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In this paper, a method has been developed for heat treatment of details with a complex surface profile with a rapidly oscillating laser beam with modulated radiation power. This method is an alternative method for the dynamic formation of the distribution of the intensity of the laser spot. A mathematical model for calculating the distribution of the intensity of the oscillating beam and temperature fields induced by laser treatment is created. An algorithm for optimizing the parameters of high-frequency oscillations of the beam based on the solution of the inverse problem of thermal conductivity to obtain uniform heating of the near-surface layer of the material is developed. [ABSTRACT FROM AUTHOR]

The results of experimental studies into the impact of laser radiation on the depth of the hardened layer of cutting dies made of carbon and alloy tool steels U8, 40KhN2MA, 5Kh2S, 9KhS, and KhI2M are presented. Following laser hardening, the amount of retained austenite was found to be 1.5–2.5 times higher than following volumetric hardening. It was established that, following laser processing, steels of various structural groups exhibit different depths and hardness within the hardened layer. The highest depth and hardness are observed for eutectoid steel U8 and hypereutectoid steels 9KhS, while the lowest values are found in pre-eutectoid steel 40KhN2MA and ledeburite steel Kh12M. Processing experimental data showed that, in the first approximation, the depth of the first zone of the hardened layer is proportional to the thermal conductivity coefficient. For the parts that require larger depth of the hardened layer subjected to the operating conditions, it is recommended to use steels with a high silicon content, especially within the surface layer. [ABSTRACT FROM AUTHOR]

A new method to determine a fractal network in chaotic systems is presented together with its application to the microstructure recognition of robot-laser-hardened (RLH) steels under various angles of a laser beam. The method is based on fractal geometry. An experimental investigation was conducted by investigating the effect of several process parameters on the final microstructures of material that has been heat-treated. The influences of the surface temperature, laser speed, and different orientation angles of the laser beam on the microstructural geometry of the treated surfaces were considered. The fractal network of the microstructures of robot-laser-hardened specimens was used to describe how the geometry was changed during the heat treatment of materials. In order to predict the fractal network of robot-laser-hardened specimens, we used a method based on intelligent systems, namely genetic programming (GP) and a convolutional neural network (CNN). The proposed GP model achieved a prediction accuracy of 98.4%, while the proposed CNN model reached 96.5%. The performed analyses demonstrate that the angles of the robot laser cell have a noticeable effect on the final microstructures. The specimen laser-hardened under the conditions of 4 mm/s, 1000 °C, and an impact angle of the laser beam equal to 75° presented the maximum fractal network. The minimum fractal network was observed for the specimen before the robot-laser-hardening process. [ABSTRACT FROM AUTHOR]

This research focuses on studying the mechanical, tribological, and corrosion behaviors of alloy steels: AISI 4340, AISI 5140, and AISI 8620 by laser hardening, respectively. In light of the tests which have been carried out meticulously, it is concluded that the optimum laser hardening parameter for all steel grades is 4 mm/s scanning speed and 1300 °C surface temperature. Micro-structural changes, Vickers hardness as mechanical properties, and tribological properties with reciprocating wear tests were carried out. Furthermore, corrosion tests were conducted. The test results reveal that the maximum hardness is achieved 50-300 µm below the surface for all laser-hardened steels. Additionally, this study demonstrates that the wear resistance of steel is enhanced by the implementation of laser hardening. This study also determines that laser hardening has a positive impact on lifting the corrosion resistance behavior of AISI 4340 steel. In contrast, the corrosion resistance properties of AISI 8620 steel were reduced nearly by 54.17%. [ABSTRACT FROM AUTHOR]

Decarburization deteriorates the surface mechanical properties of steel. It refers to the loss of carbon from steel's surface when exposed to an open-air environment in elevated-temperature conditions. Despite the short interaction time and fast thermal cycle of the laser surface-hardening process, decarburization may still occur. This paper investigates if decarburization occurs during the laser surface hardening of AISI 420 martensitic stainless steel. For comparison, surface-hardening results and decarburizations in a conventional air furnace-heated hardening process (water-quenched and air-cooled) of the same steel material were also investigated. Decarburization seems to have occurred in the laser surface hardening of AISI 420SS. However, the decarburization might not be significant, as the hardness of the steel's surface was increased more than three times to 675 HV during the laser surface hardening, and the hardness drop due to decarburization was estimated to be only 3% with the decarburization depth of 40 μm. Simulations using ThermoCalc software to get the carbon concentration profiles along the depth for both laser-hardened and furnace-heated samples were also investigated. [ABSTRACT FROM AUTHOR]

Obtaining uniform hardening of the near-surface area to a given depth requires precise selection and control of laser radiation parameters, depending on the geometry of the part and its properties. Since laser irradiation is performed locally with step-by-step processing of the entire surface, the accumulated heat leads to an increase in the hardening depth and surface melting. In order to avoid uneven depths, it is necessary to vary the laser energy supply during processing to maintain stationary heating of the material. Experimental selection of technological parameters usually takes an excessive amount of time and material resources. This article presents a technique for the mathematical modeling of a high-carbon tool steel hardening process by calculating the temperature fields induced by laser radiation. The boundary of the hardening zone was determined as the isotherm of the corresponding austenitizing critical temperature in accordance with the heating rate. Experimental verification of the model was carried out on tool steels with carbon contents of 0.7 and 1.2%. The influence of the main processing technological parameters (radiation power, the laser spot diameter, and scanning speed) on the hardening zone size is shown. The paper also presents the use of the model for selection of the technological parameters of multi-track treatment to harden materials to a constant depth without surface melting. The effect of back tempering in overlapped regions is also considered. [ABSTRACT FROM AUTHOR]

