INFLUENCE OF ATMOSPHERIC PRESSURE PLASMA TREATMENTS ON THE OXIDE FILM AND THE CORROSION RESISTANCE OF TITANIUM AND TITANIUM ALLOY

摘要

In the industrial plants, plasma is often used for cleaning and activating the surfaces and/or for the formation of different types of coatings. In the past, the plasma technology required the use of low pressures with consequent economic and technological problems. The development of plasma technologies that can work at atmospheric pressure overcomes the disadvantages of traditional vacuum operation and permits to apply this technology in a larger number of applications for example in continuous in line manufacturing. In this study, the influence of a treatment carried out with an atmospheric pressure plasma jet (APPJ) on the passive oxide films of titanium and titanium alloys and the correlation between these changes and the corrosion properties were studied. The treatments were realized on commercially pure titanium (grade 1) and a Ti6Al4V (grade 5) titanium alloy using a plasma generated by air at 1.5 bar. Different process parameters were tested. In detail, the effect of the distance plasma torch-sample and of the rate of movement of the plasma torch during the treatment (useful to simulate an in line continuous process) were studied. The corrosion resistance of the samples was analyzed with potentiodynamic polarization and electrochemical impedance spectroscopy tests, using as electrolyte the Ringer solution. The effects of the treatment on the oxide layer were studied using secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The plasma treatment allowed the growth of the passive film and improved the corrosion resistance of both titanium and titanium alloy.