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Hybrid welding combining a laser beam with a MIG/MAG-arc has high potential to fill joint gaps and to shape the weld surface. The geometrical variations and the oxidation of the joint edges can have significant influence on the resulting weld surface shape and on fatigue life. In the presented study, edge tolerances such as edge mismatch were measured. By consequent scanning of the tolerances, high speed imaging of the melt pool flow dynamics and scanning of the resulting weld surface profile, a systematic identification and explanation of the weld quality on the joint edge conditions can be achieved, even for complex products in rough industrial environment. A corresponding general procedure is presented. From a case study, the limits of quality aspects such as undercuts were quantitatively identified and qualitatively explained.

Laser-assisted generating by the blown powder process is investigated, both, experimentally and theoretically, with respect to layer cross section, grain growth, mechanical testing, track remelting and wall surface roughness compared to postremelting.

Laser remote fusion cutting is analyzed by the aid of a semi-analytical mathematical model of the processing front. By local calculation of the energy balance between the absorbed laser beam and the heat losses, the three-dimensional vaporization front can be calculated. Based on an empirical model for the melt flow field, from a mass balance, the melt film and the melting front can be derived, however only in a simplified manner and for quasi-steady state conditions. Front waviness and multiple reflections are not modelled. The model enables to compare the similarities, differences, and limits between laser remote fusion cutting, laser remote ablation cutting, and even laser keyhole welding. In contrast to the upper part of the vaporization front, the major part only slightly varies with respect to heat flux, laser power density, absorptivity, and angle of front inclination. Statistical analysis shows that for high cutting speed, the domains of high laser power density contribute much more to the formation of the front than for low speed. The semi-analytical modelling approach offers flexibility to simplify part of the process physics while, for example, sophisticated modelling of the complex focused fibre-guided laser beam is taken into account to enable deeper analysis of the beam interaction. Mechanisms like recast layer generation, absorptivity at a wavy processing front, and melt film formation are studied too.

Aspirin (ASA) does not effectively lower platelet aggregation in all people. The platelet aggregation (PA) score is an easily used clinical method for measuring the effect in individuals of antiplatelet medications. Fifteen apparently healthy subjects (2 men and 13 women), selected for their resistance to ASA's antiaggregation effect, completed a se quential trial of ticlopidine, Alka-Seltzer®, and ASA + citric acid (CTA). Ticlopidine was the strongest aggregation inhibitor and the ASA + CTA combination was more inhibitory than Alka-Seltzer. It was determined that measuring antiaggregation effects of a particular agent in an individual prior to usage would optimize treatment. The PA score methodology provides a means for testing patients prior to antiplatelet therapy for prevention and treatment of the thrombotic complications of vascular disease.

A new method for segmentation of the EEG, based on a nonparametric statistical analysis, is proposed. A nonparametric approach was chosen because it minimises the need for a priori information about a signal. The method provides detection of change-points (quasi-stationary segments' boundaries) in almost any EEG characteristic for a given level of false alarm probability. The method was applied to 8-channels spontaneous EEG recordings obtained from 12 subjects in eyes closed and eyes open conditions to detect rapid fluctuations of the alpha rhythm power. After preliminary adjustment of false alarm probability values all the recordings were analysed in unsupervised regime with the same parameters. From 15 to 119 change-points were found per minute and EEG channel. Automatically detected change-points were in good correspondence with visual estimation of the instants of change in alpha activity.

