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The relative paucity of deceased donor organs and the progressive increase in patients with cirrhosis have led transplant centers to consider organs from marginal donors (elderly donors, prolonged stay in the intensive care unit (ICU), liver steatosis-steatotic grafts, severe hypernatremia, and use of inotropes). Recently, the use of those marginal grafts has increased, but splitting liver is still debatable. Herein, we present a 28-year-old deceased donor who had a history of traumatic brain injury. The patient stayed in ICU for 3 days with high sodium level (188 mEq/L) and was hemodynamically supported with single inotrope. At the time of procurement, core biopsies were taken from the right lobe and left lateral segment of the liver, with results demonstrating 5% necrosis. A decision was made for split liver transplant as left lateral sector and extended right lobe. Liver graft was divided into a left lateral segment to be transplanted to a 4-year-old child with secondary biliary cirrhosis due to previous liver transplant and a right extended liver lobe for an adult patient with hepatocellular carcinoma waiting 10 months on the waiting list. Both liver transplants were performed uneventfully. Patients were discharged on the 11

Objective: living liver and kidney donor surgeries are major surgical procedures applied to healthy people with mortality and morbidity risks not providing any direct therapeutic advantage to the donor. In this study, we aimed to share our simultaneous and sequential living liver-kidney donor experience under literature review in this worldwide rare practice. Material and methods: between January 2007 and February 2018, a total of 1109 living donor nephrectomies and 867 living liver donor hepatectomies were performed with no mortality to living-related donors. Eight donors who were simultaneous or sequential living liver-kidney donors in this time period were retrospectively reviewed and presented with their minimum 2-year follow-up. Results: of the 8 donors, 3 of them were simultaneous and 5 of them were sequential liver-kidney donation. All of them were close relatives. Mean age was 39 (26-61) years and mean BMI was 25.7 (17.7-40). In 3 donors, right lobe, in 4 donors, left lateral sector, and in 1 donor, left lobe hepatectomy were performed. Median hospital stay was 9 (7-13) days. Two donors experienced early and late postoperative complications (Grade 3b and Grade 1). No mortality and no other long-term complication occurred. Conclusion: expansion of the donor pool by utilizing grafts from living donors is a globally-accepted proposition since it provides safety and successful outcomes. Simultaneous or sequential liver and kidney donation from the same donor seems to be a reasonable option for combined liver-kidney transplant recipients in special circumstances with acceptable outcomes. / Giriş ve amaç: canlı karaciğer ve böbrek verici ameliyatları tamamen sağlıklı bireylere uygulanan cerrahi işlemlerdir. Bu cerrahiler vericiye doğrudan bir faydası olmayan, ölüm ve komplikasyon riski taşıyan büyük bir işlemdir. Bu çalışmamızda dünya genelinde çok yaygın olmayan eş zamanlı veya birbirini takip eden canlı karaciğer ve böbrek verici ameliyatı deneyimimizi literatür irdemesi ile birlikte paylaştık. Gereç ve yöntem: Ocak 2007-Şubat 2018 tarihleri arasında merkezimizde, alıcısı ile yakınlık ilişkisi olan vericilere toplam 1109 canlı böbrek verici ameliyatı ve 867 canlı karaciğer verici ameliyatı verici kaybı yaşanmadan gerçekleştirilmiştir. Bunlardan eş zamanlı veya birbirini takip edecek şekilde canlı karaciğer ve böbrek verici ameliyatı olan 8 verici minimum 2 yıllık takipleri ile incelenmiştir. Bulgular: bu 8 vericiden 3 tanesi eş zamanlı ve 5 tanesi birbirini takip edecek şekilde canlı karaciğer ve böbrek verici ameliyatı olmuşlardır. Hepsi alıcının yakın akrabasıydı. Ortalama yaş 36 (26-61) ve ortalama BMI 25,7 kg/m (17,7-40) idi. Vericilerden 3’üne sağ lob verici hepetektomisi, 4’üne verici sol lateral sektör hepatektomisi ve 1’ine sol lob verici hepetektomisi gerçekleştirilmiştir. Median hastanede kalış süresi 9 (7-13) gündü. Vericilerden 2’sinde erken dönemde komplikasyon gelişmiştir (Dindo Grade 3b ve Grade 1). Verici ölümü ve başka bir geç dönem komplikasyonu gelişmiştir. Sonuç: verici havuzunun genişletilmesinde canlı vericilerin güvenli olarak başarılı sonuçlar ile kullanılması dünya genelinde kabul görmektedir. Aynı vericinin eş zamanlı veya takip eden ameliyatlar ile karaciğer ve böbrek vericisi olması özel durumlarda kombine karaciğer ve böbrek alıcıları için güvenli bir seçenek olabilmektedir., NA

Liver transplantation is the final treatment option for end-stage liver disease and acute liver failure, although availability of donor organs is a major limitation. The large gap between the growing list of patients awaiting liver transplantation and the scarcity of donor organs has fueled efforts to maximize the existing donor pool and identify new avenues. We treated a 13-year-old boy who had acute liver failure, due to Wilson's disease, with transplantation of a liver from a deceased liver donor with a calcified hydatid cyst. After 3 years of follow-up, liver function tests remained normal, hydatid cyst serology was negative, and no hydatid cyst or other problems were observed.