An untreated graphite electrode has been observed to have limited applications based on the wear behavior and mechanical properties in the Electrical Discharge Machining (EDM) of superalloys. Hence, to reduce the wear of graphite electrodes below this level, a Plasma Nitriding (PN), Laser Hardening (LH) and a duplex process (PN + LH) on graphite electrodes are proposed to reduce the frontal and lateral wear. In this work, the influences of pulse duration, current and Silicon Nitride (SiN) added EDM oil on frontal and lateral wear of untreated and treated graphite electrodes are investigated. The hardness in untreated graphite and treated graphite electrode surfaces are also studied. The result confirmed that the duplex process produced graphite has 54% higher hardness as compared to the untreated/raw graphite. The 49% frontal and 42% lateral wear are reduced using a duplex process with 900 µs pulse duration. [ABSTRACT FROM AUTHOR]

In the present paper, continuous Ytterbium Laser Systems (YLS) fiber laser hardening of cylindrical AISI 4340 steel specimens was studied using experimental and statistical analyses. Three laser parameters, namely laser power, laser feed speed, and sample rotation speed were selected to evaluate their influence on the depth of the hardened zone and the maximum surface hardness. Mathematical models were developed as a function of these three parameters and the analysis of variance (ANOVA) was used to conduct the statistical study. Microhardness measurements revealed three distinct regions in the heat-affected zone (HAZ) of all samples: the hardened zone (Z1) near the surface, with the highest value of hardness, the hardness loss zone (Z2), where hardness had started to decrease, and the overheated zone (Z3) adjacent to the core, with hardness values that were less than those of the base metal. Based on experimental measurements, a maximum surface hardness of 60.8 HRC was attained. Furthermore, the maximum depth of the hardened zone was observed as 500 µm. The microstructures of laser-hardened samples were studied using optical and scanning electron (SEM) microscopes. The hardened region appeared to have a hard martensitic microstructure. By comparing the predicted and measured data for maximum microhardness values, it was revealed that the models represent the experimental values with correlations close to 100%. [ABSTRACT FROM AUTHOR]

Although a laser beam with a small diameter (< 1 mm) can significantly improve surface morphology, the polishing efficiency is very low, and the improvement of surface hardness is negligible. In this work, a novel laser polishing-hardening (LPH) method with integration and high efficiency for the treatment of AISI D2 tool steel using a large-size laser beam (Φ2.8 mm) was proposed, and the effects of laser hardening (LH), laser polishing (LP), and LPH treatments on the surface topography and microhardness were examined. The results show that the LH method had a negligible effect on the surface roughness of the treated sample, while the surface roughness Ra of LP and LPH specimens was reduced by 74.6% and 80.9%, respectively, indicating that the milled surface topography had been significantly improved, especially LPH was more effective in reducing the roughness. Besides, the polishing efficiency of LPH was 10 times that of the LP approach. In terms of hardness improvement, the near-surface microhardness of LH and LPH samples increased by 1.5 times and 1.3 times, respectively, and the effective hardened zone (EHZ) depth was 0.42 mm and 0.24 mm, respectively, demonstrating that these two laser processing methods had a beneficial effect on the cross-section microhardness of D2 tool steel, while the increase of LP on the microhardness was insignificant. The comprehensive analysis of the surface morphology and microhardness of the LPH specimen indicates that LPH was a feasible laser surface treatment method for D2 tool steel. On the premise of ensuring a high surface finish, the polishing efficiency can be remarkably improved, and the subsurface microhardness and EHZ depth of processed specimen can be also significantly increased, which provided a feasible idea for the application of laser surface treatment technology in industrial mold production. [ABSTRACT FROM AUTHOR]

Basing on the SYSWELD-driven FEM simulations and dilatometric experiments, we propose a method to predict structural changes in laser hardened austempered 30HGSNA steel containing 18.9 vol% of retained austenite. The ability to predict effects through simulation is very valuable for the design of unconventional hybrid treatments, especially when the initial microstructure is not ferritic-pearlitic. For 2 out of 3 evaluated variants, there was a satisfying prediction of a hardened – transition zone border with the prediction error in the 1.5–8.0 % range. In addition to the methodology adopted in the simulation, the impact of the increased heating rate of the austenitic transformation under continuous heating conditions was also described. The progressive shift of A c1 and A c3 temperatures towards higher values occurring at heating rates of tens of °C per second and higher was explained by the accumulation of atomic jumps. Mutual influence of the heating rate and retained austenite on A c1 temperature and hardness decrease of tempered bainite below A c1 temperature were shown. Austempered steel's hardness after rapid reheating to laser hardening temperatures and microstructural changes were presented. [Display omitted] • PN 30HGSNA steel with submicron bainite microstructure was laser hardened. • SYSWELD simulations were used to design heat treatments imitating laser hardening conditions. • SYSWELD, dilatometry and machine learning allowed prediction of hardening results. • Simulations aimed to predict depth of border between hardened and transition zones. • For 2/3 variants the error of prediction was in the range of 1.5–8.0 %. [ABSTRACT FROM AUTHOR]

Laser hardening is a thermal process that improves the surface mechanical properties of metallic materials. Efficiency enhancement of the thermal process of laser hardening is a long-term challenge. The article develops an approach called selective laser hardening that utilizes an absorptivity modification of the surface areas of the part to be processed by laser hardening. Laser surface treatment is used to modify the surface absorptivity. Subsequently, standard laser hardening can be performed on the entire surface. The change of material microstructure occurs only in the areas with increased absorptivity while the areas without surface modification remain structurally unchanged. The methods of laser absorptivity modification including subsequent thermal treatment and analysis of optical properties are described. The results of spectral absorptivity and absorptivity for wavelengths of commonly used hardening lasers (808, 1030 and 1064 nm) are presented for carbon steel EN 10083-2: C45. An important increase in the absorptivity of the laser-modified surface has been found up to 136% of the value of the basic material. This absorptivity difference decreases with increasing temperature of heat treatment, for examples to 7% at 800 °C for a laser wavelength of 808 nm. Further, the influence of laser surface modification parameters on the resulting absorptivity and the ability of increased absorptivity to withstand the elevated temperature during laser hardening are also discussed. [ABSTRACT FROM AUTHOR]