Research work was aimed at the welding of thin sheets using high power CO2 laser. Process parameters, evaluation of the weld by micro, macro and mechanical are briefly given. Characteristics of the laser welding are described. Optimal process parameters which are power, weld speed, gas flow, focal point, gap distance, were used. Microstructural evaluation by light microscope and transmission electron (TEM) microscope for substructural analysis was employed. Therefore general weld imperfections were observed and laser weld evaluation was made with EN ISO 13919-1. Mechanical performance of welded sheets was done by uniaxial tensile test, Erichsen test, and microhardness test. Uniaxial tensile test was employed transverse- weld oriented to the tensile direction and longitudinal-weld oriented to the tensile direction. Results were compared with base metal properties. Maximum tensile strength was obtained from the longitudinal-weld with reduced ductility. In transverse-weld direction fracture was far from the weld. Microhardness test was applied to the cross section of the welded sheets. Maximum hardness was obtained from the weld fusion zone (FZ) where hardness was increasing from HAZ to weld FZ center. Therefore hardness results were verified by empirical equations, which are proposed by various authors. Erichsen test was employed for the ductility evaluations of the welded sheets whereby two types of defect were observed from the Erichsen test. The First one was observed in the weakest sheet (lowest gauge or lowest strength). It is occur when the major strain direction is perpendicular to the weld seam. The second one was occurred across the weld by the higher strength and lower elongation of the weld while major strain direction was parallel to the weld seam. Process parameters, microstructural and substructural analyses were compared with mechanical performance of the welded sheets. As a result the laser welded thin sheets were evaluated in many aspects.Research work was aimed at the welding of thin sheets using high power CO2 laser. Process parameters, evaluation of the weld by micro, macro and mechanical are briefly given. Characteristics of the laser welding are described. Optimal process parameters which are power, weld speed, gas flow, focal point, gap distance, were used. Microstructural evaluation by light microscope and transmission electron (TEM) microscope for substructural analysis was employed. Therefore general weld imperfections were observed and laser weld evaluation was made with EN ISO 13919-1. Mechanical performance of welded sheets was done by uniaxial tensile test, Erichsen test, and microhardness test. Uniaxial tensile test was employed transverse- weld oriented to the tensile direction and longitudinal-weld oriented to the tensile direction. Results were compared with base metal properties. Maximum tensile strength was obtained from the longitudinal-weld with reduced ductility. In transverse-weld direction fracture was far from the ...

In order to improve the understanding of the mechanisms of laser surface treatment and to optimize industrial applications, a general model of laser surface treatment has been accomplished which enables calculation of the thermodynamic phenomena and analysis of the process. With particular emphasis on laser cladding and alloying, powder heating has been investigated in detail, which can be divided into heating during travelling through the laser beam and subsequent heating by the melt pool. While the time scale of the former heating mechanism is of the order of 1 ms, pool heating takes place within 10 microsecond(s) , hence almost immediately. While the pool temperature determines whether powder will be melted or not, in principle any powder, even WC, can be melted when passing the beam, as long as the calculated threshold intensity range is exceeded. Laser cladded tracks prove to be determined by the melt pool shape which is calculated analytically for non-gaussian beams, as well. While for low powder feeding rates cladding is limited by the mass balance, for substantial powder delivery the energy balance turns out to be the limiting criterion, while dilution diminishes. Increased degree of overlap between two tracks decreases the roughness of the cladded surface.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A laser clad and machined cylindrical structural steel rod was fatigue tested under four-point bending load. The resulting fracture could be tracked back to a spherical surface pore in the Co-based coating. Due to an oxide inclusion, the pore was not identified by dye penetrant inspection. Two circular buckling strain patterns that were detected beside the pore at the surfaces after fracture confirm local plastic deformation prior to crack initiation. In order to calculate the stress field around the surface pore, linear elastic finite element analysis was carried out. For four-point bending load, a surface pore generally exceeds the maximum stress of a smooth rod as long as the pore is located within an azimuthal angle of ±55°, which was the case for the presented as well as for another pore initiated sample.

A new laser welding process is presented which delivers a porosity free, spatter free weld. The process involves a donut shaped melt with a central hole of the same order of magnitude as the material thickness. The laser illuminates only the leading section of this melt. The hole is kept open by the melt surface tension.

