Hydrogen Isotope Retention And Permeation In Copper And Its Alloys

Copper has good thermal conductivity. Its alloys can remain high strength at high temperatures and the precipitation can relieve the hardening and swelling of the materials induced by irradiation. As a result, the copper and its alloys are widely used as the heat sink materials in the fusion devices. The retention and permeation behavior of hydrogen isotopes may occur for all the materials that are exposed to hydrogen isotopes in the fusion devices, which then raises safety and economy issues. So it is vital to study the retention and permeation behavior of hydrogen isotopes in copper and its alloys. Until now, relevant research work on deuterium retention and permeation behavior in copper and its alloys (especially Al2O3 dispersion strengthened copper alloy) is limited. Experiments employing thermal desorption spectroscopy (TDS) and gas driven permeation (GDP) can provide basic data of copper for potential fusion application.The oxygen-free copper, CuCrZr and two kinds of Al2O3 dispersion strengthened copper alloys (imported and domestic) have been exposed in deuterium gas, followed by TDS experiments. The results show that both the CuCrZr and oxygen-free copper have one desorption peak, while two kinds of Al2O3 dispersion strengthened copper alloys have two desorptfon peaks. The total desorbed amount of the CuCrZr and the domestic Al2O3 dispersion strengthened copper alfoy is higher than that of the imported Al2O3 dispersion strengthened copper alloy. By comparison, deuterium retention in the oxygen-free copper is the lowest. It was found by a nitrogen-oxygen analyzer that free oxygen content in the domestic Al2O3 dispersion strengthened copper alloy is larger than that in the imported one. The high content of free oxygen may be one of the reasons that the domestic Al2O3 dispersion strengthened copper alloy has relatively larger total desorbed amount, which are also confirmed by deuterium water pressure for the four tested materials in the TDS experiments and the SEM observation. The TDS experiment of the copper is simulated using the TMAP (Tritium Migration Analysis Program). However, modeling using defect density distribution of both uniformly bulk detects and surface detects cannot fit the TDS results. The desorption peaks of the deuterated water and the deuterium gas of the copper are consistent, which implies that the desorption of the deuterium water may be an reason for the deuterium gas desorption in oxygen-free copper.The permeation behavior of deuterium in the Al2O3 dispersion strengthened copper altoy has been investigated in this work as well. The deuterium permeability and diffusion coefficient have been measured at temperatures from 621 K to 803 K. The equilibrium permeation flux is directly proportional to the square root of the driven gas pressure The permeability and diffusion coefficient are consistent with the Arrhenius equation in this temperature range. Compared with the literature data of the oxygen-free copper and CuCrZr, the permeability of the Al2O3 dispersion strengthened copper alloy shows no significant difference, while the diffusion coefficient is tower. With the decrease of temperature, the difference in diffusion coefficient is more significant. The tower diffusion coefficient for Al2O3 dispersion strengthened copper alloy was considered to be induced by relatively high defect density and high detrapping energy for hydrogen isotopes.