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WC ceramic is considered one of the advanced engineering ceramics due to its favorable properties. The weakness of this ceramic is, however, its brittleness, which can be tackled by composite making and addition of compounds such as Co to the structure of WC. In this research, WC and WC-17Co powders were synthesized by the in-situ carbothermic reduction from active carbon raw materials including WO 3 and Co 3 O 4. The main goal of this research was to determine the appropriate amount of carbon in the composition of raw materials. For this purpose, the raw materials were mixed in different ratios of excess carbon as the primary variable. All the samples were heat treated with a heating rate of 10°C.min−1 to a temperature of 1200°C for 3 h in a hydrogen atmosphere. Thermodynamic studies showed that cobalt and tungsten were regenerated from Co 3 O 4 , and WO 3 at the temperature of 250°C and 700°C, respectively; by raising the temperature to about 1200°C, the formation of tungsten carbide was complete. According to the results, a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) and X-ray diffraction pattern (XRD) were obtained. The main reason for the lack of carbon in the total production of the WC phase was the reaction of carbon with hydrogen in the furnace atmosphere at temperatures less than 500°C, which could be solved by adding further carbon to the raw materials. The combinations (118.37gr WO 3 -147.06gr C) and (56.95gr C-23.15gr Co 3 O 4 -98.25gr WO 3) created the best conditions for the production of WC and WC-17Co powders. The results of microstructural studies also showed that the size of grains in the WC-17Co composite powder was larger (less than 200 μm) than that in the WC ceramic powder (less than 20 μm). This was related to the presence of Co 3 O 4 in the raw materials and cobalt in the WC-17Co cermet powder. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • The wear behavior of laser cladded of Ni-coated WC-12Co powder on AISI 321 stainless steel was investigated at 500°C. • The electroless Ni pre-coating offered a more homogeneous microstructure and lower microhardness compared to WC-Co coating. • The laser cladding process of WC-Co and Ni/WC-Co deposits reduced the friction coefficient and its fluctuations. • The Ni/WC-Co coating revealed enhanced wear resistance compared to WC-Co coating. [ABSTRACT FROM AUTHOR]

Highlights • The coatings created by the laser and TIG cladding methods were crack- and pore-free. • The corroded area in the laser cladded sample was thinner than that of the TIG cladded. • The laser cladded samples have a noticeably better hot corrosion resistance than the TIG cladded and the uncoated samples. Abstract 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 Na 2 SO 4 –60 wt%V 2 O 5 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, NiCr 2 O 4 spinel, and NiCO 3 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. [ABSTRACT FROM AUTHOR]

Highlights • Improvement of hot corrosion behavior of YSZ–Al 2 O 3 coating by laser glazing. • Similar mechanisms of hot corrosion for both types of coatings. • Reduction of content of m-ZrO 2 fraction from 80% in sprayed to 47% in glazed. • Reduction of roughness from 9.67 to 2.86 µm by laser glazing process. • Reduction of specific reactive surface gained by laser glazing. Abstract The evaluation of hot corrosion behavior of sprayed and laser glazed YSZ + Al 2 O 3 composite coatings was conducted in the presence of 55% V 2 O 5 + 45% Na 2 SO 4 molten salt was conducted. Inconel 718 coupons were sprayed with a Ni–22Cr–10Al–1Y bond-coat and then with an YSZ–Al 2 O 3 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 Y 2 O 3 and production of YVO 4 , leaching Y 2 O 3 from YSZ, led to a destructive phase transformation of tetragonal-ZrO 2 phase (t-ZrO 2) to monoclinic-ZrO 2 phase (m-ZrO 2) and production of YVO 4 , 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-ZrO 2 fraction decreased from 80% in sprayed coating to 47% in laser glazed YSZ + Al 2 O 3 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. [ABSTRACT FROM AUTHOR]

