The effect of rare-earth element additions on microstructural properties and irradiation behavior of an Fe-Ni-Cr alloy for LMFBR and fusion reactor applications

摘要

This study consists of a survey of the effect of yttrium, lanthanum, and cerium rare-earth additions on the microstructure and radiation swelling behavior of an Fe-25.6Ni-8.7Cr-3.3Ti-1.6Al alloy. The undoped alloy was investigated in the as-received, annealed, and arc-melted conditions, and twelve arc melted and rare-earth doped alloys were prepared (doping levels of 0.05, 0.1, 0.5, and 1.0 wt % for each of the three rare earths). The ion bombardments were carried out at 570 and 600(DEGREES)C with 4 MeV Ni or Fe ions to nominal 100 dpa and to 100 and 550 appm He. Lattice parameter, hardness, swelling, and optical and transmission electron microscopy observations were conducted;Ion bombardment at 600(DEGREES)C produced negligible swelling. For ion bombardment at 570(DEGREES)C and helium implantation to 100 appm He, the as-received, annealed, and arc-melted undoped alloy swelled 4.0, 5.1, and 3.8%, respectively. The increase in swelling upon annealing the as-received alloy is believed to be due to the removal of cold work. The subsequent decrease in swelling upon arc melting is interpreted in terms of the reduction in size of the large Ti-rich precipitate and the consequent increase in Ti in solid solution. For ion bombardment at 570(DEGREES)C and helium implantation to 550 appm He, the arc-melted undoped alloy gave 5.2% swelling (as compared to 3.8% for 100 appm He) due to the higher helium loading;The introduction of yttrium or cerium at levels between 0.1 and 1.0% gives rise to a reduction in swelling. This may be due to a decrease in the amount of G-phase precipitate and the size of the large Ti-rich particles. For concentrations above 0.5%, a rare-earth-rich precipitate appeared. At 1% concentrations, the precipitates were observed to swell themselves and to give rise to bulk matrix swelling. The optimum concentrations of Y or Ce for swelling reduction are therefore, considered to be about 0.2-0.4%. Lanthanum additions were not observed to suppress swelling;Unique surface deformations were observed as a result of ion bombardment, especially at and near grain boundaries. At low swelling, the grain boundary region was raised or ridged, probably because of the lateral extrusion-like action of the swelled grains. At higher swelling, the grain bodies were elevated above the grain boundary regions.