Hybrid laser-arc welding has a good tolerance to poor fit up as compared to simple laser welding. For a butt joint, the joint fit-up variations can be reduced to two local properties: the gap width and the vertical edge mismatch. The impact of these two properties on the resulting weld quality has been studied systematically in this paper. The original edges as well as the resulting weld surface topography have been scanned in three dimensions in order to study trends. During hybrid welding, the melt flow and the electric arc were observed at the top surface by high speed imaging to analyze the complex fluid flow phenomena.

A 31-year-old female patient with both acquired immunodeficiency syndrome and a solid silicone buttock implant presented with fever. Using ultrasound-guided aspiration of the periprosthetic space, a diagnosis of Mycobacterium avium complex infection involving the implant was made. The implant was surgically removed and the patient had a resolution of her fevers while treated with ethambutol, rifabutin, ciprofloxacin, and clarithromycin.

The modulation of the angle-dependent Fresnel absorptivity across wavy molten steel surfaces during laser materials processing, like drilling, cutting, or welding, has been calculated. The absorptivity is strongly altered by the grazing angle of incidence of the laser beam on the processing front. Owing to its specific Brewster-peak characteristics, the 10.64 μm wavelength CO2-laser shows an opposite trend with respect to roughness and angle-of-incidence compared to lasers in the wavelength range of 532-1070 nm. Plateaus or rings of Brewster-peak absorptivity can lead to hot spots on a wavy surface, often in close proximity to cold spots caused by shadow domains.

Welding distortion is an important engineering topic for simulation and modeling, and there is a need for experimental verification of such models by experimental studies. High-speed pulsed digital holography is proposed as a measurement technique for out-of-plane welding distortion. To demonstrate the capability of this technique, measurements from a laser spot weld are presented. A complete twodimensional deformation map with submicrometer accuracy was acquired at a rate of 1000 measurements per second. From this map, particular points of interest can be extracted for analysis of the temporal development of the final distortion geometry. Validerad; 2012; 20120410 (ingeri)

Applications of high power lasers in material processing can be divided into surface treatment, welding and cutting. An overview of the main physical mechanisms underlying these applications shall give a systematic basis for modeling the processes. The absorption behavior of a CO 2 -laser beam is discussed, mathematical attempts for describing the heat conduction are compared and a distinction between the several appearing melt flow phenomena is made. Further treated effects are evaporation, plasma formation and time dependence. Models of hardening, deep welding and cutting are presented to give examples for the mathematical treatment and the predictions and analysis that can be done.

During deep penetration laser welding, the focused laser beam determines the vapor capillary, called keyhole, and in turn the whole process physics. Beside spot diameter and Rayleigh length, the beam profile is another important but hardly explored part of the focused laser beam. The focusing of fiber-guided Yb:fiber, Nd:YAG or diode laser beams creates the complex situation that the beam has a top-hat profile in the focal plane but toward the far field transforms to a Gaussian beam. Such power density distribution was measured for a focused high power Yb:fiber laser beam and then approached by three different beam formulations. The beam formulations were then applied to model the keyhole shape during laser welding. Although a second order beam model approached the measured beam significantly more accurately, the first order Gaussian beam was similarly suitable to predict the keyhole shape as long as the central beam domains do not interact with the material, which occurs only for low focal plane positions. A hypothetical top-hat beam would cause a different, steeper keyhole shape. Consequently, a Gaussian beam is still a suitable formulation for a wide range of welding parameters.

Spatter, the ejection of melt from a weld pool, is a major problem whenever it occurs in a welding process. The ejection of droplets from the weld metal results in a weld with underfill, undercuts, craters, blowholes, or blowouts—all of which can have a detrimental effect on the mechanical properties of the weld. This paper presents a systematic description of the different types of spatter phenomena which occur during laser welding. A categorization system is proposed to facilitate the comparison and combination of research findings on spatter. This should allow researchers in this area to act as a more effective team in future.