Liver transplantation surgery due to cirrhosis in patients with hemophilia is rare and there are limited cases in the literature. We present a case of a patient with hemophilia A who underwent 2 consecutive surgeries owing to coronary artery disease and cryptogenic cirrhosis with hepatocellular carcinoma. After these surgeries, no bleeding or other complications were seen, and the factor VIII levels have not changed since liver transplantation in the follow-up.

Laser treatment of SiAlON surface is considered and characteristics of the resulting surfaces are studied incorporating the scanning electron and atomic force miscroscopes, X-ray diffraction and Fourier transform infrared spectroscopy. The wetting state of the laser treated surface is assessed using the droplet contact angle method while the friction coefficient of the treated surface is obtained by using the micro-tribometer. Microhardness and fracture toughness of the treated surface are also measured. Thermal and thermal stress analyses are carried out and temperature and von Mises stress fields are predicted in the laser treated region. It is found that in micro/nano size pillars are formed on the laser treated surfaces, which alters the wetting state from hydrophilic to hydrophobic with contact angle 120° and contact angle hysteresis in the order of 18.2°. In general, laser treated surface is free from large size cracks and voids; however, few locally scattered micro-cracks are observed on the surface. Microhardness increases slightly for the laser treated surface because of the dense layer formed on the surface under the high cooling rates. The fracture toughness of the surface reduces slightly and the friction coefficient of the surface improves after the laser treatment process. The laser scanning tracks, which are closely spaced, result in self-annealing effects in the laser treated region; in which case, von Mises attains low values particularly along the recently formed laser scanning tracks.

Objective: laparoscopic donor nephrectomy (LDN) has been shown to be a safe approach with better morbidity results. Impact of multiple renal arteries (MRAs) and anatomical variations has been reviewed by many authors. In our study, the relationship between the donors with MRAs and risk of perioperative vascular complications related to donor nephrectomy was investigated. Material and methods: patients who underwent hand-assisted LDNs between January 2007 and February 2018 were reviewed retrospectively. Patient age, sex, body mass index (BMI), waist circumference, side of donor nephrectomies, donors with MRAs, intraoperative vascular complications, conversion rates, hospitalization durations, and operative times were extracted. Risk factors for perioperative vascular complications were defined. Results: there were MRAs in 288 kidney donors (21.3%). The number of patients who underwent a right donor nephrectomy was 113 (8.4%). BMI, waist circumference, and postoperative hospital stay were not significantly different between donors with one artery and those with MRAs (p>0.05). The renovascular complication rate and overall conversion rate to open surgery were significantly higher in donors with MRAs (p, NA

Laser gas assisted texturing of tungsten surface is carried out towards achieving increased solar absorption at the surface. Morphological and metallurgical changes at the textured surface are examined using the analytical tools. Hydrophobic characteristics of the surface are assessed incorporating the water droplet contact angle measurement technique. The influence of environmental dust on the laser textured surface is investigated mimicking the humid air ambient. The adhesion of the dry mud on the textured surface is determined through measurement of tangential forces required to remove the dry mud from the surface. It is found that laser gas assisted processing results in surface texture composing of micro/nano pillars and formation of WO3 compounds in the treated layer. Hydrophobicity of the surface improves significantly after the laser texturing; in which case, the water droplet contact angle increases from 64° to 94°. The dry mud and dried liquid solution residues influence the UV visible absorption of the laser textured surface. In this case, absorption reduces almost 20% because of scattering of incident UV visible radiation by the residues at the textured surface.

Laser texturing of Inconel 718 alloy surface under high nitrogen gas pressure is considered and the resulting surface morphology and wetting state are examined. Analytical tools are used to characterize the laser textured surface. Environmental dust particles and liquid solution formed from the water condensate on the dust particles in humid air ambient are analyzed. The tangential force required to remove the dried liquid solution from the laser textured and as received surfaces are measured incorporating the micro-tribomoter. It is found that laser treatment results in micro/nano size pillars on the textured surface and forms nitride compounds on the surface. This, in turn, modifies the wetting state of the workpiece surface from hydrophilic to hydrophobic. A liquid solution is formed due to the dissolution of alkaline and alkaline earth metals of the dust particles into the water condensate in humid air ambient. The liquid solution has high pH and forms different sizes of crystals on the surface upon drying. The liquid solution spreads on the textured surface while forming a film. It adheres strongly to the surface upon drying; in which case, the tangential force required removing the dried liquid from the surface remains high, which is more pronounced for the as receive surfaces.

