Fabrication and characterization of He-charged ODS-FeCrNi films deposited by a radio-frequency plasma magnetron sputtering technique

He-charged oxide dispersion strengthened （ODS） FeCrNi fills were prepared by a radiofrequency （RF） plasma magnetron sputtering method in a He and Ar mixed atmosphere at 150 °C.As a comparison,He-charged FeCrNi films were also fabricated at the same conditions through direct current （DC） plasma magnetron sputtering.The doping of He atoms and Y2O3 in the FeCrNi fills was realized by the high backscattered rate of He ions and Y2O3/FeCrNi composite target sputtering method,respectively.Inductive coupled plasma （ICP） and x-ray photoelectron spectroscopy （XPS） analysis confirmed the existence of Y2O3 in FeCrNi fills,and Y2O3 content hardly changed with sputtering He/Ar ratio.Cross-sectional scanning electron microscopy （SEM） shows that the FeCrNi films were composed of dense colunnarnanocrystallines and the thickness of the films was obviously dependent on He/Ar ratio.Nanoindentation measurements revealed that the FeCrNi films fabricated through DC/RF plasma magnetron sputtering methods exhibited similar hardness values at each He/Ar ratio,while the dispersion of Y2O3 apparently increased the hardness of the fills.Elastic recoil detection （ERD） showed that DC/RF magnetron sputtered FeCrNi films contained similar He amounts （～17 at.%）.Compared with the minimal change of He level with depth in DC-sputtered films,the He amount decreases gradually in depth in the RF-sputtered fills.The Y2O3-doped FeCrNi films were shown to exhibit much smaller amounts of He owing to the lower backscattering possibility of Y2O3 and the inhibition effect of nano-sized Y2O3 particles on the He element.

Carbide Precipitation in Ferrite in Nb–V-Bearing Low-Carbon Steel During Isothermal Quenching Process

The precipitation behavior of nanometer-sized carbides in ferrite in Nb-V-bearing low-carbon steel was studied by electron microscopy and nanoindentation hardness measurements. The results indicated that interphase precipitation and random precipitation could occur simultaneously for the specimen isothermally treated at 700 ℃ for 60 min, while in other specimens, only random precipitation was observed. This phenomenon might be explained by mass balance criterion during the diffusional phase transformation. Nanohardness result indicated that the average hardness of the specimens isothermally held at 600 ℃ for 20 min was 3.87 GPa. For the specimen isothermally holding at 650 ℃ for 20 min, the average hardness was 4.10 GPa and the distribution of the nanohardness was in a narrower range compared with that of the specimen isothermal holding at 600 ℃ for 20 min. These implied that the carbides in the specimens isothermal treated at 650℃ were more uniformly dispersed, and the number density of the carbides was greater than that treated at 600 ℃. Using Ashby-Orowan model, the contribution of precipitation strengthening to yield strength was estimated to be 110 MPa for the specimen isothermally treated at the temperature of 650 ℃ for 20 min.

Sintering densification behavior and kinetic mechanism of nano-tungsten powder prepared by sol-spray drying

Due to its excellent mechanical and radiation resistance performance,fine-grained tungsten becomes an ideal plasma facing material in fusion reactors.However,the preparation of fine-grained tungsten by ultrafine powder is faced with some problems,such as low density,coarse grain and not suitable for engineering production.In this paper,nano-tungsten powders prepared by“sol-spray drying-calcination-hydrogen thermal reduction”process were sintered by non-isothermal ordinary pressureless sintering,and the densification behavior and kinetic mechanism were investigated.The results show that there exists two stages during sintering process,namely significant densification process at low temperature(1300-1700℃)and grain growth stage at high temperature(1700-2000℃).Finally,bulk tungsten material with the relative density of 96.9%and average grain size of 2-6μm was prepared at 1900℃.Moreover,electron backscatter diffraction results show the grain size is uniform and fine.By mathematical calculation,the nanocrystallization of tungsten powder significantly reduces the sintering activation energy and promotes the densification of tungsten powder at low temperature.Surface diffusion is the main transport mechanism in grain growth stage.It is easy to find that the hardness of material increased with the sintering temperature increasing,at the end of sintering densification(>1700℃),TEM observation revealed that the inner pores formed by particle combine were gradually eliminated through grain boundary diffusion with the sintering temperature increasing,resulting in the intra-crystal densification to increase the hardness of tungsten material.