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Titanium alloys require a special protecting atmosphere during the fabrication process due to their strong affinity with oxygen and nitrogen elements at high temperatures. In this study, the effects of different protection conditions on microstructure, phase characteristics, interstitial elements absorption and microhardness of additively manufactured Ti–6Al–4V alloy by direct laser deposition method have been investigated. Fabrication of specimens with similar laser parameters was carried out in three different protection conditions consist of air, closed box and argon shower. Characterization of samples was performed by utilization of OM, SEM, XRD, inert gas fusion method, micro-hardness and tensile strength analysis. Results indicated that fabrication of samples in an air atmosphere without proper protection leads to 2.5% spherical porosities, TiO2 and TiN formation in top layers, changing the c/a ratio from 1.59 to 1.61, absorption of 1870 and 500 ppm oxygen and nitrogen and 155 HV increment in micro-hardness value. Also, uncommon semi-globular microstructure in different locations of samples has been observed. The special protective atmosphere provided by argon shower led to 6.3% spherical porosities, negligible lattice parameter variation and martensite microstructure formation. It was found that in the optimal protection condition that was provided by a closed box, the typical basketweave microstructure with less than 1% porosity and 960 and 140 ppm oxygen and nitrogen absorption were achieved, which did not exceed the standard limits. In addition, the mechanical properties of UTS tensile strength, yield strength and elongation, were obtained 1042, 893 MPa and 13.2% respectively.

In this study, nanostructured WC-12Co powder was produced by ball milling and then agglomerating by spray drying. The produced nanostructured WC-12Co powder was used for laser cladding of AISI 321 stainless steel substrate. In order to evaluate the effect of argon shroud protection, the cladding process was performed with and without argon shroud protection. Microstructural and phase characterization showed that argon shroud protection can reduce the WC decarburization and the relative fraction of WC phase in clads reached up to 74%. In addition, microhardness and porosity percentage of the clads with argon shroud protection showed a significant improvement in comparison with the clads without argon shroud protection. The microhardness (to 2200 HV) and wear resistance increased and the porosity percentage decreased to less than 1%.

The present study investigated the effect of laser input energy on the quality and mechanical behavior of a 304 stainless steel–polyamide 6 joint in the laser-assisted metal and polymer direct joining (LAMP) method experimentally and numerically. After the proposed heat transfer model was validated, it was determined whether there was an optimal amount of laser input energy that could produce a joint with favorable quality and mechanical behavior. Among different laser input energies used in this study, 28-J/mm energy can provide more uniform and extensive wetting of the metal surface by the polymer, while excessive polymer degradation in the joint zone was prevented. As a result, an optimal combination of strength and toughness of the joint would be achieved. Further, it was found that the crystallinity of the polymer in the joint zone had a significant effect on the joint toughness so that the maximum toughness of the joint was recorded for the laser input energy of 50 J/mm, despite the reduced effective joint area due to excessive thermal degradation of the polymer in the joint zone.

AISI 420 Martensitic stainless steel is the major precursor for steam turbine blades. Under the operational conditions of the steam turbine, this steel undergoes erosion because of the impingement of water droplets. The aim of this research is the laser cladding of NiCr and NiCr–TiC powders and producing metal matrix composite NiCr–TiC on stainless steel substrate to enhance the rigidity and erosion resistance of AISI 420 stainless steel. The laser cladding was performed using pulsed Nd: YAG laser with concurrent powder injection. By setting the powder feeding rate, power, and laser scanning rate, the effect of each parameter on the laser cladding process was investigated and the optimal parameters for laser cladding were chosen. The elemental, phasic, and microstructural assessments and characterizations of the obtained coatings were done by optical microscope, scanning electron microscope, alongside energy dispersive spectroscopy (EDS), X-ray diffraction. It was observed that the structure of the clad from the interface upwards consists of cellular, columnar, and coaxial dendrites. It was also seen that the hardness of the composite clad containing reinforcement particles was far greater than that of cladding without such particles because of the increased effect of nucleation and the presence of TiC particles. It was also found that the weight loss of the composite clad of NiCr–TiC was less than that of NiCr and stainless steel substrate, while its erosion resistance was greater compared to NiCr and steel substrate.

The present paper addresses the solidification cracking during laser cladding of Inconel 718 powder on A-286 iron based superalloy which is known as hot crack susceptible alloy. Linear regression analysis was performed to propose empirical-statistical correlations between the key processing parameters and the geometrical attributes of single laser clad tracks. These correlations were used in the development of a processing map to study the effects of geometrical characteristics on the solidification cracking and the required conditions to obtain crack-free clads. The solidification cracking of the single clad tracks was inspected by macrostructural examinations using scanning electron microscopy in backscattered electron mode. The processing map revealed that the dilution ratio is the governing macrostructural attribute to avoid solidification cracking. The role of this macrostructural feature in reducing the susceptibility of fusion zone to solidification cracking is discussed.