Background Cardiovascular complication is one of the leading causes of mortality after liver transplantation (LT). Thus, a thorough cardiac evaluation is a must before proceeding to a liver transplant surgery. Percutaneous coronary intervention (PCI) with stent and to a lesser extent coronary artery bypass grafting (CABG) are both valuable treatment options for patients with coronary artery disease. Methods A retrospective, single-center study that included patients who underwent cardiac intervention and subsequent LT for end-stage liver disease. All patients who had PCI or CABG were included in the study. Results Twenty-nine adult patients out of 51 had a cardiac intervention before liver transplantation. Twenty-four patients had a diagnostic PCI, 3 patients had therapeutic PCI with stent, and 2 had failed PCI and proceeded to CABG before liver transplant. The mean age of the patients was 60.5 years. There were 24 men. All patients had cirrhosis. The 2 CABG cases were done during the same admission with a 13- and 18-day interval between the CABG and the transplantation. Both cases were live-related liver transplantation. No mortality was reported. Conclusion In case of PCI failure, CABG may be a valuable and safe treatment option for cirrhotic patients as a preparation for liver transplantation. Live donor liver transplantation may be a good back-up for those patients in case they develop hepatic decompensation.

Laser gas assisted nitriding of tungsten surface is carried out while incorporating the high pressure nitrogen assisting gas. Metallurgical and morphological changes in the laser treated layer are examined using the analytical tools. The nitride compounds formed in the surface vicinity are analyzed incorporating X-ray diffractogram and Fourier-transform infrared spectroscopy. The wetting state and the free energy of the laser treated surface is determined using the droplet contact angle method. The friction coefficient of the resulting surface is measured via microtribometer and UV visible absorption characteristic of the surface is analyzed. It is found that the laser texturing of tungsten surface results in micro/nano size pillars without forming micro-cracks and large size cavities. The laser treatment gives rise to hydrophobic surface characteristic with improved UV visible spectrum absorption coefficient. The microhardness increased significantly because of the nitride compounds formed at the surface and friction coefficient shows wave-like behavior because of the surface texture.

Laser circular cutting of Inconel 803 alloy is carried out. Temperature and stress fields are predicted in the cutting section using ABAQUS finite element code mimicking the experimental conditions...

Zirconium nitride is used as a selective surface for concentrated solar heating applications and one of the methods to form a zirconium nitride is texturing of zirconia surface by a high intensity laser beam under high pressure nitrogen gas environment. Laser texturing also provides hydrophobic surface characteristics via forming micro/nano pillars at the surface; however, environmental dust settlement on textured surface influences the surface characteristics significantly. In the present study, laser texturing of zirconia surface and effects of the dust particles on the textured surface in a humid air ambient are investigated. Analytical tools are used to assess the morphological changes on the laser textured surface prior and after the dust settlement in the humid air ambient. It is found that laser textured surface has hydrophobic characteristics. The mud formed during condensate of water on the dust particles alters the characteristics of the laser textured surface. The tangential force required to remove the dry mud from the textured surface remains high; in which case, the dried liquid solution at the mud-textured surface interface is responsible for the strong adhesion of the dry mud on the textured surface. The textured surface becomes hydrophilic after the dry mud was removed from the surface by a desalinated water jet.

The current research includes a practical study of the thermal performance of solar collector integral storage system (ISCS) in which different types of heat exchangers are immersed in its enclosure for comparison. The first type is a straight tube heat exchanger (ST) and the other is a heat exchanger in the form of a coiled tube (CT). The effect of single and double glass layers and fluid flow rates inside the heat exchanger on the natural convection heat transfer of ISCS system is experimentally evaluated by determining the temperature difference of inlet and outlet water through the heat exchanger immersed into the ISCS enclosure, the temperature distribution inside the enclosure, the ISCS efficiency, and the amount of thermal storage during evening times. Three sets of experiments are performed for a different water flow rates (1.0, 1.5, 2.0, and 2.5 Lpm) inside the heat exchanger that is immersed in the thermally insulated enclosure and different glassing layers. The first set represents the presence of a heat exchanger in the form of a straight tube with a single glass was layer on the top face of the enclosure that is called (STSG). The second set uses a coiled tube heat exchanger with a single glass on the upper side of the enclosure and it’s named as (CTSG). The last set of experiments is represented by a heat exchanger in the form of a coiled tube with a double glass on the upper face of the enclosure and it’s abbreviated as (CTDG). At water flow rate of 1 Lpm, the CTDG exhibited higher temperature difference (28 °C and 19.9 °C than (19.4 and 11.4 °C) for CTSG and (12 and 7.3°C) for STSG during day and night times, respectively. The results reveal that the thermal efficiency (84.5 - 77.8 %) of the (CTDG) case at water flow rate of 2.5 Lpm was higher than the efficiency (68.8 - 56.6%) of (CTSG) case and that (41.7 - 39.7%) of STSG) case during day and night times, respectively. It was also observed that the internal energy exceeds the amount of solar radiation during the day and provides a thermal storage at night due to the complete isolation of the collector. The temperature measurements near the tube allow the calculation of the Rayleigh number during the heat transfer process, and empirical relationships haves been deduced for each set of experiments between the Nusselt number and the Rayleigh number.

