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High energy femtosecond laser peening of 2024 aluminum alloy
摘要： A femtosecond laser with a pulse energy of up to 100 mJ is used to investigate the feasibility of laser peening of a 2024 aluminum alloy that is widely used in aerospace industry. Laser beam directly irradiates the as-received aluminum sample surface in air without any protective coating for laser absorption and transparent overlay for plasma confinement. The effects of pulse energy, pulse duration and beam spot size on peening performance are studied. Optical microscope and SEM are used to examine the surface morphology of laser peened samples. Vickers hardness test is used to determine the microhardness on the surface. Residual stresses on the surface and at selected depths are measured using x-ray diffraction method. It is found that femtosecond laser can impart compressive residual stresses to a depth of more than 100 μm for this material, but the surface stress condition is not altered significantly.
关键词： residual stress,aluminum alloy,hardness,femtosecond laser,surface texture,laser peening
更新于2025-09-12 10:27:22
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A Study of Laser Beam Welding, Gas Tungsten Arc Welding and High Temperature Brazing Processes on Micro hardness and Tensile Strength of AISI Type 316 Stainless Steel
摘要： Thin wall joints for elevated temperature (~550 °C) applications can be prepared by Laser Beam Welding (LBW), Gas Tungsten Arc Welding (GTAW) and High Temperature Brazing (HTB) methods. The joints have been made and tests such as helium leak test (HLT), micro hardness test and tensile test were carried out. A study has been performed on these joining techniques to recognize the suitable method for high temperature applications. No observable leak was identified during HLT. Microstructures shows dissimilarity in solidification morphology due to disparity in heat sources. It has been identified that the joint made by brazing process having higher micro hardness value. Further, it has been observed that LBW joints have better mechanical properties than GTAW joints and HTB joints.
关键词： GTAW,Micro hardness,AISI 316 stainless steels,Tensile properties,High temperature brazing,Microstructures,Nd:YAG Laser
更新于2025-09-12 10:27:22
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Numerical analysis of multi-layered laser cladding for die repair applications to determine residual stresses and hardness
摘要： Laser cladding provides numerous advantages over the traditional, ad-hoc and imprecise deposition techniques for the repair of critical structural components such as dies and molds used in cold working industries. A necessity of a good quality laser cladding is to offer durable and reliable adhesion to the substrate with reduced dilution and absence of pores, cracks, and delamination. The process can add to complications due to addition of the second layer on the surface of the first clad layer that can generate local variation in shrinkage, layers of additive material are added onto the non-planar domain and the additional distance from the substrate. Consequently, residual stresses previously induced in a first clad layer and substrate region can alter. Largely, tensile residual stresses in the clad layer or clad-substrate interface region can lead to accelerated fatigue failure. Prediction and mitigation of tensile residual stresses still remain important issues in multi-layer laser cladding. Finite element modelling is an appropriate way to estimate the residual stress profile and microstructural changes for the prediction of optimal process parameters. The current work focuses on the development of a coupled metallo-thermomechanical finite element model in ABAQUS? for multi-layered laser cladding of CPM9V powder on H13 tool steel. The residual stress evolution along the cross-section has been characterized at different process conditions and the optimal conditions corresponding to mitigation of tensile residual stresses have been identified. The hardness can be affected due to the deposition of an additional layer and tempering can occur in clad or substrate which needs to be understood. The micro-hardness values are estimated using the numerical model and compared with the measured data using a Vickers hardness tester. It has been observed that the peak magnitude of tensile residual stress in the clad region with multiple layers is lower than the peak residual stresses in single layer clad of the same height along with the hardness.
