TY - JOUR A1 - Ou, Xin A1 - Anwand, Wolfgang A1 - Kögler, Reinhard A1 - Zhou, Hong-Bo A1 - Richter, Asta T1 - The role of helium implantation induced vacancy defect on hardening of tungsten JF - Journal of Applied Physics N2 - 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. Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-5623 SN - 1089-7550 VL - 115 IS - 12 ER - TY - GEN A1 - Richter, Asta A1 - Chen, Chun-Liang A1 - Kögler, Reinhard A1 - Talut, Georg T1 - Irradiation effects in nanostructured FeCrAl oxide dispersion strengthened steel T2 - Wissenschaftliche Beiträge 2011 N2 - 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. N2 - Ferritische Legierungen mit nanodispersen Oxidpartikeln zur Härtesteigerung sind ein geeignetes Material für Behälter und Ummantelungsstrukturen in modernen Fusions- und Kernspaltungsanlagen. Diese Stähle haben eine hohe Dichte von Y-Al-O Nanoteilchen mit einem mittleren Durchmesser von 21 nm, eine hohe Versetzungsdichte und besitzen eine feine Kornstruktur. Bestrahlungsexperimente wurden mit einer Zwei-Strahl-Ionen-Quelle mit Eisen 2.5 MeV Fe+/31 dpa und Helium 350 keV He+/18 appm/dpa durchgeführt. Die Bestrahlung erzeugt atomare Defekte mit Leerstellen und Zwischengitterdefekten sowie Versetzungsschleifen. Zusätzlich zu den mikro-strukturellen Modifikationen wurde die Änderung der mechanischen Eigenschaften mit der Bestrahlung untersucht. Insbesondere im oberflächennahen Bereich führt die Ionenbestrahlung zu einer klaren Härtesteigerung. Dieses Verhalten wird mit einem synergetischen Modell zur Erzeugung atomarer Strahlendefekte und der Bildung von mit Helium gefüllten Leerstellen diskutiert. Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus-1112 SN - 0949-8214 VL - 15 SP - 73 EP - 79 ER -