Recently the fiber and the disk laser have been developed as advanced high power lasers of continuous wave type. Their beams are fiber-guided. Their low beam parameter product determines the focused beam as a high power density tool for laser materials processing. The lateral and axial power density distribution is crucial for the process. The measurement of a focused Yb:fiber laser beam is compared with its theoretical profile. While a Gauss beam describes the real beam in the far field, in the vicinity of the focus the beam is similar to a top-hat profile. In particular, the peak power density is lower around the focus than for a Gaussian beam. This provides a flatter, less varying optical tool along a certain axial range. A suitable model of the focused laser beam is achieved by superposition of a Gauss beam with a second but negative Gauss beam, each with matched parameters for power, spot diameter, and Rayleigh length. Owing to its much better accuracy with less than a 20% error, the model beam is applicable, e.g., for simulation of the welding process.

Laser weld monitoring is usually based on the feedback from three photodiodes which are intended to provide independent information about the thermal condition of the melt (the T signal), the radiation from the plume of a heated gas above the melt (the P signal) and the amount of reflected laser light (the R signal). This work demonstrates that, in fact, the plume of the hot gas above the weld pool contributes a large part of the thermal signal, which has hitherto been assumed to come only from the melt itself. It is suggested that the correlation between the T and P signals is so strong that a T-P signal would be more useful than the raw T signal in identifying the fluctuations in infrared radiation from the melt pool Validerad; 2010; Bibliografisk uppgift: Paper id:: 105705; 20100903 (ysko)

Laser cladding and the recently developed laser casting technique are similar in their physical mechanisms. A transition from cladding to casting and vice versa can be achieved by proper control of the process parameters, both for preplaced and blown powder. In the present work, the preplaced powder technique is studied at a fundamental level. Its physical nature is responsible for a large operating window of dilution free cladding on the one hand and bond free casting on the other.

Longitudinal elasticities of whole human blood clot, whole canine blood clot, Factor XIII cross-linked fibrin, glutaraldehyde-fixed human albumin, and formaldehyde-fixed collagen, gelatin and collagen/gelatin were determined and normalized to human whole blood clot. Matrices of a knitted Dacron graft were then impregnated with albumin, collagen, and collagen/gelatin and their longitudinal elasticities were determined and normalized to a preclotted graft. Comparisons were also made for the longitudinal elasticities of a virgin graft, a manipulated control for a preclotted graft, and a manipulated control for the matrix-impregnated grafts. Flexibilities were then calculated based on the weights and elasticities of these grafts and normalized to the flexibility of the preclotted graft. Fibrin had twice and 39 times more longitudinal elasticity than human blood clot and collagen, respectively. The preclotted graft has longitudinal elastic properties similar to a virgin graft, and is 2.8, 2, and 1.4 times more elastic than the albumin, collagen and collagen/gelatin grafts, respectively. The preclotted graft was 2.5, 2, and 1.4 times more flexible than the albumin, collagen and collagen/gelatin grafts, respectively.

Im Werkstuck entsteht durch Strahlintensitaten von 1010 W/m2 ein mit Plasma gefulltes Keyhole, welches Laser-Tiefschweisen ermoglicht. Zwei mathematische Modelle werden erlautert, wobei im ersten Modell die Gaseigenschaften fur den Fall vollstandiger Absorption der Strahlung im Plasma berechnet werden und im anderen Modell der gesamte Absorptionsprozes an der Keyhole-Wand vor sich geht.

In a considerable proportion of the published work on the subject of laser–oxygen cutting of mild steel, the details of the oxidation reaction are overlooked or confused. For example, it is not uncommon for the oxidized material to be attributed with the physical characteristics of iron rather than iron oxide. Also, the fact that the oxidation reaction cannot take place above a certain temperature limit is usually overlooked. This paper presents, for the first time, an in-depth analysis of the Iron to FeO oxidation reaction in the context of laser–oxygen cutting of mild steel. The paper concludes by presenting a number of guidelines for future theoretical models.

