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In this study, the laser surface melting of cobalt-based superalloy ECY768, which has been in service for 40,000 h at a temperature of 1000 °C, has been investigated. Subsequently, laser surface welding and post-welding heat treatment is performed on the samples. This study was conducted in order to restore the microstructure of the damaged service-aged gas turbine nozzle to as-cast state. The results showed that by performing laser surface remelting, the microstructure of as-cast state can be approached. Also, the results of this study have investigated the weldability, microsegregation and solidification path of this superalloy, and it can be used in the repairing this superalloy in the industry. Laser surface melting was performed using a continuous wave fiber laser at various speeds of 10, 12, 14, 20, 50, and 70 mm/s. The microstructure and phase characteristics of the samples were examined using optical and scanning electron microscopes. Upon analyzing the macrostructure of the weld metal, it was observed that the depth of the melt zone at the speed of 12 mm/s is 585 ± 40 μm. In the investigating the microstructure of the solidification modes, namely planar, cellular, columnar dendritic, and equiaxed dendritic, it was observed that microsegregation occurs during laser welding of the samples due to the presence of heavy elements such as tantalum and tungsten. The solidification distribution coefficient for tantalum was calculated to be 0.37, which increased to 0.60 after the solution annealing heat treatment, resulting in an improved segregation behavior. Characterizing the surface hardness profiles of laser-melted samples it was observed that the hardness in the melt zone significantly increased compared to the base metal. The results of the current research indicate that the weldability (resistance to various welding defects, especially hot cracks) of the cobalt-based superalloy ECY768 is acceptable, and this process can be used for rejuvenating service-aged ECY768 cobalt-based gas turbine nozzle.

This study aims to analyze the microstructure and present phases of functionally graded carbon steel - stainless steel 316L - Inconel 625 using experimental methods and computational software (JMatPro). Both FE-SEM and SEM-EDS equipment were employed to evaluate the materials. The JMatPro software accurately simulated the present phases and their formation temperatures. The microstructure in the plain carbon steel part formed the ferrite phase at 900 °C, while a small amount of pearlite structure formed at 700 °C, remaining stable at ambient temperature. Chromium phase in stainless steel 316 L layers increased with solidification, with a higher increase in the delta ferrite phase. Inconel 625 at 1130 °C, the Laves nucleated with austenite, stable up to ambient temperature. As liquid decreased, niobium and molybdenum accumulation increased, potentially leading to Laves formation. The significant increase in niobium content at the interface of stainless steel 316L-Inconel 625 is attributed to an increase in iron content. The research indicated a good correlation between the observed and predicted microstructures.

Nowadays, titanium-based implants are widely used to replace damaged or missing body organs. Poor chemical bonding with the bone and infection caused by formation of biofilm on the implant surface are the most common problems with them. So, antibacterial properties and osteoblast adhesion improvement have been intended to address these issues. The aim of this research is cell adhesion improvement and prevention of bacterial infection using surface roughness and in-situ antibiotic drug release. Here, micromachining (nanoseconds) laser with a groove distance of 10, 30, and 50 µm, was used to surface modification. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), hardness, roughness, and wettability tests were used for physical and metallurgical characterization of surface-modified samples to find the optimum laser processing conditions. Roughness has increased as a result of laser surface modification and surface characteristics of alloy exhibit sensitivity to the groove distance. The lower groove distance indicated the higher roughness and wettability. Martensite phase, α phase, and, Ti3Al were observed in the fusion zone. Also, the dissolution of the beta phase has occurred in the fusion and the heat-affected zones. No oxidation was observed. All these occurred without any change in bulk. Then optimized sample surfaces were coated by the vancomycin-loaded polyvinyl alcohol solution using electrospinning process, and toxicity, cell adhesion, and drug release rate were evaluated. The results showed laser surface modification and coating did not hurt cell viability. Modified samples demonstrated high cell adhesion and improvement in drug release compared to the unmodified samples. The drug release rate was extended from 4 h to 25 h for modified samples. So, the modified implants could indicate a sustained release of antibiotics as well.