To optimize the toughness and hardness of laser surface‐hardened high‐carbon–chromium (52100) steel, the effect of preheating on microstructure evolution and impact property is studied, and the impact fracture mechanism is analyzed. The results indicate that preheating deepens the hardened depth, facilitating grain coarsening and cementite dissolution near the surface. Regardless of preheating, the size distribution of cementite follows a typical lognormal distribution. Laser surface hardening leads to a decrease in impact absorbed energy. Preheating at 160 °C increases the impact absorbed energy by ≈25%, at which point the maximum hardness is still as high as 860 HV0.3. The impact absorbed energy of spheroidized microstructure tends to be larger before laser hardening and reduces after laser hardening. The impact toughness is the combined result of the brittleness of the hardened layer, residual stress, and substrate microstructure. Under the impact load, microcracks nucleate near the surface of the hardened layer and propagate in the form of intergranular fracture and then propagate in the form of transgranular fracture toward the inside of the hardening layer and substrate. Herein, a novelty research work on optimizing the impact properties during laser hardening through preheating and adjusting initial microstructure is provided. [ABSTRACT FROM AUTHOR]

The results of experimental studies on the modification of the surface layer of grade E-110 zirconium alloy under the influence of pulsed laser radiation are presented. It was established that, as a result of laser treatment, the morphology of the surface layer changes with the formation of nanoparticles up to 50 nm in size. The relief of the treated surface becomes structurally heterogeneous, containing phases of zirconium and monoclinic dioxide ZrO2. It was revealed that, as a result of the action of laser pulses, a significant increase in the microhardness of the surface of zirconium samples occurs to 27.1 ± 0.1 GPa. [ABSTRACT FROM AUTHOR]

Metallographic studies of hardened zones of steel 40Kh were carried out. Regression equations were obtained and the surface depth and width of the hardened zones as functions of the beam scanning speed and radiation power at different beam defocusing were plotted with the help of a full factorial experiment. Comparative wear tests showed that, with increasing hardening area to 100% of the friction surface, the wear resistance increases by a factor of 4.47 as compared to normalized steel. [ABSTRACT FROM AUTHOR]

This study provides a novel contribution toward the establishment of a new high-fidelity simulation-based design methodology for stall-regulated horizontal axis wind turbines. The aerodynamic design of these machines is complex, due to the difficulty of reliably predicting stall onset and poststall characteristics. Low-fidelity design methods, widely used in industry, are computationally efficient, but are often affected by significant uncertainty. Conversely, Navier-Stokes computational fluid dynamics (CFD) can reduce such uncertainty, resulting in lower development costs by reducing the need of field testing of designs not fit for purpose. Here, the compressible CFD research code COSA is used to assess the performance of two alternative designs of a 13-m stall-regulated rotor over a wide range of operating conditions. Validation of the numerical methodology is based on thorough comparisons of novel simulations and measured data of the National Renewable Energy Laboratory (NREL) phase VI turbine rotor, and one of the two industrial rotor designs. An excellent agreement is found in all cases. All simulations of the two industrial rotors are time-dependent, to capture the unsteadiness associated with stall which occurs at most wind speeds. The two designs are cross-compared, with emphasis on the different stall patterns resulting from particular design choices. The key novelty of this work is the CFD-based assessment of the correlation among turbine power, blade aerodynamics, and blade design variables (airfoil geometry, blade planform, and twist) over most operational wind speeds. [ABSTRACT FROM AUTHOR]

The single-pulse laser hardening of a hypereutectoid steel coated by a graphite layer was investigated using a numerical/experimental approach. Experimental tests were conducted on coated samples using a fibre laser source and without any gas shielding aiming to explore the effect of laser power, pulse energy and defocusing distance on the dimensions of the hardened region. The process operating window of the discrete spot laser hardening using the graphite layer was determined through a finite element model and compared with previous results obtained on uncoated samples. For the same laser power and interaction times, an enlargement of the hardened region was found when using the graphite coating, especially when operating at the lowest laser energy level. The process operating window remains similar in shape to the one of the uncoated steel but moves towards larger hardened diameters and much larger defocusing distances. Once the maximum temperature has been fixed, a linear relationship between the hardened diameter and the defocusing distance exists. No obvious surface oxidation occurs since the graphite coating acts as a protective layer. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mixed microstructures of laser hardened QT700-2 ductile iron, including martensite, austenite and graphite nodules, are obtained simultaneously by tailoring the laser process parameters. • The hardness of laser hardened QT700-2 ductile iron (greater than 800 HV) is 3 times greater than that of base material (250–300 HV). • The wear depth of laser hardened QT700-2 ductile iron reduces from 17.57 μm to 11.45 μm, and the coefficient of friction reduces from 0.8 to 0.6. • The combined influence of hardening effect and self-lubricating mechanism contributes to the improvement in hardness and wear performance of laser hardened QT700-2 ductile iron. As an important component of automotive engines, the crankshaft usually requires surface treatment to improve its service reliability and lifetime. This work provided a detailed laser parameter study to enhance the wear performance of the QT700-2 ductile cast iron crankshaft sample (thickness of 10 mm), using a fiber laser (maximum power of 2000 W) hardening system. FEA temperature field simulation was performed to initially estimate an appropriate parameter range, and then verified by single factor experiments to evaluate the individual laser parameter effect. The microstructural observation unveiled an evolution from pearlite in the base material to fine needle-shaped martensite with graphite nodules and retained austenite in the laser hardened layer, where phase transformation was found to be more dependent on laser scanning speed. With the optimized laser parameter set, the hardened layer hardness increased from 250 HV to more than 800 HV, reducing the corresponding wear depth from 17.57 μm to 11.45 μm and coefficient of friction from 0.8 to 0.6. The significantly enhanced wear performance was mainly resulted from wear mechanisms transition from sever ploughing wear in the base material to mild adhesive wear in the laser hardened region. [ABSTRACT FROM AUTHOR]

