Sharif Digital Repository

The effect of MoS2 lubricant particles on the microstructure, microhardness and tribological behavior of A413/SiCp surface composite, fabricated via friction stir processing (FSP), was studied. For this purpose, the FSP was carried out with tool rotational speed of 1600 r/min, tool travel speed of 25 mm/min and tool tilt angle of 3° through only a “single pass”. The optical and scanning electron microscopies, microhardness and reciprocating wear tests were used to characterize the samples. The results showed that the addition of MoS2 lubricant particles to A413/SiCp surface composite leads to the decrease of friction coefficient and mass loss. In fact, the generation of mechanically mixed... 

In the present study, hardness and tribological properties of nanostructured copper reinforced with SiC nanoparticles of various volume fractions (0, 2, 4, and 6 vol%) were investigated. The nanocomposites were fabricated by high-energy mechanical milling and hot pressing method. The Cu-SiC nanocomposites showed enhanced hardness and wear resistance against WC counterface. The hardness and wear resistance of the nanocomposite increased with increasing the amount of SiC nanoparticles up to 2 vol% in the matrix, but they decreased at higher percentages of SiC (4 and 6 vol%). Flake formation-spalling and abrasion were identified as the predominant wear mechanisms. It was found that reducing the... 

10Ce-TZP/Al2O3 nanoparticles as reinforcement can be a good substitute in aluminum matrix composites prepared through powder metallurgy. In this work, the effects of sintering temperature on the hardness, friction, and wear characteristics of Al-10Ce-TZP/Al2O3 composites have been investigated. Ce-TZP/Al2O3 nanocomposites were synthesized by the aqueous combustion method. About 7 wt% 10Ce-TZP/Al2O3-aluminum composites in the form of cylindrical samples were prepared at the sintering temperatures of 400°C, 450°C, and 500°C under an applied pressure of 600 MPa for 60 min. The experimental results show that the distribution of Ce-TZP/Al2O3 nanocomposite into the metal matrix is homogenous and... 

An experimental study of wear characteristics of electroless Ni-10% P coating sliding against hard AISI 52100 steel pin is investigated. Experiments are carried out at room and 550°C temperatures. Heat treatment effects on tribological behavior of this coating are studied. The wear surface and the microstructure of the coatings are analyzed using optical microscopy, scanning electron microscopy, energy dispersion analysis X-ray, and microhardness testing equipment. It is observed that the forming of continuous oxide film on contacting surfaces of pin and disk improves wear resistance and decreases friction coefficient of the Ni-10% P coating. The results indicate that the wear resistance of... 

LM13 alloy is widely used in piston industry, due to its low coefficient of thermal expansion, excellent castability and hot tear resistance. In this research effect of casting process on wear behavior of LM13 alloy was investigated. First, samples were produced using two casting processes and heat treated. Then wear behavior of these samples under dry sliding condition was examined. Results of hardness and strength tests indicated that squeeze cast specimens exhibited higher mechanical properties. Wear experiment results showed that in both squeeze and gravity cast specimens, amount of weight loss increases with increase in sliding distance which is accompanied by reduction in wear rate and... 

The phenolic-based brake friction composites containing 0, 1, 2 and 4 vol% carbon fiber were fabricated in this study. Thermogravimetric analysis (TGA) revealed the adverse impact of carbon fiber on the thermal stability of the composites under air atmosphere. Differential scanning calorimetry (DSC) of the uncured samples indicated the positive impact of carbon fiber on the crosslink density of the phenolic resin. Viscoelastic results drawn from the dynamic-mechanical analysis (DMA) suggested that inclusion of carbon fiber increased the storage modulus and decreased the damping factor of the frictional composites. The tribological behavior of the specimens was assessed with a chase type... 

Production of Al1050/TiO 2 -graphite hybrid nanocomposite via friction stir processing (FSP) was studied. The effect of graphite-to-TiO 2 volume fraction ratio (Gr/TiO 2 ), at a constant rotational speed (ω) and three levels of tool traverse speed (ν), on the microstructural evolution and mechanical properties of the nanocomposites was investigated. While TiO 2 is supposed to enhance the strength and hardness, graphite is believed to improve the tribological behavior. Furthermore, formation of intermetallic compounds (IMCs) through the solid-state reactions between the reinforcements and aluminum matrix may also promote the mechanical properties. To assess these assumptions, longitudinal and... 

To investigate the effect of short carbon fibre on the tribological behavior of phenolic resin-based friction materials, a reference friction composite holding various ingredients without short carbon fibre, and three friction composites holding 1, 2 and 4 vol% carbon fibre were formulated. The dynamic-mechanical and thermogravimetric analyses showed the increase of storage modulus and reduction of thermal stability, respectively, with incorporation of carbon fibre into the brake composites. The tribological characterizations revealed that the coefficient of friction (COF) and specific wear rate of the friction composites dropped with addition of carbon fibre into the composites. Carbon... 

Reactive friction stir processing (RFSP) has been employed to modify the surface properties of AA5052 Al-Mg alloy through grain refinement and the distribution of ultrafine hard nanoparticles (2 to 6% volume fractions of 50 nm titanium dioxide). The heat generated induced solid state reactions between the metal matrix and the reinforcement to form Al3Ti/MgO inclusions. The role of grain refinement and distributed hard nanoparticles on the tribological behavior of the alloy under dry sliding wear condition was evaluated. The wear rates and friction coefficient as well as macro- and micro-features of the worn surfaces indicate that the wear mechanism (at 3–7 kgf and 0.5 m/s) is abrasive. The...