Structural and Magnetic Properties of Mechanically Alloyed Fe-Co Powders

The Fe-Co alloys are well known as ferromagnetic materials exhibiting high values of saturation magnetization, Curie temperature and magnetostriction. In powder form they are commonly used in the magnetic recording media. In this paper the structural and magnetic properties of a series of Fe-Co alloy powders prepared by mechanical alloying are presented. The Fe-Co powders (with 30, 45, 50 and 60 wt. % of Co) were prepared by mechanical alloying of high purity powder elements mixture in a planetary ball mill (Retsch PM 4000). The milling of all samples was performed in argon atmosphere with the ball-to-powder weight ratio of 15:1 and the speed of 180 rpm for 30 hours. The X-ray diffraction investigations show, that the alloying of fcc-Co into bcc-alpha-Fe took place during the milling, leading to the formation of the bcc-FeCo solid solution. It was found, that the lattice parameter (with values from 0.2861 nm to 0.2866 nm) of the investigated mechanically alloyed Fe-Co samples is larger for samples containing higher concentration of Co. The process of mechanical alloying was confirmed by Mössbauer spectrometry. The structure and powder size were observed by both TEM and SEM investigations. The coercivity (with values from 2.4 kA m-1 to 3.9 kA m-1) of the powders (measured by a Förster Koerzimat at room temperature) containing higher Co content exhibit larger values.JRC.F.4-Nuclear design safet

Study of Oxide-Dispersion-Strengthened Ferritic Steels after Ion Implantation

This paper is focused on four different commercial oxide-dispersion-strengthened ferritic steels (MA 956, ODM 751, MA 957 and ODS Eurofer) with different chromium content and the change of their microstructure after helium ion implantation. The samples were implanted with kinetic energy of ions up to 500 keV and the implantation depth was up to 1.2 μm. The implantation was performed at Institute of Nuclear and Physical Engineering, Slovak University of Technology in Bratislava. The samples were observed prior and after the implantation by positron Doppler broadening spectroscopy with slow positron beam (energy up to 36 keV) which is one of the most suitable techniques due to its sensitivity to surface and subsurface layers up to 1.6 μm. The results showed visible change of defect presence in all samples and defect depth profiles are in a good accordance with SRIM software calculations displaying the Bragg peak. According to measured data, ODS Eurofer (9% Cr) seems to be the most radiation resistant from the group of all investigated steels and MA 956 (20% Cr) as the most radiation affected steel