Using standard continuous cooling transform (CCT) diagrams for finding hardness of surfaces obtained by laser or small-size induction hardening is discussed. Their misuse may lead to differences between the values obtained from the model and experimental data because unlike hardening of large surfaces, the produced heat is mostly transferred away not by convection to the environment, but mainly by conduction to the interior of the metal material at a very high rate (at the level of many hundred Kelvins per second). The paper explains the details and offers a methodology of suppressing errors based on a combination of theoretical and experimental approaches. The methodology is illustrated with an example. [ABSTRACT FROM AUTHOR]

Abstract Laser surface hardening, used to achieve hardened surface without affecting bulk properties of steels, generally employs continuous-wave laser to do the job. The purpose of this paper is to systematically investigate the use of different pulsed lasers for surface hardening of 50CrMo4 steel. A continuous-wave laser and various pulsed lasers with pulse duration ranging from fs to ms were used for the experiment. It was found that millisecond laser utilizing about 9 times lower power is as effective as continuous-wave laser for surface hardening. It produced an average surface hardness of ~719 HV (2.7 times higher than base material hardness) and ~200 μm hardened depth, which is comparable with continuous-wave laser hardening. Similarly, nanosecond laser could induce both surface hardening effect and material removal depending on the parameters used. However, a shallow hardened depth (of mere ~80 μm) was achieved compared to continuous-wave laser. Furthermore, femtosecond and picosecond lasers did not produce any observable surface hardening effect; instead they resulted in direct surface ablation. Graphical abstract Unlabelled Image Highlights • Millisecond laser of 9 times lower power is as effective as cw laser in surface hardening and produces hardness as high as 719 HV. • Nanosecond laser is less effective than cw laser in surface hardening. It produces shallow hardened depth (~80 μm) with hardness of about 642 HV. • Femtosecond and picosecond lasers result in no hardening of surface. [ABSTRACT FROM AUTHOR]

Highlights • High Power Diode laser used for comparing Surface Hardening of AISI 410 and 420. • Geometry of the hardened area, micro hardness and microstructure are investigated. • In the same parameters depth & width of hardness of AISI 410 is more than AISI 420. • Effects of material properties and laser absorption on the laser hardening process. Abstract Laser surface hardening process is one of the new technologies for improving the surface of metals, especially steels, which in recent decades has received a lot of attention. This paper surveys the capability of laser surface hardening of AISI 410 and AISI 420 martensitic stainless steel by using continues wave diode laser with a maximum power of 1600 W, experimentally. Microstructure of the laser treated area by using optical microscope (OM), Field emission Scanning Electron Microscope (FESEM), and XRD were investigated and compared. Geometrical dimension, micro-hardness deviation (MHD) from the micro-hardness of the base metal, ferrite percentage, and the grain size of the hardened zone are the other considered responses. The results indicate that in the same input parameters the AISI 420 has higher surface hardness and less penetration depth and width than the AISI 410 stainless steel. Observations showed that a laser surface hardened layer of AISI 410 is about 620 HV with 1.8 mm depth and while for AISI 410 is about 720 HV with 1.2 mm depth is obtained. Comparing the results with the furnace hardening heat treatment show that the laser hardening process is more effective and precise than conventional processes. [ABSTRACT FROM AUTHOR]

A problem on heating of a cutting tool by triangularly shaped pulsed laser radiation has been solved numerically in a three-dimensional formulation by the finite-element method. The developed model takes account of the influence of both the geometry of the tool and the spatial and temporal characteristics of laser radiation on the formation of a temperature field in the laser-processing zone. A study has been made of the temperature distribution on the front face of the tool and over the depth of the laser-impingement point for different positions of the center of a laser-processing spot relative to the major cutting edge. For different tool angles, the regularities of formation of a temperature field during the hardening by pulsed laser radiation have been established; processing regimes (energy density, the multiplicity of processing, and the position of the center of the laser-processing spot relative to the tool's cutting edges) that ensure the best parameters of the laser-impingement point (maximum hardening depth and the hardening-zone length) have been determined. A procedure to select technological parameters for the process of hardening of the cutting tool has been developed. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The Laser Surface Hardening Process of real components must achieve a uniform hardened profile to get constant mechanical properties and must deal with the energy distribution in the proximities of geometrical singularities to prevent them from overheating. Classical approaches like the overlapped laser tracks or uniform beams by fixed optical arrangements introduce the problems of annealing and lack dynamic adaptability capability, respectively. The present work uses a galvanometric scanner to get a user-defined laser intensity distribution, by iteratively scan a flat pattern, capable of creating uniform hardened profiles and dynamically adapting in real time to handle geometrical singularities. The experimental setup to obtain it and its characteristics as a function of the scanning frequency of the flat pattern are presented. Experimental results were obtained in crankshafts of automotive engines achieving uniform hardened profiles and good surface finish around the geometrical singularities. [ABSTRACT FROM AUTHOR]

The question about the thickness of informative layer under magnetic-noise testing of hardened layers is considered in [1–7], where it is estimated to be up to 800 μm. This paper presents experimental studies of the thickness of informative layer using instances of technologies used for surface-deformation and laser thermal hardening processes. It is shown that in the latter case, the thickness of informative layer is of greater importance. Applied mechanical stresses practically do not change the thickness of informative layer for a wide class of steels. [ABSTRACT FROM AUTHOR]

