The research paper focuses on evaluating the dry sliding wear behaviour of plasma sprayed coatings like red mud (RM), RM + 5% Fly Ash (FA) and RM + 5% FA + 5% Al on mild steel cylindrical shape substrate. Spraying was done at 10 kW operating power level. A conventional pin on disc wear tester is adopted for wear analysis. The wear test was performed at track diameter of 50 mm and sliding speed of 60 rpm (0.157 m/s) with normal load of 10 N. The duration of sliding varies from 54 minutes for pure red mud coating to a maximum value of 102 minutes for RM + 5% FA + 5% Al composite coating. A significant decrease in wear rate (in terms of mass loss) is observed by reinforcement of fly ash and aluminium to red mud, which might be due to improved interfacial properties.
Coating technology is an emerging research in engineering application. Wear resistive materials are fabricated by means of coating for wide tribological applications. Plasma spraying technology is widely adopted for coating thereby enhancing the surface properties. Surfaces with coating can protect from abrasive, adhesive and corrosive wear mediums. Commonly conventional coating materials are nickel, iron, cobalt and molybdenum based alloys, and carbides of ceramic and tungsten [
Several factors may influence the tribological behaviour of a coated surface. Such as geometry of contact, material characteristics, basic mechanical properties, operating parameters controlling the coating deposition and finally the microstructure [
The resources of red mud and its comprehensive utilizations are reviewed [
The primary raw material for the study is red mud (RM). The red mud powder was collected from National Aluminium Company (NALCO), Damonjodi, Odisha, India. The additive like fly ash was obtained from Rourkela steel plant. Aluminium powder was procured from Rourkela market. After obtaining the precursor, the same was dried to make it moisture free. Powders chosen for plasma spraying are tabulated in
Each raw material was sieved to obtain a particle size range of 80 - 100 μm and thoroughly blended to obtain uniformity in composition. The substrate selected for plasma coating is of mild steel. Commercially available mild steel rod was chopped to pieces of cylindrical dimension having l = 30 mm and Φ = 10 mm. Spraying was done on both the cross section of the specimen. The average roughness of the specimen cross section is 7.2 μm. Specimens were pre cleaned in ultrasonic cleaning unit before plasma spraying. The raw materials were thermally sprayed using atmospheric plasma spraying technique. The parameters governing the spraying process are reported in
Dry sliding wear tests were carried out using a pin on disc friction and wear monitor test ring (DUCOM) according to ASTM G 99 standard. The cylindrical substrates with coating on both the cross sections were tested against a disc made of hardened ground steel (EN-32, hardness 72 HRC, surface roughness Ra = 0.07 μm). The schematic diagram of the pin on disc wear tester is shown in
The cylindrical test specimen was held stationary and hardened disc rotates anticlockwise against it. A normal force was applied on the test specimen by means of pulley, lever and spring mechanism. All wear experiments were carried out at normal atmospheric temperature and pressure. A normal load of 10 N was applied on substrate keeping track diameter at 50 mm and sliding speed of 60 rpm (At a velocity of 0.157 m/s). Wear rates are expressed in terms of mass loss in mg. Frictional force (F) was calculated directly from the apparatus in Kg.
Sl. No | Coating powder | Composition by weight % |
---|---|---|
1 | Red mud (RM) | 100 |
2 | RM + Fly ash (FA) | 95 + 5 |
3 | RM + FA + Al | 90 + 5 + 5 |
Operating variables | Set point |
---|---|
Plasma arc current ( ampere) | 200 |
Arc voltage (Volt) | 50 |
Torch input power (kW) | 10 |
Plasma gas (Argon) flow rate (Litre/Min) | 20 |
Powder feed rate (gm/min) | 10 |
Torch to base distance (mm) | 120 |
Arc length range (mm) | 3, 6, 9, 13 |
Spray angle (In degree) | 90 |
The Characterization of red mud powder was done using a SEM (Scanning electron microscope, JEOL; JSM- 6480 LV). The captured image and EDS (Energy dispersive spectroscopy) reports are shown in
The elemental analysis report is composed in
Further Characterization of red mud powder was carried by means of X-RD. The X-Ray diffractogram was captured using a Philips X-Ray diffractometer. The report is shown in
Element | Weight % | Atomic % |
---|---|---|
O K | 0.70 | 1.90 |
Na K | 1.77 | 3.35 |
Mg K | 2.41 | 4.32 |
Al K | 7.76 | 12.54 |
Si K | 3.88 | 6.02 |
K K | 0.71 | 0.79 |
Ca K | 1.19 | 1.29 |
Ti K | 46.63 | 42.44 |
Cr K | 0.68 | 0.57 |
Mn K | 1.76 | 1.40 |
Fe K | 32.53 | 25.39 |
Totals | 100 |
The morphology of each coating type was studied using FESEM (Field emission scanning electron microscope, NOVA Nano SEM-450). The captured images are shown in
also visible. Large scale cavity areas were found. As the composition changes to RM + 5% FA, very marginal changes in morphology pattern (
At first the coating surfaces were cleaned with acetone using tissue paper for removing the embedded particles if any. Then substrates were analysed for wear loss fixing in the pin holder. The operating parameters were secured at its values as mentioned earlier.
An inclusion of 5% FA to RM reduces the wear rate as visible in
Wear morphology for stipulated coating samples were captured.
The above available research remarks a noteworthy accomplishment. The red mud, an industrial waste from
alumina plant is proved to be conveniently coat able on metal like mild steel; and might be an alternative source for replacing conventional coating materials. Additives like fly ash and aluminium boost up the surface properties by modifying the physical and interfacial characteristics. The extended road map for the researchers could be to find out suitable tribological application areas. Studies on evaluating the resistance towards corrosive wear in different environmental conditions could be implemented. A subsequent inspection on the effect of heat treatment and high temperature application of these coatings may be emphasized.
Harekrushna Sutar,Debashis Roy,Subash Chandra Mishra,Rabi Ranjan Murmu, (2016) Sliding Wear Performance Evaluation of Red Mud (RM), RM + Fly Ash (FA) and RM + FA + Al Coatings on Mild Steel. Materials Sciences and Applications,07,171-179. doi: 10.4236/msa.2016.73017