A Kevlar laminate has negative thermal expansion coefficient, which makes it difficult to machine at room temperaures using the conventional cutting tools. Contararily, laser machining of a Kevlar laminate provides advantages over the conventional methods because of the non-mechanical contact between the cutting tool and the workpiece. In the present study, laser circular cutting of Kevlar laminate is considered. The experiment is carried out to examine and evaluate the cutting sections. Temperature and stress fields formed in the cutting section are simulated in line with the experimental study. The influence of hole diameters on temperature and stress fields are investigated incorporating two different hole diameters. It is found that the Kevlar laminate cutting section is free from large size asperities such as large scale sideways burnings and attachemnt of charred residues. The maximum temperature along the cutting circumference remains higher for the large diameter hole than that of the small diameter hole. Temperature decay is sharp around the cutting section in the region where the cutting terminates. This, in turn, results in high temperature gradients and the thermal strain in the cutting region. von Mises stress remains high in the region where temperature gradients are high. von Mises stress follows similar to the trend of temperature decay around the cutting edges.

Laser gas assisted surface treatment of steel 309 is carried out and the characteristics of the resulting surface are analyzed using the analytical tools. Scanning electron and 3-D optical microscopes are used to assess the morphological and metallurgical changes in the laser treated layer. Energy spectroscopy and X-ray diffraction are carried out to determine the elemental composition and compounds formed on the laser treated surface. The friction coefficient of the laser treated surface is measured using the micro-tribometer and compared to that of the as received surface. The corrosion resistance of the laser treated and as received surfaces is measured incorporating the electrochemical tests. It is found that laser treatment results in a dense layer and formation of nitride compounds at the surface. This enhances the microhardness at the laser treated surface. The friction coefficient attains lower values at the laser treated surface than that corresponding to the as received surface. The corrosion rate of the surface reduces significantly after the laser treatment process, which can be attributed to the passive layer at the surface via formation of a dense layer and nitride compounds in the surface vicinity. In addition, the number of pit sites decreased for the laser treated surface than that of as received surface.

Laser pulse heating of steel mixing with tungsten carbide (WC) particles is carried out. Temperature field in the irradiated region is simulated in line with the experimental conditions. In the analysis, a laser pulse parameter is introduced, which defines the laser pulse intensity distribution at the irradiated surface. The influence of the laser parameter on the melt pool size and the maximum temperature increase in the irradiated region is examined. Surface temperature predictions are compared with the experimental data. In addition, the distribution of WC particles and their re-locations in the treated layer, due to combination of the natural convection and Marangoni currents, are predicted. The findings are compared to the experimental data. It is found that surface temperature predictions agree well with the experimental data. The dislocated WC particles form a streamlining in the near region of the melt pool wall, which agree with the experimental findings. The Gaussian distribution of the laser pulse intensity results in the maximum peak temperature and the maximum flow velocity inside the melt pool. In this case, the melt pool depth becomes the largest as compared to those corresponding to other laser pulse intensity distributions at the irradiated surface.

Urinary tract infection is the most common infectious complication following kidney transplant. Anatomic abnormalities, bladder dysfunction, a positive history of febrile urinary tract infection, and recipient age are reported risk factors. The aim of this study was to determine the risk factors for fUTI, which necessitated hospitalization in the first year after renal transplantation in our pediatric transplant population. A retrospective review of 195 pediatric patients who underwent kidney transplant between 2008 and 2017 from a single institution was performed. All patients admitted to the hospital with fUTI were marked for further analyses. The risk factors including age, gender, dialysis type, history of urologic disorders, and preoperative proteinuria for fUTI in the first year after kidney transplantation and graft survivals were investigated. Independent-sample t test and chi-square tests were used for univariate analysis. Exhaustive CHAID algorithm was used for multivariate analysis. The data of 115 male and 80 female patients were retracted. The mean ages of our cohort for males and females were 9.5 ± 5.1 and 10 ± 4.8 years, respectively. The age of the patients at transplant and their gender were found to be a statistically significant risk factors for developing fUTIs. Multivariate analysis showed that fUTI was common in female patients and a subgroup of male patients who had preoperative proteinuria, but no neurogenic bladder had higher risk compared with male patients without proteinuria. Patient surveillance and antibiotic prophylaxis algorithms can be developed to prevent febrile urinary tract infections seen after pediatric kidney transplantation in risky population.

Laser machining of different diameter holes into alumina tiles is carried out. Temperature and stress fields are predicted by using the finite element code. Surface temperature and residual stress predictions are validated through the thermocouple data and X-ray diffraction measurements. Morphological changes in the cutting section are examined by incorporating optical and scanning electron microscopes. It is found that the predictions of surface temperature and the residual stress formed at the cut section agree well with the experimental findings. In general, cut sections are free from large asperities; however, local dross attachments at the kerf edge and crack network formation at the kerf surface are observed.

