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Revealing the Role of Gold in the Growth of Two-dimensional Molybdenum Disulfide by Surface Alloy Formation
摘要： Formation of Mo-Au surface alloy during Au-assisted chemical vapor deposition (CVD) of MoS2 was confirmed by a series of control experiments. We adapted a metalorganic chemical vapor deposition (MOCVD) system to conduct two-dimensional MoS2 growth in a controlled environment. Sequential injection of Mo and S precursors, which does not yield any MoS2 on a SiO2/Si, grows atomically thin MoS2 on Au, indicating formation of an alloy phase. Transmission electron microscopy of a cross-section of the specimen confirmed the confinement of the alloy phase near the surface only. These results show that the reaction intermediate is the surface alloy and that the role of Au in the Au-assisted CVD is formation of an atomically thin reservoir of Mo near the surface. This mechanism is clearly distinguished from that of MOCVD, which does not involve formation of any alloy phases.
关键词： Molybdenum Disulfide,Surface Alloy,Two-dimensional Material,Chemical vapor deposition,Metalorganic Chemical Vapor Deposition
更新于2025-09-23 15:21:01
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Microstructure and properties of Tia??Zr congruent alloy fabricated by laser additive manufacturing
摘要： In the present work, Ti40Zr (atomic percent) congruent alloy, as well as four other Ti-Zr alloys near the congruent point, was fabricated using laser additive manufacturing (LAM) on pure titanium substrate. Comparative analyses of these alloys were performed based on microstructure, mechanical properties, tribological properties, corrosion resistance, and formability. The results show that the microstructure of the alloys develops sequentially from the Widmanst?tten structure to nearly full b -(TiZr) columnar crystals for 40 at.% Zr, to b -(TiZr) columnar crystals plus granular a -(TiZr) with the increase of Zr addition. The Ti60Zr40 congruent alloy with nearly full b -(TiZr) structure presents a novel combination of ductility, corrosion resistance, and formability, but it has a slightly lower hardness, less strength and poor tribological properties, compared with the other Ti-Zr alloys near the congruent point. Therefore, to develop the congruent alloy as a high strength LAM material through alloying is very significant.
关键词： Congruent Alloy,Laser additive manufacturing,Titanium alloy,Properties,Microstructure
更新于2025-09-23 15:19:57
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The impact of laser surface treatment on the microstructure, wear resistance and hardness of the AlMg5 aluminum alloy
摘要： Light metal alloys due to several unique properties such as low density and high corrosion resistance are increasingly used in various technical applications, where the automotive industry is one of the most important sectors. The automotive applications use mostly aluminum alloys, where the strength to density ratio of the material plays a crucial factor. Unfortunately, relatively low mechanical properties limit their applications for parts where a high surface hardness and wear resistance is expected. The classic heat treatment of aluminum alloys can only in some limited ranges improve the bulk material properties. Despite this, surface treatment with laser processing has developed significantly over the past 20 years. The laser beam treatment allows the introduction of a wide range of alloying elements to the surface layer of an aluminum alloy and thus, as a result of the precipitation of numerous intermetallic phases, significantly increases hardness, and abrasion resistance. The purpose of this work was to modify the aluminum surface layer using high-power fiber laser (HPFL). During this process, a mixture of titanium and iron powders (90/10 wt.%) was introduced onto the surface of the AlMg5 alloy. The microhardness tests carried out by the Vickers method and tribological tests showed a significant increase in mechanical properties in the entire volume of the obtained layer. Research on light and scanning microscopy revealed fragmentation of primary precipitates and the formation of numerous intermetallic phases rich in titanium and aluminum.
关键词： Aluminium alloy,Laser treatment,EDS analysis,Tribological properties,High power fibre laser
更新于2025-09-23 15:19:57
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Effect of laser shock peening on mechanical and microstructural aspects of 6061-T6 aluminum alloy
摘要： Laser shock peening (LSP) of 6061-T6 aluminum alloy was performed and parametric effects post LSP on mechanical aspects and microstructural evolution are meticulously studied using various means of characterization techniques such as residual stress analysis, surface roughness, Vickers microhardness, tensile testing, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). Work hardened layer of ~1500 μm depth is obtained with significant improvement in cross-sectional microhardness up to 33.04%. Beneficial compressive residual stress of maximum magnitude up to -273 MPa was induced in laser peened specimens concentrating its overall effect around the depth of 100 μm along the effective depth region. Second phase Mg5Si6 (β?) precipitates were observed post LSP while analyzing XRD profiles along with the peak broadening and peak shifting towards higher 2θ angle justifying the results obtained in microhardness profile. High angle grain boundaries (HAGBs) fraction was increased in LSPed specimens and its effect is noticed in residual stress profile. Mg5Si6 (β?) precipitates are attributed as contributing precipitates in improving the mechanical properties of LSPed specimens along with the dense dislocation density caused by severe plastic deformation during LSP. The collective contribution of strain hardening, second phase precipitates, peak broadening, dislocation density and increased fraction of HAGBs is observed in mechanical and microstructural aspects of LSPed specimens. The results are discussed in detailed and are strongly correlated with each other.
