Surface alloying of commercially pure titanium with aluminium and nitrogen using GTAW processing

In the present work, surface modification of pure titanium with aluminium and nitrogen during GTAW processing has been investigated. In this regard, Al wire (grade 1100) was deposited on commercially pure Ti surface by means of GTAW process under various N2 / (N2 + Ar) ratios (from 1/10 to 2.5/10) in shielding gas. The alloyed layers were characterized using X-ray diffraction (XRD), optical and scanning electron microscopy (OM & SEM). The corrosion behavior of the coatings was also examined in NaCl 3.5% electrolyte by potensiostat analysis. The results indicated that, Al/Ti3Al2N2-Ti3Al composite coating can successfully form on Ti surface during GTAW cladding process. All prepared coatings have much higher hardness (270-460 Hv) than pure Ti substrate (160 Hv) and the hardness has shown an increasing trend by increasing the N2 / (N2 + Ar) ratio up to 2.5/10. More increasing in this ratio, lead to the formation of high percentage of defects in alloyed layer. By annealing the produced coatings, the metastable Ti3Al2N2 phase was transformed to Ti2AlN phase and the coating/substrate interface was covered with a smooth and continuous layer of Ti2AlN. The hardness and corrosion resistance of the prepared coatings was also enhanced during annealing process.