Due to the distinct physical and metallurgical characteristics of titanium and steel, the welding of these two materials poses challenges and holds significant importance. This study investigates the impact of brazing time and temperature on the microstructure and mechanical properties of dissimilar brazing between 17-4 PH stainless steel and Ti–6Al–4V using BNi-2 as a filler metal, focusing on the formation of brittle compounds like FeTi and Fe2Ti during the brazing process. The joint between these materials is commonly utilized in various industrial applications. The assessment involved the use of optical microscope, scanning electron microscope, shear – tensile test, microhardness test, and wettability measurement. Brazing of the base metals was conducted at temperatures of 1050/1100 °C for durations of 15 and 30 min to determine the optimal temperature and time combination. The results indicated that the best joint properties were achieved at 110 °C for 15 min, with an average shear strength of 38.46 MPa. Contact angle measurements revealed that BNi-2 exhibited superior wettability on 17-4 PH compared to Ti–6Al–4V. Furthermore, increasing the temperature from 1050 to 1100 °C led to a reduction in contact angle from 9.98 to 8.83° for 17-4 PH, and from 16.51 to 10.12° for Ti–6Al–4V indicating an improvement in wettability.

This work utilized a gradient method of joining plain carbon steel to stainless steel 316 L and then to Inconel 625 using wire arc additive manufacturing. The research investigated the quality of Functionally Graded Materials (FGM) structure, continuity, defect formation, microstructure, and mechanical properties of gradient regions. The investigation showed a strong, defect-free metallurgical bond between plain carbon steel and stainless steel 316 L and stainless steel 316 L and Inconel 625. The microstructure of stainless steel 316 L resulted from the solid-state transformation of ferrite-austenite (FA), with a significant presence of delta ferrite in the austenite matrix. In Inconel 625, the Laves intermetallic phase formed discontinuously between dendritic arms due to the microsegregation of alloy elements like niobium and molybdenum during solidification. The hardness values of Inconel 625, stainless steel 316 L, and plain carbon steel were 194–257 HV, 171–178 HV, and 159–170 HV, respectively. The ultimate tensile strength, yield strength, and elongation were achieved at 487 ± 10 MPa, 300 ± 6 MPa, and 40 % ± 0.15, respectively. The tensile test samples failed on the plain carbon steel side, indicating higher tensile strength at the interface and a well-bonded joint between the two alloys. Small, homogeneous dimples on the fracture surface confirmed the ductile fracture mode. The research demonstrates the use of wire-arc additive manufacturing (WAAM) to fabricate gradient materials with the required properties.

Due to the distinct differences in physical and metallurgical properties, it is hard to join titanium alloys to stainless steels directly via conventional welding processes. In this research, the grade 5 titanium alloy was subjected to brazing with austenitic stainless steel through the vacuum furnace, and the process was conducted above the β transition temperature (BTT). In order to reduce brittle intermetallic formation, a nickel base filler metal (Ni-6.6Cr-4.5Si-3B) was employed under a vacuum condition, and the effect of time on the microstructure and mechanical properties of the joints was investigated. The brazing temperature led to the thickening of the interface to 400 µm, toward the titanium alloy, and the FeTi formed adjacent to the diffusion affected zone (DAZ). Moreover, the isothermal solidified zone (ISZ) widened during the whole process, which, led to higher dissolution of the titanium base metal in the ISZ. Because of the widening of the interfaces, there were no Ni-rich compounds or residual filler metal in this region. SEM result showed that TiB strengthening borides, which were distributed after 45 min, and this evolution caused an increase in the shear strength of the joint up to 67 MPa. Fractography analyses and XRD results of the fractured surfaces revealed that the Ti2Ni phase, which formed in the athermaly solidified zone (ASZ) during a two-step solidification reaction, caused the brittle fracture in all joints.

