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The roles of stress in the thermal shock failure of YSZ TBCs before and after laser remelting
摘要： In order to reveal the roles of stress in the thermal shock failure of thermal barrier coatings (TBCs), yttria-stabilised zirconia (YSZ) TBCs were prepared via atmospheric plasma spraying and then remelted by a laser remelting process. Subsequently, thermal cycling tests of the as-sprayed YSZ TBCs and remelted YSZ TBCs were carried out at 1100 °C. The thermal shock failure mechanism of the two TBCs was investigated comparatively from the perspective of stress, i.e., phase transformation stress of ceramic coating, growth stress and thermal mismatch stress generated by thermally grown oxide (TGO). The results showed that, compared with the as-sprayed YSZ TBCs, there was no m-ZrO2 in the remelted YSZ TBCs, which avoided the ceramic coating phase transformation stress produced by the transformation between m-ZrO2 and t-ZrO2 during thermal cycling. Therefore, the thermal shock failure mode of the as-sprayed YSZ TBCs was severe buckling driving delamination, while that of the remelted YSZ TBCs was slight edge delamination. In addition, the TGO growth stress and the thermal mismatch stress between the TGO and the bonding coating were reduced by the laser remelting treatment, leading to the spallation tendency of YSZ TBCs was decreased. Consequently, the remelted YSZ TBCs exhibited superior thermal shock resistance to the as-sprayed YSZ TBCs. Therefore, the phase transformation stress, growth stress and thermal mismatch stress determined the thermal shock failure mode and thermal shock life of these two YSZ TBCs.
关键词： Stress,Laser remelting,TGO,Thermal shock failure mechanism,TBCs
更新于2025-09-23 15:19:57
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Correlation between laser energetic parameters and magnetic properties of GO laminations under surface treatments with long, short or ultra-short pulsed lasers
摘要： Electromagnetic components mostly incorporate soft magnetic materials used as flux multipliers. Hence, any reduction in iron loss of the magnetic core yields in saving energy. Among the techniques, the local laser treatment is a non-contact method applied for 180° domain refinement (Patri et al. [1]). The present study reassessed the impact of laser treatment on the magnetic properties of grain oriented silicon steels. Various laser pulse widths are used: an ultra-short pulse laser mainly adapted to the ablation process and a long and short pulse durations used for both irradiation and scribing processes [2]. The power loss is measured with a Single Sheet Tester (150 × 150 mm2). Each type of treatment resulted in a power loss reduction of 15–35% at peak induction 1.5 T and frequency 50 Hz. However, only the scribing and the ablation improved also the apparent permeability. In this work, the laser energy parameters are used to estimate the laser impact on the heat affected zone, the groove depth, the induced thermal stress, and on the internal properties of a magnetic behavioral model: static permeability and dynamic magnetization property [3].
关键词： Groove depth,Heat affected zone,GO laminations,Induced thermal stress,Laser treatment,Magnetic properties
更新于2025-09-23 15:19:57
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Evaluation of stress on metal surfaces by laser-induced breakdown spectroscopy
摘要： In this study, we evaluated the feasibility of using laser-induced breakdown spectroscopy (LIBS) to determine the stress generated in metal materials by comparing measured stress levels with those determined by x-ray diffraction (XRD). Magnesium (Mg) alloy specimens underwent impact stress generated under ultrasonic peening. Stainless steel specimens were subjected to bending stress. The reference stress for each specimen was measured using XRD. LIBS measurements were performed to determine the correlation between stress distribution and the ratio of ionic to atomic spectral line intensity. The stress distribution from the surface to the interior of the ultrasonic-peened specimens measured by LIBS showed a similar tendency to that measured by XRD, but there was a difference in the maximum measurable depth. Additionally, the tensile and compressive stress distributions measured by LIBS on bending specimens showed similar trends to those of XRD. From these results, it was possible to measure the correlation between the stress state of the metal matrix and the spectral line strength of LIBS, thus confirming the potential for stress measurement using LIBS.
