الفهرس 
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Abstract
The focus of most research nowadays in the field of material engineering is on the increasing hardness of industrial components. High-power fiber lasers are now a very attractive device that found a great number of applications in manufacturing. It provides the most reliable and convenient solid-state laser available. Across the automotive sector, ductile cast iron is used in engine connecting rods, cylinders, crankshafts, truck axles, and gears, among other items. The term “laser surface hardening process” refers to the thermal hardening of a material based on specific surface heating and rapid cooling under the effect of the laser beam. The primary benefit of laser surface treatment is the quick heating of the thinner surface layers, which eliminates the need to use energy-intensive traditional heat treatment methods to heat the entire material. This thesis investigates the influence of high-power ytterbium fiber laser parameters, including laser beam power, scanning speed, defocusing distance, and shielding gas condition, on the surface hardness of ductile cast iron. Light microscopy was used to evaluate the treated samples (OM). Transmission electron microscopy and energy dispersive microanalysis (EDS) were employed to identify the phases in the surface and interfacial areas (TEM). For various circumstances, the depth of the hardened surface and corresponding micro-hardness were both measured. The results demonstrated that the maximum surface hardness and the deepest hardened zone can be attained more effectively with higher laser power, smaller spot sizes, and slower processing speeds. Using a 1.6 KW laser, 89 mm defocusing distance, and a processing speed of (0.8, 1) m/min, a hardened zone with a depth of (240, 200) µm and surface hardness of (1150, 1033) HV0.3 was created.