Sharif Digital Repository

In this research, friction and wear behaviors of 2024 Al and 2024 Al-20 vol.% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 20- 250°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.5 m/s, an applied load of 20 N, and a sliding distance of 2500m using a pin-on-disc apparatus. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects. Worn surfaces and wear debris were also examined by using SEM, EDS and XRD techniques. All specimens showed a transition from mild to severe wear above a critical temperature. In the mild wear regime, the wear rate and the friction... 

Al /Al3Ti in-situ composite have been fabricated by mechanical alloying and two-step hot pressing of powders containing Al and 20%wt Ti. Samples were characterized by using optical microscopy, density measurement, brinel hardness, XRD analysis. An increasing density was observed with increasing pressure until certain pressure and after that the density of composite decreased, which can be attributed to the increase in the level of porosity level and the amount of forming Al3Ti. The samples that hot pressed under cycle 5 and 6, showed the most volume fraction of in-situ phases on the matrix. The wear behavior of Al based composites reinforced with in situ Al3Ti particles has been investigated... 

Rotor contact with a stationary element of a rotating machine and the subsequent rubbing at the contact area is a serious malfunction that may lead to the machine’s catastrophic failure. In the past decades, many studies have been done on the rubbing phenomena, its different regimes and its various consequences on the machine performance and safety. However, most of them have used a simple model to investigate the rubbing interaction between the rotor and the stator. This simple model consists of the Jeffcott rotor, as a model for the real rotors, and a rigid annular block surrounding the rotor, as a model for the real stators. The objective of this thesis is to build an algorithm to... 

Regard to high temperature and using dry fuel in engines with CNG (Compressed Natural Gas), wear problems and instability of valve seat insert (VSI) in these types of engines have been increased. Today some of high alloy steel (consist of Cr,Ni,Co,W,Mo, . . .), Ni-base alloy or Co-base alloy are used in manufacturing VSI. It's clear these materials have high price. In powder metallurgy methods high percentage alloy is used for manufacturing VSI. These are the reasons why casting method for VSI manufacturing has been pleasant to be used.
In this project the cast iron has been used for CNG engine VSI, by adding some elements like Mo,V,W, and Nb. The graphite has been used as solid... 

This project related to gas purification according to difference in the deposition point in the fludized bed.The main reason for choosing fluidized bed is increasing overall heat transfer coefficient compare in to other heat exchangers. Separation process, by cooling the wall causes the self- deposition gas phase shifts to solid phase. Solid formed on the wall, act as an insulating layer and greatly reduces the heat transfer. To solve this problem, the fluidized bed system is offered because fluid particles in addition to remove the insulating layer, improving convection heat transfer coefficient . Laboratory tests show the feasibility of preventing the formation of insulating layer by... 

In recent years, Total Knee Replacement is a highly common surgery. Other than the injuries caused by trauma in accidents among different ages, a need for Total Knee Replacement can arise due to diseases such as Knee Osteoporosis among the elderly which leads to loss of balance in the physiologic properties of knee joint and a failure in load transfer from distal femur to proximal tibia. Currently, the practice of Total Knee Replacement is performed by implanting a mechanical knee between femoral and tibial shafts. Increase in life expectancy of the people with replaced knee, causes the failure of some prostheses due to various factors. Following the failure, a second operation is required... 

The most common type of polymer based composite friction materials are usually in vehicles as the brake pads are used and must characteristics such as high wear resistance, low weight, durability, low noise and stable friction coefficient. Polymer matrix, in addition to providing other material suitable for storage, the final properties, including mechanical properties, heat, friction and wear is also effective. Thermoset resin polymer matrixes (usually phenolic resin) are used in the brake pads which used for automotive and in some cases, rubber particles as powder formulations may be entered, in order to achieve good properties of rubber and resin simultaneously. Nanofillers because of... 

Magnesium alloys are used in various industries, due to their excellent combination of low density, high strength to weight ratio and biocompatibility. However, a main drawback of Mg alloys is their poor corrosion and tribological behavior which could be improved by different surface treatments such as plasma electrolytic oxidation (PEO). Recently, PEO method as a simple and economic process is used to provide thick ceramic coating on Mg alloys. Based on some problems in zirconia coating on Mg substrates, two step PEO coating was introduced. The aim of the present study is to prepare and investigate the properties of zirconia-containing coating by two-step PEO process on the AZ31 Mg alloy... 

In this study, Aluminium based nanocomposite with Al3Ti and Al2O3 nanoparticles have been elaborated by mechanical alloying. For this purpose, Al and TiO2 powders have been blended with weight ratios of 10, 20 and 30 percents and were milled using a planetary mill. Morphological variations in different timing periods of mechanical milling process was investigated by Scaning Electron Microscopy (SEM) and The optimal times for alloying were determined for each combination. The pure Aluminium and the powder with 10, 20 and 30%wt reinforcement had coax morphology after respectively for 44, 30, 24 and 14 hours. after studing phase transformations by XRD analysis, the final powders were cold... 