Abstract 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% H 2 SO 4 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 H 2 SO 4 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 H 2 SO 4 solutions; however, it had a negative effect on the corrosion behavior in HCl solution. Highlights • Laser cladded Ti-6Al-4V powder on Ti-6Al-4V substrate using a Nd:YAG laser. • The effect of the laser cladding process on microstructure was investigated. • The corrosion behavior in different solution after laser cladding on Ti-6Al-4V alloy was evaluated. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • Comparison of microstructure of IN-625 coatings applied to IN-738 by laser and TIG cladding methods for the first time. • The coatings created by the laser-cladding and TIG cladding techniques were crack and pore free. • The microstructure of the coating created by laser cladding is finer than that created by TIG due to the higher cooling rate. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys including Inconel 718(IN718) are widely used in aerospace industries due to their superior high temperature strength, toughness, and corrosion resistance. These alloys are difficult to machine mainly because of their low thermal conductivity and high work hardening rate, which cause steep temperature gradient and high cutting forces at the tool edge. The application of laser assisted machining is the subject of many new researches since shear forces; surface coarsening and tool wear are reduced. The aim of this investigation was to evaluate laser assisted machining behavior of a 718 Inconel superalloy from the view point of machining specific energy, surface roughness, tool wear and chip appearance. Experimental apparatuses used included optical and scanning electron microscopy, spark emission spectroscopy, and EDS analysis. The results indicated that increasing the temperature to about 540 °C just ahead of primary shear zone, can result in 35% reduction of machining specific energy, in comparison with conventional machining. Furthermore, surface coarsening and tool wear were reduced by 22% and 23% respectively. Flank wear was the main deteriorating factor on cutting tools during laser assisted machining. SEM micrographs indicated that increase in temperature has no noticeable effect on finished workpiece surface. Analysis of variance obtained from regression analysis indicated that frequency of laser beam has the most influential effect on temperature. The optimum conditions for laser assisted machining of 718 superalloy is suggested as follows: 80 Hz frequency, 400 W power, 24 m/min cutting speed, and 0.052 mm/rev feed rate along with 540 °C temperature, 2.51 J/mm 2 machining specific energy and 130 N cutting force. [ABSTRACT FROM AUTHOR]

• The Inconel 718 tracks were deposited on the Inconel 738 substrate via Direct Laser Deposition process. • The effect of three process parameters, namely scanning speed, laser power, and powder feed rate on the geometric characteristics of the deposited tracks were investigated. • Using full factorial Design of Experiment, 45 tracks were deposited for five levels of laser power, three levels of scanning speed, and three levels of powder feed rate. • The linear regression and optimization algorithm were utilized to define a compound parameter PαVβFγ and assess the effect of mentioned process parameters on the track characteristics. • Considering the obtained process parameters for geometric characteristics, a process map was drawn which is capable of predicting the geometric behavior of the track for various process parameters. Assessing the geometric characteristics of a track is the first step in indicating the results of the laser cladding process. In this research, the effect of three essential process parameters, namely scanning speed, laser power, and powder feed rate, on the geometric characteristics of the Inconel 718 track on the Inconel 738 substrate have been studied. The goal of this research was to obtain the optimal process parameters for Inconel 718 laser cladding. To investigate the impact of process parameters on the geometric characteristics, five levels of laser power, three levels of scanning velocity, and three levels of powder feed rate have been considered, and a full factorial design of experiment has been performed. Consequently, 45 tracks have been cladded, and their geometric characteristics, including penetration depth, wetting angle, track height, track width, and compound characteristics such as dilution, has been investigated. After analyzing the results, the behavior of the geometric characteristics for the same process parameters in other brackets have been predicted via linear regression and genetic optimization via MATLAB software. P α V β F γ is participating in Y = a X + b as a compound variable. The regression process is feasible via accurate estimation of exponents α , β and γ. Therefore, the genetic algorithm was used to reduce the errors of linear regression. It is concluded that all of the process parameters have quantitative and qualitative effects on the geometry of the track. Finally, based on the modeling results, a process map was drawn to predict the impact of process parameters on the track geometry. [ABSTRACT FROM AUTHOR]

Electroless Ni–P–SiC coatings are recognized for their hardness and wear resistance. In the present study, electroless Ni–P coatings containing SiC particles were co-deposited on Al356 substrate. Laser surface heat treatment was performed using 700 W Nd:YAG pulsed laser. Effects of different laser operating parameters, such as laser scan rate, laser average power and defocusing distance on microstructures were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The results of microstructural characterization indicated that the laser treatment under different operating conditions produced composite coating contained nanocrystallined Ni-based matrix with SiC particles Ni 3 P, Ni 12 P 5 , Ni 5 P 2 , Ni 8 P 3 precipitates. The microhardness measurements showed that the hardness of the coating was increased up to 60%, due to laser heat treatment, without effect on base metal. [ABSTRACT FROM AUTHOR]

In this work, a study on Nd:YAG laser welding of Waspaloy sheets has been made. Microstructures, phase changes and hardness of the laser joint were investigated using optical microscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD) and vickers microhardness (HV0.3). Corrosion behavior of the weldment at low temperature in 3.5%wt NaCl solution at room temperature was also investigated using open circuit potential and cyclic potentiodynamic polarization tests. Hot corrosion studies were conducted on samples in the molten salt environment (Na 2 SO 4 –60%V 2 O 5 ) at 900 °C for 50 h. Results indicated that the microstructure of weld zone was mainly dendritic grown epitaxially in the direction perpendicular to the weld boundary and heat transfer. Moreover, the Ti-Mo carbide particles were observed in the structure of the weld zone and base metal. The average size of carbides formed in the base metal (2.97±0.5 µm) was larger than that of the weld zone (0.95±0.2 µm). XRD patterns of the weld zone and base metal showed that the laser welding did not alter the phase structure of the weld zone, being in γ-Ni(Cr) single phase. Microhardness profile showed that the hardness values of the weld zone (210–261 HV) were lower than that of the base metal (323–330 HV). Electrochemical and hot corrosion tests indicated that the corrosion resistance of the weld metal was greater than the base metal in both room and high temperatures. [ABSTRACT FROM AUTHOR]

