**3.7.4 Effect of coating hardness on erosion rate**

It is well understood that the erosion rates are affected by various factors [4, 41-44]. These factors can be broadly classified into three types: impingement variables describing the

Erosion Behavior of Plasma Sprayed

**4. Conclusions** 

the coatings.

technique.

Alumina and Calcia-Stabilized Zirconia Coatings on Cast Iron Substrate 123

Fig. 15. Effect of Hardness on Volume Erosion of Alumina and ZrO25CaO Coatings

Fig. 16. Effect of Porosity on Volume Erosion of Alumina and ZrO25CaO Coatings

a. From the study of SEM morphology of the coatings it can be concluded that thermal stresses developed during spraying were main causes for presence of micro-cracks in

b. From the SEM cross-sections of coating systems it was observed that there is a variation in coating thickness. It is mainly due to variation in speed of the plasma gun during spraying. This variation can be minimized by applying Robot Plasma Spraying

c. For adhesion measurement, ASTM C633 tensile adhesion test was used and proved to be effective for general level of comparison. From the obtained results it can be said that the main failure location was in the bond coat/ceramic interface corresponding to the

particle flow, particle variables, and material variables. The primary impingement variables are particle velocity, angle of incidence, flux (particle concentration) and target temperature. Particle variables include particle shape, size, hardness, and friability (ease of fracture). Material variables include all the material properties, such as hardness, work hardening behaviour, and microstructure

Fig. 14. Volume Erosion Plots as Function of Angle of Impact for Alumina and ZrO25CaO Coatings

Hardness is one of the most effective factors in predicting erosion behaviour and in modeling erosion processes. The best correlation of hardness with erosion is observed for hardness measured on bulk materials [45]. However, few data concerning ceramic coatings are available till now. Here the effect of hardness of coating systems on erosion rate is studied using Vickers hardness. The relationship between erosion rate and hardness of coatings are shown in Fig. 15. It can be seen that a good correlation of hardness with erosion rate is observed irrespective of the type of ceramic. The higher erosion rate is observed at lower hardness of a ceramic coating.
