Interfacial indentation test of laser surface modified AISI H13 tool steel thermal barrier coatings

Full text: Adhesion is one of the most important parameters which influence the development of thermal spray coatings and interfacial indentation test (IIT) was used to evaluate adhesion of coatings. The effect of spraying parameters on the coatings adhesion of laser surface modification of H13 tool steel as well as its toughness was investigated. The investigation deals with the application of a continuous CO2 laser to laser surface modified H13 tool steel surface and consequently deposited by Atmospheric Plasma Spray (APS). Different laser power and scanning speed were investigated in order to improve the overall mechanical property of H13 tool steel surface. The changes in mechanical properties were investigated in terms of its' micro hardness and micro-structure using Micro Hardness Tester Machine and optical microscope. Improvements in micro hardness is performed at higher laser power and moderate scanning speed. Too much increase in power density can be detrimental to the final property of H13 surface and too slow scanning speed increase overlap percentage causes decrease in mechanical properties i.e. micro hardness. Further, the experiment continues with the deposition of thermal barrier coatings (TBC) of bond coat and top coat using Atmospheric Plasma Spray (APS) technique. Three controlled factors of input current, powder feed rate and stand-off-distance were investigated to coat the TBC layer. The coating thickness and percentage of porosity were measured using IM7000 inverted optical microscope while fracture toughness of between coatings were measured using MMT-X7 Matsuzawa Hardness Tester Machine with Vickers Indenter. The microscopy findings indicated variations of Fracture Toughness, K with coating porosity and coating thickness at different parameters settings. The obtained results revealed that the adhesion increase with the decrease in porosity and increase in coating thickness of bond coat and top coat. These findings are significant to enhance surface properties of semi-solid forming H13 tool steel die and prolong its' lifecycle. (author)