In this work, Co–Cr–Mo powder is used to form laser clads on a γ-TiAl substrate. The single-track geometrical characteristics such as width, height, penetration depth, dilution and wetting angle play the important role to control the characteristics of laser clad coatings formed by overlap of individual tracks. This paper is investigated the relations between the main coaxial laser cladding parameters (laser power P , laser beam scanning speed S and powder feeding rate F ) and geometrical characteristics of single tracks by linear regression analysis. The results show that the clad height, H , depends linearly on the FS − 5/4 parameter with the laser power having a minimal effect. Similarly, the cladding width W is controlled by the PS −2/3 parameter. The penetration depth b and dilution, D are proportional to P 2 S −1/4 F − 1/4 and P 2/3 S 1/2 F −1/2 respectively and wetting angle is controlled by the P 1/4 S 1/2 F −1/2 parameter. These empirical dependencies are observed with high values of the correlation coefficient ( R >0.9). Finally, based on these relations, a laser cladd processing map was designed to use as a guideline for the selection of proper processing parameters for a required coating. [ABSTRACT FROM AUTHOR]

Yttria nanopowder was used to fabricate transparent yttria ceramics by spark plasma sintering at temperatures ranging from 1200 °C to 1600 °C for 20 min. The microstructure of fracture cross section and optical transmittance of the products were characterized by Field Emission-Scanning Electron Microscope (FE-SEM) and Fourier-transform infrared spectrophotometer (FTIR). With increasing the sintering temperature, densification occurs up to 1500 °C, whereas the mean grain size of yttria ceramics was first increased and then decreased markedly. The highest density and the lowest mean grain size of yttria ceramic reached to 99.58% and 0.53 μm at 1500 °C, respectively. The best in-line transmittance was at 1500 °C, with transmittance being about 80% in the range of 3–5 μm, which was close to the theoretical value of yttria. [ABSTRACT FROM AUTHOR]

Abstract: ZnO nanopigments with five different morphologies were synthesized by a simple low temperature hydrothermal process by using zinc nitrate hexahydrate without using additives. ZnO nanopowders were characterized by X-ray diffraction and field-emission scanning electron microscopy. Optical properties of the ZnO nanostructures were investigated by UV/vis/NIR spectrophotometer and room-temperature photoluminescence spectroscopy. The obtained results indicated that ZnO nanopigments had high UV absorption and vis/NIR reflectance. Sizes of ZnO powders were strongly affected by hydrothermal conditions and increased gradually with the increase of the reaction temperature. The UV absorption increased with the reduction of particle size and nanoparticles showed higher UV absorption at 332nm. The vis/NIR reflectance had the highest amount at sample 4 (with particle size distribution of 250–350nm). The photoluminescence spectra from the ZnO nanostructures revealed a strong UV emission peak at 380nm and no green emission band at ~530nm. The photoluminescence spectra of the other samples exhibited a broad emission peak at ~420nm and a weak visible green emission at 530nm. [Copyright &y& Elsevier]

Abstract: In this study, the effect of laser glazing on the hot corrosion behavior of nanostructured thermal barrier coatings (TBCs) was investigated. To this end, the hot corrosion test of plasma-sprayed and laser-glazed thermal barrier coatings conducted against 45wt.% Na2SO4 +55wt.% V2O5 molten salt at 910°C for 30h in open air atmosphere. The results obtained from hot corrosion test showed that the reaction between Y2O3 and the corrosive salt produced YVO4, leached Y2O3 from YSZ and led to the progressive destabilization transformation of YSZ from tetragonal to the monoclinic phase. The lifetimes of the plasma-sprayed TBCs were enhanced approximately twofold by laser glazing. Reducing the reactive specific surface area of the dense glazed layer with the molten salts and improving the stress accommodation through network cracks produced by laser glazing were the main enhancement mechanisms accounting for TBC life extension. [Copyright &y& Elsevier]

Highlights: [•] Surface of plasma sprayed CYSZ TBCs modified by a pulsed Nd:YAG laser. [•] A dense glazed layer produced on the surface of TBCs by laser treatment. [•] The specific reaction area was reduced after laser glazing. [•] The hot corrosion resistance of TBCs was enhanced more than twofold by laser surface glazing. [Copyright &y& Elsevier]

Abstract: Nanostructured scandia (4.6mol%), yttria (0.4mol%) doped zirconia (5SYSZ) and 7wt% yttria stabilized zirconia (7YSZ) thermal barrier coatings (TBCs) were produced by plasma spraying on nickel-based superalloy substrates with NiCrAlY as the bond coat. The thermal shock behavior of the two as-sprayed TBCs at 1000°C was investigated. The results indicated that the thermal cycling lifetime of 7YSZ TBCs was longer than the 5SYSZ TBCs due to the lower thermal mismatch stress between the ceramic layer and the metallic layer at high temperature. However, the nanostructured 5SYSZ coating had higher thermal stability than 7YSZ TBC. [Copyright &y& Elsevier]