Abstract In recent years, the power conversion efficiency (PCE (%)) of perovskite solar cells (PSCs) has improved to over 26%. To enhance the photovoltaic properties of PSCs, several materials for the electron transport layer (ETL) have been investigated. Zinc oxide (ZnO) is a significant ETL due to its high electron mobility and optical transparency in PSCs. As a result of various deposition methods, ZnO ETL can be processed at low temperatures. On the other hand, based on several studies, metal-doped ZnO can facilitate electron transfer, thereby improving the performance of un-doped ZnO ETL-based PSCs. Here, to improve the PCE (%) and long-term stability of un-doped ZnO ETL-PSCs, silver (Ag)-doped ZnO 1wt% as a buffer layer is examined. In this paper, with the addition of an organic solvent (ethanol) to the dispersion of Ag-doped ZnO 1 wt% nanoparticles (NPs) in deionized (DI) water, the morphology of the buffer layer (Ag-doped ZnO 1 wt%) can be controlled. This approach focuses on reducing the wettability of the ZnO/Ag-doped ZnO 1 wt% bilayer ETLs and enhancing the stability of un-doped ZnO ETL-PSCs. According to the results, the ZnO/H2O-ethanol mixtures-Ag-doped ZnO 1 wt% bilayer ETL leads to the formation of high-quality perovskite with low defects, reducing the recombination rate, and long-term stability of un-doped ZnO ETL-PSCs in ambient conditions.

Laser surface melting (LSM) is an environmentally-safe technique in which melting and solidification occur in a very short reaction time, without affecting the bulk of the material. On the other hand, today, the use of magnesium as a very light metal, with excellent specific resistance, excellent sound damping and good casting ability, etc., has been expanded. Also, having low absorption of laser beams, strong tendency to oxidation, high thermal conductivity, etc are important drawbacks of these alloys. Today there is widespread agreement on the better resistance to hot cracking of magnesium alloys with Nd:YAG laser due to its shorter wavelength by comparison with CO2 laser. This research aims to investigate the effect of Nd:YAG laser surface melting parameters on the microstructural, phase changes and hot cracking susceptibility of the AZ80 magnesium base alloy. The results of current research showed that sample 5 with voltage, frequency, pulse duration and gas flow rate of 250V, 10 Hz, 4 ms, 5lit/min, respectively, and constant speed of 1 mms showed a remelted zone with minimum hot cracks and other defects. In conclusion by controlling the laser parameters such as pulse duration, shielding gas flow rate, laser frequency, scanning rate and the laser power, the susceptibility to hot cracking including both solidification and liquation cracking are significantly decreased.

NiTi shape memory alloy (SMA) offers a wide range of industrial applications due to its shape memory effect and superelastic properties. In this study, a dissimilar joint between NiTi SMA and Ni–20Cr alloy was fabricated, and its microstructural and mechanical properties were analyzed. As a result of the formation of brittle intermetallic compounds (IMC), the tensile characteristics were reduced, and the hardness increased dramatically. Also, the effect of various laser pulse widths on bonding characteristics was examined, and as the pulse width increased, coarser IMCs were formed in the FZ. By performing post-weld heat treatment (PWHT) on the welded samples, the microstructure and mechanical properties of the FZ changed, and the NiTi intermetallic phase was produced. The results revealed that most IMCs generated had the same chemical composition ratio as Ni3Ti and Cr2Ti IMCs. In addition, after PWHT, the plateau region in the stress-strain curves was formed, while in the welded samples without PWHT, the joints failed at low stress and strain before forming the plateau region.

This study involves investigation of metallurgical and mechanical properties of C-103 niobium alloy welded by electron beam. ICP, XRD and EDS method were used to determine the composition and phase contents of the alloy. Electron beam welding was carried out on specimens with various currents and transverse speeds. To examine macro- and micro-structural characteristics of the welded samples, stereographic, optical, electron scanning microscopy and EDS methods were used. Also, mechanical properties including micro-hardness profile and tensile strength were measured. It was observed that C-103 alloy has HfO2 precipitates with two different morphologies of spherical coarse and fine particles. Within the weld zone, primary precipitates were dissolved and new nanometer-sized ones were formed regularly throughout this zone. Morphology of the formed precipitates was mostly spherical and rarely filament-like. Due to greater number and smaller size of precipitates in weld zone, hardness of weld zone was more than HAZ and base metal zone. Tensile strength of welded sample was 317.5 MPa which is equal to 55% of tensile strength of base metal. Fracture of all welded samples occurred within weld zone which can be referred to enlargement of grains in this zone. The features presented on fracture surface of unprocessed C-103 alloy, such as cross section reduction, formation of dimples, opaque appearance of fracture surface indicate ductile nature of fracture. However, emerging of relatively smooth and sharp surface, abundant vein patterns and cleavage planes obviously indicate brittle fracture. HfO2 precipitates, as well as dissolved oxygen in the matrix, significantly affected metallurgical and mechanical properties of welded C-103 alloy samples.

