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Crack behavior in ultrafast laser drilling of thermal barrier coated nickel superalloy
摘要： Quantitative analysis is required to explore the mechanism of crack generation in ultrafast laser drilling of thermal barrier coated nickel superalloy. In this study, a simple thermo-mechanical coupled model is established to obtain temperature history, phase transformation stress and thermal stress during drilling process, in which laser beam scanning, laser intensity attenuation, the nonlinear relationship between drilling depth and drilling time are involved. The induced stress obtained from the present model is compared with the results by digital image correlation (DIC) method. According to the crack distribution around the drilled hole, the present model is used to explain the mechanism of crack behavior in drilling of multilayer materials. Finally, the strategy using low pulse repetition rate or water jet assisted method is suggested to reduce the thermal effect in ultrafast laser drilling process.
关键词： TBC,Phase transformation stress,Thermal stress,Crack behavior,Ultrafast laser,Laser drilling
更新于2025-09-23 15:19:57
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Manipulation of the Size and Phase Composition of Yttrium Iron Garnet Nanoparticles by Pulsed Laser Post-Processing in Liquid
摘要： Modi?cation of the size and phase composition of magnetic oxide nanomaterials dispersed in liquids by laser synthesis and processing of colloids has high implications for applications in biomedicine, catalysis and for nanoparticle-polymer composites. Controlling these properties for ternary oxides, however, is challenging with typical additives like salts and ligands and can lead to unwanted byproducts and various phases. In our study, we demonstrate how additive-free pulsed laser post-processing (LPP) of colloidal yttrium iron oxide nanoparticles using high repetition rates and power at 355 nm laser wavelength can be used for phase transformation and phase puri?cation of the garnet structure by variation of the laser ?uence as well as the applied energy dose. Furthermore, LPP allows particle size modi?cation between 5 nm (ps laser) and 20 nm (ns laser) and signi?cant increase of the monodispersity. Resulting colloidal nanoparticles are investigated regarding their size, structure and temperature-dependent magnetic properties.
关键词： laser melting,yttrium iron oxide,monodisperse,laser fragmentation,phase transformation,garnet,perovskite,laser ablation,ferrimagnetic nanoparticles
更新于2025-09-23 15:19:57
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Phase-Control-Enabled Enhancement in Hydrophilicity and Mechanical Toughness in Nanocrystalline Tungsten Oxide Films for Energy-Related Applications
摘要： We report on the phase-control-enabled enhancement in the hydrophilicity and mechanical properties of nanostructured WO3 films for energy-related applications. Nanostructured WO3 films were fabricated by utilizing reactive magnetron sputter deposition onto silicon (100) substrates with varying deposition temperature (Ts = 25?500 °C) at a fixed oxygen partial pressure of ～4 mTorr. Extensive characterization performed indicates that the fundamental surface/interface structure?phase?hydrophilicity?mechanical property correlation enables tailoring nanocrystalline WO3 films to meet the requirements of various technological applications. Crystal structure, surface/interface morphology, and microstructure characterization indicate the deposition processing conditions induce phase transformations and surface/interface quality variation, which in turn controls the hydrophilicity and mechanical behavior of WO3 films. Carefully tuned processing conditions induce an amorphous to crystalline structural transformation, which progresses through amorphous to monoclinic to tetragonal phases, coupled with variation in surface roughness and crystallite size. Mechanical characterization using nanoindentation reveals that the mechanical response, in terms of hardness (H), elastic modulus (E), and scratch parameters, of WO3 films is highly sensitive to their phase and microstructure evolution. Nanostructured WO3 films crystallized in monoclinic phase exhibit superior mechanical response compared to either amorphous or tetragonal phase WO3 films. The maximum hardness (～38 GPa) and elastic modulus (～320 GPa) values were obtained for WO3 films deposited at Ts = 400 °C. The phase transformation sequence coupled with surface/interface structure affects the contact angle values significantly. The contact angle decreases significantly from 70° to nearly 5° with variation in phase, microstructure, and surface/interface quality of WO3 films. A direct structure?phase?microstructure?hydrophilicity?mechanical property relationship found suggest that tuning properties of WO3 films for photoelectrochemical, photocatalytic, and energy-related applications can be achieved by tuning the deposition conditions and controlling the phase at the nanoscale dimensions.