Abstract: The main goal of this paper was to evaluate the effects of laser glazing on the microstructure and thermal shock resistance of nanostructured thermal barrier coatings (TBCs). To this end, nanostructured yttria stabilized zirconia (YSZ) top coat and NiCrAlY bond coat were deposited on Inconel 738LC substrate by air plasma spraying (APS). The Nd:YAG pulsed laser was used for laser treatment of top coat surface. The thermal shock behavior of plasma-sprayed and laser-glazed coatings was investigated by quenching the samples in cold water from 1000°C. The microstructure and phase composition of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Energy dispersive spectroscopy (EDS) was used to analyze the interface diffusion behavior of the bond coat elements. The results of SEM revealed that the laser glazing process reduced the surface roughness, eliminated the porosity of the surface and produced network cracks perpendicular to the surface. XRD results also indicated that both as-sprayed and laser glazed coatings consisted of non-transformable (T′) phase. Thermal shock test results showed that the lifetimes of the plasma-sprayed TBCs were almost doubled by laser glazing. Continuous network of segmented cracks perpendicular to the surface produced by laser glazing improved the strain accommodation and recognized it as the main enhancement mechanism for TBC life extension. [Copyright &y& Elsevier]

Abstract: Nanostructured thermal barrier coatings (TBCs) consisting of yttria stabilized zirconia (YSZ) ceramic top coat and NiCrAlY metallic bond coat were prepared by atmospheric plasma spraying (APS). The Nd:YAG pulsed laser was used for laser treatment of top coat surface. The microstructure and thermal insulation capability of plasma-sprayed and laser-glazed thermal barrier coatings were investigated. The microstructure and phase composition of the coating were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffractometry (XRD). The nanostructured plasma-sprayed coating contained non-melted or partially melted nanosized particles and columnar grains, whereas the microstructure of laser-glazed coating consisted of columnar grains in the fracture surface and equiaxed grains on the surface. Laser glazing, which helps to eliminate the surface porosities and other structural defects of coatings deposited by the plasma spraying method, should contribute to the improvement of their surface roughness. XRD results revealed that both as-sprayed and laser-glazed coatings consisted of non-transformable tetragonal (T′) phase. The results of the thermal insulation capability test indicated that the thermal insulation capability of the laser-glazed coating, as compared to the as-sprayed coating, was slightly lower due to the microstructural change in the glazed layer of top coat. [Copyright &y& Elsevier]

Abstract: The main goal of this paper was to evaluate and compare the microstructure and mechanical properties of plasma-sprayed nanostructured and conventional yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). To this end, NiCrAlY bond coat, nanostructured, and conventional YSZ coatings were deposited on Inconel 738LC substrate by atmospheric plasma spraying (APS). The mechanical properties of the coating were evaluated using nanoindentation and bonding strength tests. The microstructure and phase composition of the coating were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffractometry (XRD). The nanostructured YSZ coating contained both nanosized particles retained from the powder and microcolumnar grains formed through the resolidification of the molten part of the powder, whereas the microstructure of the conventional YSZ coating consisted of columnar grain splats only. The phase composition of the as-sprayed nanostructured coating consisted of the non-transformable tetragonal phase, while the conventional coating showed the presence of both the monoclinic and non-transformable tetragonal phases. The results of nanoindentation and bonding strength tests indicated that the mechanical properties of the nanostructured coating were better than those of the conventional coating. [Copyright &y& Elsevier]

Abstract: In this study, Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bond coat and then with a ceria and yttria stabilized zirconia (CYSZ) top coat by air plasma spraying (APS). After that, the plasma sprayed CYSZ thermal barrier coatings (TBCs) were treated using a Nd:YAG pulsed laser. The effect of laser glazing on the microstructure of the coatings was investigated. The microstructures and surface topographies of both as-sprayed and laser glazed samples were investigated using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The phases of the coatings were analyzed with X-ray diffractometry (XRD). The microstructural analysis results revealed that laser surface glazing of ceramic top coat reduced the surface roughness considerably, eliminated the surface porosities and produced a network of continuous cracks perpendicular to the surface. XRD patterns also showed that both as-sprayed and laser glazed top coats consisted of nonequibrium tetragonal (T′) phase. [Copyright &y& Elsevier]

