Effects of neutron irradiation on VPS-W coated ODS ferritic steels

In present study, the effects of neutron irradiation on the hardness of W-coated ODS steels were investigated. Vacuum plasma spraying (VPS) technique was employed to fabricate W layer on the surface of substrates. Substrate materials were K1-, K4-ODS ferritic steels and F82H steel, which are 3 mm thick plates. Tungsten powder of 99.9% high purity was used for VPS process. The powders were sprayed by the plasma jet of argon and hydrogen mixture to the surface of substrats pre-annealed at 773K. VPS-W coated specimens were irradiated at 723K to 4.5, 9.6 dpa in the High Flux Isotope Reactor (HFIR), respectively. To investigate the effect of neutron irradiation on joint area, the hardness distributions were evaluated on the cross section using a micro Vickers hardness tester. Microstructure analysis revealed that W was successfully coated on each substrate by VPS process, in spite of mismatch of the CTE between these materials. The hardness of W was significantly varied from 260 to 480 Hv because inhomogeneous cooling rate during the process. After irradiations, irradiation hardening was occurred in the VPS-W, while substrate materials did not. (author)