**1.1 Special features of plasma spraying technique**

The following are some of the unique features of the plasma spraying process.


Erosion Behavior of Plasma Sprayed

impact angles

Alumina and Calcia-Stabilized Zirconia Coatings on Cast Iron Substrate 101

material. Figure shows the schematic of the expected variation in erosion behavior with

Figure Expected Variation of Erosion Rate with Particle Impact Angle (Ref. 8)

been attributed to the failure of the individual splat boundaries.

**2.1 Plasma spraying and characterization techniques** 

**2. Experimental details** 

given in Table 1.

Most applications involve low impact angles at which erosion resistance of ceramics happens to be significant. It should also be noted, that the microstructure of plasma sprayed coatings often differs significantly from that of corresponding bulk material. The structure of plasma sprayed coatings consists of many overlapped lenticular splats which conform more or less either to the morphology of the underlying substrate or to that of previous splats. Although plasma sprayed coatings are anisotropic, their erosion rates tend to exhibit the same dependence on impact angle similar to that of the bulk material of ceramics [9]. On the other both Kingswell [10] and Zhang [11] have noted that the erosion mechanism in plasma sprayed alumina coating is different from those in bulk sintered alumina. Erosion of bulk ceramics generally occurs by a number of fracture mechanisms [12, 13]. During particle impact upon a ceramic surface, median and radial cracks develop at the impact site [14]. Upon rebounding of the particles i.e. unloading of the impact site, lateral cracks develop parallel to the surface and finally follows a curved path before propagating towards the surface, leading to chipping and loss of material. Erosion in plasma sprayed ceramics has

The surfaces of the substrate materials which are to be plasma coated were examined for dimensional accuracy and surface finish before being degreased in a vapour bath (70- 800C) of tetra chloro ethylene. The surfaces were then grit blasted by Al2O3 (-18+24 mesh) at a pressure of 455 kPa. Plasma spraying process was carried out with the help of proprietary Sulzer Metco Equipment. The composition of cast iron substrate and coating materials is

