Plasma Sprayed Red Mud-Fly Ash Composite Coatings on Mild Steel: A Comprehensive Outline

The present investigation aims at evaluating the effect of fly ash addition on coating characteristics of
pure red mud. Plasma sprayed coatings composed of red mud and a varying percentage of fly ash on
mild steel were considered for the study. Coating technologies have already gained a promising
momentum for the creation of emerging materials in the last few decades. Plasma spraying technique
was 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 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 and sliding wear test performed using a pin
on disc wear test machine. The wear test was performed for sliding distance up to 942 m 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 for
a maximum duration of 30 minutes. 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. 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. In our observation the coatings wear resistance (reverse of wear rate) decreases
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. The present study concludes that, red mud coatings possess
acceptable thermal properties. Fly ash is a beneficiary reinforcing agent for red mud, and the
composite can be coat able with favoring surface properties. These coatings can be operated at high
temperature. It is observed that, these composite coatings can also be employed for suitable
trbological applications. Plasma generating power, adversely affect the coating morphology. Our work
is a portfolio for researcher to discover many other aspects of red mud and its composite coatings.
Study of corrosion wear behaviour may be implemented by future investigators to find its distinct
application areas.