In order to obtain the knowledge about the formation of the oriented structure in the additive manufacturing process, it is required to gain an accurate understanding about the formation and growth of grains. Hence, in this paper, the simulation of laser metal deposition was performed by the volume of fluid technique to predict the primary dendritic arm spacing, fluid flows, and geometry of the deposited layer. Moreover, the laser metal deposition of the Inconel 718 superalloy was performed experimentally to verify the results of simulation. From the results of simulation, a maximum error of about 8% was observed in the prediction of the geometry of the deposited layer. In addition, the difference between the value of primary dendritic arm spacing in the experimental and simulation results was about 14%. The results have also shown that a cellular dendritic structure was formed when the ratio of the temperature gradient to the cooling rate was more than 9 × 108, while when this ratio was less than 9 × 108, a columnar dendritic structure was formed. The results of simulations and experiments showed that an increase in the laser power from 350 to 450 W led to an improvement of about 9.5% in the size of primary dendrite arms due to the reduction in the temperature gradient, while the increase in the scanning speed from 3 to 5 mm/s resulted in a reduction of about 21% in the size of primary dendrite arms due to the faster cooling rate.

A bond coating of NiCrAlY followed by top coating of Al2O3/YSZ has been applied on an Inconel-718 using an air plasma spraying method, and radiation of a Nd-YAG laser was used to glaze the coated samples. The hot corrosion response of the coatings was measured in 55%V2O5 + 45% Na2SO4 at a temperature of 1000 °C for 3 and 30 h. Leaching of Y2O3 from YSZ, due to the reaction of V2O5 and Na2SO4, was found to be the major reason for the corrosion. Eventually, this led to the formation of YVO4 and tetragonal (t) zirconia to monoclinic (m)-ZrO2 phase transformation. In parallel, the volume fraction of m-ZrO2 in the sprayed coating decreased from 62 to 46%. Reduction of the m-ZrO2 in the glazed coating indicated an improvement of hot corrosion resistance. The results demonstrate that the existence of a dense Al2O3 layer on the upper surface of the sprayed coating led to increased resistance against corrosion. In addition, the laser operation reduced the surface roughness leading to the reduction of the reactive specific surface and the effective contact area between the corrosive materials and the glazed layer.

It is requisite in laser-aided direct metal deposition (LADMD) to investigate the influence of three key process parameters (laser power, scanning speed, and powder feeding rate) on geometric characteristics of single-track deposits so as to acquire LADMD deposits with minimum defects and controlled geometric accuracy. In this study, LADMD of Inconel 718 superalloy was studied and the dependency of geometric characteristics on key process parameters was investigated as a combined parameter (PαVβFγ). A simple empirical-statistical modeling was used employing linear regression method. The results showed that the geometric characteristics had a linear relationship with a combined parameter including three/two key process parameters together. The height and wetting angle of single-track deposits were dependent on P2V−1F1 and P3/2V−1F1, respectively. The width of single-track deposits was dependent on P2V−1/4 but it was independent of powder feeding rate. The dilution of single-track deposits depended on V1F−1 while laser power had no effect on it. A process map is developed to enable optimization of the process parameters in LADMD process of Inconel 718.

This research investigates the wear performance of WC-12Co and electroless Ni/WC-Co deposits at high temperature. Dry sliding wear experiments were carried out for coated and uncoated steel substrate against alumina pin. The microstructure and wear performance of laser-cladded WC-Co and Ni/WC-Co were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques. The mass reduction, friction coefficient, and wear rate of Ni/WC-Co deposits were measured and found to be significantly lower than WC-Co coatings. Due to the presence of Ni coating around the particle of the Ni/WC-Co coating, it showed a lower microhardness, more homogeneous microstructure, and a higher wear performance compared to WC-Co coating. The results of this paper indicated that the dominant mechanisms in wearing distance were adhesive, abrasive, and pulling out from the particles.