The paper studies the effect of the parameters of laser heat treatment of the copper alloy surface on the formation of color palette during its marking. The prospects of using laser marking of the surface of metal products can be substantially broadened by managing the color of the applied image. The "color" version of the laser marking method can be effectively used in metallurgical industry for protecting the product from tampering. The authors have studied metallographic imaging of the metal surface of the samples treated with laser radiation under different parameters. The measurement of such structure elements of the sample surface as laser exposure zones (LEZ) and heat exposure zones (HEZ), and statistical treatment of the obtained data were performed. Based on the compiled contrasting color groups, the mean values of the measurements and standard deviations were determined. A correlation between the laser radiation parameters and copper alloy surface topology has been established. The colors of the obtained fixed image were identified by using the RAL color chart. It was found that such laser radiation parameters as laser beam travel speed and defocusing affect the color of the brass surfaces. These parameters were used to create four contrasting color groups. [ABSTRACT FROM AUTHOR]

A pulsed laser was employed to treat a Zr-2.5Nb alloy with laser-induced microstructures (especially dense nanotwins) characterized by electron channeling contrast imaging (ECC) imaging and electron backscatter diffraction (EBSD) techniques. Hardening effect of the nanotwins was derived by analyzing hardness contributions from various microstructural factors modified by the pulsed laser treatments (PLT). Results show that dense nanotwins, that are difficult to introduce into Zr alloys by conventional thermo-mechanical methods, can be readily produced by the PLT at laser powers of 50 and 100 W. The twinning system is determined to be the compressive type of {10–11}〈10–12〉 by orientation analyses using EBSD. After the PLT, specimen hardness is markedly increased, which could be attributed to not only grain refinement and solid solution of Nb but more considerably to the abundance of the {10–11} nanotwins, demonstrating their strong hardening effect. [ABSTRACT FROM AUTHOR]

Hybrid additive manufacturing (hybrid-AM) has described hybrid processes and machines as well as multimaterial, multistructural, and multifunctional printing. The capabilities afforded by hybrid-AM are rewriting the design rules for materials and adding a new dimension in the design for additive manufacturing (AM) paradigm. This work primarily focuses on defining hybrid-AM in relation to hybrid manufacturing (HM) and classifying hybrid-AM processes. Hybrid-AM machines, materials, structures, and function are also discussed. Hybrid-AM processes are defined as the use of AM with one or more secondary processes or energy sources that are fully coupled and synergistically affect part quality, functionality, and/or process performance. Historically, defining HM processes centered on process improvement rather than improvements to part quality or performance; however, the primary goal for the majority of hybrid-AM processes is to improve part quality and part performance rather than improve processing. Hybrid-AM processes are typically a cyclic process chain and are distinguished from postprocessing operations that do not meet the fully coupled criterion. Secondary processes and energy sources include subtractive and transformative manufacturing technologies, such as machining, remelting, peening, rolling, and friction stir processing (FSP). As interest in hybrid-AM grows, new economic and sustainability tools are needed as well as sensing technologies that better facilitate hybrid processing. Hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way goods are manufactured. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a new double cycle hybrid method of machine learning using pattern recognition with topological properties of a network in the robot laser hardened process with different angles of the laser beam. The microstructure of laser hardening is very complex. In this article we use the mathematical method visibility network to determine the complexity of these specimens. We use aa artificial neural network (ANN) and multiple regression to predict the martensite microstructure of materials after laser hardening. Finally, we use a hybrid method of these methods of intelligent systems ' a hybrid intelligent system (HIS). Relations between the microstructure and angles of the robot laser beam were formulated based on the mechanical stability of the austenite. [ABSTRACT FROM AUTHOR]

The single explicit analysis using time-dependent damping (SEATD) technique for laser shock peening (LSP) simulation employs variable damping to relax the excited model between laser shots, thus distinguishing it from conventional optimum constant damping methods. Dynamic relaxation (DR) is the well-established conventional technique that mathematically identifies the optimum constant damping coefficient and incremental time-step that guarantees stability and convergence while damping all mode shapes uniformly when bringing a model to quasi-static equilibrium. Examined in this research is a new systematic procedure to strive for a more effective, time-dependent variable damping profile for general LSP configurations and boundary conditions, based on excited modal parameters of a given laser-shocked system. The effects of increasing the number of mode shapes and selecting modes by contributed effective masses are studied, and a procedure to identify the most efficient variable damping profile is designed. Two different simulation cases are studied. It is found that the computational time is reduced by up to 25% (62.5 min) for just five laser shots using the presented variable damping method versus conventional optimum constant damping. Since LSP typically involved hundreds of shots, the accumulated savings in computation time during prediction of desired process parameters is significant. [ABSTRACT FROM AUTHOR]

Research on absorption rate could contribute to better understanding laser processing. In this paper, a mathematical model was developed to calculate the laser absorption rate of actual surface considering the fractal characteristic. Fractal parameters were determined based on the measured characteristic of surface roughness, surfaces that met the fractal nature were then built. A light tracing algorithm was developed to trace the route of light in multiple reflections through the surface rough structure, and the Fresnel equation was used to calculate the fraction of the absorbed light at each reflection. The experiment system to measure the absorption rate of blue laser in hardening based on the water calorimetric method was developed. The experimental absorption rate fit well with the theoretical value, verifying the model as a tool to calculate the absorption rate in laser hardening. [ABSTRACT FROM AUTHOR]