In this study Ni-P-Al2O3-SiO2 nano composite coating developed on aluminium alloy 6061 using electroless method. Due to oxidation of aluminium, a double zincate pretreatment performed to obtain proper adhesion of coating on substrate. Effect of solution temperature and heat treatment on thickness and property of nano composite coating was studied. Furthermore, effect of concentration of nano particles in electroless solution on thickness, morphology, micro hardness, wear behavior, corrosion resistance and particle content in coating were investigated. Field emission scanning electron microscopy (FESEM, Hitachi S-4160) with energy dispersive spectroscopy (EDS) was used to evaluate morphology... 

Railway transportation is a subsystem of the conventional land transportation mode which has considerable advantages including the reduction of air pollution, improving the economic parameters, capability of mass transport of freight and passenger, and much higher safety, in comparison to other modes. The maintenance costs originating from the low longevity of the wheels and the high detachment of wagons in railways containing sharp curves as well as the difficulty to determine the real wear behavior of train wheels are some of the important challenges of railway transportation system. In this thesis, firstly, the parameters relating to the wheels was investigated by the measurements of the... 

In this study AZ91 alloy reinforced by SiC particles processed by semi-solid casting was produced by using electromagnetic stirrer. In order to prevent ignition and oxidation of the melted AZ91 alloy 1 Wt.% of calcium was added to the melt. In order to surface oxidation of SiC particles, they were heat treated in 1100 ᵒC for 2 hours before adding to the melt. Different methods of adding SiC particles to the melt were investigated. Particle distribution in the matrix was studied qualitatively and quantitatively using microscopic images and image analysis, respectively. It is shown that higher amount of reinforcement particle need to be added to the melt in multi-steps. Frequency versus... 

Total knee replacement surgery is the most common joint replacement in the world. Considering the increasing rate of this procedure and costs and difficulties of the repeated operation, many efforts have been made to improve the performance and lifetime of implants. The Polyethylene component of the implant is the most prone component to fail due to wear. To evaluate new knee prosthesis designs, it is necessary to have a wear test simulator. Objective of this project is to detail design a knee prosthesis wear simulator according to ISO 14243 in order to investigate the performance of prosthesises in long term and under in-vivo conditions. During this project, studies have been made to get... 

In the recent decade, composites have been used in safety system of automobiles due to important characteristics such as high wear resistant and durability, low weight and also low noise pollution, stable friction coefficient, availability and low cost. In recent years, composites have attracted the attention of brake pads manufacturers because of their appropriate thermal and mechanical properties. Fibers play an important role in these material. Carbon fiber due to its features such as high strength, acceptable module, proper heat transfer coefficient and excellent resistant against thermal degradation has been considered by the experts but there is not any comprehensive research on... 

The aim of this project is electrodeposition of Cu/Ni-P multi-layer coating and investigating the nucleation and growth mechanisms of the deposits. To evaluate the effect of the selected bath on the kinetics of the process and deposition, cyclic voltammetry and chronoamperometry studies were conducted and electrodeposition mechanism was obtained three-dimensional instantaneous nucleation and growth controlled by diffusion. Potentiostatic pulse-deposition method with potential steps -0.3 and -1.1 V vs SCE was selected for deposition of Cu/Ni-P multi-layers. In order to demonstrate the effect of monolayer thickness on the properties of the final coating, multiple layers with various monolayers... 

Fe-Cr-C hardfacing alloy is the most popular alloy used in severe abrasive condition such as mining and cement industries. One of the limitation of these hardfacing alloys is their low toghness, which reduce the application of these alloys under impact wear conditions. The purpose of this thesis is to investigate the effect of microstructure on the wear and toughness properties of AISI420 hardfaced martensitic stainless steel alloy. For this purpose, after deposition of the hardfaced alloy on a steel substrate, various heat treatments such as quench, quench temper, quench and partitioning and austenite reversion are designed to change the microstructure of the hardfaced alloy from fully... 

different phenomena occur between rotor and support rub impact causing system parts failure. Still Increasing the accuracy of manufacturing and decreasing the clearance of supports but the probability of rub impact between the rotor and support grows and this phenomenon is going to be more critical. This research would rub impact at two ends of four degrees of freedom Jeffcott rotor considering supports directional degree of freedom. Because the contact points are at two ends of the rotor, the rotational degree of freedom of the rotor is also considered. The system is modeled with 8-DOF and after numerical solving and comparison, the results with other papers, the system's behavior including... 

Electrochemical deposition of multilayer coatings is one of the surface engineering techniques to create thin surface layers with a controlled structure in order to create desirable surface properties. In this research, the nickel-iron-silicon carbide multilayer coating is deposited from a single bath with a sulfate composition and by changing the current density between two values (10 and 40 mA/cm2). The number of layers in multilayer coating was 4, 8, 16, 32.The effect of current density and the number of layers on chemical composition, surface morphology, phase structure, corrosion resistance, nano hardness measurement, wear resistance of multilayer coatings respectively using electron... 

In this research, the effects of natural and artificial aging heat treatments on the mechanical and wear behavior of an aluminum alloy from the 7xxx series have been investigated. The study commenced with annealing of the received samples, which were subsequently divided into four categories. One of these categories was placed in a freezer as annealed samples, while the other two underwent artificial aging heat treatments at temperatures of 180 and 210 degrees Celsius. The final category naturally aged over time. As a result, different structures with varied distributions and morphologies of precipitates were formed, and the mechanical properties, mechanisms, and wear resistance of the...