mohsen samiee

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.

IN718 alloy is a high strength Nickel base superalloy that mainly used in moderate temperatures and corrosive service conditions. In the present study, samples produced by selective laser melting (SLM) at 1040 °C for 120 minutes were prepared under solution treatment. After solution, the samples were cooled in three cooling media of water, air and extinguished furnace with open door. Finally, the samples were aged in three standard conditions for 48 and 72 hours. To investigate the effect of cooling rate after solution and aging time on precipitates characteristics and microstructure of samples, Field Emission Scanning Electron Microscope (FESEM), X-ray diffraction (XRD) and hardness test were used. The results showed that increasing the aging time under constant solution conditions increases the volume fraction and the size of the secondary phases. Also, reducing the cooling rate in the solution step leads to increasing the hardness of the samples in the aging stage. Finally, with increasing aging time, the maximum hardness of the sample was 794H. v.

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.