Titanium alloys have been used extensively as implants. However, they generally suffer from low biocompatibility as well as antibacterial activity. To date, several strategies have been proposed to address these issues. It is of practical interest to synergistically increase both cellular adhesion and antimicrobial activity in titanium-based implants. Here, Ti–6Al–4V alloys were surface-modified by Nd:YAG laser with different scanning speeds ranging from 1 to 5 mm s−1 and subsequently coated by drug-loaded polymer nanofibers for prolonged drug release. The laser-modified samples were both physically and metallurgically characterized through XRD, OM, AFM, FESEM, hardness, and wettability tests to find the optimum laser processing conditions. Results showed that the surface characteristics of the alloys are sensitive to the scanning speed; the higher the scan velocity, the lower surface roughness and wettability were obtained. The enhanced formation of TiO and Ti6O oxides on the surfaces of laser-modified alloys was delineated. Then, a model polymer/drug system of polyvinyl alcohol/vancomycin was directly electrospun onto the optimized samples surfaces. The laser-modified, drug-loaded samples present an improved biocompatibility as the cellular adhesion and viability were increased in contact with these samples. Up to 39% increase in cell viability was obtained for the laser-modified samples by 5 mm s−1 scan speed in comparison with unmodified, uncoated samples. The increased biocompatibility was attributed to the formation of oxide layers which reduce the toxicity of vanadium and aluminum elements. Also, the drug release rate was extended from 4 h to 25 h for modified samples. So, the modified implants could present a sustained release of antibiotics as well.

The heat input is the most critical factor in pulsed Nd:YAG laser welding and affects the microstructure and mechanical behavior of the welded alloys. NiTi alloy has been used for various applications such as medical equipment and MEMS due to its unique shape memory effect, superelasticity, and excellent corrosion and fatigue performance. This research investigated the effect of heat input and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of similar NiTi shape memory wires joints. For this purpose, NiTi wires were welded with pulse widths of 5, 8, and 11 ms, and then, heat treatment was performed. Microstructures of the welded alloys were examined using optical and electron microscopes and chemical composition was analyzed with an EDS analysis system. The mechanical properties were evaluated using tensile and microhardness tests. A desirable NiTi SMA joint was achieved by Nd:YAG laser, and the properties were improved by following post weld heat treatment.Investigations showed that microstructure and mechanical properties were changed by increasing the heat input. After applying PWHT due to recrystallization and the creation of new phases in the weld zone, the final strength of the joints increased up to 80%, and the behavior of the plateau region became similar to shape memory behavior in the NiTi alloy.

In this work, the electron-beam welding (EBW) behavior of Ni/C-103 Nb-based refractory alloy was investigated, in terms of fusion-zone characteristics, texture evolution, mechanical properties, and joint efficiency. Compared to Nb, the higher concentration of Ni in weld zone indicated that the Ni side participates more in welding than the C-103 one. A continuous intermetallic layer was formed at the joint/C-103 interface composed of NbNi3, Nb7Ni6 and Hf3Ni7 phases. Continuous curved-shaped layers composed of columnar NbNi3 and eutectic Nb7Ni6+NbNi3 phases were also observed in the central and lower regions of the weld. These have been peeled off from the C-103 upper walls lateral to the weld and directed to the bottom of the weld pool due to the Marangoni flow. Solidification microcracks internal to the continuous intermetallic layers are also initiated and grown at the final stage of eutectic Nb7Ni6+NbNi3 phase formation leading to the brittle cleavage failure within this layer. The average microhardness of the joint was measured as 562 HV, which was higher than the base metals due to the presence of intermetallic compounds. Tensile strength of the joint was measured as 119.5 MPa, which is approximately one third of the value for the bead on plate weld of C-103 plate using EBW method with a tensile strength of 317.5 MPa. Nb7Ni6 and NbNi3 intermetallics were dominant phases in the fracture area.

