Changsong Liu

Low-temperature mechanical and magnetic properties of the reduced activation martensitic steel

Mechanical and magnetic properties as well as their relationship in the reduced activation martensitic (RAM) steel were investigated in the temperature range from −90°C to 20°C. Charpy impact tests show that the ductile-to-brittle transition temperature (DBTT) of the RAM steel is about −60°C. Low-temperature tensile tests show that the yield strength, ultimate tensile strength and total elongation values increase as temperature decreases, indicating that the strength and plasticity below the DBTT are higher than those above the DBTT. The coercive field (HC) in the scale of logarithm decreases linearly with the increasing temperature and the absolute value of the slope of lnHC versus temperature above the DBTT is obviously larger than that below the DBTT, also confirmed in the T91 steel. The results indicate that the non-destructive magnetic measurement is a promising candidate method for the DBTT detection of ferromagnetic steels.

Microstructure and mechanical properties of tungsten composite reinforced by fibre network

In this paper the tungsten-fibre-net-reinforced tungsten composites were produced by spark plasma sintering (SPS) using fine W powders and commercial tungsten fibres. The relative density of the samples is above 95%. It was found that the recrystallization area in the fibres became bigger with increasing sintering temperature and pressure. The tungsten grains of fibres kept stable when sintered at 1350°C/16 kN while grown up when sintered at 1800°C/16 kN. The composite sintered at 1350°C/16 kN have a Vickers-hardness of ~610 HV, about 2 times that of the 1800°C/16 kN sintered one. Tensile tests imply that the temperature at which the composites (1350°C/16 kN) begin to exhibit plastic deformation is about 200°C-250°C, which is 400°C lower than that of SPSed pure W. The tensile fracture surfaces show that the increasing fracture ductility comes from pull-out, interface debonding and fracture of fibres.

Internal friction study of ambient aging behaviors of irradiated tungsten by Si/H ions

The aging behaviors of irradiated tungsten by high energy Si3+ and H+ ions are mainly investigated using internal friction (IF) method combined with SEM technology. The SEM analysis indicates that more severe irradiation damage appears in the surface of simultaneous dual Si3+ + H+ irradiated specimen than that in the sequential dual Si3+ + H+ irradiated specimen or the single Si3+ irradiated specimens because of the synergistic effect of Si and H irradiation. The IF background of the irradiated sample is about one order of magnitude higher than that of the unirradiated sample owing to the existence of high density fresh dislocations induced by Si/H irradiation. In the sequential dual Si3+ and H+ irradiated specimen, the hydrogen Snoek-Kê-Köster (SKK) peak associated with the movement of dislocations dragging hydrogen atoms is observed and its height decreases with aging time at room temperature. As for the simultaneous dual Si3+ + H+ irradiated specimen, however, there is no such hydrogen SKK peak. The reason can be explained as hydrogen diffusion and pinning effect of dislocations.