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A 3D finite-element thermal model has been developed to estimate weld geometry and analyze thermal gradients and cooling rates in pulsed laser welding of Inconel 718 superalloy. Since Inconel 718 superalloy is sensitive to hot cracking, the extent of hot crack sensitive areas including heat affected zone, mushy zone and partially melted zone is very important in the investigation of weldability for this alloy. Because the welding process is very fast and the welding width is very thin, the numerical modeling approach can be very helpful to overcome the difficulties and limitations of experimental procedure. In this study, a finite element model is presented to simulate the process of pulsed laser welding of Inconel 718 and to predict the temperature distribution and shape of the weld pool and finally to estimate the extent of the hot cracking sensitive regions. Heat source was modeled by the combination of conical Gaussian and ellipsoid Goldak. Then, the results of numerical model were compared to the experimental results at preheat temperatures of 308, 393, 473 Kelvin. The proposed numerical model exhibits good agreements with the experimental results including the internal and external weld pool geometries and the extent of the hot cracking susceptible regions. Furthermore, detailed pulsed temperature distribution and thermal cycle containing solidification latent heat are obtained. Accordingly, this pulsed temperature history is correlated to the internal and external geometry of pulsed solidified weld pool.

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.

For planar perovskite solar cells (PSCs) to have satisfactory performance and acceptable stability, an ETL (electron transport layer) is needed that provides a high level of efficiency. It should be noted that when considering the implementation of n-type metal oxide materials, the ZnO (zinc oxide) can be a great choice for an ETL because it provides a relatively high level of mobility. The current study proposes a new design involving a reduced graphene oxide (rGO) sheet/Ag-doped ZnO bilayer to be utilized as ETL in planar PSCs. Extensive experimental and computational analyses including nano-micro structural, optical and electrical properties are carried out in order to compare the performance and governing mechanisms of rGO/Ag-doped bilayer-based planar PSC to ordinary un-doped ZnO. The results from the performed experiments show that using the rGO sheet as the buffer layer and Ag-doped ZnO significantly increase the power conversion efficiency (PCE) by more than 30% compared to un-doped ZnO ETL in planar PSCs. These improvements in the performance of PSCs can be explained based on fine tuning the energy levels of ZnO/perovskite, since this increases the charge-carrier-extraction from the perovskite layer. Moreover, the results of the study confirm the using the rGO/Ag-doped ZnO bilayer ETL as a new methodology for the creation of stable planar PSCs with low charge recombination rate and high performance.

Objective Micro-nano scale surface modification of Ti-6Al-4V was investigated through the fascinated modern fiber engraving laser method. The process was performed at a high laser speed of 2000 mm/s, under different laser frequencies (20–160 kHz) and groove distances (0.5–50 μm). Methods Topographic evaluations such as Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FE-SEM) were used to identify the quality and regularity of patterns. The proliferation of human osteoblast-like osteosarcoma cells (MG63) was analyzed by MTT assay for up to 72 h. Also, the plate counting method was used to quantify the viability potential of the modified surface against Escherichia coli bacteria. Results The cellular viability of the sample modified at the laser frequency of 20 kHz and grooving distance of 50 μm increased up to 35 and 10% compared to the non-treated and control samples, respectively. In the case of the surface modification at lower grooving distances range between 0.5–50 μm, the maximum laser frequency (160 kHz) applied leads to lower pulse’s energies and less bacterial adhesion. Otherwise, at groove distances more than 50 μm, the minimum laser frequency (20 kHz) applied reduces the laser pulse overlaps, increases the cell adhesion and antibacterial properties. Significance Surface modification by the fiber engraving laser process significantly enhances the cell adhesion on the surface. As a result of such roughness and cell adhesion enhancement, the surface toxicity feature diminished, and its antibacterial properties improved.

Kovar, due to its close thermal expansion coefficient to glass, can be used as a mediating alloy in joint of glass to metals such as AISI 304L. In the present research, the effect of parameters of pulsed laser on dissimilar welding of Kovar to AISI 304L has been investigated. For observation and investigation of the results, metallography, Energy dispersive X-ray spectroscopy (EDS) and microhardness tests have been used. Results obtained from microstructural examinations, indicated the existence of solidification crack and lack of complete mixing in the weld metal. According to the results, the heat input must have an optimum value equaling approximately 19.1 J/mm. At higher levels such as 32.6 J/mm, the TCL (total crack length) value reached 760 μm. Increasing the heat input lead to increasing thermal stresses and formation of crack in the weld metal. On the other hand, at heat input levels less than the value of 15 J/mm, cracks are eliminated and non-mixing is clearly observable because sufficient time is not provided for mixing and, then, solidification for the weld metal. The weld metal hardness is also higher than the base metals due to the fine dendrite structure and the presence of hardening elements.

Hot cracking sensitivity of AA2024-T351 in the electron beam welding (EBW) was evaluated and the effects of welding speeds and heat input on the hot cracking were investigated. In this research, welding speed was set to 15–40 mm/s and microstructure of the welded zone was studied thoroughly by scanning electron microscopy (SEM). Appearance and geometry of weldments were also observed by stereo microscope. Microstructural observations showed that the hot crack length decreased with the increasing welding speed and decreasing the heat input and, as a result, in welding speed of 30 mm/s and heat input of 150 J/mm the crack-free weldment was achieved. The relationship between the welding speed and microstructure of the welded zone was also discussed. It could be concluded that decreasing the heat input alleviated thermal stresses and strains improved the grain structure, hence prevented nucleation and growth of hot cracks in the weld metal.

Magnetic Pulse Welding (MPW) is an essential procedure for joining of dissimilar metals. The high velocity collision and jetting are the most important aspects of MPW controlled by welding parameters: discharge voltage and air gap. In this study, the collision surfaces and interface of MPW of pure Al and Cu are investigated. The effect of air gap on the bonding is studied by variation of the air gap from 0.7 to 4 mm. The collision surfaces of Cu and Al, the interface of welding and fracture surface were examined by optical microscope and SEM equipped with EDS analysis. The results revealed that the metallurgical bonding is obtained in the air gap of 0.7 mm, whereas higher air gaps (1 to 4 mm) result in debonding due to higher impact energy. The feature of collision surfaces depends on the physical properties of Al and Cu, the variation of collision angle and distance from the centerline of the collision. By increasing the collision angle and distance from the centerline of the collision, the porous and wavy structures in the collision surface of Al, and wavy structure with vortices in the collision surface of Cu are formed. Furthermore, by increasing the distance from the centerline of collision, the wavy structure with vortices is formed in the interface of welding. Also, the highest shear strength is obtained at the middle of the weld line, and the failure is occurred in Al.

A lead-free Sn-2.5Ag-0.7Cu base solder with different weight percentages of bismuth (0, 1, 2.5, 5) was used. Thermal properties, microstructure, wettability and mechanical properties were investigated. By decreasing the degree of undercooling, microstructure improved, the eutectic structure become finer and the size of β-Sn and intermetallic compounds decreased. By the addition of bismuth to SAC257 solder, the spreading ratio increased from 80.46% to 85.97, indicating an improvement in wettability. In order to investigate the joint properties, alloy solders were bonded to copper substrate, and the structure of the interface, tensile-shear strength and the fractured surfaces were studied. It was observed that the thickness of the intermetallic compounds of Cu6Sn5 at the interface decreased with the addition of bismuth, and the lowest thickness of the interfacial IMCs was found in the SAC257-1Bi solder joint, which decreased about 14% compared to the base solder. Also, the Cu/SAC257-1Bi/Cu bond had the highest tensile-shear strength and elongation percentage among the alloy solders, which has a tensile-shear strength of about 30% and an elongation percentage of about 38% higher than the base solder joint.

Solidification cracking in pulsed laser welding of aluminum alloys has been the subject of a number of researches. The purpose of this study is to analyze the possible effects of high solidification rates involved in pulsed laser welding on the solidification path of aluminum alloys and solidification cracking sensitivity. For the analysis, conditions at the interface are not necessarily considered to be at equilibrium. Accordingly, the solidification path is modified taking into account the effects of solidification rate on the solidus, liquidus, and eutectic temperatures, the liquidus slope, and the interface parameters, including the partition coefficient, the cell/dendrite tip radius, and the liquid composition in the cellular dendrite tip. In line with the previous researches, cracking susceptibility is assumed to be proportional to the range of temperature squared for solidification crack formation ( $$ \Delta T^{2} $$ ). The results of calculations for hypo-eutectic Al-Cu alloys show that cracking susceptibility increases and shifts to a higher copper composition with the increasing solidification rate. The given calculations are evaluated against the reported experimental results.

Metal-organic frameworks (MOFs) have appeared as a new option for constructing various functional materials for energy storage applications. In this work, a novel amorphous vanadium doped Co3S4 (V-CS) hollow sphere is synthesized through a facile method. Due to the unique structure, the amorphous V doped Co3S4 provides large amount of active sites for better storage energy. A remarkable specific capacitance of 1725 F g-1 at the current density of 0.3 A g-1 was achieved for this electrode. Further, the as-fabricated asymmetric supercapacitor device contains the V-CS electrode and activated carbon electrode (positive and negative, respectively) lead to outstanding performance with maximum energy and power densities of 88.29 Wh kg-1 and 486 W kg-1, respectively, that is better than traditional supercapacitors. In addition, the fabrication process illustrated in this article is facile, controllable, and economical, offering a viable method for fabricating the next generation of high-performance energy storage devices.

In this study, weldability and mechanical properties of dissimilar joint between Nb-1Zr and 321 stainless steel produced by electron beam welding were investigated. The results indicated that the optimum parameters to make this dissimilar joint possible are the electron beam offset of 50–50 and the current of 13 mA. Because of high melting temperature of Nb relative to 321 stainless steel and also high thermal conductivity of Nb, the molten weld pool was drawn to 321 stainless steel side containing 85.1%Vol 321 stainless steel and 14.9%Vol Nb. Non uniform regions were observed in the weld zone which were due to melt turbulence and its rapid solidification. The Fe7Nb6 and Fe2Nb intermetallic compounds formed in various regions of the weld zone directly govern the mechanical properties and weldability of the weld. Tensile strength of the weld was 170 MPa which was equal to 60.5% of that in autogenous weld of Nb-1Zr alloy. Tensile strength of the autogenous weld of Nb-1Zr alloy was 281 MPa. According to the Rosenthal's equations and measurements of the weld section, the recrystallization temperature of the Nb-1Zr was identified 1810 °C in the EBW condition.

In order to reduce the price of the SAC357 solder, the percentage of silver was reduced and simultaneously the Bi-element was added to improve the properties of the solder. For this purpose, the bismuth element was added to the base solder Sn-2.5 wt% Ag-0.7 wt% Cu (SAC257) with weight percentages of 1, 2.5 and 5. To evaluate the effects of the addition of bismuth on the physical properties of the new solders, microstructure, XRD, thermal properties, wettability, and density have been investigated. The specimens experienced micro hardness and uniaxial tensile tests. Finally, to evaluate the failure behavior, the fracture surface was studied. The finer microstructure, size reduction of the β-Sn dendrites, expansion of the eutectic region and formation of small precipitates (about 500 nm in size) in the β-Sn matrix were among the most important changes in the microstructure of SAC257-xBi solders. Improvement in wettability, no significant changes in density, and reduction in melting point, solidus and liquidus temperatures were other physical changes in the new solders. The mechanical properties of the new SAC257-xBi solders (x = 0, 1, 2.5, 5) such as hardness, yield strength and ultimate tensile strength increased with the addition of bismuth.

The purpose of this study is to evaluate the effects of pre-cold treatment on weldability of superalloys. The results of numerical calculations showed that the length of different welding regions including mushy zone (MZ), partially melted zone (PMZ) and heat affected zone (HAZ) decreased by 46, 46 and 56 percent, respectively. The experimental calculations indicated that the length of PMZ and HAZ, as well as the HAZ area, decreased by 2.1, 2.5 and 2.5 times, respectively. These results showed that significant improvement in weldability can be obtained by performing pre-cold treatment. Using pulsed Nd:YAG laser, grains boundary liquation was observed, followed by HAZ liquation cracking. The mechanism of HAZ liquation cracking is constitutional liquation of Nb-rich carbides and delta precipitates that encourage the formation of liquid films in the grain boundaries. With the accumulation of micro-pores in liquated grain boundaries, the cracks can be formed. With reducing the temperature of specimen from +200 to −30 °C, the penetration depth of laser welds decreased from 1624 to 1450 μm and the WTOP/WNECK ratio reduced from 1.45 to 1.24. The hardness profile at temperatures of -30 and + 200 °C indicates that the hardness of the weld metal increased using pre-cold conditions.

A 700 W pulsed Nd:YAG laser welding was employed to weld 5456 aluminum alloy plates with thickness of 5 mm. The weld penetration and tendency of liquation cracking in the heat affected zone and solidification cracking in the weld metal are investigated. It is found that hot cracks can be avoided by pulsed laser in preheated status. Increasing the laser average power in fixed pulse frequency and pulse duration resulted in a significant reduction in hot cracking tendency in pulsed laser welding. Also, the hot cracking susceptibility is reduced with increasing pulse frequency up to 50 Hz in fixed average power and pulse duration. The hot cracking tendency can be decreased by pulse duration decrement to 6 ms in fixed average power and pulse frequency. The factors contributing to the prevention or reduction of hot cracks in laser welding of aluminum alloy 5456 are the reduction in cooling rate causing change in solidification mode from columnar to equiaxed grains, and backfilling of liquated grain boundaries. With a 0.4 mm beam diameter Nd:YAG pulsed laser at 300 W average power, 6 ms pulse duration, 20 Hz pulse frequency, 5 mm/s travel speed and 150 °C preheating temperature, hot crack-free weld cross sections were achieved.

In the current investigation, the loss of magnesium (Mg) in Nd:YAG pulsed laser welding of a number of aluminum (Al) alloys was studied both experimentally and numerically. The experimental results showed that at a fixed average laser power, with the increasing pulse frequency, Mg concentration of the weld metals decreased. A numerical model was developed for the calculation of Mg evaporation from the weld pool. The model predicted a trend in the changes of Mg concentration of the weld pool, working best for alloys containing the higher levels of Mg. The calculations showed that with the increasing pulse frequency from 15 to 40 Hz, due to a decrease in the average temperature of the weld pool, Mg loss in terms of mass per unit area of the weld spot actually decreased from 230 × 10−5 to 120 × 10−5 kg/m2. However, due to a decrease in the weld penetration/volume, the effective Mg loss of the weld metal in terms of concentration increased from 110 × 10−1 to 260 × 10−1 kg/m3. It was shown that due to interactions between Mg and other main alloying elements, the activity coefficient of Mg had to be modified for the model to accurately predict Mg evaporation of the weld pool.

The effect of electron beam welding current changes on the microstructure and mechanical properties of the Nb-based alloy has been investigated. The electron beam welding was applied with 4 different values for electric current 20, 24, 30 and 35 mA on 3 mm thick plates. The aspects including different welding regions, geometry and depth of welding penetration, as well as the effect of heat input on the mechanical properties are investigated. The mechanical properties including tensile and microhardness values of the weld was measured. The results show that in a sample with a 30 mA welding current, the optimum conditions for the depth of penetration, microstructure, mechanical properties and the geometry of the weld are obtained. The welds showed a cellular structure, and intercellular dendrites in the central region of the weld have been caused due to microsegregations created between the cells. In heat-affected zone (HAZ), severe recrystallization and grain growth has occurred. Because of the high thermal conductivity of niobium, the HAZ size is relatively large. Based on the 3D Rosenthal's equation, the recrystallization temperature of alloy was calculated as 713 °C. It is observed that as G × R increases, the grain size in the central line of the weld decreases. The hardness profile shows that the hardness of the weld zone and the HAZ is significantly less than that of the base metal due to elimination of work hardening effect. The tensile strength of the weld for a sample with a current of 30 mA was 281 MPa, which is 53% of the tensile strength of the base metal and the weld was broken in the HAZ.

Using hollow structures containing more than one transition metal oxide seems to be essential to respond to the new generation of energy storage electrodes with remarkable performance for advanced expansions of new electronic devices. In this work, facile and controllable synthesis of multi-shelled V-doped Co3O4 hollow spheres derived from metal-organic framework through a solvothermal process followed by annealing as heat treatment has been studied. A comprehensive investigation of the hollow spheres in case of morphological, structural, and electrochemical behavior has been carried out. The multi-shelled V-doped Co3O4 (MS-V-CO) electrode displays well results, including electrochemical behavior (little internal resistance, fast kinetics, great reversibility, an excellent specific capacitance of 1593 F g−1), and structural features (high surface area (61.4 m2 g−1), multi shell structure, and wrinkled surface). An asymmetric supercapacitor (ASC) device has been assembled using multi shell vanadium doped cobalt oxide as the positive electrode (anode) and activated carbon (AC) as the negative electrode (cathode) and investigated for electrochemical performance. MS-V-CO//AC shows good behavior with a maximum energy density of 66.88 Wh kg−1 and power density of 240 Wkg−1 at 0.3 A g−1, relying on the total mass of active materials on both electrodes.

Dissimilar butt welding of Nb-1Zr to the 321 stainless steel was studied using electron beam welding. The aim of this study was investigation of the offset and microdilution effects on the weldability, microstructure and mechanical properties of this dissimilar joint. The offset of 50-50 and welding parameters of 13 mA and 1343 V showed the best weldability and penetration for the joint. The microdilution of Nb in the weld changes by going far from the base metals. The microdilution of Nb is the minimum at root of the weld (∼0.2) leading to formation of less brittle phases. As a result, no cracks are observed at the root. The microdilution of Nb at the top of weld just near to Nb-based alloy at a 200 μm narrow zone under surface increases (∼0.8) which leads to formation of more brittle phases and subsequent microcracks. Applying 200 μm thickness machining on the surface of weld can give a completely free of crack welds that show strength more than the Nb-alloy base. It is concluded that a sound weld can be achieved by 50-50 offset and Nb microdilution less than 0.6. No interlayer and/or transition piece are required, and appropriate mechanical properties can be obtained.

Perovskite solar cells (PSCs) based on ZnO have strikingly succeeded recently and researchers are attempting to develop the next generation of affordable and high-power conversion efficiency (PCE (%)) of PSC based on ZnO. The aim of this study is to investigate the effect of reduced graphene oxide (rGO) sheet on the PCE (%) enhancement of nickel (Ni)-doped ZnO and silver (Ag)-doped ZnO at 5 wt% as electron-transport layers (ETLs) in planar PSCs. According to results, with a comparison between Ni-doped ZnO and Ag-doped ZnO ETLs, it is obtained that Ag doping at 5 wt% is helpful in charge carrier separation and, consequently, a reduction in the recombination rate by creating defect states for ZnO-based PSCs is obtained. According to J–V characteristics, the electrochemical impedance (EIS) and Mott–Schottky (MS), using rGO sheet interlayer significantly impacts the electrical properties in un-doped and -doped ZnO-based PSCs. According to the results, the rGO sheet can passivate un-doped ZnO and doped-ZnO ETLs as well as can assist in quickly charge-carrier extraction from the perovskite layer and decrease the recombination in PSCs.

Developments in electronic industries for telecommunications and demands for decreasing electromagnetic radiation pollution result in developing researches on microwave absorption materials. The target of the present study is to design materials with high absorption properties for electromagnetic waves in the 12–18 GHz range. Thus, Fe3O4 magnetic nanoparticles were syntheses through chemical co-precipitation reinforced by ultrasonic. Then, BaTiO3 nanocrystalline powder was synthesized by the hydrothermal sol-gel method under atmospheric oxygen. Next, nano-particles of barium titanate were deposited on the multi-walled carbon nanotubes (BaTiO3@CNT). It was concluded that a magnetic-dielectric nanocomposite has superior microwave absorption properties in comparison to individual magnetic or dielectric absorbers. Also, in order to obtain an optimum absorption in a wide frequency band, dielectric-CNT nanocomposites represents higher properties than magnetic-CNT composites. It is concluded that composites with more magnetic percentage showed better absorption in low frequency band (12 GHz), whereas composites with more dielectric percentage exhibited superior absorption for high frequency band (18 GHz). 80–93% absorption was obtained in the frequency range of 16.7–18 GHz by composite 40M.20F.40C (40% paraffin, 20% magnetite, 40% multi-walled carbon nanotubes). Also, composite 40M.20B.40B@C (40% paraffin, 20% barium titanate, 40% barium titanate deposited on multi-walled carbon nanotubes) showed the absorption of 80–90%.

The present study has evaluated the surface rejuvenation of aged Inconel 617 superalloy by both GTAW and pulsed Nd:YAG laser techniques. The gas tungsten arc welding (GTAW) by heat input per unit length [Q/V (J/mm) ] of 280, 291.67, 309.74 and 225.48 (J/mm), and the pulse Nd:YAG laser process by the 15.71, 19.43 and 22.32 (J/mm), were employed. The Rosenthal equation was used for calculation of mushy zone (MZ) and partially-melted zone (PMZ). Size of MZ and PMZ in GTAW are more than 31 and 6 times than that of formed in pulsed Nd:YAG laser. According to the characterizations, solidification and liquation cracks were observed in these areas produced by GTAW whereas no cracks were identified in laser treated samples. Also, line scan EDS analyses demonstrated the interdendritic chromium and molybdenum segregation, which facilitated formation of hot cracks. With reduction in heat input per unit length, the hardness increased and the size of solidified metal microstructure reduced in pulse Nd:YAG laser. These comparative results showed that pulse Nd:YAG laser can easily be utilized as a new rejuvenation technique for aged Alloy 617 in comparison to the conventional processes due to extremely narrow MZ and HAZ and better surface soundness and mechanical properties.

The production of hydrogen by water electrolysis fundamentally requires growth of strong and effective oxygen evolutional electrocatalysts. Transition metal selenides, comprising of earth abundant elements have attracted regards as superb electrocatalysts for oxygen evolution reaction (OER) in the alkaline electrolyte. Toward defeat the huge overpotential for OER, in this manuscript we investigate the expansion of Fe doped cobalt-diselenide (Fe-CoSe2) nanostructure over 3D nickel foam (NF) through a simple and scalable electrodeposition technique. The prepared Fe-CoSe2/NF electrode demands an overpotential of only 220 and 256 mV to attain the current density of 10 and 100 mA cm−2, respectively. Moreover, the Fe-CoSe2/NF exhibits negligible tafel slope (35.6 mV dec−1) and good stability.

A quantitative relation between the γ/γ′ and γ/Laves intermetallics was investigated with the change of chemical composition, i.e., Ti, Al and Nb in the third generation of nickel-based superalloys. The results demonstrated that the maximum amount of intermetallic eutectics (i.e., 41.5%, mass fraction) has been formed in 9.8% (Ti+Al). It is predicted that high level of intermetallics formed in the 3GSA-HNM-1 (γ-9.8%(Ti+Al)) deteriorates its castability. The type and morphology of eutectic intermetallics change and the amount considerably diminishes by decreasing Ti+Al in 3GSA-HNM-2 (γ-7.6%(Ti+Al), 1.5% Nb). Thus, it is predicted that the castability for the 3GSA-HNM-2 improves. The amount of Laves intermetallics shows an ascending behavior again, however, with less intensity by increasing the Nb content in the 3GSA-HNM-3 (γ-5.7%(Ti+Al), 2.9% Nb). It can be concluded that for 3GSA-HNM-3 with composition of γ-5.7%(Ti+Al) and 2.9% Nb, the optimized castability can be anticipated, because the minimum amount of eutectic intermetallics (i.e., 4.7%) is formed.

