Structural and mechanical characterization of Al/Al2O3 nanotube thin film on TiV alloy

Abstract

In this study, the fabrication and characterization of Al/Al2O3 nanotubular arrays on Ti–6Al–4V substrate were carried out. To this end, aluminum thin films were deposited as a first coating layer by direct current (DC) magnetron sputtering with the coating conditions of 300W, 150°C and 75V substrate bias voltage. Al2O3 nanotube array as a second layer was grown on the Al layer by electrochemical anodisation at the constant potential of 20V within different time periods in an electrolyte solution. For annealing the coated substrates, plasma treatment (PT) technique was utilized under various conditions to get the best adhesion strength of coating to the substrate. To characterize the coating layers, micro scratch test, Vickers hardness and field emission of scanning electron microscopy (FESEM) were used. Results show that after the deposition of pure aluminum on the substrate the scratch length, load and failure point were 794.37μm, 1100mN and 411.43μm, respectively. After PT, the best adhesion strength (2038mN) was obtained at RF power of 60W. With the increase of the RF power up to 80W, a reduction in adhesion strength was observed (1525.22mN). From the microstructural point of view, a homogenous porous structure with an average pore size of 40–60nm was formed after the anodisation for 10–45min. During PT, the porous structure was converted to dense alumina layer when the RF power rose from 40 to 80W. This led to an increase in hardness value from 2.7 to 3.4GPa. Based on the obtained data, the RF power of 60W was the optimum condition for plasma treatment of Al/Al2O3 nanotubular arrays on Ti–6Al–4V substrate.