The aim of the present research was to investigate the effect of laser surface treatment on the thermal shock behavior of plasma sprayed Al2O3/YSZ multilayer thermal barrier coatings. In this regard, specimens of Inconel 718 were sprayed with Ni–22Cr–10Al–Y bond coat and Al2O3/YSZ top coat using an atmospheric plasma spraying approach. Then, top surfaces of specimens were under exposed to Nd-YAG laser radiation and thereby were glazed. Thermal stabilities of both coatings were evaluated by rising the environment temperature up to 1000 °C, keeping at this temperature for 15 min, and also rapid cooling of specimens in cold water. Using FESEM with EDS and XRD, the microstructure and morphology observations, elemental investigations and also phase identification were carried out. Findings displayed that both sprayed and glazed coatings were damaged as a spallation of top coats. Furthermore, by checking the life-time of coatings, the number of thermal cycles led to 20% destruction of top surfaces of coatings, increased from 232 cycles in sprayed coating to 325 cycles in laser glazed Al2O3/YSZ multilayer coating which displayed 40% improvement of thermal shock resistance after laser glazing process. This enhancement in resistance to thermal shock was due to strain adaptability improvement via a network of segmented cracks on the top surface produced by laser glazing process.

The present study investigated the effect of TIG and laser cladding of Inconel 625 coating over an Inconel 738 substrate on its hot corrosion resistance. The hot corrosion test was performed by exposing the specimens to Na2SO4–60 wt%V2O5 salt at 900 °C for 36 h. Microstructural, elemental, and phase characterization was performed using a field emission scanning electron microscope (FESEM) equipped with an energy dispersive spectrometry (EDS) detector and an X-ray diffractometer (XRD). The microstructural evaluation did not show any crack or pore in the laser-cladded specimen, but revealed a series of cracks at the surface and coating-substrate interface of the TIG-cladded specimen. The phase formed in the coated and uncoated specimens was found to be ϒ-Ni. The results were also indicative of the formation of chromium oxide, nickel oxide, NiCr2O4 spinel, and NiCO3 after the corrosion test. The corrosion-affected areas in the laser-cladded specimen, TIG-cladded specimen, and uncoated specimen had a thickness of approximately 40 ± 5 μm, 80 ± 10 μm, and 130 ± 10 μm, respectively. The results demonstrated the superior hot corrosion resistance of the laser-cladded specimen, as compared to its TIG-cladded and uncoated counterparts.

The evaluation of hot corrosion behavior of sprayed and laser glazed YSZ + Al2O3 composite coatings was conducted in the presence of 55% V2O5 + 45% Na2SO4 molten salt was conducted. Inconel 718 coupons were sprayed with a Ni–22Cr–10Al–1Y bond-coat and then with an YSZ–Al2O3 top-coat as composite coatings. The sprayed coatings were glazed using a Nd:YAG laser. The results displayed that both coatings illustrated similar mechanisms of hot corrosion. However, the reaction between corrosive molten salt with Y2O3 and production of YVO4, leaching Y2O3 from YSZ, led to a destructive phase transformation of tetragonal-ZrO2 phase (t-ZrO2) to monoclinic-ZrO2 phase (m-ZrO2) and production of YVO4, accompanied by 3–5% volume expansion during cooling which could lead to cracking and degradation of TBCs. Findings revealed that by comparing the destabilization fractions of coatings, the content of m-ZrO2 fraction decreased from 80% in sprayed coating to 47% in laser glazed YSZ + Al2O3 coating, which displayed double improvement of hot corrosion resistance in laser glazing process. Reduction of the reaction between molten salt and zirconia stabilizer was the result of a surface roughness decrease and a specific reactive surface gained by laser glazing process.

In this research, a volume of fluid (VOF) model was developed to investigate the effect of laser deposition parameters on the geometry of molten pool and deposited layer in the Inconel 718 superalloy. For this purpose, the process parameters of laser power, laser beam diameter and scanning speed were considered to estimate the geometric characteristics of the molten pool and deposited layer. In the following, the laser deposition process of Inconel 718 superalloy was carried out experimentally to validate the results of simulation. It was observed that an increase in the laser power from 100 to 400 W resulted in an improvement in the length, width and depth of molten pool, while an increase in the values of laser beam diameter (from 1 to 2 mm) and scanning speed (from 2 to 10 mm s−1) was associated with a reduction in the length, width and depth of molten pool. From the results of both simulation and experiments, a reduction was observed in the wetting angle of deposited layer when the values of laser power and scanning speed increased up to 400 W and 10 mm s−1 respectively, while the increase of feeding rate from 48 to 62 mgr s−1 indicated an improvement in the wetting angle. It was also observed that the maximum penetration depth was obtained in the rear part of molten pool due to Marangoni convection currents that pushed the melt toward the end of molten pool. The comparison of the experimental results and those predicted by the VOF model indicated that the model is capable of predicting the shape of deposition layer with sensible error.

