Vickers Microhardness Testing with Miniaturized Disk Specimens

The microhardness technique has been increasingly important for testing irradiated materials because of the necessity of small-scale specimen technology. In order to establish Vickers microhardness testing over a wide temperature range using miniaturized specimens such as transmission electron microscopy (TEM) disks, an apparatus that permits the measurements in the temperature range of well below liquid nitrogen temperature to well above room temperature is developed. Effects of indentation size, disk-specimen thickness, specimen setting and test temperature on the Vickers microhardness data of an unirradiated iron alloy are described

Development of Controlled Temperature-Cycle Irradiation Technique in JMTR

The effects of cyclic temperature changes during neutron irradiation upon radiation induced microstructure evolution and resulting property changes of materials is very important from both fundamental and engineering viewpoints. Therefore, a technique that allows us to do the controlled temperature-cycle irradiation was developed in the Japan Materials Testing Reactor (JMTR). The technique meets the following requirements : (1) the temperature-cycle irradiation is to be performed under three different conditions by changing lower and upper temperatures; 200 --- 400℃, 300 --- 400℃ and 300 --- 450℃. (2) the number and period of the temperature-cycles are to be six for 24-day full irradiation and approximately 44 h/44 h at the lower/upper temperatures. (3) the temperatures of each specimen assembly are to be maintained at the lower temperatures before start-up of the reactor and at the upper temperatures during shut-down until the complete absence of reactor power. In this paper, the details of the irradiation rig, successful results and several problems to be overcome for future improvement are presented

Low-Temperature Strengths and Ductility of Various Tungsten Sheets

We used three kinds of tungsten sheets in this study. First, we examined microstructure such as grain size distribution using an optical microscope. Secondly, we carried out three-point bend tests at temperatures between about 290 and 500 K. Then, we examined fracture surface of a failed specimen using a scanning electron microscope. Lastly, by analyzing all these results, we evaluated apparent intergranular and transgranular fracture strengths and discussed strengths and ductility of tungsten. Additionally, we compared mechanical properties of tungsten with those of molybdenum

Effect of Specimen Geometry on Charpy Impact Test Results for Ferritic Steel Irradiated in JMTR

In order to develop the small-scale specimen technology in Charpy impact testing for ferritic steels, the effects of specimen size and notch geometry on the upper shelf energy (USE) and ductile-to-brittle transition temperature (DBTT) were investigated for Japanese Ferrite/Martensite Dual Phase Steel (JFMS). Miniaturized specimens with different sizes and notch geometry, together with full size specimens, were irradiated to 3x10^n/m^2 in the Japan Materials Testing Reactor (JMTR) and were Charpy impact tested. The USE for miniaturized specimens, normalized by Bb^2 or (Bb)^ (B is the specimen thickness, b the ligament size), was essentially independent of specimen size and notch geometry and decreased by the irradiation, but the decrease was larger in full size specimens than in miniaturized specimens; the normalized USE for miniaturized specimens was distinctly higher than that for full size specimens . The DBTT of miniaturized specimens was strongly dependent on notch geometry, but its dependence decreased as compared with that for unirradiated JFMS . It is shown that these results may be useful in determining the USE and DBTT for full size specimens from those for miniaturized specimens