Laser gas assisted treatment of Ti6Al4V alloy surface is carried out and nitrogen/oxygen mixture with partial pressure of PO2/PN2=1/3 is introduced during the surface treatment process. Analytical tools are used to characterize the laser treated surfaces. The fracture toughness at the surface and the residual stress in the surface region of the laser treated layer are measured. Scratch tests are carried out to determine the friction coefficient of the treated surface. It is found that closely spaced regular laser scanning tracks generates a self-annealing effect in the laser treated layer while lowering the stress levels in the treated region. Introducing high pressure gas mixture impingement at the surface results in formation of oxide and nitride species including, TiO, TiO2, TiN and TiOxNy in the surface region. A dense layer consisting of fine size grains are formed in the surface region of the laser treated layer, which enhances the microhardness at the surface. The fracture toughness reduces after the laser treatment process because of the microhardness enhancement at the surface. The residual stress formed is comprehensive, which is in the order of −350 MPa.

Laser surface texturing of Inconel 718 alloy is carried out under the high pressure nitrogen assisting gas. The combination of evaporation and melting at the irradiated surface is achieved by controlling the laser scanning speed and the laser output power. Morphological and metallurgical changes in the treated surface are analyzed using the analytical tools including optical, electron scanning, and atomic force microscopes, energy dispersive spectroscopy, and X-ray diffraction. Microhardnes and friction coefficient of the laser treated surface are measured. Residual stress formed in the surface region is determined from the X-ray diffraction data. Surface hydrophobicity of the laser treated layer is assessed incorporating the sessile drop method. It is found that laser treated surface is free from large size asperities including cracks and the voids. Surface microhardness increases significantly after the laser treatment process, which is attributed to the dense layer formation at the surface under the high cooling rates, dissolution of Laves phase in the surface region, and formation of nitride species at the surface. Residual stress formed is compressive in the laser treated surface and friction coefficient reduces at the surface after the laser treatment process. The combination of evaporation and melting at the irradiated surface results in surface texture composes of micro/nano-poles and pillars, which enhance the surface hydrophobicity.

Laser control melting of dual matrix cast iron surface is carried out. A carbon film containing 15% WC particles is formed at the surface prior to the laser treatment and the spiral tracks are adopted for laser scanning at the workpiece surface. Morphological, metallurgical, microhardness, and scratch resistance of the laser treated surface are examined using analytical tools. Temperature and stress fields in the laser irradiated region are predicted incorporating ABAQUS finite element code. Predictions of temperature and residual stress at the laser treated surface are validated with the thermocouple and the X-ray diffraction data. It is found that surface temperature and residual stress predictions agree well with their counterparts corresponding to thermocouple data and findings of X-ray diffraction technique. Laser treated surface is free from asperities including voids and micro-cracks despite the mismatch of thermal expansion coefficients of WC and dual matrix cast iron. This behavior is attributed to the self-annealing effects of recently formed spiral tracks on the previously formed tracks during the laser treatment process; in which case, the self-annealing effect modifies the cooling rates and lowers thermal stress levels in the laser treated layer. Laser treated layer consists of a dense region composing of fine grains and WC particles, dendritic and featherlike structures below the dense layer, and the heat affected zone. (C) 2015 Elsevier Ltd. All rights reserved.

Laser controlled melting of pre-prepared H12 hot-work tool steel surface is carried out. B 4 C particles in the carbon film are located at the workpiece surface prior to the laser treatment process. Nitrogen at high pressure is used as an assisting gas during the laser melting. Morphological and metallurgical changes in the treated layer are examined using scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. Microhardness of the treated surface is measured and the residual stress formed at the treated surface vicinity is obtained using the X-ray diffraction technique. It is found that a dense layer consisting of fine grains is formed at the treated surface. Microhardness of the treated surface improves significantly because of fine grains, nitride compounds formed at the surface and micro-stresses developed due to mismatched of thermal expansion coefficients of B 4 C and the base material. The residual stress formed at the surface is suppressed by the self annealing effect of the initially formed laser scans.

Laser treatment of hot pressed mixture of aluminum (85 wt%) and B4C (15 wt%) is carried out. Metallurgical and morphological changes at the laser treated surface are examined using the analytical tools. Microhardness and fracture toughness of the workpiece surfaces are determined prior to and after the laser treatment process. Texture and hydrophobicity of the laser treated surface is assessed incorporating the atomic force microscopy and contact angle measurements. It is found that a dense layer consisting of fine grains of sub-micron sizes (0.8–0.4 μm) and B4C particles is formed at the laser treated surface. Microhardness increases at the laser treated surface because of the presence of the dense layer and the formation of AlN compounds at the surface. Fracture toughness of the laser treated surface reduces slightly because of the microhardness enhancement at the surface. The textures of the laser treated surface compose of micro/nano poles, which result in higher contact angles than that of the untreated surface, and formation of AlN compound adds to the surface hydrophobicity enhancements.

Laser treatment of B 4 C tile surfaces is carried out under high pressure nitrogen assisting gas environment. Morphological and metallurgical changes in the laser treated layer are examined by incorporating scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. Microhardness and fracture toughness of the laser treated surface are determined from the indentation data. Residual stress formed at the treated surface is obtained by using X-ray diffraction technique. It is found that laser treated surface is free from large scale asperities including cracks and voids; however, some locally scattered shallow cavities with 1.5–2 μm widths are formed at the surface because of high temperature processing. Dense layer, consisting of fine grains, and formation of nitride species (BN and BC 2 N) enhance microhardness and lower fracture toughness at the surface. Residual stress formed in the treated layer is compressive and the maximum residual stress is in the order of −0.9 GPa.