关键词： laser-induced breakdown spectroscopy,mechanical stress,spectral line
更新于2025-09-23 15:19:57
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Predictive Model for Thermal and Stress Field in Selective Laser Melting Processa??Part I
摘要： During the part forming in laser powder bed fusion process, thermal distortion is one big problem due to the thermal stress which is caused by the high cooling rate and temperature gradient. Therefore, it is important to know the effect of process parameters on thermal and stress evolution in the melt zone. In this paper, a 3D finite element model for Selective Laser Melting (SLM) process based on sequentially coupled thermo-mechanical field analysis was developed for accurately predicting thermal history and surface features, like distortion and residual stress. Temperature dependent material properties for performed material 304L stainless steel are incorporated into the model capturing the change from powder to fully dense solid stainless steel. Surface temperature gradients and thermal stress were fully presented in the development of different parameter sets, which designed for the probability of reducing defect formation. Simulation results showed that the sequent thermal cyclic melting in successive scanned tracks resulted in alternating compressive and tensile thermal stresses. A predictive model for thermal and stress field in large part by selective laser melting process is come up in Part II. After the parts cooled down to room temperature, higher residual stresses were found in longitudinal stress. This paper will provide guidance on how to achieve minimum residual stresses and deformations by the study of the process parameters.
关键词： finite element analysis,SLM,distortion,residual stress
更新于2025-09-23 15:19:57
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Predictive Model for Thermal and Stress Field in Selective Laser Melting Processa??Part II
摘要： Finite Element Analysis (FEA) is used to predict the transient thermal cycle and optimize process parameters to analyze these effects on deformation and residual stresses. However, the process of predicting the thermal history in this process with the FEA method is usually time-consuming, especially for large-scale parts. In this paper, an effective predictive model of part deformation and residual stress was developed for accurately predicting deformation and residual stresses in large-scale parts. An equivalent body heat flux proposed from the single layer laser scan model was imported as the thermal load to the layer by layer model. The hatched layer is then heated up by the equivalent body heat flux and used as a basic unit element to build up the macroscale part. The thermal history and residual stress fields of two solid parts with different support structures during the SLM process were simulated. Layer heat source method has the capability for fast temperature prediction in the SLM process, while sacrificing modeling details for the computational time-saving purpose. Thus numerical modeling in this work can be a very useful tool for the parametric study of process parameters, residual stresses and deformations.
关键词： distortion,finite element analysis,residual stress,layer heat source model,SLM
更新于2025-09-23 15:19:57
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Finite-element inverse analysis of residual stress for laser welding based on a contour method
摘要： The thermal effect of laser welding degrades the local material properties, and this inevitably leads to thermal deformation and thermal residual stress in welded joints. In this study, the residual stress distribution of laser-welded Al–Li alloy parts was measured by a combination of the contour method and finite-element simulation. First, the contour deformation of the cutting surfaces of welded parts resulting from the release of residual stress was measured by a coordinator. Then, the reverse contour deformation was applied to the finite-element model as the displacement boundary condition to invert the full-field residual stress of the cutting surface. Furthermore, a thermal/structural sequential coupling analysis method was used to establish a complete three-dimensional finite-element model of a laser-welded plate and calculate the residual stress field, taking the actual weld morphology as the characteristic parameter of the heat source, using the improved conical heat source model of laser welding. The result is consistent with the results of the contour method.