关键词： EBSD,Aluminum alloy,cosα method,TEM,XRD,Laser shock peening
更新于2025-09-23 15:19:57
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As-fabricated surface morphologies of Ti-6Al-4V samples fabricated by different laser processing parameters in selective laser melting
摘要： The surface morphology of a product plays a crucial role under mechanical loading and chemical environment. Surfaces of Selective Laser Melting (SLM) products often contain high roughness, which varies in different planes as well. The authors have explored the surface characteristics of the SLM samples that are influenced by different combinations of laser processing parameters. The considered processing parameters were Energy Density (ED) and its technological parameters namely laser power, scanning speed and hatch spacing. Additionally, a comparison study has been executed by rescanning effects considering melting with low ED and, thereafter, re-scanning by the best possible laser processing parameters. The results evidently showed that the surface morphologies differ significantly due to different laser processing parameters. Eventually, the thermal and physical behavior of materials, such as the viscosity of the melt pool, thermal and physical stability of the melt pool, solidification time, cooling time, shrinkage, capillary effect, surface tension, balling effect, and the amount of melting of a powder particle, influenced the surface properties of the samples, along with unpredictability. The results showed an interesting correlation between the processing parameters and the occurrence of microcracks on the vertical walls of the specimens caused by the partially melted adhered powder particles.
关键词： Ti-6Al-4V alloy,Selective laser melting,Laser processing parameters,Surface morphology,Rescanning
更新于2025-09-23 15:19:57
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Effects of laser shock peening on microstructure and fatigue behavior of Tia??6Ala??4V alloy fabricated via electron beam melting
摘要： Laser shock peening (LSP) is a post-treatment process that is widely used to modify the surface microstructure and mechanical properties of parts constructed by additive manufacturing (AM). In this study, the influence of LSP on the microstructure and fatigue behavior of Ti–6Al–4V alloy manufactured via electron beam melting (EBM), a popular method of AM, was investigated. The microstructure of the EBM sample consisted of the β phase (~6 vol%) and α lamellar phase. Grain refinement of the α phase occurred via both dislocation evolution and deformation twinning during LSP. A theoretical description of the microstructural evolution, particularly the distribution of deformation twins, was developed. The fatigue strength and micro-hardness of the EBM samples increased by approximately 17% and 11% after LSP treatment, respectively. The fatigue fracture morphologies at three defined damage stages (crack initiation, crack propagation, and instantaneous rupture) were examined for EBM samples before and after LSP. The dominant mechanism of fatigue strength enhancement by LSP was discussed. The effects of residual compressive stress assistant with adiabatic temperature increase and grain refinement of the α phase produced by LSP reduced the pre-existing crack size, suppressed crack initiation, and increased the required work for fatigue fracture.
关键词： Laser shock peening,Electron beam melting,Ti–6Al–4V titanium alloy,Fatigue behavior,Microstructural characterization
更新于2025-09-23 15:19:57
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Study on mechanical and metallurgical properties of fiber laser welded Nb-1% Zr-0.1% C alloy
摘要： Laser welding of Nb-1% Zr-0.1% C was attempted in butt-welding configuration using top and bottom sided inert gas shielding. The precautionary measure during welding was to limit the reactivity of niobium alloy in ambient atmosphere. The ranges of input parameters, that is, laser power (P), welding speed (V) and beam diameter (D) for full penetration welding were attempted by carrying out bead-on-plate (BOP) experiments. The selection of the combination of process parameters was such that the formed weld area could be minimized without hampering the depth of penetration. Bead-geometry, hardness and tensile strength were quantified to study the influence of input process parameters during laser welding. Base metal had an average hardness of 108 VHN and the average hardness of fusion zone (FZ) was found to lie between 278 and 546 VHN. The steeper increment in microhardness value of the FZ could be due to the grain refinement, dissolution of precipitates and formation of brittle intermetallic phases of carbide and oxides, which were evident by the result of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) phase analysis. The weld joint that failed in the weld zone exhibited the brittle failure, and ductile mode was achieved in the joint, where failure occurs at base metal. The range of elongation in laser welded joints varied in between 1.97 and 5.73 mm. The reduction of tensile strength and ductility of the joints could be due to marginal enhancement of microhardness and increment of brittle phase density in fusion zone, as were evident from XRD phase analysis. The main focus of the present work was intended towards the establishment of laser welding as an alternative technique for fabrication of reactive niobium alloy in ambient atmosphere.
