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Comparison of the Physicochemical Properties of TiO2 Thin Films Obtained by Magnetron Sputtering with Continuous and Pulsed Gas Flow
摘要： In this paper, a comparison of TiO2 thin ?lms prepared by magnetron sputtering with a continuous and pulsed gas ?ow was presented. Structural, surface, optical, and mechanical properties of deposited titanium dioxide coatings were analyzed with the use of a wide range of measurement techniques. It was found that thin ?lms deposited with a gas impulse had a nanocrystalline rutile structure instead of ?brous-like anatase obtained with a continuous gas ?ow. TiO2 thin ?lms deposited with both techniques were transparent in the visible wavelength range, however, a much higher refractive index and packing density were observed for coatings deposited by the pulsed gas technique. The application of a gas impulse improved the hardness and scratch resistance of the prepared TiO2 thin ?lms.
关键词： optical properties,scratch resistance,thin ?lms,gas impulse magnetron sputtering,microstructure,hardness,surface properties,mechanical properties,TiO2
更新于2025-09-23 15:21:21
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Weldability and mechanical behavior of laser-welded TRIP 750 steel sheets
摘要： Transformation-induced plasticity steels have been developed and widely applied in the automotive and aerospace industries. They exhibit ductility and mechanical strength associated with a high formability due to their complex microstructure of bainite-associated pro-eutectoid ferrite and significant retained austenite fractions. The weldability of these steels is limited by the high content of alloying elements in the composition, causing the thermal cycle to modify the carefully designed microstructure, which in turn generates unsatisfactory weld mechanical properties. Laser welding has a relatively low thermal input, and, therefore, a narrow heat-affected zone is obtained. As known, the literature had not been definitively reported the microstructural features of the fusion and the heat-affected zones after laser welding of TRIP steels in conjunction with their mechanical behavior. The aim of the present work is to characterize the microstructure and mechanical behavior of laser-welded TRIP steel after uniaxial tensile and Erichsen formability tests. The coupons of TRIP 750 steel sheets were subjected to different laser welding conditions in order to analyze their impact on the microstructure, hardness, and mechanical strength of the material. After some preliminary tests, the laser power was fixed at 900 W and the weld speed fixed at 50 mm/s as the best choice of operating parameters. Under these conditions, the fusion zone was almost completely martensitic, while the heat-affected zone had a mixture of ferrite and martensite. The martensite transformation is corroborated by finite elements analyses as the cooling rate was 4200 °C/s for material at martensite start temperature. The average hardness of the fusion zone was 530 HV and the heat-affected zone was 550 HV, compared with 270 HVof the base material. In terms of mechanical behavior, the tensile strength of the welded coupons was found to reach 740 MPa and the ductility reached 22% in uniform deformation. The Erichsen index for the welded sheets attained 15 mm for a load of 48.5 kN, similar with the non-welded base material. Both in the case of the uniaxial tensile testing and in the Erichsen testing, the fracture occurred in the base material away from the weld, showing a good toughness of the welded component.
关键词： Transformation-induced plasticity steels,Microstructure,Hardness,Tensile testing,Erichsen testing,Laser welding
更新于2025-09-23 15:21:01
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Influence of laser polishing on surface roughness and microstructural properties of the remelted surface boundary layer of tool steel H11
摘要： This work investigates the influence of multi-step laser polishing on microstructural properties of the remelted surface layer of tool steel H11. Four different laser polishing process parameter sets were selected that lead to a significant reduction in roughness. In a sequential process using continuous and pulsed laser radiation (Nd:YAG) a significant reduction of surface roughness was achieved on an initially annealed H11 sample. The remelted layers were analyzed using roughness measurements, white light interferometry, X-ray diffractometry, electron backscatter diffraction, glow discharge emission spectroscopy, and nanoindentation hardness measurements. Laser polishing leads to a grain refinement and a significant increase in hardness. A surface roughness of Ra 50nm was achieved in an Argon process atmosphere with an additional 6vol% CO2. In particular the carbon concentration was more than halved within the remelted layer. The lower carbon concentration is correlated with a decreased maximal surface hardness down to 366HV. High residual tensile stresses of up to 926MPa can be introduced by laser polishing. Overall, high temperature gradients and, in particular, decarburization due to carbon diffusion processes were identified to be the major driving force for significant changes in surface micro-roughness and microstructural properties.
