فهرست مطالب hadi eivazi bagheri

Induction of compressive residual stress on the surface thick-walled cylinder is a way to increase the resistance to failure and increase the fatigue life. The shrink-fit process is one of these methods. In this paper, the three-layer shrink fit for the construction of the hot isostatic press cylinders has been analyzed using experiments, analytical modeling, and finite element simulation. The stresses created due to the shrink fit process in cylinders were investigated using analytical calculation and finite element simulation. To perform the shrink fit experimentally, three cylinders were made of VCN steel and the shrink fit operation was performed. Based on the results from the finite element simulation, the maximum radial displacement for the outer cylinder is 0.89 mm and the residual stress value is 39.9 MPa. Also, the comparison of simulation results and analytical method for the middle and outer cylinder shows that the differences were 2.3% and 2.8%, respectively.

Based on the review of the previous researches, more than 50% of the cost of ceramic parts is related to machining costs, about silicon nitride (Si3N4), which is one of the most important engineering ceramics, while up to 80% has been reported. This ceramic has a combination of desirable properties such as wear and corrosion resistance and high hardness. Due to the high tool wear in machining process, the use of traditional methods is not appropriate. The electrical discharging machining process is a method that can machined all conductive materials without regard to mechanical and metallurgical properties, but machining of non-conducting ceramics such as silicon nitride is not normally possible by electrical discharging machining process. Therefore, in this research, the assisted electrode method has been used to perform the electrical discharge machining of silicon nitride ceramics. After preparing ceramic samples, copper-carbon bilayer and single copper layer were coating on the Si3N4 and they were successfully machined. In order to further examine the machined surface, imaging was performed by SEM. The results show that an increase in material removal rate in two-layer coating compared to single-layer coating. Also, after finishing machining process, EDX analysis was performed from the surface of ceramic workpiece, which indicates the presence of carbon and copper elements in the machined surface. In addition, the copper tool wear ratio in two-layer coating is less than that of single-layer coating.

One of the important parameters in electrical discharge machining is the presence of micro cracks on the workpiece surface (recast layer). Therefore, the aim of this study was to investigate the possibility of increasing the mechanical properties of aluminum surface by alloying elements (copper and nickel) diffusion to the recast layer and thus removing surface micro cracks. For this purpose, pulse on time and pulse current in with and without ultrasonic vibration have been considered as input parameters and the presence of surface micro cracks has been investigated using microscopic images. Also, the yield stress of the surface layer was calculated using the surface micro hardness. Based on the obtain results, surface without micro cracks has been created on the aluminum surface due to the diffusion of copper and nickel into the workpiece surface which increased aluminum surface yield strength from 90MPa to 280MPa without ultrasonic vibrations and to 310MPa while applying ultrasonic vibrations. In other words, ultrasonic vibrations cause an average of 20% increase in surface layer yield strength. In addition, according to the wear test, in the case of using ultrasonic vibration, improving the mechanical properties of the surface has caused thinner grooves on the aluminum surface.

Due to the thermoelectric nature of the electrical discharge process, it is important to study the surface properties of the workpieces that are surface alloyed by this method. In this study, the effect of aluminum surface alloying process using Monell 400 electrode by electric discharge method on the workpiece surface mechanical properties has been investigated. To design the experiments, the pulse on time and pulse current were considered as input parameters and the surface residual stresses and Vickers indentation depth were considered as output parameters. In addition, the electromagnetic wave absorption of the surface alloyed layer was determined using the COMSOL simulation software. According to the obtained results, the Vickers indentation depth has the lowest value at the surface and with increasing distance from the surface, the amount of indentation depth increases. By increasing the pulse on time and pulse current, due to the increase in the amount of alloy elements (copper and nickel) diffusion to aluminum surface and thus improving the surface mechanical properties, the depth of the indentation decreases. Also, by examining the magnetic absorption in the surface layer using the simulation software, it was determined that the maximum amount of absorption of alloyed layer is in the range of 11-10.5 GHz.

In this paper, effect of input parameters (pulse on time, pulse current, voltage and duty cycle) of electric discharge deposition process on surface quality parameters including surface hardness, surface deposited layer thickness and roughness of AISI H13 tool steel using Ti-Cr-Cu alloys as electrode was studied. SEM was used to investigate the thickness of the surface layer, and the hardness of surface deposited layer was measured by microhardness test. Also, XRD method was used to identify the compounds on the surface and deposited surface roughness was controlled using Ra parameter. Based on the obtained results, TiC, Cr7C3 and Fe2C are formed at the deposited layer due to surface alloying and increasing surface hardness. Also, by increasing the pulse current and the pulse on time, the surface hardness and depth of the deposited layer were increased. Furthermore, with increase in input voltage, the thickness of the surface layer is increased and the workpiece surface roughness is reduced. Also, by increasing the duty cycle due to the increase in the number of sparks in time, the depth of the surface deposited layer is increased.