Laser cutting of triangular geometry into 5-mm-thick alumina tile is carried out. Temperature and stress fields are predicted by using ABAQUS finite element code in line with the experimental conditions. Experiments are carried out to validate the predictions of temperature and the residual stress in the cutting section. Thermocouples are incorporated in temperature measurements while X-ray diffraction technique is accommodated to obtain the residual stress at the kerf surface. The morphological changes in the cutting section are examined by using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. It is found that temperature and residual stress predictions agree well with their counterparts obtained from the experiments. The optical and SEM micrographs reveal that the cut sections are free from large size defects such as large-scale cracks and sideways burnings. The maximum value of von Mises stress occurs at the mid-thickness of the workpiece due to the form...

Laser cutting of rectangular geometry into the 5 mm thick alumina tiles is carried out. Temperature and stress fields, which are developed during the cutting process, are simulated in line with the experimental conditions. The morphological changes in the cutting sections are examined using optical and electron scanning microscopes, energy dispersive spectroscopy, and X-ray diffraction technique. The predictions of surface temperature and the residual stress are validated through the experimental data. It is found that von Mises stress attains high values in the region of the mid-thickness of the workpiece. The laser cut sections are free from major cracks and large scale sideways burning. The predictions of surface temperature and residual stress agree well with their counterparts obtained from the experiment.

In the present study, the corrosion resistance behavior of untreated and laser treated Hastelloy was examined. The electrochemical tests including potentiodynamic polarization, Tafel analysis, and linear polarization resistance were carried out in deaerated 0.5% NaCl aqueous solution at room temperature. Surface roughness was measured to correlate it with corrosion resistance properties of the materials. Surface morphology of the samples after corrosion tests was examined using scanning electron microscopy and energy dispersive X-ray spectroscopy. Results showed that laser treated surface exhibited better corrosion resistance properties as compared to untreated surface.

Laser gas assisted melting of high strength low alloy steel surface is carried out. The alloy surface is pre-prepared to contain 5% B 4 C particles in a 40 μm thick carbon film prior to laser treatment process. Metallurgical and morphological changes in the laser treated layer are examined by using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The residual stress developed and the microhardness of the resulting surface is measured. It is found that B 4 C particles remain in solid phase in the surface region due to their high melting temperature. The dense layer consisting of fine grains are formed at the surface and the feathery like structure is observed below the surface vicinity, which consists of martensite and nitride precipitations. The use of nitrogen at high pressure causes the formation of nitride compounds at the surface, which contributes to the volume shrinkage in the dense layer. Surface microhardness increases considerably because of attainment of high cooling rates, formation of nitride compounds, and presence of B 4 C particles at the surface.

Electrochemical testing of laser treated bronze surface is carried out and corrosion resistance of the surface is assessed. Morphological and metallurgical changes in the laser treated layer are examined using scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. The pit sites formed at the surface are analyzed using scanning electron microscope. It is found that laser treatment improves the corrosion resistance of the treated surface. Fine grains are formed in the surface region of the laser treated layer, which are attributed to the large cooling rates from the surface.

Laser cutting of alumina tiles is carried out, and the temperature and stress fields developed in the cutting section are predicted numerically using ABAQUS finite element code. The morphological changes along the cut edge surfaces are examined using the optical and scanning electron microscopes. The residual stress formed in the cutting section is obtained after incorporating the XRD technique. The residual stress predicted is compared with the experimental data. It is found that the residual stress predicted agrees well with the experimental results. The dross attachment at the kerf exit is observed, which is associated with the high melting temperature of the workpiece.

One technique to improve tribological properties of aluminum bronze surfaces is to introduce laser controlled melting at the surface in the presence of a composition-modifying film. In this work, a 40 μm thick organic film, containing B4C particles, was formed at the workpiece surface prior to laser treatment. The organic coating provides enhanced absorption of the incident laser radiation and distributes the B4C particles uniformly across the surface. Morphological and microstructural changes in the laser treated layer were examined using scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The microhardness of the laser treated layer was measured and the residual stress formed at the treated surface was evaluated by X-ray diffraction using the sin2 ψ technique. It was found that the laser treated surface produced is relatively free from defects and asperities with a microhardness that is notably higher than that of the as-received bronze substrate. This hardening effect can be attributed to the development of a dense layer consisting of fine grains, partially dissolved B4C particles, and formation of Cu3N compounds. The residual compressive stress obtained from X-ray diffraction peak evaluation is of the order of −400 MPa.