Laser cladding of Ti-6Al-4V powder on a substrate with the same chemical composition was performed at different laser powers. The effect of laser power on the microstructure and corrosion behavior was then investigated. Electrochemical studies were performed by potentiodynamic polarization tests in different corrosive environments (3.5% NaCl, 2% H2SO4 and 5% HCl solutions). Microstructural investigation together with phase characterization revealed that laser cladded Ti-6Al-4V coatings were composed of needle-like martensite (ɑ/) and coaxial hexagonal compact (ɑ) phases. The coatings were crack-free; however, some cavities were observed in the coatings produced at high laser powers. In all three corrosive environments, the coatings showed a more noble corrosion behavior compared to the untreated substrate. The results showed that corrosion potential increases from −410 (mV) to −130 (mV) in NaCl and from −50 (mV) to −20 (mV) in H2SO4 enviroments but decreases from −60 (mV) to −270 (mV) in HCl solution. Increasing laser power had a positive effect on the corrosion behavior in NaCl and H2SO4 solutions; however, it had a negative effect on the corrosion behavior in HCl solution.

In this paper, formation of uniform and large-area micro/nanostructures on pure aluminum surfaces using a continuous-wave laser irradiation is presented. Gold nanolayer coating was utilized as a confinement layer for controlling the possible hydrodynamic phenomena in a molten area. Dependency of the laser-induced morphology on the thickness of a gold coating was investigated in this regard. Scanning electron microscopy, energy dispersive spectroscopy, grazing test of the X-ray diffraction, and optical absorption/reflection spectroscopy in UV/visible/IR ranges were employed to characterize the samples. Results showed that the formation of uniform structures of average sizes of 50 nm-5 μm on aluminum surface was possible following the irradiation of a continuous-wave CO2 laser, delivering 130 W beam power. Alterations of the surface morphology brought about an increase in specific absorption peaks at the UV region and the appearance of an absorption peak in the visible range. In addition, these structure-covered surfaces provided interesting reflection behaviors in different spectral areas, which can clearly reflect their high potential to be used as selective solar absorbers. The results of this investigation indicated that optical characteristics such as absorption and emission coefficients as well as ξ factor were 0.98, 0.13, and 7.53, respectively. It can therefore be concluded that this process can be considered an efficient and fast technique to fabricate selective solar absorbers.

The purpose of this study was to investigate the microstructure of the Ni base Inconel 625 coatings that were fabricated on the Inconel 738 substrate with two processes of laser cladding and TIG cladding. For this purpose, single-pass samples were precipitated to obtain optimal parameters. In the laser cladding method, laser power, laser scanning rate and powder feed rate were considered as variables, and current and its type were considered as variables for the TIG method. Based on the results, using the parameters of optimum single-pass samples that were free of porosity, crack and had minor geometric dilution, coatings were applied in both methods with 50% overlap. In order to microstructural, elemental and phasic characterization, field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used. Based on the results, the microstructure of coatings from surface to interface of coating/substrate consists of coaxial, columnar and cellular structure dendrites, respectively, and the laser coating has a finer microstructure due to the higher cooling rate. In addition, the austenite, carbide and Laves phases were observed in both coatings.

In this investigation, nickel (Ni)-coated WC-12Co powder was produced using an electroless nickel‑phosphorus (Ni-P) plating process and then used as a feedstock material for laser cladding of AISI 321 stainless steel substrate. The correlations that exist between key operational parameters of the process (i.e., laser power, scanning speed, powder feeding rate) and geometrical characteristics for single claddings (i.e. height, width, dilution, and wetting angle) were predicted and analyzed by regression analysis method (RA). A processing window for laser cladding of Ni-coated WC-12Co powder on AISI 321 stainless steel was developed based on an empirical-statistical model and the processing window was compared with that for laser cladding of commercial WC-12Co powder without nickel coating. Furthermore, the influence of using Ni-coated WC-12Co powder on the microstructure and microhardness was investigated and compared with those of laser cladded commercial WC-12Co claddings. The results showed that the use of Ni-coated WC-12Co powder could significantly reduce the porosity percentage and lead to high-quality claddings.

In this study, the oxidation behavior of WC-12Co and electroless Ni/WC-Co coatings is investigated by Thermogravimetric analysis (TGA), X-Ray Diffraction (XRD), and scanning electron microscope (SEM). Time dependence of weight gain showed a linear behavior for WC-Co coating and a parabolic-like behavior for Ni/WC-Co coating. This behavior is related to the reaction-controlled and diffusion-controlled oxidation processes in the WC-Co and Ni/WC-Co coatings, respectively. Oxidation resistance of coatings was determined by phase composition and formation mechanism of the protective oxide layer. The results demonstrated that the use of Ni/WC-Co powder could reduce significantly the porosity and cracks and lead to a compact and protective (Ni, Co)WO 4 layer. The apparent activation energy was measured to be about 98.3 and 229.4 kJ/mol for WC-Co and Ni/WC-Co coatings, respectively.

