Abstract
The present work aimed at investigating the effect of nanosecond laser parameters on ablation characteristics such as ablation depth and surface roughness of plasma sprayed tantalum carbide coated graphite substrates. The micro scratch tests were performed on the laser ablated and as-sprayed coatings to evaluate the critical loads and coefficient of friction. The laser ablated surface with minimum ablation depth and surface roughness was found to exhibit 18% higher critical loads when compared to that of as-sprayed surface. However, laser ablated surfaces exhibited slightly higher friction coefficient than as-sprayed surfaces due to formation of metastable oxide layer (Ta6O) on the top surface of TaC coatings as indicated by XRD. The maximum ablation and scratch resistance could be found at maximum pulse energy of 250 μJ, maximum scanning speed of 1000 mm/s and moderate hatch spacing of 20 μm. While, the failure of as-sprayed TaC coatings was attributed to local collapsing of material due to degradation of mechanical properties such as elastic modulus, surface porosity and surface roughness, laser ablated surfaces exhibited wedge spallation at the end of scratch zone only.
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