Laser surface melting of hot pressed aluminum composite tile, consisting of 90 % aluminum and 10 % WC, is carried out. Temperature and stress fields developed in the laser-treated region are modeled and predicted using ABAQUS finite element code in line with the experimental conditions. The spiral motion of the laser beam is incorporated at the surface during the laser scanning. This arrangement provides self-annealing effect on the initially formed laser scanning tracks through heat conduction from the lately formed laser scanning tracks. Surface temperature predictions are validated through the thermocouple data. Morphological and metallurgical changes in the laser-treated layer are examined using optical and electron scanning microscopes. It is found that the cooling rates in the central region of the workpiece remain low because of the self-annealing effect of the lately formed laser scanning tracks. This, in turn, lowers von Mises stress levels in this region. Stress peaks are formed below the surface because of the high thermal strain formed in this region during the cooling cycle. The spiral scanning of the laser beam causes oscillating stress levels in the surface region of the laser-treated layer; in which case, its amplitude reduces with the progressing time. Laser-treated layer is free from cracks and crack networks, which is associated with the self-annealing effect of the lately formed laser scanning tracks.

Laser controlled melting of pre-prepared Rene 41 surface is carried out. A carbon film composing of uniformly distributed 5% TiC carbide particles is formed at the surface prior to laser treatment process. The carbon film provides increased absorption of the incident radiation and facilitates embedding of TiC particles at the surface region of the workpiece during the treatment process. Nitrogen at high pressure is used as assisting gas during the controlled melting. It is found that laser treated layer extents 40 μm below the surface with almost uniform thickness. Fine grains and ultra-short dendrites are formed at the surface region of the laser treated layer. Partially dissolved TiC particles and γ, γ′ and γ′N phases are observed in the treated layer.

Laser gas assisted controlled melting of alumina tile surface is carried out in this work. A carbon coating containing 5% of B 4 C particles is formed at the tile surface prior to laser treatment process. The morphological and microstructural changes in the treated layer are examined using X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscope. The surface microhardness is measured and the residual stress formed at the surface vicinity is obtained from the X-ray diffractograms. It was found that microhardness of the surface increases significantly after the laser treatment process, which is attributed to high cooling rates and the formation of nitride species at the surface. The residual stress formed at the surface is compressive and no micro- or major-cracks are observed at the laser treated surface.

Phosphorous bronze finds applications in industry because of its resistance to fatigue and ease of heat dissipation due to its high thermal conductivity. Laser treatment of bronze surface improves the hardness of the surface through forming a dense layer in the surface region. Consequently, in the present study, laser treatment of a bronze surface is investigated. Thermal stress and temperature fields developed during the laser-treated region are modeled after considering the transient three-dimensional situation in line with the experimental conditions. An experiment is carried out, and the resulting surfaces treated by a laser beam are characterized using scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. It is found that high rate of strain developed in the heated region, due to fast-cooling rates, results in high von Mises stress in the surface region. The laser-treated region is free from cracks, and surface hardness increases almost four times above the base material hardness after the laser treatment process.

A carbon film containing 5% TiC particles is formed on a pre-prepared bronze surface prior to laser treatment. The carbon film provides increased absorption of the incident laser beam and hosts TiC particles with a uniform distribution at the workpiece surface. Optical and scanning electron microscopy are used to examine the metallurgical and morphological changes in the laser treated layer. Micro-hardness of the laser-treated surface is measured, and the residual stress formed in the surface vicinity is measured using the X-ray diffraction technique. It was found that a dense layer with fine grains was formed in the laser-treated layer. The micro-hardness of the laser-treated surface increases almost three times compared with the base material hardness. The presence of a dense layer and the formation of Cu 3N in the surface region contribute to the hardness enhancement at the surface. Copyright © 2012 John Wiley & Sons, Ltd.

Laser controlled melting in nitrogen of a preprepared steel surface has been carried out. A carbon film formed from a phenolic resin precursor containing 5 vol.-% of TiC particles was first formed at the surface of the steel before the laser treatment. The morphological and metallurgical changes in the laser treated region were examined using scanning electron microscopy and X-ray diffraction (XRD). Temperature and stress fields were predicted in the workpiece using a finite element code. The residual stress at the surface was measured using XRD. The hardness of the workpiece was measured using microindention testing. It was found that the laser treatment results in a dense layer composed of fine grains and TiC particles at the surface, which enhances surface microhardness. The presence of the carbon film at the surface and high pressure nitrogen gas enable the formation of FeN3 and Fe(N,C) phases at the surface and nitrogen diffusion into the substrate material causes nitride precipitation below the surf...

Laser straight cutting of zirconia is carried out. Temperature and stress fields developed in the cutting sections are predicted using the finite element code. The morphological changes in the cutting section are examined after incorporating the optical and scanning electron microscopes. The prediction of surface temperature is compared with its counterpart obtained from the thermocouple data. Temperature predictions agree well with the thermocouple data. The cut section is free from major cracks and dross attachment occurs at the kerf exit.

Laser straight cutting of bronze sheet is carried out. Temperature and stress fields in the cutting section are simulated using the finite element method. Temperature predictions are validated with the thermocouple measurements. The kerf surfaces are examined using optical and scanning electron microscopes. To prevent the oxidation reactions taking place during the cutting process, nitrogen at high pressure is used as the assisting gas. It is found that high stress levels are generated in the neighborhood of the cut edges due to the high temperature gradients formed in this region. Two stress peaks are observed along the cutting direction: i) one is in the re-cast layer and ii) the other is in the frontal region of the laser beam. The striations formed at the kerf surface have shallow depths and the dross attachment is observed at the edges of the kerf exit, which is associated with the low viscosity of the molten flow and the momentum loss of the assisting gas towards the kerf exit.

