Study On The Ordering Phenomenon Of Amorphous FeW Alloy Coating And Its New Functionalities

Nuclear energy is one major clean energy alternative to fossil fuel. In the area of nuclear energy application, material selection is a major issue. There are two type of nuclear energy:nuclear fusion and nuclear fission. Among the materials used for nuclear fusion application, plasma facing material (PFM) is a key material determining the development of nuclear fusion application. Two major issues of PFM is to further improve the comprehensive performance of PFMs and strengthen the connection between PFMs and Cu-based heat sink materials. Among the area of nuclear fission, pressurized water reactor (PWR) is the first type of nuclear reactor developed and it is also the major type of fission reactor currently used. Inside the PWR, the materials are exposed to high temperature, high pressure and radiation produced by nuclear reaction. The harsh environment demands a higher requirement for materials.Amorphous FeW alloy coating is one type of functional material coating with excellent corrosion resistance. Amorphous FeW alloy coating has been well applied in industry. Meanwhile, it is also a potential material which could be applied in nuclear industry. In this thesis, based on the propose to study the ordering phenomenon of FeW amorphous alloy coating and its new functionalities, we studied the effect of electroplating parameters on the amorphous alloy coating. In the ordering phenomenon, effect of temperature on coating morphology, structure and corrosion resistance has been studied. We studied the bonding between dissimilar metals using FeW amorphous alloy coating as an intermediate layer. We also studied the corrosion resistance of the coating under radiation and investigated its hydrophobic surface-modification. The detailed study and results are as follows:(1) FeW amorphous alloy coating has been fabricated using direct current (DC) electroplating and double pulse electroplating. In DC electroplating, when current density increases to 0.1 A/cm2, the plating particle grows larger, with shallow pits being produced. When the current density further increases to 0.5 A/cm2, the plating particle becomes smaller, with the generation of large amount of pores of micrometer size. In pulse electrodeposition, compact and homogenous coating has been acquired when positive duty cycle is 10% and negative duty cycle is 30%.(2) Under vacuum condition, effect of heat treatment temperature on coating morphology, structure and corrosion resistance has been studied. When temperature reaches 700℃, the amorphous FeW alloy coating would be completely crystallized. When the temperature is 500℃, the coating shows optimum corrosion resistance.(3) We firstly proposed using amorphous FeW alloy coating as intermediate layer to achieve the diffusion bonding between W and Cu and between W and W/Cu alloy. When the bonding temperature is 950℃, the tensile strength of the bonding interface reaches 146 MPa. The new W/Cu-PFC module could withstand-30 min short-pulsed plasma in-situ radiation. The specimen with 100×100 mm2 size has been fabricated, which satisfies the requirement of the divertor to actual module.(4) We firstly studied the corrosion resistance of amorphous FeW alloy coating under gamma radiation. Under gamma radiation, strong oxidizing water radiolysis product, such as H2O2 has been produced. Therefore, the corrosion of Fe and W shows different reaction pathways. In addition, the presence of gamma radiation increases the corrosion potential of the sample.(5) For homogeneous porous coating prepared using DC electroplating, after heat treatment at 500℃ and 600℃, the surface was modified using (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane. Hydrophobic surfaces have been obtained with roughness of 82.2 and 117.5, respectively and contact angle of 111°±1°,134°±1°, respectively. After surface modification, the hydrophobic surfaces show higher corrosion resistance than hydrophilic surfaces without surface-modification.