Development and Characterisation of Metal Matrix Composite Using Cenosphere for Wear Resistant Applications

Abstract

Environmental pollution is the major problem associated with rapid industrialisation, urbanisation, and rise in living standards of people. However, industrialisation, on the other hand, causes serious problems relating to environmental pollution. Industrial wastes seems to be a hindrance on the path of industrial growth. The major generators of the industrial solid waste are the thermal power plants producing fly ash. Fly ash is an inexpensive resource material. Continuous efforts have been made by different researchers worldwide, for proper utilisation of fly ash for various applications. The small scale of fly ash has successfully utilised for making building materials. However, large-scale utilisation is yet to take off. In the last few years, considerable development has occurred for potential use of this waste in the area of metal matrix composites for automotive applications. Considerable trials have been done on the use of metal matrix composites like aluminium-silicon carbide composites for connecting rods, brake rotors, drive shafts and several other components. However, cost still remains a major barrier in designing aluminium composite components for wider applications in automotive industries. In order to reduce the cost of composites, the fly ash particles, a waste by-product from power plants, have been incorporated in molten aluminium alloy to make low cost aluminium–fly ash composites. In these composites, fly ash generally acts as a filler replacing energy intensive metal without deleterious loss of desirable properties.
Fly ash is a coal combustion by-product, which consists primarily of aluminosilicates, and the oxides or mixed oxides of silicon, aluminium, iron, calcium. Small amounts of other oxides of common elements such as magnesium and titanium are also present. Fly ash particles generally contain either solid spheres called precipitator fly ash or hollow spheres termed cenosphere fly ash. Precipitator fly ash often has pores and its density ranges from 2.1 to 2.6 gm/cm3. While cenosphere fly ash particles have density in the range of 0.4 to 0.6 gm/cm3.
Aluminium matrix composites are not a single material but a family of materials whose stiffness, strength, density, thermal and electrical properties can be tailored by varying the type of reinforcement material, its volume, shape, location and fabrication method can all be varied to achieve required properties. The present work includes Aluminium alloy (LM6) as metal matrix. LM6 matrix alloy has good casting characteristics. The major alloying element in LM6 is silicon. The alloy has good fluidity and hot tearing properties that make to produce thick and thin casting sections. It has a high strength, which can be used for structural components in the automobile industry.
The present thesis deals with the mechanical and tribological behaviour of LM6-cenosphere metal matrix composites. The composites are fabricated using two types of casting processes viz. stir casting and squeeze casting. The volume fraction of reinforcement (wt. %) is varied from 5-12% for stir casting and 5-15% for squeeze casting with an increment of 2.5 during the fabrication process.
The work presented in this dissertation involves investigation of three distinct problems of LM6-cenosphere composites.
•Study of favourable mechanical properties with various characterisation analyses of both stir and squeeze cast composites.
•An experimental investigation of abrasive wear behaviour of both stir and squeeze cast composites.
•An experimental investigation of erosive wear behaviour of squeeze cast composites.
To study the mechanical properties of the composites, with various volume fraction of reinforcement (wt. %) varied from 5-15%. The composites are synthesised through the stir casting and squeeze casting methods. The microstructure analyses of the composites are carried out using optical microscope. The hardness test of the composites are carried out using Vickers micro hardness tester. It was found that the squeeze cast composites shows fine microstructure compare to stir cast composites. The hardness of the squeeze cast composites are higher than the stir cast composites.
The abrasive wear behaviour of stir cast and squeeze cast composites are carried out using pin-on-disc wear tester as per ASTM standards with various experimental parameters such as sliding velocity, sliding distance, track radius, applied load etc. It has been concluded that the wear resistance of the squeeze cast composites are better than the stir cast composites.
The erosive wear behaviour of squeeze cast composites are performed on an air-jet erosion tester as per ASTM standards with various parameter like impingement angle, impact velocity, standoff distance, abrasive particles, flow rate, pressure etc. The solid particle erosion test clearly indicates that the composites behaviour is semi-ductile in nature.
The results from the present thesis indicate that addition of cenosphere up to 10 wt. % is very effective in improving its wear resistance with stir casting method; whereas 12.5 wt. % of cenosphere gives better wear resistance in squeeze casting. Also for erosion behaviour of the composite, maximum erosion occurs for different wt. % of cenosphere is in the range of 45º- 60ºwhich indicates that the present material is semi ductile in nature.