关键词： Laser welding,Residual stress,Contour method,Thermal/structural finite-element analysis,Improved conical heat source model
更新于2025-09-23 15:19:57
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Development of a Flexible Tunable and Compact Microstrip Antenna via Laser Assisted Patterning of Copper Film
摘要： Design and rapid prototyping of a tunable and compact industrial, scientific and medical (ISM) band microstrip antenna for applications is presented in this paper. Laser machining is introduced as a fast and accurate method for the antenna fabrication. The antenna, with an overall dimension of 65 × 46 × 0.127 mm, was fabricated by sandwiching a flexible Kapton polyimide substrate, with a dielectric constant of 3.5, between two flexible copper tapes, as the radiating patch and ground plane, respectively. The radiating patch was patterned in a meander configuration, with three slots, demonstrating the capability to reduce the resonant frequency of the microstrip antenna from 2.4 GHz to 900 MHz, without increasing the overall size of the antenna (87% compact). The effect of mechanical stress on the antenna performance was investigated by performing bend and stretch tests. The antenna was subjected to compressive bend with a minimum radius of curvature of 86 mm and 150 mm along the x- axis and y- axis which resulted in a maximum increase of resonant frequency by 3.1% and 1.3%, respectively. Similarly, the antenna was subjected to tensile bend with a minimum radius of curvature of 79 mm and 162 mm along the x- axis and y- axis which resulted in a maximum decrease of the resonant frequency by 4.2% and 0.3%, respectively. An overall 0.9% decrease in the resonant frequency was measured for an applied strain of 0.09% during stretching the antenna along the y- axis.
关键词： mechanical stress,flexible Kapton substrate,Compact tunable antenna,microstrip patch antenna,laser machining
更新于2025-09-23 15:19:57
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High-performance monolayer MoS2 photodetector enabled by oxide stress liner using scalable chemical vapor growth method
摘要： MoS2, as a typical representative of two-dimensional semiconductors, has been explored extensively in applications of optoelectronic devices because of its adjustable bandgap. However, to date, the performance of the fabricated photodetectors has been very sensitive to the surrounding environment owing to the large surface-to-volume ratio. In this work, we report on large-scale, high-performance monolayer MoS2 photodetectors covered with a 3-nm Al2O3 layer grown by atomic layer deposition. In comparison with the device without the Al2O3 stress liner, both the photocurrent and responsivity are improved by over 10 times under 460-nm light illumination, which is due to the tensile strain induced by the Al2O3 layer. Further characterization demonstrated state-of-the-art performance of the device with a responsivity of 16.103 A W?1, gain of 191.80, NEP of 7.96?×?10?15 W Hz?1/2, and detectivity of 2.73?×?1010 Jones. Meanwhile, the response rise time of the photodetector also reduced greatly because of the increased electron mobility and reduced surface defects due to the Al2O3 stress liner. Our results demonstrate the potential application of large-scale strained monolayer MoS2 photodetectors in next-generation imaging systems.
关键词： photodetector,Al2O3,stress liner,monolayer MoS2
更新于2025-09-23 15:19:57
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Successes and Challenges Associated with Solution Processing of Kesterite Cu2ZnSnS4 Solar Cells on Titanium Substrates
摘要： Roll-to-roll (R2R) processing of solution-based Cu2ZnSn(S,Se)4 (CZT(S,Se)) solar cells on flexible metal foil is an attractive way to achieve cost-effective manufacturing of photovoltaics. In this work we report the first successful fabrication of solution-processed CZTS devices on a variety of titanium substrates with up to 2.88% power conversion efficiency (PCE) collected on flexible 75 μm Ti foil. A comparative study of device performance and properties is presented aiming to address key processing challenges. First, we show that a rapid transfer of heat through the titanium substrates is responsible for the accelerated crystallisation of kesterite films characterised with small grain size, a high density of grain boundaries and numerous pore sites near the Mo/CZTS interface which affect charge transport and enhance recombination in devices. Following this, we demonstrate the occurrence of metal ion diffusion induced by the high temperature treatment required for the sulfurization of the CZTS stack: Ti4+ ions are observed to migrate upwards to the Mo/CZTS interface whilst Cu1+ and Zn2+ ions diffuse through the Mo layer into the Ti substrate. Finally, residual stress data confirm the good adhesion of stacked materials throughout the sequential solution process. These findings are evidenced by combining electron imaging observations, elemental depth profiles generated by secondary ion mass spectrometry, and x-ray residual stress analysis of the Ti substrate.
关键词： SIMS,titanium,CZTS,solar cell,stress
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