关键词： residual stress,multi-layered deposition,Additive manufacturing,metallo-thermomechanical model,micro-hardness
更新于2025-09-12 10:27:22
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Fabrication of fine wires using direct laser melting process
摘要： With the rapid development of micro electro-mechanical-systems and micro system technology, parts made of micro-wire are widely applied in biomedical, automotive, and consumer electronics. Therefore, the manufacturing of micro-wire has played an important role in manufacturing micro parts. However, when dimensions of metal parts downscale to micro scale, the plastic deformation behaviors and thermal properties which dependent on the specimen size are different from those in the macro scale, and size effects occur. The direct laser melting process can directly build full-density, high-performance, complex metal parts by melting metal powder with laser scanning. This study investigated the direct laser melting method to fabricate fine linear-bead that can be potentially substituted for micro-wire has been investigated. Laser process parameters, such as laser power, laser scanning speed, powder grain size and powder layer thickness were found to be an important variable affecting shape of linear-bead. Surface shape and cross-sectional properties were analyzed using microscope and hardness tester.
关键词： Direct laser melting (DLM),Linear-bead,Hardness,Roundness
更新于2025-09-12 10:27:22
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Local heat treatment of a laser build-up
摘要： Laser cladding or laser metal deposition involves the deposition of any weldable material onto the surface of a metal substrate by means of a laser beam. Although clad deposits are fully fusion-joined to the substrate material, the very low heat-input associated with laser cladding results in extremely low dilution as well as relatively small heat-affected zones (HAZ). Subsequent to the clad-repair process, heat treatment is normally not necessary, but some critical components may require it due to the high hardness obtained in the HAZ. Conventional heat treatments are most often time-consuming, costly and could cause possible distortion of the component. In this study local laser heat treatment of the HAZ after laser cladding has been investigated on different substrate materials (21CrMoV5-11, X22CrMoV12-1, 34CrNiMo6) as an alternative to full post-weld heat treatment (PWHT). Due to the focused heat of the laser beam, the required time at temperature for heat treatment was only a fraction compared to that of conventional heat treatments. It was observed that the HAZ hardness could indeed be lowered significantly by controlling the temperature and interaction time of the local treatment. For 21CrMoV5-11 the HAZ hardness was decreased to below 400 HV with most treatments at 800 °C, but the 8 s interaction time was found to be optimal. The X22CrMoV12-1 material showed the highest resistance to PWHT and only the longest interaction time at 800 °C resulted in HAZ hardness close to 400 HV. The largest decrease in HAZ hardness was obtained with the 34CrNiMo6 material and the longest interaction time at 700 °C resulted in the lowest hardness.
关键词： heat-affected-zone,hardness,local heat treatment,Laser,cladding
更新于2025-09-12 10:27:22
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Surface treatments of forged steel AISI6F3 by using high power CO <sub/>2</sub> laser
摘要： The hardness of forging dies is highly affected by the hot forming processes; especially by the long exposure to a wide thermal range, which leads to a decline in the level of hardness due to the tempering of the microstructure, thus failure occurs and the die breaks. The microstructure and hardness have been studied to demonstrate the relationship between them and their direct effect on the regions generated by the laser treatment of high capacity. The selected samples were chosen within a combination of laser variables to reach the appropriate structure that achieves the best hardness and indeed the highest hardness value (965 Hv) with laser processing parameters included the power 3000 W, beam diameter 1mm and scanning speed 25 mm/s with its characteristic microstructure as well as its high cooling rate.
关键词： High power laser,Forged steel,Hardness,Microstructure
更新于2025-09-12 10:27:22
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Wear Tribo-Performances of Laser Cladding Colmonoy-6 and Stellite-6 Micron Layers on Stainless Steel 304 Using Yb:YAG Disk Laser
摘要： Stainless steel material has been widely used in aeronautical, chemical and nuclear industries due to good corrosion resistance. However, the material has less hardness and wear resistance. In this study, two various depositions namely Colmonoy-6 and Stellite-6 have produced on 304 Stainless steel. Besides, the coating was examined to reveal their metallurgical, mechanical and tribological properties. In addition, wear mechanism, wear debris and roughness averages were studied. The outcomes indicate that both coatings show with dendrite structure due to rapid cooling rates. Hardness of the clad surface has improved than substrate material. The results of friction coefficient of specimen with Colmonoy-6 is lower than that of specimens Stellite-6 and substrate. Also, wear resistance of Colmonoy-6 has increased 49 times than substrate sample, which reveals that Colmonoy-6 laser cladding plays role on wear resistance. Adhesive and abrasive are the major wear mechanisms in the present study.
