This paper explains the sliding wear performance of red mud, fly ash, and carbon composite coating on mild steel. The complex mixture of red mud, fly ash, and carbon is plasma sprayed at 9 kW operating power level. The coatings are examined to study the coating morphology, XRD phase transformation, wear rate, and wear morphology. Wear rate (in terms of cumulative mass loss) with sliding time has been demonstrated in the study. At first pure red mud is plasma coated to observe the coating characteristics and then compounded with 20% carbon, 30% carbon, and 20% carbon + 30% fly ash, separately by weight and sliding wear test conducted using pin on disc wear tester. The trial was performed at fixed track diameter of 100 mm and at sliding speed of 100 rpm (0.523 m/s) at a load of 30 N. The results are compared. Declined cumulative mass loss by inclusion of fly ash and carbon is seen. This might be due to augmented interfacial tension and dense film build-up at boundary layer.
In the present scenario coating technologies manifest a promising momentum for emerging materials. Wear resistive coatings are claimed to be better tribological applications. Surface modification by improving wear resistance is most widely adopted by plasma spraying technique, which could affirm a great versatility and its application to a wide spectrum of materials. Wear resistive coatings can protect against different wear mediums like abrasive, adhesive, and corrosive. Some common wear resistive coating materials are nickel, iron, cobalt and molybdenum based alloys, carbides of ceramic, and tungsten [
Examinations on the basis of the wear behaviour of Mo and Mo + NiCrBSi thermally sprayed coatings being performed for the application as next generation ring face coatings [
Red mud as an industrial waste material is considered to be the material of choice for coating applications. It is necessary to mention here that red mud in present decade should be considered as alternative wealth for replacing some conventional expensive coating materials. Utilization of red mud and its implications are made available in the literature [
The coating powder was formulated considering the raw materials as red mud, fly ash, and carbon. At incipient pure red mud is plasma coated. Then a powder mixture made up of red mud and different percentage of fly ash and carbon was being prepared separately. Table
Powder composite.
Sl. Number | Material | Composition by weight % |
---|---|---|
1 | Red Mud (RM) | 100 |
2 | RM + Carbon (C) | 80 + 20 |
3 | RM + C | 70 + 30 |
4 | RM + C + Fly Ash (FA) | 50 + 20 + 30 |
To perceive the significance of activated carbon SEM and EDS analysis images have been reported in Figure
(a) SEM and (b) EDS analysis of activated carbon.
EDS analysis of (a) RM + 20% C and (b) RM + 20% C + 30% FA powder.
The primary raw material as red mud was collected in powder form from National Aluminium Company, located at Damanjodi in the state of Odisha, India. The as-received powder was sieved to obtain particles in the required size range of 80–100
The mild steel rod is chopped to
Coating of the substrate was done using conventional atmospheric plasma spraying (APS) unit available at surface engineering department of IMMT, Bhubaneswar, Odisha, India. All the mild steel specimens were coated from one cross section at 9 kW operating power level by controlling the voltage and current input to the arc. The powder feed rate was maintained to be constant at 15 gm/min by using a turntable type volumetric powder feeder. Plasma generation implemented by purging argon as primary and nitrogen as secondary gas agent. Spraying was done at an angle of 90° by maintaining the powder feeding as external to the gun. A compact outline of APS is reflected in Figure
Compact outline of APS.
The wear test was conducted using a pin on disc appliance allotted by MAGNUM Engineers, Bangalore, India. A comprehensive outline of the setup is materialized in Figure
A comprehensive outline of pin on disc apparatus.
Interparticle bonding of the sprayed powders and coating surface adherence plays an important role to characterize the coating morphology [
Coating morphology: (a) RM, (b) RM + 20% C, (c) RM + 30% C, and (d) RM + 20% C + 30% FA.
To discover the different phases occurring in the precursor powder and its coating; a Philips X-Ray Diffractometer is incorporated. Figure
XRD of activated carbon.
XRD of red mud.
The XRD of RM + 20% C powder primarily contains phases of sodium sulfite (Na2SO3), iron oxide (Fe2O3), and aluminium iron oxide (AlFeO3). After plasma coating there is a major phase change to fayalite (Fe2SiO4) and dolomite as visible in Figure
XRD of (a) RM + 20% C powder and (b) RM + 20% C coating.
Figure
XRD of (a) RM + 20% C + 30% FA powder and (b) RM + 20% C + 30% FA coating.
The wear tests were carried out as per ASTM G-99 standard under unlubricated condition at standard atmospheric temperature and pressure. Sliding wear test was conducted at normal load of 30 N at a rotational speed of 100 rpm. The track diameter was retained at 100 mm. The test was conducted for a total duration of 54 minutes for each coating type. Total duration of sliding was divided into 18 intervals with 3-minute time gap each. Mass loss in each intervening time was added and expressed as cumulative mass loss. The behaviour of cumulative mass loss with sliding time is expressed in Figure
Wear behaviour plot.
It is observed that the cumulative mass loss is always more for pure red mud coating for all time intervals. As the carbon content in the red mud increases (addition of carbon by 20% and 30% by weight), the cumulative mass loss declines. Figure
Wear morphology at 30-minute time interval: (a) RM, (b) RM + 20 C, (c) RM + 30% C, and (d) RM + 20% C + 30% FA.
The above work attempted to study the dry sliding wear behaviour of red mud compounded with a limited extent of reinforcement of carbon and fly ash. A further study can be conducted to expand the limitations. It is obvious from this research that carbon and fly ash enhances the coating property of red mud by amending the surface physical properties. The work strongly attracts tribologists to investigate the response towards corrosion wear of prevailing coatings. An optimization technique may be implemented to find the optimum percentage of carbon and fly ash. High temperature application for thermal security may be evaluated at suitable operating conditions. Further heat treatment of the coatings may be employed to disclose the acceptable demands.
The authors have declared that no competing interests exist.