امیر عبدالله زاده

The properties of coatings deposited by cold spray depend on the parameters of the process. The aim of this research is to investigate the effect of gas pressure and stand-off distance of cold spray process of zinc on a low carbon steel substrate.

In this research, zinc powder was sprayed at pressures of 20 and 30 bar and stand-off distances of 20 and 30 mm. The microstructure of the coatings was investigated using optical and scanning electron microscope and the micro-hardness of the coatings was measured. Then, the selected coating and steel substrate were subjected to polarization corrosion test.

The results showed that increasing the gas pressure from 20 to 30 bar decreased the porosity and increased the micro-hardness due to further deformation. Also, for a constant pressure, the stand-off distance of 20 mm has the lowest porosity and the highest micro-hardness due to the higher temperature of the particles when impact the substrate. The results obtained from the polarization test show that the coating has a sacrificial nature compared to the substrate and reduces the corrosion current density by 48% and corrosion rate by 33% compared to the substrate.

In this study, the effect of gas pressure and stand-off distance of cold spray process of zinc on low carbon steel substrate was investigated. The results showed that increasing the gas pressure from 20 to 30 bar and reducing the stand-off distance from 30 to 20 mm improved porosity and increased coatings micro-hardness. The results of this study can be used to optimize the parameters of the cold spraying of zinc for use in various industries such as automotive, power plants and marine infrastructure.

The purpose of this study is to investigate the microstructure and surface properties of titanium-aluminum nitride (TiAlN) nanostructured coatings produced at different deposition temperatures. The TiAlN nanostructured coatings were deposited on nitrided hot-work tool steel (H11) using pulsed direct current plasma assisted chemical vapor deposition method (DC- PACVD). The coatings were produced under the same conditions such as duty cycle, frequency and H2/Ar/N2 gas ratio at 33%, 10 kHz and 400/150/50 sccm, respectively. Also the specimens were deposited at temperatures of 470, 485, 500 and 515 °C by PACVD method. TiN coating interlayer was used to improve the adhesion strength of TiAlN coatings to the substrate. FESEM , SEM and XRD devices were used to characterize the coatings and Vickers micro-hardness and scratch test were used to evaluate the mechanical properties and adhesion strength of the coatings. The results indicated that the maximum hardness of TiAlN coating produced at 485 °C. It is attributed to various factors such as lattice parameter, crystallite size and amount of chlorine in the chemical composition of the coating. Also, due to the formation of a nanoscale- thin layer of Fe4N at the interface between the coating and the substrate at the temperatures above 500 °C, the adhesion strength of the TiAlN coating reduces. By quantitative evaluation of the adhesion of the coatings, it was found that the coating formed at the temperature of 485 °C withstands the maximum critical load (23 N) of the scratch.

The purpose of this study is to produce Zn/ZnO Nanocomposite coatings using cold spray process for sputtering targets applications. Nanocomposite powders were synthesized with different weight percentages of 25, 50 and 75 of ZnO nanoparticles using mechanical milling process. The feedstock was sprayed on pure copper substrates using nitrogen gas at a constant temperature of 150 °C, pressure of 15 bar and the stand-off distance of 35 mm. The morphology of composite powders was studied using transmiton electron microscopy; and the wear surface, microstructure and wear debris were studied using scanning electron microscopy. The effect of different values of ZnO nanoparticles on the wear behavior, adhesion strength and surface roughness of the coatings were studied. The coatings are evaluated by scanning electron microscopy, optical microscopy, three‐point bending tests, roughness analysis. The results showed that by increasing the nanoparticles, due to breaking and crushing of powders, as well as the lack of proper bonding of the ZnO particles to the substrate, the friction coefficient decreases and then increases with decreasing the surface roughness of the coldsprayed surface, While the adhesion strength, first increases and then decreases. It was also found that increasing the ceramic particles, change the mechanism of adhesive wear to abrasive wear.