Abstract: Thermal control coatings (TCCs) play an important role in thermal management of spacecrafts and satellites by their thermo-optical properties including low solar absorptance (α s) and high thermal emittance (ε t). In this research, two novel TCCs were prepared by incorporating the pre-synthesized MCM-41 and Zn-MCM-41 into the potassium silicate binder. The results of solar absorptance measurement show that both prepared coatings are able to reflect almost all UV radiation and therefore they are much less susceptible to solar radiations than conventional TCCs. In addition to, the lower pigment to binder ratio (PBR) and dry film thickness (DFT) are attainable with these novel TCCs, that finally lead to weight reduction, improvement of mechanical properties and lower porosity. [Copyright &y& Elsevier]

Abstract: In the present work, well-dispersed two new structures of scale- and spindle-like ZnO were successfully synthesized by using zinc nitrate hexahydrate as the starting material and also the low temperature hydrothermal process and any additional surfactant, organic solvents or catalytic agent. The ZnO structures were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Optical property of the ZnO structures was investigated by room-temperature photoluminescence (PL) spectroscopy. The results revealed that ZnO powders have hexagonal (wurtzite-type) crystal structure and a large amount of well-dispersed ZnO scale- and spindle-like structures was formed. The thickness of scales was in the range 40–60nm and the diameter of spindles was in the range 50–70nm. Room-temperature PL spectra from the ZnO structures showed a weak UV emission peak at ∼382nm and a very strong visible green emission at ∼530nm, that was ascribed to the transition between VoZni and valence band. [Copyright &y& Elsevier]

Abstract: In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ; ZrO2−25wt%CeO2−2.5wt%Y2O3) topcoat by air plasma spraying (APS). Hot corrosion studies of plasma sprayed thermal barrier coatings (TBCs) were conducted in 45wt%Na2SO4+55wt%V2O5 molten salt at 1000°C for 30h. The results showed that the coating defects, such as pores and microcracks play important roles as effective paths for the salt penetration in hot corrosion. Based on the results, the reaction between molten salt and stabilizers of zirconia (Y2O3 and CeO2), the formation of YVO4, CeVO4 and CeO2 crystals, the detrimental phase transformation of zirconia from tetragonal to monoclinic due to the depletion of stabilizers and finally, the creation of stresses were recognized to be in the degradation mechanism of CYSZ ceramic coatings in the presence of molten sulfate–vanadate salt. [Copyright &y& Elsevier]

Abstract: In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ) topcoat by air plasma spraying (APS). After that, the plasma sprayed CYSZ thermal barrier coatings (TBCs) were treated using a pulsed Nd:YAG laser. The effects of laser glazing on the microstructure and thermal shock resistance of the coatings were evaluated. Thermal shock test was administered by holding specimens at 950°C for 5min and then water quenching. More than 20% of the spalled region of the surface of the topcoat was adopted as the criterion for the failure of samples. The microstructures of both the as processed and the tested TBCs were investigated using scanning electron microscope (SEM). The phases of the coatings were analyzed with X-ray diffractometry (XRD). XRD analysis revealed that both as sprayed and laser glazed topcoats consisted of nonequilibrium tetragonal (T′) phase. The results showed that the life times of the as sprayed TBCs were enhanced around fourfold by the formation of a continuous network of segmented cracks perpendicular to the surface and the increase in strain accommodation. [Copyright &y& Elsevier]

• The thermal-mechanical simulation of the coating was carried out in order to investigate the residual stresses and strains. • The most important factors for the formation of crack in the coating layer are the geometrical shape of the cladding. • When the wetting angle of the coating is less than 44º, the stress concentration is maximized at the top of the coating. • When the wetting angle is more than 44º, the stress concentration the crack formation is transferred to the substrate. In the present research, thermal–mechanical simulation of laser cladding of Stellite 6 powder on X19CrMoNbVN11-1 steel substrate was carried out to study the influence of scanning speed and laser power on the remaining stresses/strains and thus the formation of cracks in the cladding layer. In order to demonstrate the accuracy of the simulation results in prediction of the crack formation, the laser cladding process was also implemented experimentally. The results have shown that the highest temperature of the molten pool (1753 °C) was obtained at a laser power of 250 W, a powder injection rate of 0.3 g/s and a scanning speed of 3 mm/s. With the increase in scanning speed, the geometric shape of the cladding layer has changed from a semicircle to an oval shape. Moreover, at low scanning speed, the maximum strain is produced in the substrate and at high scanning speed, the maximum strain is created at the top of the coating layer. The lowest value of residual stress and strain was obtained at a scanning speed of 3 mm/s, while at a scanning speed of 5 mm/s the highest value of residual stress and strain was obtained. Furthermore, when the wetting angle is greater than 44°, the stress concentration is transferred from the top of the cladding layer to the substrate and the possibility of crack formation decreases. [ABSTRACT FROM AUTHOR]

