نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 66 (پاییز 1402)

In this research, thermal shock behavior, three types of yttria-stabilized zirconia (YSZ), yttria-stabilized zirconia and mullite coating (YSZ/Mullite) and gradient coating of yttria-stabilized zirconia and mullite (YSZ/Mullite) thermal barrier coatings on Inconel 738 low carbon nickel base superalloy along with bond coated by plasma spray method was compared.Using scanning electron microscopy (SEM) and X-ray diffraction (XRD), microstructure and phase analysis were done. The percentage of porosity and thermal shock of coatings at 1100°C temperature was investigated and compared. The results showed that with the increase of mullite in layer and gradient on YSZ coatings, the number of holes and porosity decreases, which is due to the increase in the amount of melted mullite particles. The percentage of porosity related to layer and gradient coating of mullite was obtained as 8 and 3.5% respectively. Using the results of the thermal shock test, it was determined that the lifetime of the mullite layer coating is longer than the mullite gradient coating and the YSZ coating. The maximum lifespan of the layered coating of mullite was recorded as 70 cycles of 10 minutes in a furnace with a temperature of 1100°C. The gradient coatings of mullite showed a higher percentage of shrinkage in thermal shock than the layered mullite coating.

Silicon nitride ceramics are materials with excellent mechanical, dielectric and thermal properties which with such properties is one of the main candidates for use in high temperature environments. In this study, the effect of sintering temperature on microstructure control and densification and optimization of mechanical and dielectric properties of silicon nitride ceramics prepared by hot pressing at different temperatures of 1500 °C, 1600 °C, 1700 °C and 1800 °C has been investigated. Scanning electron microscopy and X-ray diffraction have been used to study the microstructure and analysis of the formed phases, respectively. According to the X-ray diffraction pattern and the Gazara-Mesier relationship, in the sintered samples at 1600 °C and 1700 °C, all alpha phases were converted to beta, and in the sintered samples at 1500 °C, the conversion rate was 95.45%. Is. The results show that increasing the sintering temperature from 1500˚C to 1800˚C leads to larger rod-shaped grains and achieves dual microstructure and the average grain diameter has increased from 0.7 µm to 1.34 µm. sintered specimen at 1500 °C, with the lowest average diameter (0.7 µm) among other specimens, has the highest flexural strength of 550 ± 9.5 Mpa. Is By increasing the average grain size and decreasing the α/β phase ratio due to the increase in fusion temperature, the mean dielectric constant and tangent of the sample loss increased from 4.5 to 9.2 and from 0.099 to 0.22, respectively

Alumina-C refractories have been widely used as slide gate submerged entry nozzles and mono block stoppers in steelmaking due to their unique physical and mechanical properties.In this research,the effect of different source of alumina having unlike surface areas(nano and mesoporous)and MWCNT additives on physical and mechanical properties of Al2O3-C refractories was investigated.In this regard mesoporous alumina was synthesized by sol-gel method.Then the mesoporous and nano alumina precursors were added to the functionalized MWCNT.In order to better distribution of 0.5-1.5 wt% nano additives the additives were firstly added to the matrix and then mixed with coarse particles of Al2O3-C refractories. Following in order to physical and mechanical properties investigation, all samples pressed under 150Mpa pressure by uniaxial then pressed and tempered at 200 ℃ for 6h, and afterward fired under coke atmosphere at 1450℃ for 2 h.The bulk density apparent porosity and cold crushing strength were determined according to their respective standard. Moreover their microstructure and phase analysis was investigated by XRD and SEM.The results confirmed that the sample containing1wt% nano Al2O3-MWCNT composite showed the highest CCS of about 137 Mpa,and sample with1.5 wt% mesoporous Al2O3 showed the lowest CCS (94 Mpa).The improvement of mechanical properties could be related to the higher SiC formation in the presence of nano Al2O3- MWCNT by vapor- solid mechanism. The main reason for decreasing mechanical properties in the presence of mesoporous additives could be attributed to limiting of gas-solid reaction due to trap of gases and therefore lower formation of SiC whiskers through the matrix.

Implant surface modification by creating laser surface texturing is the best known method to increase adhesion. The best pattern of laser surface texturing is still unknown. In order to investigate other features of the new pattern proposed by the authors, in this research, first, the new surface patterns of intersecting lines with angles of 0, 15, 30, 45, 60, 75, and 90 degrees on the surface of Ti6Al4V alloy using pulse Nd: YAG laser was created. Then the contact angle of water droplets was measured by two 1- recording and analyzing the image of the droplet and 2- using Extrand and Moon equations. Water droplets were selected in two volumes of 1 μlit and 25 μlit. Using metallurgical microscope, SEM, applying Wenzel and Cassie equations and drawing the corresponding diagrams, the effect of the angle between the lines, height, separation, and width of the surface texture columns on the contact angle of the droplet was investigated. The classical model of textures wettability was determined. The results showed for droplet with volume of 1 μlit the contact angle in both methods is almost constant and independent of the angle of the intersecting lines which is in good agreement with the results of previous researches. For droplet with volume of 25 μlit the contact angle in both methods is variable and dependent on the angle of the intersecting lines. The classical model of textures wettability in both droplet volumes is consistent with Wenzel's model.

In targeted drug delivery, the drug is released at specific points and conditions, and in this study, magnetite nuclei were used to target the drug system. First, magnetite nanoparticles were synthesized by co-precipitation of two- and three coordinated iron chloride salts (FeCl2 and FeCl3).Carbon dioxide quantum dots, which had been hydrolyzed by citric acid and whose surface was ineffective by diethylamine, were then placed in silica cavities by physical absorption. The effective drug melatonin was also loaded on the system by physical absorption, and the method of releasing this drug by dialysis bag was carefully examined in the simulated environment of blood and cancer tissue, and the quantum yield of the system was determined. The accuracy of the operations performed by electron microscopy, nitrogen uptake and absorption, factor characterization, X-ray diffraction, magnetometry and infrared spectroscopy were investigated. The results showed that the loading of melatonin and carbon quantum dots was well performed on silica nanoparticles with magnetite nuclei, and the system also releases the drug well at room temperature.

One of the most important finishing operations that is usually performed as the final process when producing a part is the modification of surface properties with surface engineering operations. Many metals can be coated by the electroless-coating method. Electroless nickel-boron coatings have been widely used in the industry due to their cheap price and uniform coating capability. In this article, nickel-boron-nanodiamond electroless coating with different concentrations of nanodiamond was applied on AISI 4140 steel, and its structural properties and wear behavior were investigated. The structural properties of the coatings were investigated with the help of X-ray diffraction tests, scanning electron microscopy, and hardness test. Also, the friction coefficient and wear properties of the samples were studied using the pin-on-disc test. The results show that with the increase in nanodiamond concentration, the structure of the coating changes from amorphous to semi-crystalline. In addition, the electron microscope images and the hardness test results show that adding nanodiamonds to the electroless bath increases the hardness. Adding nanodiamonds to a concentration of 0.5 g/L improved the wear resistance and reduced the friction coefficient. However, increasing the concentration of nanodiamonds up to 1 g/L due to the agglomeration of nanodiamonds caused an increase in the specific wear rate of the coating.