With the development of the applications of magnesium components in many industries, relatively low corrosion and wear resistance of this alloy leads to the development of different protective layers. In this paper, the effect of SiC reinforcement on the cold spraying behavior of Al-SiC powder on a magnesium alloy substrate is addressed. The pure Al powder is blended with different amount of SiC powder including 25, 50 and 75 wt.%. The feedstock is sprayed on sand blasted AZ31B substrate. The process is carried out with 30bar pressure and 300°C temperature of process gas (Nitrogen). A 20mm standoff distance is used for spraying. The effect of different values of SiC on the deposition behavior of the Al-SiC powders are investigated. The coatings cross-section is evaluated by scanning electron microscopy, image analysis software and microhardness test. The results showed that the high velocity reinforcement particles leads to the SiC particle breaking during the process. This phenomenon increases the porosity of the coating. Furthermore, the higher value of reinforcement in initial powder leads to the homogenous distribution of them and the higher coating hardness. The hardness of the Al-75wt% SiC coating is about 90 HV, which is increased by 80% compared to pure Al coating microhardness.

In this study, Al-Al2O3 composite coating produced by cold spray method on Al-7075-T6 sheet. The pure Al powder is blended with different amount of Al2O3 powder including 25, 50 and 75 wt. %. The feedstock is sprayed on sand blasted substrate using nitrogen gas at a constant temperature of 300 °C, pressure of 30 bar and the stand-off distance of 20 mm. The effect of different values of Al2O3 on the deposition behavior of the Al-Al2O3 powders are investigated. Microstructural characteristics of the coatings are evaluated by scanning electron microscopy, image analysis software, microhardness and X-ray diffraction tests. The results showed that the high velocity of particles leads to the Al2O3 particle breaking during the process. This phenomenon increases the porosity of the coatings Furthermore, the higher value of reinforcement in the initial powder leads to the homogenous distribution of them and the higher coating hardness. The hardness of the Al-75Al2O3 coating is 104 HV, which is increased by 85% compared to pure Al coating. X-ray diffraction test indicated the fine-grained structure, no-oxidation and no phase transformation in the pure and composite coatings.

In the present research, FSW of thin sheets of the 7075-T6 aluminum alloy were investigated. Welding speed was held at 50 mm/min. The tool rotational speeds were 600, 1000 and 1600 rpm. The microstructure was investigated by both transmission electron microscope (TEM) and electron backscattered diffraction scans (EBSD). The results indicated that several phenomena occur instantly during FSW in the stir zone, such as precipitation, continuous dynamic recrystallization (CDRX), grain growth and precipitates dissolution which have a severe effect on the mechanical properties. It could also be concluded that for thin sheet of 7075-T6 aluminum alloy, plastic strain is the dominating factor over heat input of the FSW in determination of the microstructure of the weld zone.

In this work, joining of 4014 Aluminum tube to 7075 rod is studied using magnetic pulse welding process. The effect of impact angle (4, 6 and 8 degrees) and welding voltage (6 and 7 kV) on the joint are investigated. The microstructure of the weld cross section was evaluated using optical and scanning electron microscopy and mechanical properties of the welds were evaluated by microhardness and tensile tests. The results showed that, for the impact angles of 4 and 6º, the increase of welding voltage from 6 to 7 kV, leads to the change morphology of interfacial from straight to wavy. While, for the impact angle of 8º, the increase of the welding voltage increases local melting and results in the degradation of the interface. At the same angle, increasing the welding voltage increases the hardness due to the higher work hardening and severe plastic deformation. On the other hand, the effect of welding voltage on the hardness is dominant compared to the impact angle. The results of the tensile test showed that, for the low impact angles, increasing the welding voltage increases the shear strength, while, for the higher impact angles, it decreases the shear strength because of creating holes in welding interface. The results showed that joining of aluminum tube/rod with impact angle of 6º and welding voltage of 7 kV leads in uniform and wavy interface with higher shear strength in comparison with other conditions.

In this study, in order to improve surface properties of 316 austenitic stainless steel and its erosive properties, nanostructured TiN layers by PACVD method were developed. The TiN coatings were deposited on AISI 316 austenitic stainless at three different temperatures 470, 490 and 510 °C and duty cycle 33% by means of PACVD method. Microstructure and cavitation resistance were characterized by techniques such as field emission scanning electron microscopy (FE-SEM), XRD, micro hardness, erosion tests. The results indicated that with increasing deposition temperature from 470 to 510 °C, grain size of coating increased from 12 to 47 nm. It was found that at 470 °C, has the best erosive properties.

