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Analysis of microstructure and mechanical strength of lap joints of TZM alloy welded by a fiber laser
摘要： The application of molybdenum alloys to structural components is severely limited due to their poor weldability with serious defects of porosity and joint embrittlement after welding despite their high melting temperature, hot strength and creep resistance. A systematical experimental study has been conducted to explore the potential of laser welding of 0.5 mm-thick Titanium-zirconium-molybdenum (TZM) alloy in a lap welding configuration. Porosity was found to be the most serious problem in the TZM laser lap welding process. Introducing an interface gap of 0.09 mm had the most positive effect in reducing the porosity compared to using helium gas, different shielding gas flow rates, adding alloy element and different heat input rate. With the use of 0.09 mm-interface gap, the porosity of the weld joint was reduced to 3%. The tensile stress of the bead on plate (BOP) welded joint could achieve about 60% that of the base metal. The fracture stress of the lap welded joint obtained by using 0.09 mm-interface gap in tensile-shear test was about 142 MPa. The porosity and embrittlement were responsible for the reduction of the strength and ductility of the welded joint.
关键词： Porosity,Mechanical property,Molybdenum alloy,Laser welding
更新于2025-11-28 14:24:20
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Effects of titanium on grain boundary strength in molybdenum laser weld bead and formation and strengthening mechanisms of brazing layer
摘要： Molybdenum has tremendous application potential in the nuclear power field, but its application is limited by the grain-boundary embrittlement of fusion-welded joints made of it. In this study, titanium was selected as an alloying element to reduce brittleness of laser weld beads in molybdenum "cladding-end plug" socket joints. Brazing was also performed to enhance the joint strength. Joints with the same strength as base material and a hydraulic bursting pressure of 60 MPa were produced using a combination of the two methods. The analysis indicates the following. After being added to the weld bead, titanium was able to combine with the free oxygen, forming TiO2 and reducing the MoO2 content on grain boundary surface. Oxygen and MoO2 are both the main causes of the embrittlement of molybdenum grain boundaries. In addition, by taking advantage of the high melting point and thermal conductivity of molybdenum, a titanium foil pre-placed between the tube and rod in the socket joint was melted, forming metallurgical bonding, which further improved the bearing capacity of the joint.
关键词： laser beam welding,titanium,brazing,molybdenum,grain boundary embrittlement
更新于2025-11-28 14:24:20
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Effect of Heat Input on Porosity Defects in a Fiber Laser Welded Socket-Joint Made of Powder Metallurgy Molybdenum Alloy
摘要： Porosity defects are still a challenging issue in the fusion welding of molybdenum and its alloys due to the pre-existing interior defects associated with the powder metallurgy process. Fiber laser welding of end plug and cladding tube made of nanostructured high-strength molybdenum (NS-Mo) alloy was performed in this work with an emphasis on the role of welding heat input. The distribution and morphology of porosity defects in the welded joints were examined by computed tomography (CT) and scanning electron microscopy (SEM). Preliminary results showed that laser welding of NS-Mo under low heat input significantly reduced the porosity defects in the fusion zone. The results of computed tomography (CT) showed that when the welding heat input decreased from 3600 J/cm (i.e., 1200 W, 0.2 m/min) to 250 J/cm (i.e., 2500 W, 6 m/min), the porosity ratio of the NS-Mo joints declined from 10.7% to 2.1%. Notable porosity defects under high heat input were related to the instability of the keyhole, expansion and the merging of bubbles in the molten pool, among which the instability of the keyhole played the dominant role. The porous defects at low heat input were generated as bubbles released from the powder metallurgy base metal (BM) did not have enough time to overflow and escape.
关键词： fiber laser welding,molybdenum alloy,porosity defects,heat input
更新于2025-11-28 14:24:20
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Effects of Power Modulation, Multipass Remelting and Zr Addition Upon Porosity Defects in Laser Seal Welding of End Plug to Thin-Walled Molybdenum Alloy
摘要： Aiming to solve the serious porosity defects in laser welded girth joints of thin-walled tube and end plug made of nano-sized Ce2O3 doped Mo alloy (NC-Mo), the influences of laser power modulation, multipass remelting and zirconium (Zr) addition on the number, size and distribution of porosity defects were experimentally studied. By utilizing X-ray computed tomography (XCT), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) analysis, transmission electron microscope (TEM) and Raman spectrum (RS), the porosity feature of welded joints achieved under various conditions was analyzed. The results showed that welding cycles had a significant influence on the porosity ratio of fusion zone (FZ) while the amplitude and frequency of laser power waveform slightly influenced the porosity. When the welding cycles increased from 2 to 8, the porosity ratio of FZ decreased from about 1.00% to about 0.48% and the maximum and average pore diameters reduced by about 53% and 27%, respectively. Adding minor Zr in molten pool can further reduce the RP of FZ to about 0.35%. Through analysis, it can be seen that the pores in FZ can be divided into irregularly-shaped keyhole-induced pores and spherical metallurgy-induced pores. The latter was generated possibly because some impurity elements (including O and H) pre-existing in base metal (BM). Increasing welding cycles can promote the gas in molten pool to float and outflow, thus significantly decreasing the porosity. Moreover, Zr added in molten pool can be preferentially reacted with O to generate ZrO2, which can inhibit the precipitation of volatile MoO2 to thus suppress the generation of metallurgy-induced pores.