On-line process monitoring of laser welding defects by detecting characteristic changes of the process emissions via photodiodes has high potential but, due to the complex process, lack of directly interpretable and thus controllable correlations. Deep analysis of the process by high speed imaging in combination with modelling enables one to discuss the correlations between the signal and the process, as was demonstrated for quasi-steady state conditions and for transient phenomena. Despite improved knowledge through the study, several uncertainties like the emissivity, the keyhole radiation characteristics and the temperature field need to be identified more accurately for a complete theoretical description of the signal causes.

Ausgehend von der Annahme, das nur jener Anteil des Strahles, der in das Keyhole eindringt, als Warmequelle dient, wird die Keyholegeometrie uber das Modell einer bewegten, 1 inienformigen Warmequelle bestimmt. Die Dynamik von Kondensation und Verdampfung bewirken, das die Temperatur an der Oberflache der Schmelze im Keyhole von der Siedetemperatur deutlich abweichen kann. Der Druck des im Keyhole befindlichen Metalldampfes, der diese stabile Form aufrechterhalt, ergibt sich im wesentlichen aus der Kompensation des Staudrucks, hervorgerufen durch thermokapillare Stromung und aus der Oberflachenspannung, die von der Wandtemperatur des Keyholes abhangt. Gleichsetzung mit dem auch von der Temperatur abhangigen Sattigungsdampfdruck ergibt die tatsachliche Wandtemperatur. Die durch den Uberdruck an den Stirnflachen des Keyholes auftretenden Metallatome bringen Zusatzverluste mit sich und werden daher ebenfalls berucksichtigt. Fur den Fall maximal moglicher Schweii3geschwindigkeit kann schlieslich der Keyholeradius bestimmt werden.

The measurement of absorptance is important for the analysis and modeling of laser-material interactions. Unfortunately, most of the absorptance data currently available consider only polished pure metals rather than the commercially available (unpolished, oxidized) alloys that are actually being processed in manufacturing. We present the results of absorptance measurements carried out at room temperature on as-received engineering grade nonferrous metals (Al, Cu, and Zn alloys). The measurements were made using an integrating sphere with a Nd:YLF laser at two wavelengths (1053 and 527 nm, which means that the results are also valid for Nd:YAG radiation at 1064 and 532 nm). The absorptance results obtained differ considerably from the existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified. For all 22 cases studied the absorptance was higher than for ideal pure, polished metals. For all Al and Cu samples the absorptance was higher for the green than it was for the infrared wavelength, while for all Zn coatings this trend was reversed. No clear correlation between absorptance and surface roughness was found at low roughness values (Sa 0.15-0.60), but one rougher set of samples (Sa 2.34) indicated a roughness-absorptance correlation at higher roughness levels. Validerad; 2007; 20070924 (bajo)

Carbon-nanotube (CNT)-reinforced hydroxyapatite composite coatings have been fabricated by laser surface alloying. Microstructural observation using high-resolution transmission electron microscopy showed that a large amount of CNTs remained with their original tubular morphology, even though some CNTs reacted with titanium element in the substrate during laser irradiation. Additionally, measurements on the elastic modulus and hardness of the composite coatings indicated that the mechanical properties were affected by the amount of CNTs in the starting precursor materials. Therefore, CNT-reinforced hydroxyapatite composite is a promising coating material for high-load-bearing metal implants.

This work discusses energy absorption mechanisms in CO2 laser welding and how they are affected by changes in the process speed. Two main energy absorption processes govern the welding interaction: ...

The notion of a paving sequence in a C* -algebra is introduced and several properties of C*-algebras which admit such sequences are studied.

