Systematic study of laser effect on surface integrity of cemeted carbides
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Data2017-06-21
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Abstract
Laser is an exceptional technique for surface modification, due to the absence of tool wear, high precision, efficiency and high stability on the process. Laser ablation is a well-suited treatment of cemented carbides, regarding edge rounding and surface modification, for improvement of tribological properties. Moreover, it is an effective method to selectively remove cobalt from the surface of cemented carbides, required for improving adhesion of diamond coating. Finally, it is currently being used as an effective way to generate micronotches used for fatigue life evaluation in metals. However, little work has been done in this direction for cemented carbides. In this report, the effect of nanosecond laser pulses on the surface integrity of cemented carbides is systematically studied. To do so, laser ablation was done at three different levels of laser fluence, on two cemented carbide grades: WC-Co grade, with fine, medium and coarse mean grain sizes; and WC-NiCrMo grade with medium mean grain size. Surface integrity after laser ablation, and dimensions (depth, diameter, redeposition height) of the notches, were evaluated by means of optical microscopy (OM), laser scanning confocal microscopy (LSCM), white light interferometry (WLI), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). The adjacent affected area, as well as the area under the ablated surface, were evaluated by means of FESEM-focused ion beam (FIB) milling. Results demonstrate that an increase in pulse number generates deeper notches, but the system reaches a point of instability where notches are filled with debris material. After 100 pulses at fluence 1.29J/cm2 some recast can be seen laying inside the notch. Product of the ablation process was determined to be a recast material that forms a layer in the inner face of the dimple. Recast material was neither WC nor Co. EDX results confirm that the recast material belongs to a lower carbon WC phase. This is in agreement with many studies that support carbon escape during laser ablation. Cross section of a notch revealed several microcracks that extend to the base material following both transgranular and intergranular paths. Microcracks extend for approximately 1.6μm. It was possible to observe microvoids in a microcracks situated in the base of the notch in the cobalt phase, between two adjacent WC grains. The repetitive production of a specific notch with the same parameters yielded small variations (about 10%); thus, it may be considered as reproducible.
TitulacióMÀSTER UNIVERSITARI EN CIÈNCIA I ENGINYERIA DE MATERIALS (Pla 2014)
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TFM RITA LIMA.pdf | Memòria | 3,813Mb | Accés restringit |