关键词： WO3 thin films,hydrophilicity,phase transformation,nanostructure
更新于2025-09-23 15:19:57
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Effect of Firing Temperature and Duration on Fused Silica Investment Shell Strength at Room Temperature
摘要： Fused silica is widely used in investment casting shell molds as ?our, stucco and binder for its superior properties, such as low linear thermal expansion coef?cient and high thermal shock resistance. Investment shell molds are usually ?red after the de-wax process to remove the residue pattern material, and to improve shell strength through sintering. The ?ring temperatures are generally high enough to affect the phase constituent and microstructure of the shells, which further in?uences the shell strength. Firing duration at ?ring temperature is another important factor having an impact on the shell strength due to grain coarsening, but it is often overlooked by investment foundries. In this article, the room temperature moduli of rupture of investment shells ?red at different conditions were determined. The crystallinity of fused silica shells was determined using X-ray diffraction. The differences on the shell strength were discussed and correlated with the microstructure and phase constitution in the shells after different ?ring processes.
关键词： phase transformation,modulus of rupture,firing duration,firing temperature,investment shell
更新于2025-09-19 17:15:36
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Tailoring the Band Gap in the ZnS/ZnSe System: Solid Solutions by a Mechanically Induced Self-Sustaining Reaction
摘要： The complete ZnSxSe1?x solid solution was successfully obtained by the mechanochemical process denoted as a mechanically induced self-sustaining reaction. Excellent control of the chemical stoichiometry of the solid solution was possible by adjusting the atomic ratio of the starting Zn/S/Se elemental mixture subjected to milling. A mixture of both wurtzite-2H (hexagonal) and zinc blende (cubic) structures was always obtained, although for a similar milling time the proportion of the zinc blende structure increased with the Se content in the solid solution. However, wurtzite was the major phase for S-rich compositions when milling was stopped just after ignition. It was demonstrated that milling induces the wurtzite-to-zinc blende phase transition. The 8H hexagonal polytype was also observed in samples subjected to long milling times. Variation of the lattice parameters for both structures with the x value in the solid solution presented an excellent linearity, confirming the validity of Vegard’s law. However, variation of the band-gap energy (Eg) with x was not perfectly linear, and a small bowing parameter of 0.34 was obtained. It was possible to tune the Eg value between those of the end members of the solid solution in a continuous manner by adjusting the stoichiometry of the solid solution. The morphology and crystalline domain size can also be controlled by adjusting, in this case, the postignition milling time of the mechanochemical process.
关键词： band gap tuning,phase transformation,Vegard's law,ZnS/ZnSe solid solution,mechanically induced self-sustaining reaction,mechanochemical synthesis
更新于2025-09-19 17:15:36
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UV light enabled photocatalytic activity of α-Fe2O3 nanoparticles synthesized via phase transformation
摘要： In this work, hematite (a-Fe2O3) nanoparticles (NPs) were synthesized by co-precipitation method involving chemical precipitation of aqueous salts of iron (Fe2+/Fe3+) using NaOH aqueous solution. The synthesis of a-Fe2O3NPs via phase transformation and its photocatalytic application under ultra violet (UV) light is rarely reported. The maximum removal of methylene blue (MB) dye (92%) was achieved at pH 10 and 200 mg amount of catalyst, whereas the concentration of dye was 10 ppm. The removal percentage of MB dye was found to vary with pH of the solution, concentrations of dye, and amount of a-Fe2O3 NPs for certain interval of time. Moreover, plot of ln(Ct/C0) Vs time exhibited almost a linear relationship between them which suggested the pseudo-?rst order kinetics reaction of photocatalytic degradation of MB.
