Influence of process parameters and initial microstructure on the oxidation resistance of Ti48Al2Cr2Nb coating obtained by laser metal deposition

Abstract

Ti6Al4V have been the most important and versatile titanium alloys currently used, due to their excellent combination of low density and good mechanical properties, despite their application temperature being limited to up to 300 °C. In this work, a Ti6Al4V sheet was coated with a Ti48Al2Cr2Nb alloy by laser cladding process, with the process parameters resulting in laser-specific energy densities of 70, 80, 90 and 180 J/mm2, laser power between 600 and 900 W and scanning speed of 100 to 300 mm/min. In order to analyze the oxidation resistance at elevated temperature, isothermal oxidation tests were carried out at 800 °C for 5, 10, 25, 50, 100 and 150 h in static air. The oxidized samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM), field emission microscopy (FESEM) with energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. Two groups of coatings with similar microstructures were obtained, and their influence on the formation of thermally oxidized growth layers was studied. From the isothermal oxidation tests, it was observed that the Ti48Al2Cr2Nb coatings have good resistance to oxidation in air at 800 °C in comparison with the Ti6Al4V substrate by obtaining layers of oxides up to 12 μm thick after 150 h of oxidation. The structure of the oxide layers is complex and comprises the growth of successive layers from the outer surface of the coating. The effect of the microstructure of the coating on the density of the oxide layer formed was evaluated.