关键词： Wear debris,Microstructure,Stainless steel 304,Roughness,Wear performance,XRD,Laser cladding,Hardness
更新于2025-09-12 10:27:22
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Cr12MoV Die Repair Experiment Based on Laser Cladding with Wire
摘要： In this paper, SKD11 steel wire has been deposited on Cr12MoV plate using Nd: YAG pulsed laser for repairing the die surface damage. The effects of laser power, wire feeding speed, scanning speed and surface roughness on clad geometry have been studied with OM and LSCM. hardness distribution of the cladding layer is also obtained by microhardness tester. Experiment results indicate that the surface roughness is important for clad characteristics due to the light trapping effect. With the increases of roughness, the laser absorption ratio can be raised, both the clad depth and the dilution rate increase, the height decreases. The essence of influence mechanism is effective body energy Ev and specific filling rate ω, and can be used as critical process factors. When Ev is 80~100 J/mm3 and ω is 1~3, a flat cladding layer can be obtained with low dilution, less fusion defects and high hardness.
关键词： laser cladding with wire,clad geometry,hardness,Cr12MoV,surface roughness
更新于2025-09-12 10:27:22
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Effect of Gamma Irradiation on Electrical Properties of CdTe/CdS Solar Cells
摘要： The effect of Co-60 Gamma irradiation on electrical characteristics of CdTe/CdS solar cell has been analyzed using in-situ current-voltage characterization (I-V) in dark condition. The irradiation was done over a wide range of doses from 1kGy to 100 kGy. Electrical parameters such as ideality factor (n), series resistance (RS) and reverse bias leakage current (IR) for each dose have been calculated from the I-V characteristics. The ideality factor of the pristine solar cell is found to be 1.80 and it gradually increased up to 3.38 for the dose of 10 kGy, then it is around 3.38-3.61 for higher doses up to 100 kGy. The I-V characteristics showed significant increase in forward bias and drastic increase in reverse leakage current. The value of IR is 16.8 μA for pristine solar cell and it increases to 1.46 mA for 10 kGy. Further there is four times observable change in the value of IR. However the value of Rs is 0.80 ohm for pristine and continuously decreases to 0.34 ohm for 50 kGy dose. Further there is slight increase in the series resistance to 0.38 ohm for 100 kGy dose.
关键词： CdS,Radiation hardness,CdTe,Space application,Solar cells,Gamma Irradiation
更新于2025-09-12 10:27:22
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Laser Surface Treatment of Sintered Stainless Steels for Wear Resistance Enhancement
摘要： In the present study, sintered austenitic stainless steel type 316L was laser surface alloyed with Inconel 625 powder by the fibre optic laser. The Inconel 625 spheroidal powder of grain size 60-150 μm was introduced by the coaxial feeding head directly to the liquid metal, during laser surface alloying. The process parameters were selected to melt and fully dissolve alloying powder into the alloyed surface. As a result of laser alloying, the porosity of sintered stainless steel was eliminated, a uniform distribution of nickel and molybdenum in the entire alloyed zone was obtained. The alloyed surface shows fully austenitic microstructure of 17%Cr, 18%Ni, 3%Mo. The superficial hardness, microhardness and surface wear resistance were significantly improved in respect to an untreated substrate material. The presented technique of laser surface alloying can be easily applied for sintered austenitic stainless steel components where selected component surfaces require an improved surface performance.
关键词： Inconel 625,laser surface alloying (LSA),sintered stainless steels 316L,hardness,wear resistance
更新于2025-09-12 10:27:22