关键词： Hematite,Phase transformation,Nanoparticles,FTIR,UV irradiation,Photocatalyst
更新于2025-09-19 17:13:59
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Numerical and experimental investigation of the formation mechanism and the distribution of the welding residual stress induced by the hybrid laser arc welding of AH36 steel in a butt joint configuration
摘要： Formation mechanism of the welding residual stress (WRS) is a key part of welding research. However, there is a lack of meaningful numerical models of the WRS. In this work, a thermal-metallurgical-mechanical (TMM) model was developed using SYSWELD to investigate the distribution and the formation mechanism of WRS during the hybrid laser arc welding of AH36 steel. A series of simulations were conducted to explore the effects of various factors on the WRS. The numerical results matched well with the experimental data. The computational accuracy was improved by considering the typical “wine glass” weld profile and the dilution rate during simulation. The evolution of the WRS is strongly affected by the interaction of phase transformation and strain hardening. The austenite-martensite transformation has a great potential to reduce the WRS whereas the austenite-bainite transformation produces high levels of WRS. The phase transformation temperature has a great influence on WRS.
关键词： Hybrid laser arc welding,Welding residual stress,Phase transformation,Numerical modeling
更新于2025-09-19 17:13:59
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Oxygen gain and aluminum loss during laser metal deposition of intermetallic TiAl
摘要： For manufacturing turbine parts for the aeronautical industry, lightweight structural materials like titanium aluminides are used. One well-known example is the alloy Ti-43.5Al-4Nb-1Mo-0.1B (atomic percent) with the commercial name TNM. In previous studies, experiments on laser metal deposition of TiAl were performed to evaluate the potential of the technology to repair defective, damaged, or worn blades. Process conditions including postprocess heat treatment were successfully adjusted. However, oxygen pick-up is still a crucial aspect in laser-based additive manufacturing of Ti- and TiAl-based alloys. In this work, approaches were made to analyze the oxygen pick-up as a function of processing parameters and the powder particle size. The results show that the build rate and the powder particle size affect the oxygen content in the consolidated material.
关键词： laser processing and cladding,intermetallics,phase transformation,aero-engine components,microstructure
更新于2025-09-19 17:13:59
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The In-Depth Studies of Pulsed UV Laser-Modified TiO2 Nanotubes: The Influence of Geometry, Crystallinity, and Processing Parameters
摘要： The laser processing of the titania nanotubes has been investigated in terms of morphology, structure, and optical properties of the obtained material. The length of the nanotubes and crystallinity, as well as the atmosphere of the laser treatment, were taken into account. The degree of changes of the initial geometry of nanotubes were checked by means of scanning electron microscopy, which visualizes both the surface and the cross-section. The phase conversion from the amorphous to anatase has been achieved for laser-treated amorphous material, whereas modification of calcined one led to distortion within the crystal structure. This result is confirmed both by Raman and grazing incident XRD measurements. The latter studies provided an in-depth analysis of the crystalline arrangement and allowed also for determining the propagation of laser modification. The narrowing of the optical bandgap for laser-treated samples has been observed. Laser treatment of TiO2 nanotubes can lead to the preparation of the material of desired structural and optical parameters. The usage of the motorized table during processing enables induction of changes in the precisely selected area of the sample within a very short time.
关键词： laser treatment,TiO2 nanotubes,phase transformation,surface modification
更新于2025-09-16 10:30:52
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Subsurface damage and phase transformation in laser-assisted nanometric cutting of single crystal silicon
摘要： Single crystal Si subsurface damage and phase transformation caused by laser-assisted nanometric cutting were investigated in this paper through the ultraprecision cutting experiments and molecular dynamics simulation. Post-cutting examination of a crystal’s subsurface revealed a distorted Si-I layer and an amorphous Si with embedded nanocrystalline Si-III and Si-XII. As a result of insufficient contact pressure during laser-assisted cutting, the amorphous Si was directly generated from the Si-I through the collapse of the crystal lattice rather than from the intermediate high-pressure phase Si-II. The newly-formed amorphous Si crystallized partially during the laser-assisted cutting and transformed into metastable Si-III and Si-XII phases caused by the laser annealing effect. In comparison to machining without laser assistance, it was found that dislocation activity was increased by a factor of ~8×1014 when laser assistance was applied. This gave rise to enhancement of plastic deformability of the material, with the critical ductile-brittle transition depth of cut increasing from 150 nm to 395 nm and the thickness and extent of stress in the distorted Si-I subsurface layer being reduced.
关键词： single crystal silicon,laser assisted,phase transformation,nanometric cutting,subsurface damage
更新于2025-09-16 10:30:52