Some biological surfaces were proved to have excellent anti-wear performance. Being inspired, Nd:YAG pulsed laser was used to create striated biomimetic laser hardening tracks on medium carbon steel samples. Dry sliding wear tests biomimetic samples were performed to investigate specific influence of distribution of laser hardening tracks on sliding wear resistance of biomimetic samples. After comparing wear weight loss of biomimetic samples, quenched sample and untreated sample, it can be suggested that the sample covered with dense laser tracks (3.5 mm spacing) has lower wear weight loss than the one covered with sparse laser tracks (4.5 mm spacing); samples distributed with only dense laser tracks or sparse laser tracks (even distribution) were proved to have better wear resistance than samples distributed with both dense and sparse tracks (uneven distribution). Wear mechanisms indicate that laser track and exposed substrate of biomimetic sample can be regarded as hard zone and soft zone respectively. Inconsecutive striated hard regions, on the one hand, can disperse load into small branches, on the other hand, will hinder sliding abrasives during wear. Soft regions with small range are beneficial in consuming mechanical energy and storing lubricative oxides, however, soft zone with large width (>0.5 mm) will be harmful to abrasion resistance of biomimetic sample because damages and material loss are more obvious on surface of soft phase. As for the reason why samples with even distributed bionic laser tracks have better wear resistance, it can be explained by the fact that even distributed laser hardening tracks can inhibit severe worn of local regions, thus sliding process can be more stable and wear extent can be alleviated as well. [ABSTRACT FROM AUTHOR]

The present study deals with the effects of laser surface treatment on microstructure evolution and wear resistance of AISI H11 hot work tool steel in quenched and tempered condition. The most upper laser-affected zone is characterized by re-melted microstructure consisting of dendrite cells with fresh non-tempered martensite, retained austenite and inter-dendritic carbidic network. The subsolidus microstructure just beneath the re-melted zone represents the most laser surface hardened zone consisting of fresh non-tempered martensite with fine and coarse carbides as a result of overheating the original QT substrate microstructure. The highest microhardness values in the range from 775 to 857 HV were measured for the LSH microstructure and the most softened microstructure exhibited the minimum hardness of 530 HV. The laser treated samples showed the improvement of their surface wear resistance by 35%. [ABSTRACT FROM AUTHOR]

The combination of a susceptible material, tensile stress, and corrosive environment results in stress corrosion cracking (SCC). Laser shock peening (LSP) has previously been shown to prevent the occurrence of SCC on stainless steel. Compressive residual stresses from LSP are often attributed to the improvement, but this simple explanation does not explain the electrochemical nature of SCC by capturing the effects of microstructural changes from LSP processing and its interaction with the hydrogen atoms on the microscale. As the hydrogen concentration of the material increases, a phase transformation from austenite to martensite occurs. This transformation is a precursor to SCC failure, and its prevention would thus help explain the mitigation capabilities of LSP. In this paper, the role of LSP-induced dislocations counteracting the driving force of the martensitic transformation is explored. Stainless steel samples are LSP processed with a range of incident laser intensities and overlapping. Cathodic charging is then applied to accelerate the rate of hydrogen absorption. Using XRD, martensitic peaks are found after 24 h in samples that have not been LSP treated. But martensite formation does not occur after 24 h in LSP-treated samples. Transmission electron microscopy (TEM) analysis is also used for providing a description of how LSP provides mitigation against hydrogen enhanced localized plasticity (HELP), by causing tangling and prevention of dislocation movement. The formation of dislocation cells is attributed with further mitigation benefits. A finite element model predicting the dislocation density and cell formation is also developed to aid in the description. [ABSTRACT FROM AUTHOR]

This study focuses on laser-hardened 40CrNiMo steel, which meets the requirements for use in sprag clutch wedges; specifically, the microhardness characteristics as well as the phase and element characteristics and formation mechanism at different depths are investigated after laser hardening. The results show that the hardness of the arc-shaped specimen with a laser-hardened layer fluctuates significantly after reaching a certain depth. With increasing depth, the original austenite grain size decreases exponentially, it becomes easier for acicular martensite to form near the surface, and the martensite bulge phenomenon near the surface is more pronounced. The proportion of small-angle grain boundaries decreases, while that of large-angle grain boundaries increases after laser hardening. The angle of the small-angle grain boundaries of the adjacent grains of the hardened layer is mostly below 5°, while that of the large-angle grain boundaries is predominantly between 50° and 60°. After laser hardening, the preferred orientation of the grains in the hardened layer is not clear. The aggregation of C atoms is an important factor determining the structural characteristics of the hardened layer. • The outline of the hardened layer is characterized by a moon shape with a thick middle and thin ends. • The closer to the surface, the larger the original austenite grain size. • The proportion of large-angle grain boundaries increases in the hardened layer. • The preferred grain orientation in the hardened layer is not clear. • The aggregation of C atoms is an important factor determining the characteristics of hardened layer. [ABSTRACT FROM AUTHOR]

Synchroniser hubs are powder metal components often used in vehicles for manual transmissions and dual clutch transmissions. Conventionally, these components are often through hardened, case carburised or induction hardened, although such processes can lead to deterioration of dimensional accuracy and increased costs. Synchroniser hubs which have both high strength and high dimensional accuracy are developed by optimising the material composition and introducing the newly developed roller-hearth-type high temperature sintering furnace. Besides, a laser hardening process can be applied locally to the necessary portion. Furthermore, the second whole hardening process and extra process cost can be eliminated using sinter-hardening process after high-temperature sintering. [ABSTRACT FROM PUBLISHER]

The influence of process parameters viz., plate thickness, laser power and welding speed in enhancing the tensile strength of laser welded austenitic 316 stainless steel is presented. The experiments based on Taguchi analogy were conducted in a Nd:YAG laser welding machine and the signal-to-noise ratio (SNR) was computed to determine the optimum parameters. The contribution of each selected parameter is determined by analysis of variance (ANOVA). Mathematical model based on regression analysis is developed to predict the tensile strength of the 316 stainless steel welded joints at any given conditions using statistical software. In addition, tensile strength of the post weld heat treated 316 stainless steel joints were correlated with the as welded joints. [ABSTRACT FROM AUTHOR]

