@article{OuAnwandKoegleretal.2014, author = {Ou, Xin and Anwand, Wolfgang and K{\"o}gler, Reinhard and Zhou, Hong-Bo and Richter, Asta}, title = {The role of helium implantation induced vacancy defect on hardening of tungsten}, series = {Journal of Applied Physics}, volume = {115}, journal = {Journal of Applied Physics}, number = {12}, issn = {1089-7550}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-5623}, year = {2014}, abstract = {Vacancy-type defects created by helium implantation in tungsten and their impact on the nano-hardness characteristics were investigated by correlating the results from the positron annihilation spectroscopy and the nano-indentation technique. Helium implantation was performed at room temperature (RT) and at an elevated temperate of 600 °C. Also, the effect of post-annealing of the RT implanted sample was studied. The S parameter characterizing the open volume in the material was found to increase after helium irradiation and is significantly enhanced for the samples thermally treated at 600 °C either by irradiation at high temperature or by post-annealing. Two types of helium-vacancy defects were detected after helium irradiation; small defects with high helium-to-vacancy ratio (low S parameter) for RT irradiation and large defects with low helium-to-vacancy ratio (high S parameter) for thermally treated tungsten. The hardness of the heat treated tungsten coincides with the S parameter, and hence is controlled by the large helium-vacancy defects. The hardness of tungsten irradiated at RT without thermal treatment is dominated by manufacturing related defects such as dislocation loops and impurity clusters and additionally by trapped He atoms from irradiation effects, which enhance hardness. He-stabilized dislocation loops mainly cause the very high hardness values in RT irradiated samples without post-annealing.}, language = {en} } @misc{RichterChenKoegleretal.2011, author = {Richter, Asta and Chen, Chun-Liang and K{\"o}gler, Reinhard and Talut, Georg}, title = {Irradiation effects in nanostructured FeCrAl oxide dispersion strengthened steel}, series = {Wissenschaftliche Beitr{\"a}ge 2011}, volume = {15}, journal = {Wissenschaftliche Beitr{\"a}ge 2011}, issn = {0949-8214}, doi = {10.15771/0949-8214_2011_1_10}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus-1112}, pages = {73 -- 79}, year = {2011}, abstract = {Nanostructured ferritic oxide dispersion strengthened (ODS) alloy is an ideal candidate for fission/fusion power plant materials, particularly in the use of a first-wall and blanket structure of a next generation reactor. These steels usually contain a high density of Y-Al-O nanoparticles, high dislocation densities and fine grains. The material contains nanoparticles with an average diameter of 21 nm. Irradiation of these alloys was performed with a dual beam irradiation of 2.5 MeV Fe+/31 dpa and 350 keV He+/18 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. Additionally to structural changes, the effect of the irradiation generated defects on the mechanical properties of the ODS is investigated by nanoindentation. A clear hardness increase in the irradiated area is observed, which reaches a maximum at a close surface region. This feature is attributed to synergistic effects between the displacement damage and He implantation resulting in He filled vacancies.}, language = {en} }