A quasi-state on d is a positive quasi-linear functional p on d that satisfies the normalization condition sup{ p(A)IA E d, A > 0, (IA I( < 1 } = 1. If d is unital with unit 1, this is equivalent to the condition p(l) = 1. In this paper we are concerned with the question of when positive quasilinear functionals on C*-algebras are linear. In view of the condition (iii) and since positive quasi-linear functionals are scalar multiples of quasistates, this reduces to the question of additivity of quasi-states on the self-adjoint elements of a C*-algebra. This question and its various forms, depending both on the nature of quasi-states and on the structure of the underlying algebra, were considered before [ 1, 3, 4, 6, 7, 9-13, 17, 181; substantial progress had been made in a number of cases. One of the most remarkable advances was the pioneering work of Gleason [6] in which the question was settled in the allirmative for quasistates on B(X), the algebra of all bounded operators acting on a Hilbert space 2, with the property of being completely additive on orthogonal projections, provided the dimension of Y? is different from 2. In the twodimensional case the answer is, in general, negative-one can construct discontinuous quasi-states by simple geometrical arguments; so that one cannot expect all quase-states to be linear on C*-algebras that admit two-dimensional irreducible representations. Following Gleason’s result, contributions to the problem were made by Aarnes [l] and Gunson [7], and in recent years the general problem for von Neumann algebras was 111

This paper is concerned with the study of the dual of a C ∗ {C^ * } -algebra as a matrix ordered space. It is shown that an n × n n \times n matrix of linear functionals of a C ∗ {C^ * } -algebra, satisfying the generalized positivity condition, induces a representation of the algebra that generalizes the classical Gelfand-Naimark-Segal representation. This allows analysis of the relationship between the comparability of cyclic representations of the algebra and the matricial order structure of the dual. We consider the problem of unitary diagonalization of linear functionals and show that positive normal functionals on a matrix algebra over a semifinite von Neumann algebra can always be diagonalized.

During laser materials processing the direct interaction between the laser beam and the processing zone essentially determines the process. A self-regulating processing front develops. A simplified mathematical model was applied to describe this first order mechanism. In particular, a high power Yb:fibre laser beam was characterized and modelled. The dependence of the keyhole shape on different beam models was studied. While a top-hat beam would cause a very different interaction, the impact from the more accurate beam model hardly differed from a Gaussian beam, as can be explained by interaction solely with selected peripheral domains of the beam.

That the final quality of a welded joint, using a laser hybrid arc process, is sensitive not only to the geometrical joint conditions, but also to the content of elements in the surface itself, is already known. However the description of the mechanisms forming undercut defects is still vague. In the following study two kinds of undercuts were identified. It is shown how the mill scales affects the melt motion and what mechanisms actuate the creation of the defects. The conclusion that surface oxides affect the severity of weld undercuts is straight forward but here also the mechanism is explained.

Laser arc hybrid welding combines the advantages but also the complex physical mechanisms of gas metal arc welding and laser keyhole welding. From manifold mainly experimental but also theoretical research results a map with versatile functions was initiated for the first time. The purpose is to survey the overall context and to facilitate navigation to the various phenomena that are shown through case studies accompanied by theoretical explanations and guidelines for optimization. Though not complete, the map enables systematic and graphical navigation to relevant publications. Based on a fundamental structure of the map, which was decided early, it is inherently extendable in the future by adding existing and new knowledge, also from other research groups, enabling evolution. The fundament of the map structure comprises gouge thickness, joint type and metal grade, in coherence with product and weld designers’ starting points. The next hierarchy level of the map offers options in the joint type as well as in hybrid welding techniques. The latter contains techniques like double-sided welding, pulse shaping management of the arc or laser, CMT arcs, tandem arcs, or remelting of undercuts. In addition to laser-arc hybrid welding, other hybrid laser techniques like multilayer hot-wire laser welding of narrow gaps or hybrid laser friction stir welding can be taken into account. At the other end of the hierarchy, the map offers via a database-like archive electronic navigation to research results like weld macrographs, high speed imaging or numerical simulation results of the welding process.