Steam Turbines can generate electricity by using various sources of heat. This is the main reason it is one of the most common type of turbine used in power plants. Steam turbines are composed of various number of stages and each stage is composed of one set of blades. Towards the last stages, water in the steam increases and due to the fact that water velocity is higher than steam velocity, water droplets scatter with the momentum striking at the surface of the turbine blades and causes erosion. Steam turbine blade service life is expected to be not less than 100.000 hours which is approximately 12 years. Blade materials should be considered carefully and necessary surface modifications should be made accordingly. The material is usually selected as martensitic stainless steel due to the service conditions. Steam turbine blades, especially those working in the low pressure region, are subjected to wet steam and their tips are eroded heavily. In this study, a typical low pressure turbine blade material, 1.4021, steel surface has been modified with laser hardening, tungsten carbide coating, and chromium carbide coating. The samples were tested using erosion testing equipment and the results were compared. [ABSTRACT FROM AUTHOR]

Surface laser hardening of steels is a well-established industrial technology. The surface of the specimen is scanned with a high-power laser beam along the trace to be hardened. The rapid cooling due to the non-heated surroundings of the laser-treated zones leads to local hardening of the material. Non-destructive evaluation of some mechanical properties (hardness, residual stresses, etc) of the hardened region and the heat-affected zone are of technological importance. A previous paper reported non-destructive testing (NDT) experiments (by scanning of the specimens) made with the 3MA-II (Multiparameter Micromagnetic Microstructure and Stress Analysis) equipment developed by the Fraunhofer Institute for Non-Destructive Testing (IZFP), Saarbrücken. This contribution presents an X-ray diffraction evaluation of the residual stresses in laser-hardened SAE 1045 steels and metallographic studies of the affected areas. The results are compared with the previously reported 3MA-II output. [ABSTRACT FROM AUTHOR]

The use of laser ablation phenomenon with the "thermal effect" to produce surface textures, mainly lubricant micro-containers in the form of spherical micro-bowls in the surface layer of 100CrMnSi6-4 alloy of bearing steel. This is interesting research topic. The application the local (zonal) laser hardening of the steel surface layer on the surface of the bearing raceway or casts gives technological opportunities to deploy those technologies in the production process. The article presents the selected results of the own laboratory studies of hardness, microstructure and surface stereometry bearing steel 100CrMnSi6-4 in different states after volume hardening and low tempering, as well as those obtained as a result of laser surface texturing and laser pulsed hardening. The study results can be used to modify the surface layer of 100CrMnSi6-4 bearing steel and in the nearest future use ablative laser texturing of the rolling bearings treadmill surface in the production of lubricanting micro-containers, for improving the wear resistance tribological pair of roller - raceway in the friction conditions. [ABSTRACT FROM AUTHOR]

Laser hardening is becoming a consolidated process in different industrial sectors such as the automotive industry or in the die and mold industry. The key to ensure the success in this process is to control the surface temperature and the hardened layer thickness. Furthermore, the development of reliable scanners, based on moving optics for guiding high power lasers at extremely fast speeds allows the rapid motion of laser spots, resulting on tailored shapes of swept areas by the laser. If a scanner is used to sweep a determined area, the laser energy density distribution can be adapted by varying parameters such us the scanning speed or laser power inside this area. Despite its advantages in terms of versatility, the use of scanners for the laser hardening process has not yet been introduced in the thermal hardening industry because of the difficulty of the temperature control and possible non-homogeneous hardness thickness layers. In the present work the laser hardening process with scanning optics applied to AISI 1045 steel has been studied, with special emphasis on the influence of the scanning speed and the results derived from its variation, the evolution of the hardened layer thickness and different strategies for the control of the process temperature. For this purpose, the hardened material has been studied by measuring microhardness at different points and the shape of the hardened layer has also been evaluated. All tests have been performed using an experimental setup designed to keep a nominal temperature value using a closed-loop control. The tests results show two different regimes depending on the scanning speed and feed rate values. The experimental results conclusions have been validated by means of thermal simulations at different conditions. [ABSTRACT FROM AUTHOR]

In this work the single-pulse laser irradiation of a hypereutectoid steel was investigated using a fiber laser source, in a range of process parameters enabling surface hardening and remelting. Effects of laser power, pulse energy and defocusing distance were investigated using a numerical/experimental approach. Laser surface treatments were conducted on uncoated samples without any gas shielding, changing both the laser power and the pulse energy, and exploring a wide range of defocusing distances. Numerical simulations were conducted using a finite element model calibrated by means of an optimization procedure based on a specific calculation algorithm and using a subset of experimental data producing surface melting. Using both simulations and experiments, the process operating windows of the discrete spot laser treatment were determined: it was found that, when varying the laser power between 250 W and 750 W, melt-free hardened zones are produced with a maximum extension between 0.7 mm and 1.0 mm; on the contrary, in case of more tightly beam focusing conditions, surface melting occurred with a size of the re-melted areas ranging between 1.0 mm and 1.4 mm. Results further showed that a small change (generally 2–3 mm) of the defocusing distance suddenly brings the material from melting to a non-hardening condition. [ABSTRACT FROM AUTHOR]

With the rapid development of high-speed and heavy-haul trains, it is challenging to improve the service life of rails. In order to ensure toughness and contact fatigue resistance (CFR) of rails, the present technical standards restrict the hardness of rails to be beneath HB400 and forbid the martensite structure in rails. In this study, a novel laser surface compositing (LSC) based on selective laser quenching is proposed to strengthen the rails. By designing the hardening area sizes and proportions rationally, the wear resistance of the rails is enhanced by 2.2–3.5 times without noticeably deteriorating their contact fatigue resistance (CFR). Furthermore, the wear and contact fatigue behaviours of the LSC rails were investigated systematically. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive approach developed to design an effective prediction model for hardness profile in laser surface transformation hardening process. Based on finite element method and Artificial neural networks, the proposed approach is built progressively by (i) examining the laser hardening parameters and conditions known to have an influence on the hardened surface attributes through a structured experimental investigation, (ii) investigating the laser hardening parameters effects on the hardness profile through extensive 3D modeling and simulation efforts and (ii) integrating the hardening process parameters via neural network model for hardness profile prediction. The experimental validation conducted on AISI4340 steel using a commercial 3 kW Nd:Yag laser, confirm the feasibility and efficiency of the proposed approach leading to an accurate and reliable hardness profile prediction model. With a maximum relative error of about 10 % under various practical conditions, the predictive model can be considered as effective especially in the case of a relatively complex system such as laser surface transformation hardening process. [ABSTRACT FROM AUTHOR]