Abstract In the present paper, the interrelated aspects of additive manufacturing-microstructure-property in directed energy deposition of SS316L-IN718 multi-material were studied through numerical modeling and experimental evaluation. The printability concept and solidification principles were used for this purpose. The printability analysis showed that the SS316L section is more susceptible to composition change and lack of fusion, respectively due to the high equilibrium vapor pressure of manganese and the more efficient heat loss in the initial layers. However, the IN718 section is more prone to distortion due to the formation of a larger melt pool, with a maximum thermal strain of 3.95 × 10−3 in the last layer. As the process continues, due to heat accumulation and extension of the melt pool, the cooling rate decreases and the undercooling level increases, which respectively result in coarser microstructure and more instability of solidification front in the build direction, as also observed in the experimental results. The difference is that the dendritic microstructure of the IN718 section, due to the eutectic reaction L → γ + Laves, is formed on a smaller scale compared to the cellular microstructure of the SS316L section. Also, the decrease in cooling rate caused the secondary phase fraction in each section (delta ferrite in SS316L and Laves in IN718) to increase almost linearly. However, the hardness calculation and measurement showed similarly, even though with the transition from SS316L to IN718 the hardness is significantly increased due to higher yield strength of the matrix and the presence of Laves intermetallic phase (~ 260 HV0.3), the hardness in each section decreases slightly due to the coarsening of the microstructure from the initial layer to the final.

Functionally graded materials (FGMs) are a good response to those advanced applications that service requirements are diverse and require high performance. Additive manufacturing (AM) technology, with its many advantages, including high flexibility for complex geometries and near-net-shape integration, has attracted special attention in the development of FGMs. In this research, the solidification behavior and microstructure evolution in the laser additive manufacturing of thin-walled stainless steel 316L-Inconel 718 graded materials have been studied with the help of solidification concepts in the welding metallurgy, according to the common principles of welding and additive manufacturing processes. For this purpose, optical and electron microscopy techniques, X-ray energy dispersive spectroscopy, and microhardness measurement were used along the build direction of FGMs with different transition designs. Microstructure evaluation showed that due to re-melting of layers, despite the increased undercooling in the build direction, morphological evolution occasionally occurred periodically between solidification modes, and due to thermal accumulation, a coarser microstructure is formed in the final layers. In addition, in the chemical analysis, it was observed that the mixing of adjacent layers caused by dilution led to a deviation of the composition distribution from the desired design. Also, the microsegregation of some elements during the non-equilibrium solidification of the process caused secondary phases such as carbides and intermetallic compound of Laves, which can have an adverse effect on the mechanical properties of the structure. However, microhardness variations along the cross-section of the samples showed that the gradation of the dissimilar thin-walled structure can effectively bring the properties and behavior of adjacent layers closer together and therefore be very useful in improving the service life.

One of the candidate alloying elements is Cr which is used to make solder suitable for severe conditions. The current study has been conducted to investigate the addition of Cr along with Bi to Sn–Cu base solder. Accordingly, the effect of adding Cr on the joint properties of the new Sn-0.8Cu-1.8Bi-xCr (x = 0, 0.01, and 0.1 wt%) solders is compared to Sn-0.8Cu and Sn-0.8Cu-1.8Bi base solders. For investigating the joint interfacial microstructure and phase transformation, the synthesized solders were bonded to the Cu-substrate. Also, to evaluate the joint properties, the shear test, fractography, and microhardness were carried out. The characterizations are carried out using SEM-EDS to predict the mechanism governing the grain refinement and decrease of intermetallic compounds (IMCs) thickness. The presence of Cr and Bi improved the IMC layer microstructure and changed the joint properties of Sn–Cu. The thickness of the IMCs at the solder/substrate interface decreased by the addition of selected alloying elements because of the Sn and Cu diffusion power changing. Also, the Sn–Cu–Bi-0.01Cr/Cu joint showed the best shear properties and elongation among the others. The best metallurgical, mechanical and fracture behavior results were obtained from the Sn–Cu–Bi-0.01Cr/Cu joint.