关键词： Cooling rate,Laser welding,Grain refinement,Niobium alloy,Mechanical properties,Nb-1% Zr-0.1% C
更新于2025-09-23 15:19:57
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Investigation on the microstructure and mechanical behaviors of a laser formed Nb-Ti-Al alloy
摘要： Nb-Ti-Al alloys have attracted much attention as a potential candidate for high-temperature structural applications beyond the scope of Ni-based superalloys. Previously, Nb-Ti-Al alloys were prepared by arc-melting or hot-pressing. In this study, laser forming of the Nb-23Ti-15Al alloy is explored, and the microstructure and mechanical behaviors are systematically investigated. The results indicate that the nearly defectless Nb-Ti-Al alloy with fine dendrites could be obtained through laser forming. Three phases, β, δ and Ti(O,C), present in the alloy, and the β/δ matrix displays a columnar microstructure. Moreover, the Ti(O,C) phase, a solid-solution of TiO or TiC, appears in the alloy. Ti(O,C) is formed due to the introduction of the O and C from the elemental powder, which has a face-centered cubic (FCC) structure and a moderate lattice parameter between that of TiO and TiC. Two morphologies of Ti(O,C), large cobblestone-like particles and small dispersive particles, are observed in the alloy. Forbidden reflections of δ phase occur due to double diffraction and slight superlattice reflections of β phase arise. Furthermore, refined β/δ phases and dispersed small Ti(O,C) result in higher microhardness and fracture toughness. In brief, our results indicate that laser forming is a potential method for manufacturing Nb-Ti-Al alloys with prominent properties.
关键词： Laser forming,Double diffraction,Mechanical behavior,Ti(O,C),Nb-Ti-Al alloy,Microstructure
更新于2025-09-23 15:19:57
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[Laser Institute of America ICALEO?? 2017: 36th International Congress on Applications of Lasers & Electro-Optics - Atlanta, Georgia, USA (October 22a??26, 2017)] International Congress on Applications of Lasers & Electro-Optics - A composite stellite alloy hardfacing with improved laser cladding behavior and wear resistance
摘要： To solve the existing wear and corrosion problems in power generation industry, this research investigates the wear and corrosion behavior of Stellite alloys in NaOH solution, which simulates the amine media in the feedwater service of power generation plants. The Stellite alloys under this study include Stellite 6 and a composite Stellite alloy. The composite Stellite alloy hardfacing, which consists of 70% Stellite 3 and 30% Stellite 21, is created via laser cladding for control valve seat sealing surfaces, aiming at enhancing hardness and wear resistance, compared with Stellite 6 hardfacing, and improving cracking in laser cladding process, compared with Stellite 3. The composite Stellite alloy hardfacing is made on 316 stainless steel substrate and it does not show any cracking. The microstructure of the hardfacing is analyzed using SEM, EDS and XRD. The hardness, dry sliding wear resistance and cavitation-erosion resistance in NaOH solution are evaluated. Stellite 6 hardfacing is prepared with the same laser process parameters and is also analyzed and tested under the same conditions with the composite Stellite alloy hardfacing for comparison. The experimental results and real industrial test demonstrate superior performance of the composite Stellite alloy hardfacing to Stellite 6 hardfacing for control valve seat sealing application.
关键词： Cavitation-erosion,Hardfacing via laser cladding,Stellite alloy,Dry-sliding wear
更新于2025-09-23 15:19:57
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Numerical simulation of the surface morphology and residual stress field of IN718 alloy by Gaussian mode laser shock
摘要： Laser shock processing (LSP) is a new surface modification technology that can improve mechanical properties and extending fatigue life. The numerical simulation was utilized in this work, the IN718 alloy was treated by Gaussian mode laser with the laser pulse energy of 3?7 J, laser pulse width of 12 ns and laser spot in diameter of 3 mm. And the effects of laser pulse energy on the surface morphology and residual stress field of material was investigated. The numerical simulation results showed that after the treatment of LSP, the plastic deformation and compressive residual stress layer with a certain depth is formed on the near surface of material. The amount of the plasticity deformation of material was increased with the laser pulse energy. And the compressive residual stress in surface and the direction of depth are increased with the laser pulse energy too. With the laser pulse energy from 3?7 J, the maximum compressive residual stresses are appeared at the center of the surface corresponding to the laser spot. When the laser pulse energy is increased from 3 J–7 J, the plastic deformation in depth is increases from 0.50 μm–1.86 μm, and the maximum compressive residual stress is increased from 362 MPa–742 MPa. In conclusion, LSP can improve mechanical properties of IN718 significantly, and the laser pulse energy is the most important factor to affect the LSP effect. This work can provide a certain theoretical guidance for researchers to study the IN718 alloy treated by LSP.
关键词： Residual stress,Gaussian mode laser,Surface morphology,Laser shock processing,IN718 alloy,Laser pulse energy,Numerical simulation
更新于2025-09-23 15:19:57