关键词： Molybdenum alloy,Multipass remelting,Power-Modulated laser welding,Zirconium addition,Porosity
更新于2025-11-28 14:24:20
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Enhanced mechanical performance of fusion zone in laser beam welding joint of molybdenum alloy due to solid carburizing
摘要： It is unable to strengthen molybdenum (Mo) through solid-state phase transformation, while exploring the effect of carbon (C) on microstructures and properties of fusion zone (FZ) of laser beam welding (LBW) joints of Mo alloy with serious grain boundary embrittlement is significant. An analysis was made on changes of bonding strength of grain boundary and precipitates on the grain boundary surface in the FZ of Mo carburized welded joints, and the existing form and strengthening mechanism of carbon. At first, solid carburizing (SC) can achieve the goal of adding the C to welded joints and C mainly appeared as C atoms and Mo2C in Mo alloy. Afterwards, C could increase the grain boundary strength and the plasticity of grains in the FZ. Therefore, the compatibility of deformation at grain boundary and grain interior was improved. Finally, Mo2C distributing at the grain boundary can inhibit the crack propagation during the deformation. As a results, the tensile strength of carburized weld joints rose by 426% compared with that of uncarburized weld joints, meanwhile the above results provide a new idea for the method for strengthening the Mo fusion weld joints.
关键词： laser beam welding,grain boundary embrittlement,carbon,molybdenum
更新于2025-11-28 14:24:20
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70?nm, broadly tunable passively Q-switched thulium-doped fiber laser with few-layer Mo0.8W0.2S2 saturable absorber
摘要： In this work, a thin Mo0.8W0.2S2 film is proposed and fabricated for the use as a saturable absorber (SA) in a thulium-doped fiber laser (TDFL) cavity. The few-layer Mo0.8W0.2S2 nanoparticles are obtained through hydrothermal exfoliation as a thin film and suspended in a polymer host, which is then placed between two fiber ferrules to serve as an SA. The proposed laser is capable of generating outputs with a maximum repetition rate of 65.79 kHz and a minimum pulse width of 1.84 μs at the maximum pump power of 168.92 mW, as well as pulse energies and peak powers as high as 35.73 nJ and 13.92 mW. The laser also has a broad tuning output from 1927.2 nm to 1996.8 nm, giving a tuning band of about 70 nm. The generated pulses are stable with a signal-to-noise ratio of 50.0 dB. The proposed laser has a high potential for operation near the 2000 nm wavelength region, with multiple bio-medical and sensing applications.
关键词： Thulium,Molybdenum compounds,Q-switching lasers
更新于2025-11-28 14:24:03
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Tunable passively Q-switched ytterbium-doped fiber laser using MoWS2/rGO nanocomposite saturable absorber
摘要： We demonstrated a tunable Q-switched ytterbium-doped fiber laser (YDFL) using MoWS2/rGO nanocomposite as passive saturable absorber. Further, the Mo1?xWxS2/rGO nanosheets, with x proportion of 0.2, are synthesized using hydrothermal exfoliation technique. The proposed nanocomposite-PVA based thin film is fabricated by mixing the MoWS2/rGO nanosheets with polyvinyl alcohol (PVA). The fabricated thin film is sandwiched between two fiber ferrules to realize the proposed saturable absorber (SA). Further, the proposed MoWS2/rGO-PVA based thin film SA exhibits a fast relaxation time and a high damage threshold which are suitable to realize a Q-switched pulsed laser with a tunable wavelength range of 10 nm that extends from 1028 nm to 1038 nm. For the highest pump power of 267.4 mW, the generated Q-switched pulses exhibit a narrow pulse width of 1.22 μs, the pulse repetition rate of 90.4 kHz, the highest pulse energy of 2.13 nJ and its corresponding average power of 0.193 mW. To the best of author’s knowledge, this is the first realization of a tunable Q-switching fiber laser in a 1 μm wavelength using MoWS2/rGO nanocomposite saturable absorber.
