Effect of helium implantation on mechanical properties of EUROFER97 evaluated by nanoindentation M. Roldán a,⇑ , P. Fernández a , J. Rams b , D. Jiménez-Rey c , C.J. Ortiz a , R. Vila a a National Fusion Laboratory-CIEMAT. Avda. Complutense 40, 28040 Madrid, Spain b Rey Juan Carlos University, C/Tulipán s/n, Móstoles, 28933 Madrid, Spain c Centre for Micro-Analysis of Materials (CMAM, UAM), C/Faraday 3, 28049 Madrid, Spain article info Article history: Received 27 May 2013 Accepted 13 February 2014 Available online 20 February 2014 abstract Helium effects on EUROFER97 mechanical properties were studied by means of nanoindentation. The steel was implanted with He ions in a stair-like profile configuration using energies from 2 to 15 MeV at room temperature. Firstly, a deep nanoindentation study was carried out on as-received state (normal- ized + tempered) in order to obtain a reliable properties database at the nanometric scale, including aspects such as indentation size effect. The nanoindentation hardness of tests on He implanted samples showed a hardness increase depending on the He concentration. The hardness increase follows the He implantation concentration profile with a good accuracy according to BCA calculations using MARLOWE code, considering the whole volume affected by the nanoindentation tests. The results obtained in this work shown that nanoindentation technique permits to assess any change of hardness properties due to ion implantation. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Nowadays in the field of fusion materials, there are several can- didates to be used as structural materials on the future fusion reac- tor. Those materials used on breeder blanket or first wall will be exposed to severe conditions of high irradiation and high temper- ature during their service life. One of them, EUROFER97, which be- longs to reduced activation ferritic–martensitic steels, has been selected as structural material for fusion applications due to its re- duced activation potential, high temperature of operation, good corrosion resistance and good behavior under neutron irradiation [1–3]. The metallurgical properties of EUROFER97 steel have been extensively studied for more than one decade [4]. As result of these investigations the EUROFER97 was selected as European reference structural steel for the first wall and blanket breeder of a future fu- sion energy Demonstration Power Plant (DEMO) [4]. Several studies on reduced activation ferritic–martensitic mate- rials have been conducted to evaluate the mechanical properties of irradiated materials by using neutrons [5,6], but helium effects on mechanical properties is still one of the key issues. High concentra- tions of He will be produced within the material by transmutation reactions during fusion reactor operation. Nowadays one of the major challenges within the scientific community is to acquire knowledge concerning transmutation products (He, H) effects on structural materials, but it is difficult to analyze the effect of he- lium on structural materials for fusion due to a lack of a facility that reproduce the neutron fusion environment. Nevertheless, to evaluate the material behavior caused by the He content, it is nec- essary to incorporate it into the material. There are some methods to do it, such as neutron irradiation with B and Ni doping material [7] or doping with 54 Fe ions [8]. However, these methods have important disadvantages such as composition changes, formation of new phases during irradiation, nuclear activation or high cost [9,10]. A suitable method that eliminates theses effects is the direct implantation of He ions into the material. Nevertheless this tech- nique presents as main disadvantage that the volume of implanted materials is very small. So, the volume affected by irradiation can be observed by microscopy studies predicted by computational simulation programs based on the Binary Collision Approximation (BCA) such as MARLOWE which simulates with high accuracy the implantation of helium ions in different polycrystalline materials [11,12]. Consequently, the mechanical characterization should be performed using nano and micro mechanical testing. Among other techniques, nanoindentation seems the most appropriate technique to study the mechanical properties on small volumes of material and on thin layers. It can be applied very locally and it can be used to evaluate the effect of ion damage on the properties of materials [13] or the mechanical differences between two or more phases present in a material [14]. For that http://dx.doi.org/10.1016/j.jnucmat.2014.02.020 0022-3115/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +34 676824178. E-mail address: marcelo.roldan@ciemat.es (M. Roldán). Journal of Nuclear Materials 448 (2014) 301–309 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat