zahrasadat seyedraoufi

In this Article, laser-based additive manufacturing (AM) of Ni-based superalloys has been evaluated. By reviewing past research and recognizing the challenges and benefits of additive manufacturing, the future of this path can be well described. For this purpose, it is very important and useful to know the target industries, the resulting microstructure, the relationship between the microstructure and the mechanical properties of the final part. In addition, the ways to prevent possible defects of this process are summarized in the report. This report tries to introduce this process in the direction of less damage to the environment and available resources. To be introduced as an environmentally friendly method for manufacturing parts needed for energy supply and transmission. In the future, more reports of this process will be provided by the authors of this review article.

In the present study, Ni-P-GO nanocomposite coating with different pH values of path was applied on the AZ31D alloy by electroless. After coating, heat treatment was performed at 400°C for 1 h. The results of microstructural investigations by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) showed that the coating with semi-amorphous structure and cauliflower morphology was formed on the surface of the substrate. According to the EDS results, with the increase in the pH of the electroless bath, the amount of phosphorus coating and absorption of graphene oxide (GO) nanosheets increased. After the heat treatment, maintaining the morphology and growth of colonies, the coating was completely crystallized and nickel phosphide compounds such as Ni2P, Ni3P and Ni5P3 were formed, which increased the hardness. The microhardness test results showed that the hardness and toughness of the coating decreases with the increase of phosphorus. By heat treatment, the maximum hardness reached 1151 H.v. and the toughness decreased to 2.3 (MPa/√m). The results of the polarization test showed that the coating leads to an increase in the corrosion resistance of the substrate and a decrease in the corrosion density up to 0.443 µA/cm². Although heat treatment led to a decrease in corrosion resistance compared to before. Also, increasing the phosphorus of matrix to increase the density of the hypophosphite layer and absorb more GO leads to an increase in corrosion resistance.

In this research, after pressing in a cylindrical mold, the AA 7075 alloy swarf was melted and cast in a wet sand mold. After rolling and cutting, sheets with two different thicknesses of 6 and 20 mm were obtained. The sheets after homogenization were solutionized at 485°C for 30 and 90 minutes, respectively, due to differences in thickness and thermal gradients. The solutionized samples were quenched in 3 polymer solutions containing 10, 30, and 50% Poly Alekylene Glycol. The results showed that melting, casting, rolling, and heat treatment of AA7075 alloy swarf similar properties to this alloy is achievable. Microstructural studies by optical microscopes (OM), Field Emission Scanning Electron Microscopy (FESEM), and X-ray diffraction (XRD) showed that by increasing the quenching rate after the solutionizing process, precipitation increases during aging. The tensile test results indicated that as the quench rate and internal energy increase, the diffusion driving force would increase the precipitation of alloying elements. Hence, this leads to an increase in hardness and reduction of its strain after aging.

Thermal Barrier Coatings (TBCs) reduce the working temperature of the substrates and protect them from hot corrosion and oxidation. In recent years, scientific research into the TBCs and their innovative applications have gained increasing popularity insofar as since 1980, the number of relevant published articles has increased up to about 400 times annually. These coatings play an essential role in enhacing the efficiency of the substrate and engines and for this reason, tracking their research process can help advance future research studies and accelerate their progress expansion rate. According to the results from scientometrics and tracking research, the United States was initially ranked first in article production in this field of surface engineering, followed by Germany and England. However, since 2011, China has remained in the first place by a large margin. The combined annual growth rates of Iran and India reached their highest value, indicating that these countries concentrated on the gas turbine and energy sectors. Since these coatings play a significant role in improving the performance of gas turbines, variations in their scientific progress can be considered one of the leading indicators of material engineering progress in such turbines.

1.4923 stainless steel is one of the options for producing Iranian gas turbine (IGT25) compressor blades and upgrading IGT25 +., as well as the importance of wear resistance in turbine parts and the small number of studies in the field of wear as a destructive mechanism of turbine parts, in this research the effect of residual stress caused by shot peening on the wear resistance of steel 1.4923 was investigated. To create the compressive residual stress, shot peening operations were used at 5, 10, 15 and 20 minutes. Microstructural studies by optical microscopy (OM) and scanning electron microscopy (SEM) showed that with increasing shot peening time, the thickness of the plastic deformation area increases so that the plastic deformation area can be divided into three plastic deformation areas. Severe, ordinary plastic deformation and the area affected by plastic deformation. Calculations on the results of X-ray diffraction (XRD) showed that with increasing shot peening time, the amount of compressive residual stress increases to 694 MPa. With increasing compressive residual stress on the surface, the wear resistance of the samples increased up to 90% due to the increase in the density of dislocations and grain refining.  Also, the investigation of worn surfaces by SEM showed that the wear mechanism in the samples is oxide adhesive wear and increasing the residual stress of the samples causes the transfer of the wear regime to mild wear abrasion with the appearance of crater areas.

In this research, nickel was electrodeposited on AA2024 aluminum using direct current. The coated specimens were then heat-treated at different temperatures of 450, 500, and 550°C for 30, 60, 90 and 120 minutes under argon shielding gas. The treated specimens were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction analysis (XRD). The presence of Al3Ni2 and Al3Ni intermetallic compounds were noticed at 450°C after 120 minutes and 500 and 550°C after 60 minutes. Microstructural studies also demonstrated that heat treatment at 550°C for 90 and 120 minutes leads to cracks at the coating/substrate interface. The maximum hardness reached 1000 Vickers after heat treating at 500°C for 120 minutes.

In this study, Ni-P-GO nanocomposite coating was applied on the AZ31D surface by the electroless method. After coating, the crystallization process was carried out at 250 °C and 500 °C temperatures for one hour. As a result, microstructural studies by X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that a coating with the semi-amorphous cauliflower morphology formed on the surface. Moreover, after the crystallization process not only the morphology was preserved and the coating colony experienced growth, but also the intermediate phase of nickel phosphide was formed. Therefore, the results showed that as P content increases, the tendency to absorb GO nanoparticles increases. At low temperatures, the Ni2P phase was initially formed. However, as the P content and the crystallization temperature increased Ni2P transformed to Ni3P. As a consequence, this improved the hardness due to both precipitation of the intermediate phases and the crystallization process. As the P increased at 500 °C, the energy needed for forming unstable Ni5p < sub>2 and Ni8p < sub>3 phases was provided. The results of the polarization test showed that applying the coating in comparison with the substrate leads to an increase in corrosion resistance. Besides, increasing P in the field increases the density of the hypophosphite layer which leads to an improvement in corrosion resistance. Corrosion resistance diminished as heat treatment was conducted. Also, as the temperature of the heat treatment increased, 0.424 A/cm2µ passed the surface, which is still lower than 1.328 A/cm2µ, this is specific to the uncoated substrate

In the present study, cast IN718 superalloys solutionized at 1050◦C for 150 min. Afterwards, the samples were quenched with three various cooling rates including 240◦C/s, 5◦C/s and 0.1◦C/s. After solutionizing, the samples were aged at 750◦C for 30, 60, and 90 hrs. Microstructural investigation was carried out by optical microscopy (OM), Field Emission Scanning Electron Microscopy (FESEM), and X-ray diffraction (XRD). The results indicated that as the cooling rate increased, the conditions for complete dissolution were provided and only a small amount of MC carbide (TiC) phase remains in the matrix. By reducing the cooling rate and increasing aging time, due to the increase in volume fraction and size of secondary precipitates, the shear transformation of the γ'' to δ increases, and consequently, the δ precipitates increased. After solutionizing, as the cooling rate increased, the hardness due to the decrease in the amount of cooling precipitates decreased. Besides, as the aging time increases, due to the abnormal growth of precipitates, hardness first increased and then experienced a decrease.

In the present study, IN738LC superalloy ingot was re-melted and cast, then heat treated under ‎standard conditions. Microstructural studies with field emission scanning electron microscopy ‎‎(FESEM) equipped energy dispersive spectroscopy (EDS) showed that after re-melting and ‎controlled casting, the amount of porosity and size of γ' precipitates decreases. Also, with ‎applying the standard heat treatment cycle, the primary γ' precipitates less than 1µm in size and ‎cubic morphology and nano‏spherical‏ ‏secondary γ' precipitates appeared and eutectic γ-γˈ ‎regions were completely eliminated. Vickers hardness test results under a load of 10 Kg showed ‎that the lowest hardness is related to the solutionized sample due to remove the coarsened γ' ‎precipitates and the highest hardness (833 H.V.) is obtained after aging. According to the results ‎of the tensile test at ambient and 750◦C temperatures, by re-melting and applying the standard ‎heat treatment due to structural modification, strength and elongation increased at both ambient ‎temperature and 750◦C. Also, with applying the standard heat treatment, failure mechanism of ‎IN738LC superalloy was transferred from brittle trans-dendritic failure to brittle inter-dendritic ‎failure with little footprints of ductile fracture.‎

