Study on the IFBA pellets coating process

ZrB₂ coating was deposited on UO₂ ceramic surface using domestic multi- target magnetron sputtering machine. The coating thickness, morphology, phase structure, composition, adhesion of ZrB₂ coating and deposition rate were analyzed by OM, SEM, XRD, ICP-OES, Peel test with adhesive tape. The effects of coating process conditions such as cleanliness pellet surface, sputtering gas pressure, sputtering power density and speed of the drum were studied to know the changes in deposition rate and adhesion. The results are as follows: ZrB₂ coating deposition rate increases with increasing power density; ZrB₂ coating deposition rate sharply declined when the drum speed is greater than 0.6 rpm; when sputtering gas pressure is 1.8 mtorr, the maximum deposition rate is got and the adherence of coating and pellet base is very good; when the average kWh value within 44 kWh∼54 kWh, coating pellet adhesion (Z values) after heat shock treatment are much smaller than 0.0008 g, adhesion strength shows no significant change. After comparison, the adherence of coating and pellet base is better when UO₂ has higher surface cleanliness; the ZrB₂ coating has single-phase which growing perpendicular to the substrate surface and uniform thickness, and fine grain size. In summary, ZrB₂ coating meets the performance of IFBA pellets. (authors)