Indian Journal of Science and Technology

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Background/Objectives: The study aims to improve surface properties of aluminium A356 alloy by surface alloying it with nitrided titanium, in a nitrogen environment, using Gas Tungsten Arc (GTA) as heat source. Methods/Statistical Analysis: Nitrided titanium sheets were surface alloyed with cast aluminium A356 blocks, in nitrogen environment, with GTA as heat source for melting. The cross-sectional microstructure of the specimens was studied using inverted metallurgical microscope. Further analysis was carried out using SEM/EDS to identify the formation of nitrides and intermetallic compounds. The hardness of the specimens was measured using Vickers hardness tester and the wear rate was determined using pin-on-disc wear tester. Findings: Microstructure analysis revealed a uniform and granular refined structure in the modified layer compared to the coarse and dendritic structure of the cast block. EDS analysis indicated the formation of hard-intermetallic compounds. The hardness was measured to be highest at the surface of the central fusion zone, with a maximum value of 656 HV while as-cast aluminium block exhibited only 76 HV. The measured wear rate was 10×10-4 mm3/m for the modified layer, compared to 52×10-4 mm3/m of the substrate. Alongside, the loss in weight after wear dropped by 4 mg. The coefficient of friction of the modified surface showed a constant trend during the wear-off period. The enhancement in these surface properties is attributed to the formation of nitrides and other intermetallic compounds that in the modified layer during surface alloying. Additionally, the use of GTA as heat source renders the surface alloying process to be economically feasible relative to other employable methods. Applications/Improvements: The devised surface alloying method used to enhance the surface properties of A356 is cheap, flexible and effective and finds intensive application in marine, automotive and manufacturing sectors.

Keywords

A356, Gas Tungsten Arc, Hardness, Nitriding, Surface Alloying, Titanium, Wear Rate.
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