• Tungsten-Carbide particles with the Nickel coat is synthesized. • The synthesized WC-Ni powder was used laser cladding of AISI 321 substrate. • The effect of laser cladding parameters on geometrical shape of clads was studied. • Improvement of mechanical behavior was observed by WC-Ni laser cladding. In this study, The WC-Ni composite powders were fabricated by the electroless plating of nickel-phosphorus, followed by the appliance of the obtained particles as a coating on an AISI 321 steel by laser cladding method. Effects of main laser parameters, including power, scanning speed, and powder feed rate on the geometric properties were reviewed. The optimum single-pass specimen was chosen after considering the geometrical shape, dilution, and crack and porosity amount of the single-pass specimens. It was found that the increase in laser power and powder feed rate results in the rise of the height and the width of the coatings. In contrast, coatings with lower height and width were achieved by employing lower laser power and powder feed rates. The procedure was followed by the laser cladding of the WC-Ni powders on 321 steel substrate under the optimum coating parameters with a variety of overlap amounts; 30, 50, and 70 percent. By investigating the formed phases and microstructure of the overlap specimens, the 70 percent overlap coating was chosen as the optimal one. Mechanical and wear tests were conducted on the optimal overlap specimen. Experiments indicated that the hardness, elasticity modulus, and fracture toughness of the coating were, respectively, 1457 Vickers, 6.24 Mpa.m1/2, and 250 GPa. The micro-hardness of the WC-Ni coating was 1.2–1.6 times higher than the WC-Ni, WC-Co and WC-Co-Ni coatings, made by thermal spray coating. Also, the toughness of the coating was 1.5 times higher than the WC-Co thermal sprayed coat. The elasticity modulus of the WC-Ni coating (250 GPa) was 1.1 times more than the WC-Co coating manufactured with the laser cladding method. [ABSTRACT FROM AUTHOR]

WC-Co coating, which is a subcategory of Tungsten Carbide-based coatings, is prominent among a variety of industries. However, because of its expense, poisoning, and low corrosion resistance of Cobalt in acidic environments, alternative compositions have been designed. One of these alternatives is the Iron Aluminide intermetallic compound which can replace Cobalt. This study investigates laser cladding of WC-FeAl powder on a 321 Stainless-Steel substrate. WC-FeAl powders were synthesized by mechanical alloying of initial Aluminum and Iron powders, milled for 20 h, followed by an hour of annealing at 800 degrees Celsius. Then, the annealed particles were mechanically alloyed with WC powders for 50 h. The result of the X-ray diffraction (XRD) analysis showed that no brittle and destructive phase was formed during synthesis. Subsequently, powders were coated on the stainless-steel substrate by laser cladding method. Effect of the main parameters of the laser cladding, including laser power, laser probe velocity, and powder spray rate, on the coating properties, such as porosity, geometry, thickness and, dilution were studied. Results indicate that with a higher power of the laser, the penetration depth and the width of the coating increased. Besides, with a higher velocity of the laser probe, dilution and penetration depth decreased. Furthermore, the Higher rate of powder spray led to a thicker coating. The optimum parameters of different samples were 250 W power, 4 mm/s probe velocity, and 400 mg/s powder spray rate. Evaluation of the mechanical properties indicated that the 1600 Vickers hardness, 5.7 MPa.m1/2 fracture toughness, and 355 GPa Young's modulus were obtained. Besides, The evaluation of the mechanical properties of the coating showed that the hardness, fracture toughness, and elasticity modulus are 1600 V, 5.7 MPa.m1/2, and 355 GPa respectively. Obtained results revealed that in comparison with the WC-FeAl composite coating with 500 ppm additional Boron and WC-Co coating both fabricated by thermal spray coating, for the WC-FeAl coating studied in this investigation, respectively the hardness is 1.16 and 1.21 times higher and the fracture toughness is 2.5 and 2.8 times higher. As well, Young's modulus of the coating was 1.56 times higher than the WC-Co coating made by the laser cladding method. • Milling of tungsten carbide and iron aluminide to achieve WC-FeAl composite powder • Agglomeration process on WC-FeAl composite powders to increase their fluidity and suitability for laser cladding process • Performing laser coating process for the first time for WC-FeAl composite Powder • The effect of laser cladding parameters on geometrical shape of clads was studied [ABSTRACT FROM AUTHOR]

• Laser cladding of Inconel 718 superalloy was performed. • The effect of parameters on the solidified microstructure was investigated. • The dendritic secondary arms spacing was calculated and the cooling rate was determined. • The structural defects and phase analysis were examined. The development of directional or completely equiaxed microstructures by the laser cladding process can determine the final properties and applications of Inconel 718 alloys. The main purpose of this study is to investigate the effect of laser cladding process parameters on the solidification and final microstructure of Inconel 718 alloy. In this study, Inconel 718 powder was cladded on the Inconel 718 substrate by Nd: YAG laser using laser power of 150–300 W, scanning rate of 4–6 mm/s and powder feeding rates of 150, 200, 250, 300 and 400 mg/s and the effect of them on the solidified microstructure at three zones of the interface, middle and surface of coating was studied. The dendritic secondary arms spacing was calculated and the cooling rate was determined in each zone. The structural defects including cracks, porosity and segregation and finally phase analysis were examined. The results showed that with increasing laser power from 150 to 300 W and also laser scanning rate from 4 to 6 mm/s due to decrease in the G/R ratio, so that the more part of microstructure was equiaxed. In addition, by taking distance from the interface, the dendrite secondary arms spacing decreased from 1.08 to 0.98 and the cooling rate increased from 2.3649 × 104 k/s to 3.2641 × 104 k/s. With increase in the powder feeding rate the equiaxed zone increases. However, the effect of the powder feeding rate cannot be directly and specifically determined. The all samples were free crack but, the small amount of porosity was observed in cladding sample. Results showed that between the laser parameters and the percent of porosities were not exist of the clear relation. [ABSTRACT FROM AUTHOR]