Inspired by nature, advanced functionally graded materials (FGMs) are an appropriate response to high-performance multi-functional applications. The introduction of modern additive manufacturing technology to the processing of gradient metallic materials opened up a great opportunity for further development of this class of engineering materials owing to several advantages of this technology, e.g., high manufacturing flexibility. The phenomena prevailing in the additive manufacturing of gradient metallic materials, such as melting and solidification, have drawn special attention to this field from the viewpoint of materials science and engineering to the extent that many experimental and numerical research studies have been done in this regard in recent years. After briefly introducing FGMs and providing a brief overview of manufacturing methods with a focus on additive manufacturing processes, this paper discusses experimental studies in three sections: metal–metal, metal-ceramic, and metal-intermetallic gradient materials. Then, numerical studies are reviewed from the perspective of materials science and engineering. In the end, important results achieved so far are summarized and an outlook is provided for further research in the future.

According to the European Union's (EU) legislation in 2006, the Restriction of Hazardous Substances (RoHS) led to eliminating Sn–Pb conventional solders from electronic assemblies. Despite this elimination, the use of lead-bearing solders in car electronics was persisted, and eventually, in 2014 the lead usage prohibition was introduced for the automotive industry. The reliability and safety issues are still arguable in this industry, notwithstanding the lead-free solders substitution. The Sn–Cu solder is one of the alternatives modified by alloying elements to improve its moderate mechanical properties. In order to fabricate a cost-effective solder that has simultaneously a good level of mechanical properties and oxidation behavior, the Cr along with Bi was added to the Sn–Cu base solder. In this research, a comparative study has been conducted on the Sn-0.8Cu-1.8Bi-xCr (x = 0, 0.01, 0.1 wt.%). The effect of adding these alloying elements on the physical and mechanical properties is studied compared to Sn-0.8Cu and Sn-0.8Cu-1.8Bi solders. The physical properties of synthesized solders such as microstructure, XRD, thermal properties, wettability, oxidation behavior, and density were investigated. Also, these experienced mechanical tests such as uniaxial tensile test, microhardness test, and fractography to evaluate the effect of Cr and Bi on mechanical properties. The results showed that the addition of the minor amount of Cr along with Bi can consequently improve the microstructure, add some kinds of new IMCs, modifies the oxidation behavior and the wettability. The mechanical properties of the base solder got better by the adding these alloying elements.

The thermal regime and microstructural phenomenon are studied by using finite-element (FE) modelling and the analytical Rosenthal equation during laser welding of aluminum alloy 5456 (AA5456) components. A major goal is to determine the merits and demerits of this analytical equation which can be an alternative to FE analysis, and to evaluate the effect of imperative assumptions on predicted consequences. Using results from the analytical and numerical approaches in conjunction with experiments, different physical features are compared. In this study, the results obtained from experiments in terms of melt pool shapes are compared with the predicted ones achieved from the numerical and analytical approaches in which the FE model is more accurate than the Rosenthal equation in the estimation of the melt pool dimensions. Furthermore, as to the partially melted zones, the estimations achieved from the numerical modeling are more genuine than ones from the analytical equation with regards to the experimental results. At high energy density, near keyhole welding mode, the reported results show that experimental melt widths are supposed to be narrower than the fusion widths estimated by the analytical solution. The primary explanation could be the influence of thermal losses that occurred during convection and radiation, which are neglected in the Rosenthal equation. Additionally, the primary dendrite arm spacing (PDAS) estimated with the numerical modeling and the analytical Rosenthal solution is comparable with the experimental results obtained.