Abstract     Nowadays, magnesium alloys such as a new generation of biodegradable materials have been noticed by researchers. In this study, to the sanitation of biodegradability and biocompatibility of magnesium alloys, TiO2/MgO dual layer coating was formed by magnetron sputtering on AZ91 and the microstructure, corrosion behavior and biocompatibility properties of coating were investigated. The coating microstructure was studied via field emission scanning electron microscopy (FESEM) X-ray diffraction (XRD). The corrosion resistance of the substrate and coated sample was evaluated by electrochemical polarization test in simulated body solution (SBF). To evaluate biocompatibility MTT and cell viability tests were used. The results showed that the corrosion potential after the surface coating with TiO2/ MgO was more positive, changing from 1.532 V for the uncoated sample to 1.436 V for the coated sample.. The coating was observed in quasi-spherical morphology with MgTi2O5 and MgTiO3 phases in interface of coating and substrate and two layers of coating too according to XRD analysis results. The results of the biocompatibility tests also showed that the viability of the osteoblastic cells on the coated sample increased compared to substrate.

In this study, due to the poor corrosion resistance of Mg alloys in aquatic environments, TiO2 ceramic coating applied by the magnetron sputtering technique to enhance the corrosion resistance and biocompatibility of AZ91D alloy. The Microstructural studies by field emission scanning electron microscopy (FESEM) and X-Ray diffraction (XRD) analysis showed that the coating formed uniformly with semi spherical morphology containing TiO2, Mg2TiO4 and MgTi2O5 spinels, so that above of the substrate was Ti diffiusion affected. The polarization corrosion test in simulated body fluid (SBF) solution showed that applying the coating by reducing the corrosion current by about 100 times improves the corrosion resistance of the magnesium substrate so that MTT results show that density and number of cells on the coated sample is higher than substrate without coating due to cell joint stronger. The viability of MG67 cells on the samples increased from 77% in the substrate to 89% in the coated sample.

In the present study, the service-exposed gas turbine blade was rejuvenated after 80000 hr of service. In this report, the effect of cooling on liquid nitrogen and cryogenic after two stages of solution (full and partial) was investigated. Microstructural studies by scanning electron microscopy (SEM) showed that increasing of the cooling rate in full solution resulted decrease in the size and percentage of volume fraction of γ´ precipitates after aging. whereas the cryogenic effect at full solution stage was less than the cooling rate. The effect of high cooling rate on partial solution was a decrease in γ´ precipitates volume fraction after aging compared to similar effect on full solution stage. Cryogenic treatment after partial solution increased the secondary γ´ precipitates volume fraction and size till 230 nm. High cooling rate of partial solution resulted in the maximum of hardness after aging and high cooling rate of full solution resulted in minimum of hardness after aging.

In this study, IN738LC super alloy samples were solutionized at 1210 °C for 5 hours. After solutionizing, the samples were cooled in both air and liquid nitrogen. One of the air-cooled samples after reaching the room temperature was stored in liquid nitrogen for 2 hours. To investigate the effects of high cooling rate and sub-zero operations on the microstructure and hardness, the samples were characterized by scanning electron microscopy (SEM) and hardness test. Deeper sub-zero operations reduced the size of the sediment to 117 nm. While cooling in liquid nitrogen reduced the size of the sediment to 76 nm. This suggests that the cold weather in the air has provided the opportunity for growth to precipitate. By increasing cooling rate and keep at deep zero, the hardness of the samples decreased, so that the minimum hardness was related to the sample stored in liquid nitrogen. The results of this research can be applied to new blades after casting and also under service and to help improve the heat treatment process.

In the present study, in order to increase the wear resistance and surface hardness of Ni-Br-Al alloy, coating process of electroless plating was used to make nickel-boron coating. Microstructural investigations by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) showed that the nickel-boron coating was uniformly formed with completely amorphous structure, thickness of about 7 µm, and the cauliflower morphology on the substrate. The resulting coating with a hardness of 788 (Hv50) increased the hardness of the substrate by about 40%. To increase the hardness, the coated samples were heat treated at three temperatures of 310, 410, and 510°C for 70 minutes. After the heat treatment, the hardness of the samples increased to 1365 (Hv). By increasing the temperature of the heat treatment from 410°C, the hardness of the samples decreased. XRD results showed that at 310°C temperature, the coating structure was maintained amorphous and at temperatures of 410 and 510 °C, a completely crystalline structure was created. Also, XRD analysis showed the formation of Ni2B and Ni3B precipitates in samples after the heat treatment. According to results of the wear test on the disk, the highest wear resistance was related to the sample coated and heat treated at 410 °C temperature.