• Surface modification of Al-Co-Rare Earth (Ce-La) alloys via Laser Surface Melting process. • The effects of different laser scanning speeds on the micrstructure and corrosion resistance were investigated. • Rapid solidification of Al-Co-Ce-La alloys by the laser surface melting process resulted in the exhibition of different corrosion behaviors compared to the as-cast alloys. • The laser surface treated alloy with a scanning speed of 20 mm/s showed the best corrosion properties. • The particle sizes and the inter-particle distance decreased significantly and the microstructure become finer and more homogeneous. • No trace of microcrack, indentation, or protrusion was observed in the surfaces of all the laser-treated samples. The development of Al-RE (rare earth) alloys is primarily attributed to their excellent thermal stability, corrosion resistance, and tunable properties based on Co and Ce elements. Considering the need for a high critical cooling rate, it is a challenging phenomenon to develop fine and homogeneous Al-TM-RE alloy in bulk form. Therefore, it is a suitable alternative to use surface modification techniques to produce refined and homogenized coatings or thin films for achieving better corrosion resistance in the surface. In this study, the surface of two types of Al–Co–Ce–La alloys were treated by the Laser Surface Melting method with two different laser scanning speeds, and the effects of this process on the microstructure and corrosion properties were evaluated compared to the as-cast samples. The microstructural characteristics, chemical composition, phase change, and corrosion properties were evaluated. The results indicated that the particle sizes and the inter-particle distance in the Al matrix decrease significantly. The microstructure of the LSM samples are much more refined and homogenized, Compared to the as-cast crystalline material. The depth of microstructural affected zone by the laser surface process increased to an acceptable level (590 µm). No trace of microcrack formation and distortion were observed in the LSM samples. The decreased linear line energy from 83.6 to 41.8 j/mm led to the reduced interaction time and decreased amount of crystalline phases, thereby increasing the probability of amorphous structure. The best corrosion properties were obtained in the laser-treated Al 83.0 Co 10.0 -Ce 4.3 -La 2.7 alloy with a scanning speed of 20 mm/s. [ABSTRACT FROM AUTHOR]

Co x Ni 1−x Fe 2 O 4 ferrites (x=0, 0.2, 0.4, 0.4, 0.6, 0.8 and 1) were prepared by a sol-gel auto-combustion method. The samples were structurally characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectroscopy (FTIR). The XRD patterns confirmed single phase formation of spinel structure. Cation distribution estimated from XRD data suggested the mixed spinel structure of ferrite. The EDX analysis was in good agreement with the nominal composition. The results of FTIR analysis indicated that the functional groups of Co-Ni spinel ferrite were formed during the combustion process. According to FE-SEM micrographs, by addition of cobalt ion the average particle size of substituted nickel ferrite was gradually became smaller from 450 nm to 280 nm. Magnetic measurement using vibrating sample magnetometer (VSM) showed an increase in saturation magnetization and coercivity by Co 2+ substitution in nickel ferrite. For Co 0.8 Ni 0.2 Fe 2 O 4 sample, M s and H c reaches as high as 93 emu/g and 420 Oe, respectively. The reflection loss properties of the nanocomposites were investigated in the frequency range of 8–12 GHz, using vector network analyzer (VNA). Cobalt substitution could enhance reflection loss of NiFe 2 O 4 ferrite. The maximum reflection loss value of the Co 2+ substituted Ni ferrite was ~ −26 dB (i.e. over 99% absorption) at 9.7 GHz with bandwidth of 4 GHz (RL<– 10 dB) through the entire frequency range of X-band. [ABSTRACT FROM AUTHOR]

