Advanced Materials Research Vols. 264-265

Abstract: In order to study the wear properties of Fe-C-Si and Fe-C-Al alloy systems, castings were produced in resin bonded sand mould of suitable design, which provides information regarding various thicknesses of the castings. Gray cast iron is an inexpensive and readily available material used for manufacturing of roller, roller shell, piston rings, cylinder liners, etc. Its low melting point is characterized as unique combination of superior properties like good friction and wear properties and economic in manufacturing. In the present study, wear behavior of the Fe-C-Si and Fe-C-Al cast irons were investigated using a pin-on-disk type apparatus at room temperature. Alumina ball of 3 mm diameter was used as pin, while the cast sample served as the disk. The tests were carried out at a normal load of 5.0 N and a sliding velocity of 250 mm/s for 30 min. The Fe-C-Al cast iron showed a wear rate of 3.3203×10-5 mm3/m/N compared to 12.42×10-5 mm3/m/N of Fe-C-Si cast iron. The worn surfaces were analyzed using optical profilometer and SEM.

Abstract: Two types of cast irons with Fe-C-Si and Fe-C-Al. alloy systems were investigated in the present study. In order to modify the microstructure and properties of cast iron, Al was added to low silicon pig iron that is in Fe-C-Al (Sorel metal) alloy system. Its effect was then studied with comparing to normal Fe-C-Si alloy system. Both cast irons were produced in sand mould of suitable design to provide all information regarding the structure and properties. The microstructure was analyzed using optical microscope which showed the distribution of graphite flakes in pearlite or ferro-pearlite matrix. The size of the graphite flakes in Fe-C-Al system was smaller and more evenly distributed compared to the Fe-C-Si alloy system. The cast product was also characterized by using XRD. The maximum hardness of the Fe-C-Al alloy was measured as 110.2 HRB compared to 89.32 HRB of the conventional Fe-C-Si alloy system. The impact test results showed that Fe-C-Al cast iron has higher impact property than Fe-C-Si cast iron.

Abstract: Al based MMCs have attracted a lot of attention particularly for their desirable combination of high stiffness and low specific gravity. In the present study, Al-4.5Cu-3.8Fe in-situ composites were manufactured by using solidification process. During solidification Al-Fe intermetallic was formed in a matrix of Al-Cu alloy. The composite was hot rolled at different degree using a two high rolling mill. Subsequently the composites were characterized by SEM, XRD, hardness measurement and wear testing. Wear testing was conducted on a pin-on-disk machine by applying 10 KN load. After the wear tests, the worn surfaces of the composite specimens were examined under an optical microscope. According to experimental results, as cast in-situ composites exhibited the highest wear rate. The hardness increased and wear rate decreased with the extent of rolling. The presence of reinforcing Al3Fe phase and fragmentation of those particles during hot rolling are suggested to contribute to the better wear resistance of the composites. The extent of abrasive wear was largest in the case of as cast composites, as evidenced by deep grooves on the worn surface and highest weight loss.

Abstract: The quality laser cutting of thick sheet metals is demanding due to requirements of high precision, lost cost, and short processing time. However, the surface plasma is formed during the cutting process to influence the end product quality. The surface plasma is transiently hot and lowers the resulting cutting quality via increasing thermal erosions from the cut edge edges. In the present study, the surface plasma characteristics are examined using the Langmuir probe. Electron temperature and electron number density are determined in the surface plasma. The cutting quality is, then, related to the plasma characteristics. Scanning Electron Microscopy (SEM) is carried out to examine the microstructural changes at the cut edges. It is found that cutting quality improves at a particular assisting gas pressure; in which case, the influence of surface plasma on the cutting process becomes the minimum.

Abstract: This work studied the effect of sonication time and dispersing medium on the dispersion state of 0.1%wt multi-wall carbon nanotube (MWCNT) in the MWCNT/epoxy nanocomposite system. Epoxy, hardener, and epoxy/solvent were used as dispersing mediums in this study. Tensile strength, strain at failure, Young's modulus and fracture toughness were measured under different dispersion state of MWCNT. The results indicate that with the increase in sonication time, initially there was an increase in tensile strength and fracture toughness values which was followed by a drop in values at longer sonication times. The highest Young's modulus values were seen in epoxy dispersion and the highest tensile strength and fracture toughness values were observed when the hardener was used as dispersing medium. The results also indicated that the effect of sonication time was more pronounced in the case of epoxy dispersion. The effect of time was least when the epoxy / solvent system was used as CNT dispersing medium. It should also be pointed out that the Young's modulus for the nanocomposite sample obtained after 1h of dispersion in hardener showed good agreement with a modified Halpin-Tsai theory. The scanning electron microscope (SEM) was used to characterize the dispersion state of MWCNT. A good dispersion was obtained when either hardener or solvent were selected as the dispersing medium.

Abstract: In this study, the effects of the machining parameters in electrical-discharge machining (EDM) on the machining characteristics of AISI D2 steel using copper electrodes were investigated. The response functions considered material removal rate (MRR) and Surface Roughness (Ra),while machining variables are pulse current, pulse on time, pause time and gap voltage. A Response surface methodology was used to reduce the total number of experiments. Empirical models correlating process variables and their interactions with the said response functions have been established. The significant parameters that critically influenced the machining characteristics were examined, and the optimal combination levels of machining parameters for material removal rate, and surface roughness were determined. The models developed reveal that pulse current is the most significant machining parameter on the response functions followed by voltage and pulse off time for MRR. However for, for Ra also pulse current is most significant followed by pulse on time and discharge voltage the respectively. The model sufficiency is very satisfactory as the coefficientR2of is determination (R2) is found to these be greater than 98 %. These models can be used for selecting the values of process variables to get the desired

Abstract: HVOF coating finds application in industry to protect the surface from the harsh environments such as high temperature, corrosion, and abrasion. In the present study, HVOF coating consisting of Inconel 625 powders blended with WC particles and sprayed on to 304 steel is carried out. The mechanical properties, such as elastic modules and fracture toughness, of the resulting coating are determined using the indentation tests. The influence of the mass fraction of WC on the fracture toughness and elastic modulus of the coating are also examined. It is found that addition of WC particles in Inconel 625 powder enhances the fracture toughness of the resulting surface. This is attributed to increased elastic modules and hardness.

Abstract: Effects of wear testing temperature and sliding speed on the wear behavior of nitrided and untreated 31CrV3 steel were investigated. The specimens were tested at wear testing temperatures of 25°C and 500°C under a normal load of 15N at a sliding speed of 1m/s. The increase in the wear temperature from 25°C to 500°C led to a decrease in the wear rate and coefficient of friction of the nitrided steel samples. At 25°C, the wear resistance of the nitrided steel improved by 2.3 times compared to the untreated specimen. There was about 57 times improvement in wear resistance as the wear temperature increased to 500oC for the nitrided specimen. Scanning electron micrographs showed that the formation of compact and protective oxide layers on the worn surface of the nitrided steel was responsible for the improvement in the tribological behavior of nitrided steel at elevated temperatures. The effect of sliding speed on the wear of the samples was further tested at 500oC under a normal load of 15N at sliding speeds of 0.5 and 1.5m/s. The results showed that there was higher wear resistance at lower sliding speeds.