In the present research porous Mg-Zn scaffolds with different Zn amount and porosities were synthesized by powder metallurgy process as potential degradable materials for orthopedic applications. The microstructures, composition, mechanical properties and in vitro biodegradability of the scaffolds were investigated. Optic microscopy (OM) images showed that the Mg-Zn scaffolds exhibit homogeneously distributed and interconnected pores with the size of about 150–400 µm. The X-ray diffractometer (XRD) results indicated the formed intermetallics consist of Mg12Zn13 and Mg51Zn20 in the Mg matrix. Compressive tests showed that decrease of porosity and the addition of Zn increases the compressive strength of specimens. Electrochemical tests indicated that with increase of porosity, the corrosion current density of scaffolds increased and Mg-Zn scaffolds synthesized improved the in vitro biodegradability property of the Mg; the best biodegradability property was obtained with 3% Zn and the porosity of about 7% ; further increase of Zn content up 4% deteriorates biodegradability. It is found that the products of immersion in simulated body fluid (SBF) are identified to be HAP, (Ca,Mg)3(PO4)2 and Mg(OH)2 and MG63 cells adhere and proliferate on the surface of the scaffolds, making them a promising choice for orthopedic application.

In this paper, effect of solution heat treatment media of IN738LC superalloy on the microstructure and hardness was investigated. Two solution heat treatment medias were selected, solubilizing in the normal or conventional furnace, and solubilizing in the salt base. For this purpose, the samples were solubilized in a temperature range of 1090-1200°C for 20-30 minutes in normal condition and 10-12 minutes in the salt bath, and then aged at 248°C in 850°C. The results of the scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM) showed that increasing the heating rate improves the solution process, and with increasing the temperature and time, the volume fraction of 'γ precipitates decreased by 26% in normal condition and 29% in salt bath. The size of the residual 'γ precipitates after solution in the salt bath is smaller than normal state, and at high temperatures, due to the activation of the aggregation mechanisms, the size and volume fraction of residual precipitates in the salt bath increased compared to the normal condition. Solution in the salt bath reduced the size of the primary'γ compared to the normal condition and increased the volume fraction of the secondary 'γ after the aging. After aging, the total volume fraction of precipitates increased by about 30% and 40%, respectively, in the normal condition and in salt bath. The results showed that the secondary 'γ precipitates are about 16nm smaller than usual and the hardness of the alloy is strongly influenced by the characteristics of 'γ precipitates and the variables of the solution treatment. Increasing the heating rate at the solution resulted in a further increase in hardness after aging and a further reduction in hardness after solution, and in both conditions increasing temperature and time of solution reduced the hardness of the samples after solution and increased after aging.

The aim of this research is to synthesize and study the microstructure and mechanical properties of biodegradable Mg-Zn scaffolds for orthopedic applications. For this purpose, Mg-Zn scaffolds containing 3 and 5 wt. % Zn were prepared using 15, 25 and 35 Vol% of urea by powder metallurgy and were subjected to heat treatment at different temperatures of 500, 550, 565, and 580 C to determine the optimum sintering temperature. Then, the chemical composition, microstructure and mechanical properties of the scaffolds were investigated. According to the results, the average diameter of macro- pores and micro- pores in the scaffolds are about 400-200 and less than 100 ?m, respectively. The results showed that the compressive strength of Mg-Zn scaffolds increases with decreasing porosity amount. In fact, the porosity in the sample reduces the mechanical strength of the scaffold due to the stress concentrating areas and the reduction of the effective surface of scaffold against external stresses. Also, by increasing the Zn content, the strength of the Mg-Zn scaffold increases through the strength of the solid solution and dispersion strengthening. However, in all of the made scaffolds, the compressive strength is in the range of compressive strength of the human body's bone. The results of the SEM micrographs also showed that, by adding Zn, the intermetallic compounds Mg7Zn3 and MgZn could be formed. The results of polarization test showed that, by adding 5 wt.% of Zn in comparison with samples containing 3 wt%, due to the formation of more intermetallic compounds, the corrosion resistance decreased. According to the results of cytotoxicity measurement, the cell viability of scaffolds containing 3 wt% Zn was higher than those containing 5 wt% Zn.

Nickel base superalloys are used for their unique properties in the construction of various components of ground and air gas turbines. In the present study, the IN738LC superalloy was solubilized at a temperature of 1090 ° C to 1200 ° C and at a time of 30 to 120 minutes. The samples were aged for 24 hours after solution heat treatment at 800 °C. Before and after aging, samples were examined by optical microscopes (OM), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM). The results showed that increasing the temperature and time of solution heat treatment reduces the volume percentage and the size of the g¢ precipitates, while the volume percentage and size of the g¢ precipitates are increased and decreased, respectively, after aging. Micro hardness tests showed that hardness of the superalloy was strongly influenced by the characteristics of sediments. By increasing the solubility time and reducing the volume percentage of g¢ precipitates, the hardness decreased and increased after aging.