关键词： Saturable absorber,Molybdenum,Tungsten disulfide,Q-switched fiber laser,Transition metal dichalcogenides
更新于2025-11-28 14:24:03
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Investigation of Surface Plasmon Resonance (SPR) in MoS2- and WS2-Protected Titanium Side-Polished Optical Fiber as a Humidity Sensor
摘要： In this paper, we report the effects of a side-polished fiber (SPF) coated with titanium (Ti) films in different thicknesses, namely 5 nm, 13 nm, and 36 nm, protected by a thin layer of transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2), which provide ultra-sensitive sensor-based surface plasmon resonance (SPR) covering from the visible to mid-infrared region. The SPF deposited with Ti exhibits strong evanescent field interaction with the MoS2 and WS2, and good optical absorption, hence resulting in high-sensitivity performance. Incremental increases in the thickness of the Ti layer contribute to the enhancement of the intensity of transmission with redshift and broad spectra. The findings show that the optimum thickness of Ti with 36 nm combined with MoS2 causes weak redshifts of the longitudinal localized surface plasmon resonance (LSPR) mode, while the same thickness of Ti with WS2 causes large blueshifts. The redshifts are possibly due to a reduced plasmon-coupling effect with the excitonic region of MoS2. The observed blueshifts of the LSPR peak position are possibly due to surface modification between WS2 and Ti. Changing the relative humidity from 58% to 88% only elicited a response in Ti/MoS2. Thus, MoS2 shows more sensitivity on 36-nm thickness of Ti compared with WS2. Therefore, the proposed fiber-optic sensor with integration of 2D materials is capable of measuring humidity in any environment.
关键词： tungsten disulfide (WS2),side-polished fiber (SPF),molybdenum disulfide (MoS2)
更新于2025-11-28 14:23:57
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Molybdenum Disulfide Catalytic Coatings via Atomic Layer Deposition for Solar Hydrogen Production from Copper Gallium Diselenide Photocathodes
摘要： We demonstrate that applying atomic layer deposition-derived molybdenum disulfide (MoS2) catalytic coatings on copper gallium diselenide (CGSe) thin film absorbers can lead to efficient wide band gap photocathodes for photoelectrochemical hydrogen production. We have prepared a device that is free of precious metals, employing a CGSe absorber and a cadmium sulfide (CdS) buffer layer, a titanium dioxide (TiO2) interfacial layer, and a MoS2 catalytic layer. The resulting MoS2/TiO2/CdS/CGSe photocathode exhibits a photocurrent onset of +0.53 V vs RHE and a saturation photocurrent density of ?10 mA cm?2, with stable operation for >5 h in acidic electrolyte. Spectroscopic investigations of this device architecture indicate that overlayer degradation occurs inhomogeneously, ultimately exposing the underlying CGSe absorber.
关键词： hydrogen evolution,molybdenum disulfide,photoelectrochemical water splitting,atomic layer deposition,copper gallium diselenide
更新于2025-11-19 16:56:35
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Electronic transport in MoSe <sub/>2</sub> FETs modified by latent tracks created by swift heavy ion irradiation
摘要： Unique characteristics of transition metal dichalcogenides (TMDCs) such as their tunable band gap and ultra-thin body thickness make them potential candidates for applications in optoelectronic, gas sensing and energy storage devices. In this work, 1.8 GeV Ta ions at different ion fluences ranging from 1 × 109 ions cm?2 to 6 × 1010 ions cm?2 were used to introduce amorphous defective regions, latent tracks, in MoSe2 to study the electronic transport behavior in irradiated TMDC-channel field-effect transistors (FETs). Defects in these materials induced by the swift heavy ion irradiation play a vital role in the device applications. The results show that carrier mobility decreases while resistance of the devices increases abruptly with increasing ion fluences. The impact mechanism of the latent tracks on electronic transport behavior in TMDC-channel FETs was analyzed in detail. It was assumed that the Bloch wave of electrons was strongly localized by the latent tracks induced by the SHI irradiation and the Bloch wave of electrons can be scattered by the latent tracks as well. This study helps to investigate the influence of the latent tracks on electronic transport in other 2D materials as well.
关键词： latent track,field-effect transistor,molybdenum selenide,electronic transportation,swift heavy ion irradiation
更新于2025-11-14 17:03:37