This study concerns that the high-silicon alloy steel treated by the laser hardening with an in-situ thermal treatment (LHITT) between M s and M d temperature. The shear band, such as nano-twin and ε-martensite is expected to be obtained by the aid of thermal stress during laser hardening process to strengthen the steel. The in-situ thermal treatment temperature of the steel was confirmed by thermal mechanical simulator and thermodynamic model. The residual stress of the hardening layer was measured by X-ray stress analyzer. The phase structures were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Moreover, the nano-hardness was evaluated by the nano-mechanical tester. The experimental results demonstrate that the stacking faults were generated by the laser thermal stress which drives high density dislocations motion on { 111 } γ planes. The shear band is formed by the overlapping of the stacking faults in austenite during the LHITT process. Besides, the high surface hardness (7.9 GPa) can be achieved by the LHITT. The hard points (9.5 GPa) in LHITT sample are related with the shear band as the analysis of the elastic modulus. [ABSTRACT FROM AUTHOR]

This study examines the possibility of applying lasers for the formation of laser-affected bands in hardenable steel sheets, with a specific focus on how the formation of these hardened bands can improve the accuracy of the single point incremental forming process (SPIF). For this purpose, the process parameters for the hardening process have been chosen using finite-element (FE) modeling. The results of the modeling have been validated by temperature field measurements obtained from IR camera observations. The microstructural analysis of the laser-affected zones has been performed using optical microscopy (OM) and scanning electron microscopy (SEM). These investigations confirm a phase transformation to a martensitic structure during laser scanning, and microhardness (HV0·1) results show a hardness increase by a factor of about three in the laser-affected region in comparison to that of the base metal (BM). Finally, using a laser assisted single point incremental forming (LASPIF) setup, hardened bands have been generated for preprocessing and intermediate processing during the different phases of a SPIF procedure. Geometric accuracy studies show that appropriate use of hard martensitic bands can increase the process accuracy through significantly reduction of an unwanted sheet deformation, and has the potential to eliminate the need for a backing plate. [ABSTRACT FROM AUTHOR]

A numerical model is presented for evaluation of residual stresses following laser surface treatment of mechanical components with arbitrary geometry. Following on from previous temperature and microstructural models, stress evaluation is performed by considering the resulting deformation from thermal expansion, elastic and plastic deformation, and microstructural changes. A 3.3 kW diode laser with wavelength of 930 nm and 34 mm × 2 mm rectangular spot is utilized to perform heat treatment experiments on an AISI 9810 steel cam, with x-ray diffraction measurements performed before and after laser exposure to determine circumferential and axial surface stresses. Verification of model accuracy is performed by comparing calculated stresses with the measured values. The influence of incident laser fluence and scanning velocity on the hardened depth and residual stress state is then investigated numerically for the same component. It is found that higher laser fluence, or an increase in exposure velocity at constant fluence, leads to an increase in the hardened depth and a reduction in compressive residual stresses. [ABSTRACT FROM AUTHOR]

Laser-based welding of thick 17-4 precipitation hardening (PH) martensitic stainless steel (SS) plates in a tubular butt joint configuration with a built-in backing bar is very challenging because the porosity and cracks are easily generated in the welds. The backing bar blocked the keyhole opening at the bottom surface through which the entrapped gas could escape, and the keyhole was unstable and collapsed overtime in a deep partially penetrated welding conditions resulting in the formation of pores easily. Moreover, the fast cooling rate prompted the ferrite transform to austenite which induced cracking. Two-pass welding procedure was developed to join 17-4 PH martensitic SS. The laser welding assisted by a filler wire, as the first pass, was used to weld the groove shoulder. The added filler wire could absorb a part of the laser beam energy; resulting in the decreased weld depth-to-width ratio and relieved intensive restraint at the weld root. A hybrid laser-arc welding or a gas metal arc welding (GMAW) was used to fill the groove as the second pass. Nitrogen was introduced to stabilize the keyhole and mitigate the porosity. Preheating was used to decrease the cooling rate and mitigate the cracking during laser-based welding of 17-4 PH martensitic SS plates. [ABSTRACT FROM AUTHOR]

Laser surface hardening is a promising technology to improve wear and fatigue properties of steel surfaces. When the dimensions of the surface to be treated are larger than the cross section of the laser beam several overlapped tracks are needed, and the distance between consecutive tracks becomes a fundamental design parameter. This work aims to optimize that parameter with the purpose of fulfilling a set of initial requirements for the process. A laser hardening temperatures/oxidation coupled model available in the literature is applied for the first time to the case of an overlapping process, extending its capabilities to take into account the tempering of the second track over the martensite of the first one. This model in conjunction with a convenient geometrical characterization of the heat affected zone enables a design strategy to be implemented which, using metallurgical and hardness maps, has the capability of attending different criteria. All the conditions proposed in the design of a suitable overlapping distance have been reproduced empirically for the case of the 42CrMo4 steel, and a comparison of hardness has been carried out, showing a good degree of agreement. [ABSTRACT FROM AUTHOR]

Results of experimental studies of low-carbon steel 20 and high-carbon steels of types 70 and 65G after carburizing, heat treatment and laser hardening are presented. The variation of the microhardness of the surface layers of the steels and of their wear resistance due to different variants of hardening is determined. Optimum modes of treatment aimed at raising the strength and wear resistance are suggested for the steels used for working members of cultivating machines. [ABSTRACT FROM AUTHOR]