Geng An

Oxidation layering mechanism of graphene-like MoS2 prepared by the intercalation-detonation method

Graphene-like MoS2 has attracted significant interest because of its unique electronic, optical, and catalytic properties with two-dimensional lamellar structure. Three kinds of intercalated MoS2 samples were prepared using different oxidation layering methods, which are the first steps of intercalation-detonation. The oxidation layering mechanism of graphene-like MoS2 was systematically characterized using Fourier transform infrared, X-ray photoelectron, and Raman spectroscopy techniques. The bulk MoS2 sample was gradually oxidized from the edge to the interlayer in the presence of concentrated H2SO4 and KMnO4. A large number of hydroxyl groups were bonded to the sulfur atom layer, forming S–OH bonds in the basal planes of the MoS2 structure. The addition of deionized water to concentrated H2SO4 generated a large amount of heat, promoting the generation of more S–OH bonds, destroying residual Van der Waals forces between the layers, and finally stripping off parts of the flakes. The continuous addition of deionized water in the high temperature stage resulted in the largest oxidative intercalation effect. Additionally, the η factor was determined to compare the intensities of B1u and A1g peaks in the Raman spectra and quantify the effect of oxidative intercalation. The highest value of η was obtained when deionized water was added continuously during the preparation of intercalated MoS2.

Preparation and Influencing Factors of Molybdenum Targets and Magnetron-Sputter-Deposited Molybdenum Thin Films

Aiming to produce qualified molybdenum (Mo) target for sputter deposition, Mo targets were prepared by utilizing powder metallurgy method in this research. The influences of sintering modes, press working modes and total deformation on microstructure and properties of Mo target were studied. Furthermore, magnetron sputtering test was conducted in vacuum environment by using the prepared Mo targets to deposit Mo thin films of which the surface morphologies, electrical conductivities, and crystalline properties were analyzed. The results show that vacuum presintering followed by hydrogen sintering mode can greatly decrease the impurity contents of Mo slabs. It is favorable to obtain the Mo target with fine and uniform grains on size and distribution by using forging mode or forging cogging mode and more than 70% total deformation. With the increase of sputtering currents of Mo target, the grain size and the thickness of the Mo thin films significantly rise, while FWHM of diffraction peaks of grain orientation (110), surface roughness and electrical resistivity of thin films decrease accordingly.

Fiber Laser Welding of Fuel Cladding and End Plug Made of La2O3 Dispersion-Strengthened Molybdenum Alloy

The study investigated the laser lap welding of fuel cladding and end plug made of molybdenum (Mo) alloy. The research results showed that the tensile strength of the welded joint when a weld was located at the Mo tube was significantly larger than that at the fit-up gap between the fuel cladding and end plug. Moreover, preheating can also greatly increase the tensile strength of the lap joint. The weld zone was filled with bulky coarse columnar crystal structures while there were numerous coarse recrystallized structures in the heat affected zone (HAZ). The weld zone and HAZ were both subjected to a significant softening. The tensile strength and elongation rate of fuel cladding made of Mo alloy were about 750 MPa and 36.7%, respectively. The welded joint did not undergo any plastic deformation during the tensile process and presented a brittle fracture. Under the optimum processing conditions, the tensile strength of the welded joint reached 617 MPa, taking up 82.3% that of the base metal. The results of composition analysis indicated that there was only Mo inside the columnar crystals in weld zone while significant oxygen segregation was observed at the grain boundary. This was the main reason causing that the strength of welded joint was lower than that of the base metal. Additionally, under the optimum processing conditions, there were numerous slender columnar crystals on the cross section of the joint entering the weld zone in fuel cladding side from that in end plug side where the crystals were nucleated and grew upwards. The analysis results suggested that the presence of these slender columnar crystals crossing the interface between fuel cladding and end plug was favorable for improving the capacity of the joint for bearing the shear loads.

Research on the Mechanical Behaviors of TZM Alloys at Room and Elevated Temperatures Prepared for Isothermal Forging Die

TZM alloys used as isothermal forging die at high temperature were prepared by a new powder doping process combined with the rational design of sintering technique and hot working technology. In this paper, tensile properties of TZM alloys at room temperature and properties such as tensile properties, fracture toughness and stress rupture at elevated temperatures were investigated. The results show that the mechanical properties at room temperature were excellent in accord with the ASTM B386-03 (2011) standard. At the temperature of 1100 °C, the tensile and yield strength were 552 and 514 Mpa respectively, and the endurance life is 250 h under the load stress of 160 Mpa, the TZM alloys can be used as isothermal forging die material at temperature of 1100 °C or above.