Undercuts are usually an imperfection in welding that either continuously or sporadically form, especially when welding at high speed. Efforts, usually lowering the welding speed or overfilling, are applied to avoid undercuts as they can significantly lower the fatigue properties of the welded workpiece. Undercut formation is complex and occurs by various means, mainly based on temperature and melt flow mechanisms. When having two power sources as in laser arc hybrid welding, the melt flow can be tailored to suppress undercut formation. This can be done e.g. by narrowing the width of the gouge or by optimum positioning of the power sources relative to each other. The present paper shows and explains the main reasons of various types of undercut formation. By following the herein generated guidelines, the critical welding speed during laser arc hybrid welding can be further increased, free of undercuts.

High speed imaging has been used to analyze the sensitivity of the Hybrid laser welding process to variations in the laser-arcworkpiece geometry along the axis of the laser beam. The welding process was found to be stable within a certain range of workpiece positions. Outside of this range the process became unstable. If the workpiece was too close to the laser/arc combination, the two energy sources did not supplement each other sufficiently. If the workpiece was too far away the droplets from the arc interfered with the laser-keyhole interaction.

Conduction limited laser welding is commonly used in electronic and battery applications, where a high width-to-depth ratio weld is desirable. A laser beam with Gaussian or top-hat distributions is often used to produce conduction limited spot welds. Both these energy distributions result in a higher proportion of the laser beam energy being introduced towards the centre of the welded spot and consequently, a reduced penetration weld towards the circumference of the beam spot. The use of diffractive optical elements to tailor the energy distribution of the laser beam has been evaluated. An incident laser beam with an energy distribution in the shape of a ring or C-shape was projected onto the material, which results in heat propagating towards the centre, producing a shallow weld with a consistent depth of penetration across the entire overlapped joint. The results confirmed a corresponding thermal model which predicted an even distribution of heat at the joint interface.

Laser welding of ferritic steel in normal atmosphere gives rise to weld embrittlement and poor formability. This paper demonstrates that the addition of an argon gas shield to the welding process results in tough, formable welds. Post weld heat treatment and microscopic analysis has suggested that the poor ductility of welds produced without a gas shield is, to some extent, the result of the presence of oxides in the weld metal.

Laser cladding is overlay welding method to manufacture high performance, fusion bonded metal and metal matrix composite (MMC) coatings on metallic substrates with low dilution. Owing to steep thermal gradients, rapid solidification and possible mismatch in coefficients of thermal expansion (CTE) between coating and substrate, laser cladding induces large tensile residual stresses in coating layer, potentially affecting the service life of clad component under external load-induced stresses. In this study, 4-point bending and torsion fatigue tests were conducted on relatively large round laser clad steel bars to determine the effect of laser cladding on fatigue strength. Quenched and tempered (QT) 42CrMo4 steel clad with Inconel 625 and S355 structural steel clad with Stellite 21 were subjected to various stress levels for relatively large number of cycles with and without post weld heat treatment (PWHT). The results showed that Stellite 21 decreased the fatigue life of S355 at all the applied loads whereas Inconel 625 increased the fatigue life of 42CrMo4 at high loads but decreased at low loads. Applied PWHT did not show any positive influence on fatigue life.Laser cladding is overlay welding method to manufacture high performance, fusion bonded metal and metal matrix composite (MMC) coatings on metallic substrates with low dilution. Owing to steep thermal gradients, rapid solidification and possible mismatch in coefficients of thermal expansion (CTE) between coating and substrate, laser cladding induces large tensile residual stresses in coating layer, potentially affecting the service life of clad component under external load-induced stresses. In this study, 4-point bending and torsion fatigue tests were conducted on relatively large round laser clad steel bars to determine the effect of laser cladding on fatigue strength. Quenched and tempered (QT) 42CrMo4 steel clad with Inconel 625 and S355 structural steel clad with Stellite 21 were subjected to various stress levels for relatively large number of cycles with and without post weld heat treatment (PWHT). The results showed that Stellite 21 decreased the fatigue life of S355 at all the applied loads where...