关键词： AISI H11,micro hardness,laser polishing,decarburization,surface roughness,martensite formation
更新于2025-09-23 15:21:01
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Proton Radiation Hardness of Perovskite Tandem Photovoltaics
摘要： We propose and test monolithic perovskite/CIGS tandem solar cells for readily stowable, ultra-lightweight space photovoltaics. We design operando and ex situ measurements to show that perovskite/CIGS tandem solar cells retain over 85% of their initial power-conversion efficiency after high-energy proton irradiation. While the perovskite sub-cell is unaffected after this bombardment, we identify increased non-radiative recombination in the CIGS bottom cell and nickel-oxide-based recombination layer. By contrast, monolithic perovskite/silicon-heterojunction cells degrade to 1% of their initial efficiency due to radiation-induced defects in silicon.
关键词： Perovskite/SHJ,Proton Radiation Hardness,Space Photovoltaics,Perovskite Tandem Photovoltaics,Perovskite/CIGS
更新于2025-09-23 15:21:01
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Characterization and correlation of microstructure and hardness of Tia??6Ala??4V sheet surface-treated by pulsed laser
摘要： A hot-rolled Tie6Ale4V (Ti-64) sheet was surface-treated by pulsed laser at two different powers (100 and 200 W), with microstructural features and hardness before and after the laser surface treatment (LST) systematically investigated. Results show that after the LST at both powers there are two modi?cation zones with distinct microstructural characteristics: melted zone (MZ) near the laser beam center, completely composed of ?ne martensitic plates with dense {10e11} nanotwins inside them; heat-affected zone (HAZ) far away from the laser beam center, comprised of mixed structures of short-rod b particles, martensitic plates and untransformed bulk a grains. Hardness measurements reveal that the hardness of the Ti-64 sheet can be markedly increased (especially in the MZ) after the LST. In-depth analyses suggest that the hardness increase in the MZ can be ascribed to combined contributions from grain re?nement, presence of nanotwins and solid solution of alloying elements, while only the structural re?nement by ?ne plate structures contributes to hardening in the HAZ. Comparisons between both the LSTed specimens reveal that increasing the laser power from 100 W to 200 W can effectively enlarge the laser-modi?ed zones (both the MZ and the HAZ) and simultaneously re?ne plate structures, leading to further hardness increase.
关键词： Ti-6Ale4V,Hall-petch relation,Hardness,Electron backscatter diffraction,Pulsed laser
更新于2025-09-23 15:19:57
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Enhancing Hardness and Wear Performance of Laser Additive Manufactured Ti6Al4V Alloy Through Achieving Ultrafine Microstructure
摘要： Refining microstructure is an important issue for laser additive manufacturing (LAM) of titanium alloy. In the present work, the microstructures of LAM-fabricated Ti6Al4V alloy were refined using a low energy density with the combination of a small spot diameter, a low laser power, and a high scanning speed. The microstructure, hardness, wear performance, and molten pool thermal behavior of LAM-fabricated Ti6Al4V coatings were studied. The results show that the grain sizes of both prior β and α phases are strongly dependent on the cooling rate of the molten pool. The fine prior β grains and submicron-scale acicular α phases were obtained under a low energy density of 75 J mm?2 due to the high cooling rate of the molten pool. In addition, the as-fabricated Ti6Al4V sample with submicron-scale acicular α phase showed a very high hardness of 7.43 GPa, a high elastic modulus of 133.6 GPa, and a low coefficient of friction of 0.48. This work provides a good method for improving the microstructure and mechanical performance of LAM-fabricated Ti6Al4V alloy.
关键词： wear properties,hardness,laser additive manufacturing,titanium alloy,microstructure
更新于2025-09-23 15:19:57
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Laser Welding of ZE41 Mg Alloy: Experimental Investigations on the Effect of Parameters and Nondestructive Testing
摘要： Laser beam welding is an essential metal joining method for magnesium and its alloys with their growing applications in automotive, aerospace, marine, etc. In this research paper, the experimental modelling for laser beam welding of ZE41 Mg alloy and the mechanical and metallurgical characterisation after welding are reported. The effects of weld scan speed and laser beam power on the weld geometry for bead on plates of ZE41 Mg alloy using a continuous-wave CO2 laser system were analysed in this work. The microstructure, hardness, and radiography analysis were discussed. The results indicate the in?uence of laser parameters and the validity of the regression equations developed for the optimisation of process parameters.
