Alumina powder was sprayed on low carbon steel substrate using atmospheric plasma spray process. Two different powders namely crushed and agglomerated powders were used and current was varied to study their effect on fracture toughness. Theoretically, with increase in arc current, melting of ceramic oxide shall increases and in turn dense coating should form. However, it was observed that if the arc power is too high and particle size of the powder being small (∼ 30 μm), the particles tend to fly away from the plasma core. Similarly, particle size distribution and powder morphology also affects the coating properties. Smaller particle should allow more melting resulting in dense coating and agglomerated powder allows flowability as well as better coating efficiency. Conversely, smaller particles tend to fly away from the plasma making the process difficult while the agglomerated particles showed a bimodal structure marked by presence of unmelted region in the splat core. All these factors lead to substantial variation in the fracture toughness of the coating. The present paper attempts to correlate plasma spraying parameters and microstructure of the coating with fracture toughness of the same.

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