreasing the coating thickness would improve its thermal stability.The thermal shock resistance of the coating reached up to 150 times when the thickness was lower than 30μm.The composite coating was fabricated by combining thermal chemical reaction method and plasma spraying technology.The test results showed that the composite coating was more compact and smooth.Surface roughness decreased from 2.123μm to 0.216μm.The sealing thickness of the plasma sprayed coating was about 15-25μm,and the density was improved remarkably with porosity decreased from 3.19%to 0.24%.The performance of the composite coating after sealing treatment showed that the permeability reduction factor（PRF）of the coating increased from 4 to 64.Binding force reached 13.2 MPa.Thermal shock resistance of alpha-Al2O3/AlPO4 coating with thickness of 80μm was about 60 times,while the thermal shock resistance of the composite coating with the same thickness was up to 180 times.The Vivtorinox hardness of bottom layer and top layer of the composite coating was 220 HV and 1097 HV,respectively. |