关键词： ZE41 magnesium alloy,Hardness,Optimisation,X-ray radiography,Laser beam welding
更新于2025-09-23 15:19:57
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Laser Cutting Parameters Effect on 316L Stainless Steel Surface
摘要： Laser cutting is a cutting technology that enables fast processing in high precision. This technology utilizes high temperatures generated by engine to perform the cutting process. Selection of cutting parameters becomes the main factor to determine the cutting surface quality. Cutting parameters in the form of cutting speed and gas pressure are varied between 60 mm/minute - 100 mm/minute and 17 bar - 21 bar to examine the effect on surface character. The character of the laser-cutting surface on 316L series stainless steel material was observed related to the roughness, hardness and microstructure. The results showed that the parameters of cutting speed and gas pressure had an effect on the cutting surface. Changes in cutting speed has more effect on surface roughness while gas pressure has more effect on cutting surface hardness. Observations on the surface also illustrated that there were differences in cutting quality along with the deeper penetration performed by the laser.
关键词： gas pressure,hardness,cutting speed,surface roughness
更新于2025-09-23 15:19:57
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Investigation of hole quality in drilled Ti/CFRP/Ti laminates using CO2 laser
摘要： The machinability of titanium (Ti) and carbon fiber reinforced plastic (CFRP) (Ti/CFRP/Ti) laminates using CO2 laser is presented in this work. The effect of line energy and laser frequency on output responses such as heat affected zone (HAZ), taper angle (TA), metal composite interface (MCI) damage, surface roughness, dross height, and circularity were investigated. Line energy - the most influential parameter - demonstrated a threshold behavior; no drilling was observed below a certain line energy. Scanning acoustic microscopy (SAM), scanning electron microscopy (SEM), micro-computed tomography (μ-CT), and other imaging techniques were used to establish a correlation between laser parameters and CO2 laser machined damage in Ti/CFRP/Ti laminates. The results show that using a higher frequency and lower line energy can significantly improve the hole quality. However, dross free holes with minimum taper can be obtained using higher line energy.
关键词： Surface roughness,Circularity,Micro-hardness,CO2 laser,Dross height,HAZ,Drilling,Ti/CFRP/Ti,MCI damage factor,TA
更新于2025-09-23 15:19:57
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Structural, electrical and mechanical properties of ВС films prepared by pulsed laser deposition from mixed and dual boron-diamond/graphite targets
摘要： Relatively low and high deposition rates of BCх films were realized by pulsed laser ablation of mixed B–diamond and dual B–graphite targets, respectively. Deposition was performed at 500 °C and the rate of film deposition was determined with respect to the number of atomic monolayers (obviously less or more than one monolayer) grown for one laser pulse. In the case of BCх films formation with a low deposition rate, doping with B facilitated the growth of the nanocomposite structure, which possessed an increased fraction of sp3 bonds, a very low electrical resistance, and an improved mechanical performance. The change of the sheet resistance of these films as the temperature was reduced from 300 to 65 K had a metallic character. For about 95-nm-thick films with bulk compositions of BC1.7 and BC0.6, the resistivity at room temperature were approximately equal to 1.5 mΩ·cm, and the lowest resistivity of 0.23 mΩ·cm was detected for B-enriched film at 85 K. With an increase in the B atom concentration in such films, the charge carrier (holes) concentration decreased, and their mobility increased from 180 to 10,500 cm2·V?1·s?1 due to samples cooling. The application of a higher deposition rate from the dual B–graphite target activated surface migration of condensed atoms, which caused the development of granular morphology, the B segregation and the reduction of the sp3 bond fraction. The hardness and electrical conductivity of such films were obviously inferior to those of the films obtained by PLD with a low deposition rate.
关键词： Hardness,Thin films,Resistivity,Pulsed laser deposition,Boron,Diamond-like carbon
更新于2025-09-19 17:15:36