**2.2 Solid particle erosion test**

Erosion tests on coated and uncoated test samples were carried out according to ASTM G76- 02 [16] standards. The test parameters are shown in Table 3. The sample was first cleaned in acetone using an ultrasonic cleaner, dried and then weighed using an electronic balance having a resolution of 0.01 mg. The sample was then fixed to the sample holder of the erosion rig and eroded with silica sand at the predetermined particle feed rate, impact velocity and impact angle for a period of about 5 min. The sample was then removed, cleaned in acetone and dried and weighed to determine the weight loss. This weight loss normalized by the mass of the silica particles causing it (i.e. testing time x particle feed rate) is then computed as the dimensionless incremental erosion rate. The above procedure was repeated till the incremental erosion rate attained a constant value independent of the mass of the erodent particles or, equivalently, of testing time. This constant value of the

Erosion Behavior of Plasma Sprayed

Fig. 3. Topology of Al2O3 Coatings Cast Iron

**3.2 Morphology of coatings** 

(Fig.3).

Alumina and Calcia-Stabilized Zirconia Coatings on Cast Iron Substrate 105

Al2O3 coated test samples viz., CI-S1, CI-S2, CI-S3 are characterized by their disc shaped grains (Fig.3). These grains are found to be the flattened solidified droplets of the coating material. The molten particles are found to be distributed more or less evenly producing a smooth coating surface. Enlarged view of marked region of CI-S1 sample (Fig.3) indicates a network of microcracks. Cracks are also observed on the surface of flattened droplets. This may be possibly due to the presence of residual stresses introduced by thermal shocks resulted during the spraying process. Changing the thickness of top coat appears to have no significance on the microstructure as in the case with test samples CI-S2, CI-S3

Enlarged View of the Region Marked in CI-S1 Showing Micro-cracks


incremental erosion rate is defined as the steady-state erosion rate. On each coating system, three tests were conducted. The test parameters are given in Table 3.

Table 3. Erosion Test Parameters
