Study of Tribological Behavior of Plasma Sprayed Red Mud Composite Coatings

Abstract

The present investigation aims at evaluating the effect of fly ash, carbon and aluminium addition on coating characteristics of pure red mud. Plasma sprayed coatings composed of red mud and a varying percentage of fly ash, carbon and aluminium on mild steel are considered for the study. Plasma spraying technique is used with varying levels of power namely 6, 9, 12 and 15 kW. Plasma spray is one of the most widely used techniques involved in surface modification by improvement of wear resistance, which may affirm the great versatility and its application to a wide spectrum of materials. Investigations of the coatings focused on tribological properties like sliding wear behaviour, wear morphology, wear mechanism and frictional force. Different coating characteristics like surface morphology, hardness, porosity, thickness, deposition efficiency, bond strength and new phase formation are studied. The sustainability of these coatings towards high temperature at air environment up to 1000°C is evaluated by finding their adhesion strength. DSC and TGA techniques are implemented to observe the coating behaviour to heat. The coatings show remarkable resistance towards high temperature by virtue of adhesion strength compensation. It is feasible to use these coatings limiting < 800°C otherwise dislodging of coating from metal. Fly ash with 10, 20 and 50% by weight was mixed with red mud. Carbon and Aluminium powder with 20 weight %each are premixed to red mud separately and plasma sprayed. Sliding wear test are performed using a pin on disc wear test machine. The wear test is performed till the survival of coatings with track diameter of 100 mm and at a sliding speed of 100 rpm (0.523 m/s); applying a normal load of 10 N. The variation of wear rate and frictional force with that of sliding distance and time has been presented. The addition of fly ash with red mud reduces the wear rate by enhancing the coating property. But the optimum percentages of fly ash required for better coating material still impact a question mark for the researchers. Addition of aluminium and carbon further reduces the wear rate. It is observed that for the early stage the wear rate increases slowly and then rises drastically with sliding distance for all coating type and finally becomes stagnant. Operating power level proved to be the remarkable variable for different coating property. The observation signifies the coatings wear resistance (reverse of wear rate) increases until an optimum value at 12 kW, afterwards indicating some other dominating parameters. Significant wear resistance was visible with the addition of fly ash due to an increase in bond strength and dense film at the interface. Wear rate decreases with operating power up to 12 kW, thereafter increases with initiating other dominating parameters. At the end, design of experiment is conducted to analyse the dominating parameters to wear. The present study concludes that, red mud coatings possess acceptable thermal properties. Fly ash, carbon and aluminium are beneficiary reinforcing agent for red mud, and the composite can be coat able with favouring surface properties. These coatings can be operated at high temperature. It is observed that, due to low material cost, these composite coatings can also be employed for suitable trbological applications. Plasma generating power, adversely affect the coating morphology. This work is a portfolio for researcher to discover many other aspects of red mud and its composite coatings. The study may be extended by future investigators to find its distinct application areas.