Processing and Characterization of Plasma Spray coatings of Industrial Waste and Low Grade Ore mineral on metal substrates

Abstract

Emerging portable applications and the rapid advancement of technology have posed rigorous challenges to Metallurgical engineers for development of an efficient material which
can sustain for long period at any type of environment. The foremost objectives are to develop required surface properties with economical process. Now-a-days the investigation explores the coating potential of industrial wastes. Fly-ash emerges as a major waste of thermal power
plants. It mainly comprises of oxides of silicon, iron, aluminium, and titanium along with some other minor constituents. Fly-ash premixed with quartz and illmenite which are low cost
minerals available in plenty are excellent candidates for providing protection against abrasive wear and resistant to erosion.
Plasma spraying is gaining acceptance for development of quality coatings of various materials on a wide range of substrates. Utilization of such kind of industrial waste as coating material minimizes the cost of plasma spray coating deposition, which posed to be the major hindrance to its wide spread application due to high cost of the spray grade powders. Fly-ash+quartz+illmenite (weight percentage ratio: 60:20:20) is deposited on mild steel and copper substrates by atmospheric plasma spraying, at various operating power levels ranging from 11 to 21kW and then characterization of the coatings is carried out. The
properties of the coatings depend on the materials used, operating condition and the process
parameters. The plasma spraying process is controlled by the parameter interdependencies,
co-relations and individual effect on coating characteristics. The particle sizes of the raw
materials used for coating are characterized using Laser particle size analyzer of Malvern
Instruments. Coating interface adhesion strength is evaluated using coating pull out method,
confirming to ASTM C-633 standard. Deposition efficiency is an important factor that
determines the techno economics of the process. It is evaluated for the deposited coatings. In
view of tribological applications, hardness is one of the most required mechanical properties.
Hardness measurement is done on the polished cross section of the samples using Leitz Micro-
Hardness Tester. Coating porosity is measured by image analysis technique. Coating thickness
is measured on the polished cross-sections of the samples, using an optical microscope. To
ascertain the phases present and phase changes/transformation taking place during plasma
V
spraying, XRD analysis is made. The coating quality and behavior depends on Coating
surface & interface morphology are studied with Scanning Electron Microscope. For wear
resistance application, wear properties of these coatings are studied by “Air Jet Erosion Test
Rig”. The erosion wear behaviour of these coatings is evaluated with angular solid particle
erosion tests under various operating conditions.
In order to optimize the surface property for different application, one of the challenges is to
recognize parameter interdependencies; correlations and their individual effects on process so
that the coating can be useful for a specific application. This challenge can be
analysed/predicted by Artificial Inteligence Methods. Statistical analysis of the experimental
results using Artficial Neural Network and Taguchi experimental design is been made.
Spraying parameters such as impact angle, size of the erodent, standoff distance and impact velocity are identified as the significant factors affecting the coating tribological property. This work establishes that fly-ash+quartz+illmenite composite mixture can be used as a
potential coating material suitable for depositing plasma spray coating. It also opens up a new
pathway for value added utilization of this industrial waste and low-grade ore mineral.