In the first step, gadolinium substituted cobalt ferrite nanoparticles with composition of CoFe 2-x Gd x O 4 (x = 0–0.05 in a step of 0.01) were synthesized by a hydrothermal technique and without subsequent annealing. X-ray diffraction and field-emission scanning electron microscopy evaluations exhibited that single phase spinel ferrites with narrow size distribution were achieved. The EDS analysis confirmed that the applied process for fabrication of CoFe 2-x Gd x O 4 nanoparticles is a proper process for the synthesis of spinel cobalt ferrites with homogeneity in composition. Mössbauer spectroscopy was utilized to distinguish the site preference of constitutive elements. A well-resolved doublets pattern of ferrite nanoparticles is mainly attributed to the superparamagnetic behavior. The results of magnetic hysteresis revealed that the gadolinium substituted cobalt ferrite nanoparticles exhibit superparamagnetic trend at a room temperature. The zero field cooled magnetization curves of gadolinium substituted cobalt ferrite nanoparticles showed that with an increase in gadolinium content, the blocking temperature increases. Fitting the experimental data of susceptibility with the Neél-Brown model expresses that there are powerful interactions between nanoparticles of gadolinium substituted cobalt ferrite and the Neél-Brown model was not operate for such ferrites. In the second step, the gadolinium substituted cobalt ferrite nanoparticles were annealed and the structural characteristics, magnetic properties and microwave absorptive behavior were evaluated. The Mössbauer spectras show a well-resolved six-line pattern of ferrite nanoparticles which is mostly imputed to the ferrimagnetic treatment. The magnetic hysteresis loops at a room temperature confirmed that the coercive field increased from 802 Oe for x = 0 to 965 Oe for x = 0.02 and then at higher contents, decreased. The magnetic hysteresis curves of CoFe 1.98 Gd 0.02 O 4 for fields applied parallel and perpendicular to the sample axis, expresses high value of magnetocrystalline anisotropy field of 13 kOe which exhibits that the resonance frequency can be shifted to higher frequency. Consequently the microwave absorber can be covered a wide-band of electromagnetic waves in the X-band. [ABSTRACT FROM AUTHOR]

CoFe 2 O 4 /FeCo hard/soft core-shell system with different shell thickness was obtained by precise control of surface treatment conditions of the CoFe 2 O 4 nanoparticles under reduced condition. CoFe 2 O 4 nanoparticles were subjected to surface reduction treatment for various period of times (10, 15, 20, 25, and 30 min) at 550 °C in order to optimize the thickness of FeCo soft shell. The phase evolution, morphology, coercivity and magnetization of the nanocomposites were examined by X-ray diffraction, electron diffraction pattern, transmission electron microscope, and vibrating sample magnetometer. The single-phase-like hysteresis loops and Henkel plot reflect the existence of the exchange coupling phenomenon in the core-shell nanocomposite. The enhancement of maximum energy product, (BH) max , by 50% with respect to the pure CoFe 2 O 4 nanoparticles is obtained for a sample treated at 20 min. [ABSTRACT FROM AUTHOR]

CoFe 2 O 4 CoFe2 hard–soft nanocomposites were prepared via reduction of the cobalt ferrite CoFe 2 O 4 in hydrogen atmosphere at different temperature. The structure and the room temperature magnetization of the samples were characterized by X-ray diffraction, field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM). It was found that the saturation magnetization of the nanocomposite powders increases by reduction temperature while their coercivity decreases. The highest M r /M s ratio of 0.52 was obtained for sample reduced at 550 °C. Single smooth hysteresis loops of nanocomposites show that these nanocomposites behave as the single-phase materials. This result indicates the presence of exchange coupling between two different hard and soft phases. [ABSTRACT FROM AUTHOR]

In the present study, the laser cladding of Al 2 O 3 on the top surface of air plasma sprayed (APSed) yttria stabilized zirconia (YSZ) coatings was carried out to improve the hot corrosion resistance of the thermal barrier coatings (TBCs) in the presence of molten salts. The coatings with and without laser cladding were subjected to a hot corrosion test at 1000 °C for 30 h in which a mixture of 55 wt% V 2 O 5 and 45 wt% Na 2 SO 4 was used as the corrosive salt. SEM micrographs and EDS analysis confirmed the formation of YVO 4 rod-shaped crystals dispersed on the surface of the APSed YSZ coatings after hot corrosion test, while these crystals were hardly detected in the laser clad coatings. The SEM micrograph of the cross section of the APSed YSZ coatings revealed cracks and a thermally grown oxide (TGO) layer in the bond coat/top coat interface, which led to the complete delamination of the coatings. Supporting the SEM micrographs, XRD patterns indicated the transformation of metastable tetragonal zirconia (t ′ -ZrO 2 ) to monoclinic zirconia (m-ZrO 2 ) after hot corrosion test. This structural transformation was due to the reaction of the molten salts with Y 2 O 3 (zirconia stabilizer) which destabilized the t ′ -ZrO 2 . To compare the hot corrosion resistance of the APSed YSZ and the laser clad coating, the volume percentage of the undesirable m-ZrO 2 was then calculated after the hot corrosion test. This calculation revealed a higher amount of m-ZrO 2 in YSZ (about 70 vol%) compared to that of the laser clad coating (about 13 vol%). [ABSTRACT FROM AUTHOR]