Investigation into the laser remelting of zirconia surfaces in a nitrogen gas environment is carried out. The thermal stress fields during and after the laser treatment process are predicted numerically. The microstructural and morphological changes in the laser-treated region are examined using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The residual stresses are determined using the XRD technique. It is found that the residual stress predicted remains high along a depth of 50 µm below the laser-treated surface. The predictions of residual stress agree well with the XRD data. A fine dendritic structure is formed in the vicinity of the surface, which contributes to the surface hardness. In addition, transformation of t-ZrO2 to c-ZrO2 at high temperature is accompanied by the formation of ZrN in the surface vicinity.

Hastelloy G alloy has good high temperature strength and oxidation resistance. The hardness and tribological properties of the alloy surface can be improved through the laser nitriding process under a controlled environment. Laser gas assisted surface nitriding of Hastelloy G alloy is carried out using a CO2 laser. Temperature and stress fields in the nitrided layer are modeled using the finite element model. Metallurgical and morphological changes in the nitrided region are examined using SEM, energy dispersive spectroscopy, and X-ray diffraction. It is found that a uniform nitride layer is formed in the surface region of the workpiece and the depth of the nitride layer extends over 40mm below the surface. The nitride layer is free from cracks and surface abnormalities such as cavity and pores. Copyright # 2011 John Wiley & Sons, Ltd.

PurposeLaser bending is a good candidate to replace the flame bending process. The electrochemical response of laser bending region changes due to the microstructural modifications and high level of residual stress developed in the laser‐irradiated region after the bending process. Consequently, investigation into laser bending and microstructural changes in the irradiated region as well as the electrochemical response of bending section becomes essential. This paper aims to focus on the laser bending process.Design/methodology/approachThe laser bending of steel sheets was carried out. The microstructural changes in the bending region are examined using the scanning electron microscopy and X‐ray diffraction. The electrochemical response of the bended sections is investigated through potentiodynamic tests.FindingsIt is found that laser‐irradiated surface is free from cracks and cavitations. However, deep pit sites due to secondary pitting are observed in the bending sections.Research limitations/implicationsThe experiment is limited to certain thickness of the steel sheets. Increasing workpiece thickness reduces the bend angle. However, introducing high‐intensity laser beams improves the bend angle on the expense of high surface roughness in the bend section.Practical implicationsLaser bending process is involved with non‐mechanical tooling with low cost and precision of operation. Moreover, laser bending is a good candidate to replace the flame bending process. Consequently, laser bending finds application in industry. However, under the corrosive environment care should be taken.Originality/valueThe work presented is original and has not been published anywhere before. The findings will be useful for researchers and engineers working in the sheet metal forming area.

Laser hole cutting into Ti-6Al-4V alloy is carried out. Temperature and stress fields during the cutting process are predicted using the finite element code. Temporal variation of surface temperature in the region close to the kerf edge is monitored by a thermocouple and compared with the predictions. The residual stress formed in the cutting region is obtained from the XRD technique and compared with the predictions. The morphological changes around the kerf surfaces are examined incorporating optical and scanning electron microscopes. It is found that von Mises stress attains slightly higher values at the top circumference as compared to that corresponding to the bottom circumference of the hole cut. The prediction of temperature variation agrees well with the thermocouple data. The residual stress predicted also agrees with the results of the XRD technique.

High stresses formed around the laser cut edges limit the practical applications of the parts produced. In the present study, laser cutting of small diameter hole into Ti–6Al–4V alloy is carried out. Temperature and stress fields developed in the cutting region are simulated, in line with the experimental parameters, via incorporating the finite element code. The temperature predictions are validated with the thermocouple data. The residual stress developed at the vicinity of the cut surface is obtained using the XRD technique. The features of the hole section are examined using the optical and scanning electron microscopes. It is found that temperature decay is gradual, due to the annealing effect, in the region where the cutting ends; in which case, the peak value of von Mises stress reduces in this region. The residual stress predicted agrees well with the data obtained from the XRD technique.

Laser control melting of silicon surface is carried out at nitrogen gas environment and temperature rise as well as thermal stress developed in the irradiated region is simulated using the finite element method. The residual stress developed in the surface region after the laser treatment is measured using the XRD technique and the measurement results are compared with the predictions. The fracture toughness of the laser treated surface is also measured using the indentation tests. The structural and morphological changes in the laser irradiated region are examined using the scanning electron microscope. It is found that β phase silicon nitride was formed in the surface region of the laser treated workpiece. The temperature gradient close to the laser beam spot attains significantly high values due to the high heating and cooling rates. This, in turn, results in high stress levels in this region during the laser treatment process. The laser treated surface was free from the defects including microcracks, ...