ABSTRACT
This investigation has studied the formation of Ti and TiB2 coatings on a Ti substrate using the coaxial laser cladding process. The implemented laser was a continuous NdYAG of 1Kw. The purpose was to analyze the influence on the coating of both the alloying elements percentage and the presence of the alloying elements in the substrate as well as the changes suffered by the ZAC in the substrate.
To obtain the appropriate experimental analysis, the main process parameters which are power and velocity of the scan, powder flow were gradually changed within the chosen range. Correlations were made between the main process variables, the geometry of the single tracks and the added powder transformations.
The overlapping of single tracks was carried out once the ones with best combination of geometrical, microstructural and hardness characteristics were determined. The thermal effect on the redistribution of the phases and the chemical element diffusion of the coatings was analyzed.
The coatings obtained had a good track area and low dilution area. The microstructure was composed of a titanium matrix with TiB and TiB2 compounds, homogeneously (uniformly) distributed and firmly jointed to it. The resulting hardness was up to 8 times greater than the original titanium.
The adequate parameters to obtain the powders of the Ti+TiB2 alloy, by mechanical alloying, were identified. The process window for the fabrication of the Ti+TiB2 alloy was determined. The approximate bore composition was established thanks to the Wavelength Dispersive Spectrometry. The compounds encountered were mechanically characterized by nanohardness techniques. The phases and compounds present in the coatings as well as their distribution were identified by Electron Backascatter Diffraction.
This project is part of a general objective in the improvement of the superficial characteristics of titanium investigation. Therefore thanks to the knowledge acquired during this thesis, new investigations can be carried out on the behavior of the coatings when submitted to wear and corrosion.