In this article, Ti-6Al-4V powder alloy was directly deposited on Ti-6Al-4V substrate using laser cladding process. In this process, some key parameters such as laser power (P), laser scanning rate (V) and powder feeding rate (F) play important roles. Using linear regression analysis, this paper develops the empirical-statistical relation between these key parameters and geometrical characteristics of single clad tracks (i.e. clad height, clad width, penetration depth, wetting angle, and dilution) as a combined parameter (PαVβFγ). The results indicated that the clad width linearly depended on PV−1/3 and powder feeding rate had no effect on it. The dilution controlled by a combined parameter as VF−1/2 and laser power was a dispensable factor. However, laser power was the dominant factor for the clad height, penetration depth, and wetting angle so that they were proportional to PV−1F1/4, PVF−1/8, and P3/4V−1F−1/4, respectively. Based on the results of correlation coefficient (R > 0.9) and analysis of residuals, it was confirmed that these empirical-statistical relations were in good agreement with the measured values of single clad tracks. Finally, these relations led to the design of a processing map that can predict the geometrical characteristics of the single clad tracks based on the key parameters.

The aim of this study is to synthesize MgO–Y2O3 nanocomposite by combustion sol–gel method from sucrose as a combustion agent. The influence of the ratio of sucrose (Su) to the transition metals (TM) on the phase and particle size of the composite nanopowder was investigated using a combination of X-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy techniques. In order to prediction of phase growth, the kinetics of crystallization of MgO–Y2O3 nanocomposite was also studied in the isothermal conditions using a differential scanning calorimetric technique. Results show that increasing the concentration of sucrose reduced the particle size from 29.3 to 21.6 nm. The ratio of Su to the TM optimized on 4 value. The Avrami exponent was found to be about 3 indicating 3-dimensional growth. The activation energy of crystallization was also determined to be 34.9 ± 0.01 kJ mol−1. Finally, the TEM results confirmed the 3-dimensional growth of MgO–Y2O3 nanopowders.

Due to very high strenght, low thermal conductivity, and high work hardening rate, the machinability of nickel-based superalloys is poor at room temperature. Laser-assisted machining (LAM) can provide a better aspect of machining such alloys. Since the wavelength of Nd:YAG laser is about 1/10th of that of CO2 laser, absorption and heating efficiency of Nd:YAG laser is much higher on metals and especially superalloys. Transmission of Nd:YAG laser through fiber optics to the heating point on the workpiece is a simple task during machining. This makes the LAM process more convenient and practical than the CM process. In this study a model is introduced for LAM of waspaloy, and its machinability is evaluated in terms of ease of material removal. Also, a temperature generation model is introduced for the Nd:YAG laser beam. Furthemore, wear behavior of an uncoated tungsten carbide and the formed chips were compared during the LAM and the CM of waspolay. To study the wear mechanism, the worn cutting tool was studied via scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The formed chips were also evaluated via SEM and optical microscopy. Based on the results, the optimum LAM conditions were obtained at a cutting speed of 24 m/min and a feed rate of 0.06 mm/rev when a 400 W laser mean power and 80 Hz frequency are applied. Under these conditions, the temperature ahead of the cutting tool edge on the surface of workpiece was estimated to be 524°C. In comparison with CM, a significant improvement in tool wear and a better chip morphology were achieved through LAM, and also specific cutting energy and surface roughness were reduced by 25 and 20%, respectively.

Creating laser texture on dental implants is a novel method for accelerating osseointegration and prolongation of lifespan. The purpose of this research was twofold: (1) Creating intersecting lines pattern with different angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) on the surface of Ti6Al4V, using pulse Nd:YAG laser with a wavelength of 1064 nm and a pulse length of 170 ns and (2) comparing optical and SEM images, EDS analyses, contact angles (CAs), and surface free energies (FEs) for different intersecting lines angles. CA and FE depended on the intersecting lines angle according to Y=Y0+Asin(xB+C), where Y is the CA or FE; x is the intersecting lines angle; and Y0, A, B, and C are constants. Oxygen was present on all samples. The lowest CA and the highest FE occurred at 60° intersecting lines. FE was independent of minor changes in the microgrooves' depth, intersections' number, and the number of texture lines.