The present research aims to establish a quantitative relation between microstructure and chemical composition (i.e., Ti, Al, and Nb) of newly designed nickel-based superalloys. This research attempts to identify an optimum microstructure at which the minimum quantities of γ/γ′ and γ/γ″ compounds are achieved and the best castability is predicted. The results demonstrate that the highest quantity of intermetallic eutectics (i.e., 41.5wt%) is formed at 9.8wt% (Ti + Al). A significant quantity of intermetallics formed in superalloy 1 (with a composition of γ − 9.8wt% (Ti + Al)), which can deteriorate its castability. The type and morphology of the eutectics changed and the amount considerably decreased with decreasing Ti + Al content in superalloy 2 (with a composition of γ − 7.6wt% (Ti + Al), 1.5wt% Nb). Thus, it is predicted that the castability would improve for superalloy 2. The same trend was observed for superalloy 4 (with a composition of γ − 3.7wt% (Ti + Al), 4.4wt% Nb). This means that the amount of Laves increases with increasing Nb (to 4.4wt%) and decreasing Ti + Al (to 3.7wt%) in superalloy 4. The best castability was predicted for superalloy 3 (with a composition of γ − 5.7wt% (Ti + Al), 2.8wt% Nb).

The purpose of the present study is to introduce the weld quantitative solidification paths in the newly designed third-generation superalloys. The research has been conducted using both computational and experimental approaches. The model used the Scheil solidification relations to correlate the partitioning elements with their effects on the solidification paths. Accordingly, the k values were calculated for all the participating elements in the superalloy welds. The results of model demonstrated that these were very close to unity for austenite former elements, i.e. Ni, Co, Cr and Fe, while the other elements such as Ti, Nb and Mo displayed a significant tendency for segregation. The mathematical equations were calculated for weld solidification paths of superalloys. In all the welds, a remarkable segregation behaviour was observed, especially for Nb and Ti. The solidification path equations predicted type and amount of secondary phases. The solidification paths were compared with eutectic reac...

It is observed that in laser welding of aluminum alloys, magnesium can evaporate, and the weld penetration is dependent on Mg content of the alloy and Mg loss from the weld pool. In this research, it is proposed that the presence of Mg not in the base metal alloy, but rather the presence of Mg vapor in the plasma plume over the weld pool affects the laser absorption, and it is through this phenomenon that the weld profile and penetration is affected. Numerical simulation was performed to determine the relationship between the weld profile to estimate the effective laser absorption coefficient of four Al alloys and in parallel EPMA technique was used to determine the Mg losses of the weld metals. The combined analysis of the results showed that increasing the laser pulse energy (decreasing laser pulse frequency), Mg evaporation is increased, and that, in turn, increased the effective laser absorption coefficient. However, more laser power absorption does not necessarily mean more weld penetration. Laser absorption results in weld penetration, once the threshold Mg evaporation rate of 200 × 10 - 6 g/cm2 is passed.

Titanium alloys are commonly used in orthopedic devices due to their good corrosion resistance, high specific strength and excellent biological response. The direct contact between the implant surface and the host tissue results in notable effect of surface properties such as surface topography on the biological responses. The aim of this study is to investigate the effect of frequency of pulsed Nd-YAG laser on Ti6Al4V alloy surface topography and its influence on the improvement of biocompatibility while other laser parameters kept constant. The range of applied frequency values were selected from 1 to 20 Hz. The range of surface roughness was found between 452 nm and 3.37 μm. The untreated sample and also samples with the highest and the lowest average surface roughness parameter were subjected to the further analyses. Characterization of the samples was performed with surface roughness tester, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). The high rate of melt and solidification during the laser treatment led to the martensite formation and consequently an increase about 12–25% in hardness. Furthermore, in vitro study was carried out using MG-63 osteoblast like cells. The analyses of cell viability for 3 culture times, cell morphology and cell spreading area revealed that sample with the highest average surface roughness parameter is more biocompatible. 10 Hz frequency was found as the optimum parameter which led to the highest surface roughness and thus the biocompatibility enhancement. In conclusion, the pulsed Nd-YAG laser with an optimum value of applied frequency can be utilized as an effective technique to improve the biological characteristics.