The purpose of this paper is a qualitative evaluation of the mechanical properties of titanium aluminum nitride (TiAlN) hard nanostructured coatings applied on cutting tools using X-ray diffraction (XRD). Deposition of TiAlN and TiN nanostructured coatings were carried out by a pulse DC plasma-assisted vapor deposition (DC-PACVD) and a high power impulse magnetron sputtering (HIPIMS) machines. At first, for enhancement the adhesion of TiAlN nanostructured coating on the steel substrate, TiN inter-layer was deposited for the all samples. Nano-indentation, micro-hardness tester, and field emission scanning electron microscope (FE-SEM) were used in order to measured and compare the qualitative results with the real and experimental values. The results indicate that XRD pattern and their analysis can be a suitable qualitative method to evaluate the mechanical properties of the coatings. The lattice parameter, micro-strain, residual stress, texture coefficient, the crystal grain size and density of dislocation are used to demonstrate the relationship between the mechanical properties of the coatings and the XRD patterns. As a result, this method can be used as non-destructive and inexpensive method for quantitative comparison and evaluation of mechanical properties of thin film materials.

In this study, friction stir processing (FSP) was utilized tofabrcation Fe based nano structure Fe48Cr18Mo7Nb6C4B16Y1 particles. For this reason, wc cone shape tool and constant tool rotation rate and travel speed 800 rpm and 100mm/min was used respectively. Microstructural, tribological properties and hardness has been studied. The results show that the hardness was increased by The presence of reinforcing particles and improved microstructural by FSP. The study of wear behavior shows that wear resistance was increased then steel base. Also investigation of wear surface showed that The dominant wear mechanism in the not reinforcement steel is lamination wear that with composite fabrication it to become abrasive wear.

This study is concerned with a correlation between the microstructure and mechanical properties of 42CrMo4 steel which was subjected quenched-tempered and step-quenching heat treatment. Quench tempering and step quenching heat treatment produced a tempered martensite and an equiaxed Ferrite-Bainite-Martensite (F-B-M) microstructure, respectively. Tensile test results indicated a yield drop effect in F-B-M microstructure with ferritic matrix. This effect was not observed on the specimens with tempered martensite and F-B-M microstructure with hard phase B-M matrix. This effect can be attributed to dislocation generation in ferrite phase during bainitic and martensitic transformations. Fractographic investigations indicated intergranular cleavage in F-B-M microstructure and micro-void coalescence in tempered martensite microstructure can be attributed to carbide formation in martensitic structure during tempering micro-void coalescence in tempered martensite microstructure

The effect of aluminium content on the precipitation of in rapidly quenched Ni-Al binary alloys was investigated. Microstructural analyses of annealed and quenched samples indicate a transition from uniform to bimodal phase distribution in the composition range between 15.3 and 17.5 at.%Al. This transition is accompanied by changes in the morphology of precipitates. The microstructural observations are discussed in view of both kinetic and crystallographic considerations.

The initial stages of the γ′ precipitation in a dilute Ni-Al binary alloy, Ni-11. 6 at. %Al, were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron diffraction and electron microscopy (FEG-SEM and TEM) techniques. Three samples were similarly solution treated and then cooled to room temperature under different cooling rates, 170، 25 and 0. 03oCs-1. The results indicate a clearly homogenous γ′ nucleation during rapid quenching which takes place via simultaneous ordering and phase separation. However, by decreasing the cooling rate to 25oCs-1 the nucleation mechanism changes to heterogeneous on the preferred nucleation sites. The capability of the mentioned empirical techniques for studying the initial stages of the γ′ is another subject which is studied in this article.

In this study, in addition to forming a steel tube of D6AC by direct flowforming, in order to examine the effects of different parameters of heat treatment process on the a for mentioned part properties, different cycles of heat treatment process are designed and after doing so, mechanical properties and microstructural changes of flowformed tube are investigated. For this purpose, at 850, 900 and 950 ˚C austenitizing temperatures for 15 and 30 minutes and AUS-BAY quenching at 510 ˚C for 10 minutes, and then quenching at 60 ˚C oil are used. Initial tempering for 2 hours at 250 ˚C and final tempering for 2 hours at 250, 300, 350 and 450 ˚C was performed. Investigations show that the optimum heat treatment cycle is austenitizing at 850 ˚C for 30 minutes, and final tempering at 300 ˚C, because of creating high strength and suitability for fracture toughness. Due to small grains of initial austenite, the ductility properties are also adequate.