In this paper, considering the importance of surface integrity, effect of ultrasonic vibration of the Monel 400 electrode with a frequency of 20 kHz on the output parameters of the aluminum surface properties (surface hardness and wear resistance, thickness of the surface layer, the depth of copper and nickel diffusion to the aluminum surface and surface roughness) by the method of electrical discharge surface alloying has been studied. Based on the results of the SEM images, the surface layer thickness in the combination of ultrasonic vibration with the electrical discharge alloying process is more than the non-vibration mode. Therefore, increasing the thickness of this layer increases the surface wear resistance. Also, the microhardness test results show that surface hardness of the aluminum has increased to 450 vickers after the combination of ultrasonic vibration with the alloying process. According to the results of EDX analysis, the diffusion depth of alloying elements (copper and nickel) is higher in ultrasonic electrical discharge alloying, So that the surface layer thickness is up to 50 microns. Also, based on the results of surface roughness measuring, ultrasonic vibrations reduce the aluminum surface roughness after surface alloying.

Although the electrical discharge process is a material removal process, it is attempted to be used for surface operations as well, so considering the new method, it is important to analyze the mechanism of the electrical discharge surface alloying process. Nickel base alloys are widely used due to their high resistance to corrosive environments, especially at high temperatures, especially in environments where stainless steels and duplexes lose their performance. This paper first discusses the mechanism of surface alloying by electric discharge method and then, as an experimental work, examines the surface alloying of aluminum with nickel-copper alloy (Monel 400) to improve its surface properties. Therefore, the parameters of pulse on time and pulse current are considered as input parameters and the depth of hardened layer as output variable. The results of this study show that using Monel 400 electrode with negative polarity as an alloying electrode is a successful method to improve the surface properties of aluminum by eliminating harmful layers resulting from electrical discharge machining.

The creation of modified layer on metal surfaces using new methods is one of the procedures in surface engineering which can improve the surface mechanical properties. The electrical discharge process is a new method that can form a modified layer on the metal surfaces. This study aims to improve of pure aluminum surface properties through Electrical Discharge process with Monel 400 electrode. In order to design the experiments, the pulse on time and the pulse current were considered as input parameters. The SEM images indicated that the increase in the pulse on time and the pulse current can increase the thickness of the modified layer. Based on the obtained results, the thickness of improved layer varied between 35 to 75 microns. The results of the EDX analysis showed the diffusion of the copper and nickel to the aluminum surface. Moreover, the results of microhardness testing of the surface layer showed that after Electrical discharge process, the surface hardness has increased and the surface hardness as 35 Vickers has reached more than 400 Vickers.

In this study electrical discharge process was used to increase surface wear resistance of pure aluminum. Pulse-on-time and pulse current were considered as input parameters of the electrical discharge process. Experimental results reveal that the electrical discharge process is a successful method for improving the surface wear resistance of aluminum, so that this method has greatly increased the surface wear resistance of aluminum parts. Results indicate that with increase input parameters (pulse-on-time and pulse current) weight loss of the aluminum specimens is reduced and the wear resistance increases. The XRD analysis demonstrated that Al3Ni2 and AlCu intermetallic compound and Al4C3 were formed on alloyed surface. The presence of these compounds and hard particles at the surface increases the wear resistance. Also, friction coefficient measurements show that, after electrical discharge process and improving surface wear resistance, the friction coefficient slightly increased due to the presence of hard particles on the alloyed surface.

Surface engineering in many manufacturing industries plays an important role in improving product performance and increasing the operating time of parts. Pure aluminum has a very high electrical conductivity, good corrosion resistance and strength to weight ratio. However, due to very low hardness and wear resistance, its application is limited. Therefore, this paper is studied may improve the surface properties of pure aluminum using copper and nickel as alloying elements using electric discharge process. The pulse on time and pulse current as input parameters and surface hardness, alloyed layer texture and surface roughness as output parameters have been considered. According to the microhardness testing results, in this alloying method, the average hardness of the aluminum parts is about more than 8 times and in some parts of the 38.5 Vickers reached up to 450 Vickers, Based on the results of XRD analysis, the formation of intermetallic compounds Al3Ni2, ALCu, and Al4C3 increased surface hardness. The results show that by increasing the pulse on time surface hardness increased and surface roughness becomes greater. Also, Increasing pulse current the surface roughness increasing trend.

Thermite welding is a chemically reaction welding process. The weld joint is produced by pouring of superheated molten metal around the joint to be welded، applying with or without of pressure. the importance of mechanical properties and microstructure of thermite welded components، this paper studies the effects of Mn (it is one of the available choices to improve mechanical properties of steels microstructure) on mechanicaland metallurgical properties (hardness، impact resistance، tensile strength، elongation and wear resistance) of St49 steel in thermite welding process. The results show that with the increases of Mn in welded metal، tensile strength and impact resistance are increased but when the Mn content exceeds a certain level (% 2. 5)، the characteristic values ​​of the welded metal is reduced. Also، results show that with the increases of Mn wear resistance and the hardness of the welded metal were increased and the highest hardness in the railhead is 700 (Bhn) and in of rail web is 600 (Bhn).