PREPARATION OF AL THIN-FILMS BY THERMO-ELECTRON ACTIVATION ION PLATING AND THEIR CORROSION-RESISTANCE

Al thin films were prepared on SPCC steel substrates by a thermo-electron activation ion plating process. The influence of argon gas pressure and substrate bias voltage on the crystal orientation and morphology of the films was determined by using X-ray diffraction and scanning electron micrography (SEM), respectively. And the effect of crystal orientation and morphology of the Al thin films on corrosion behavior was estimated by measuring the anodic polarization curves in deaerated 3%NaCl solution. The crystal orientation of the Al films deposited at high argon gas pressure exhibited a (200) preferred orientation, regardless of the substrate bias voltage. Film morphology changed from a columnar to a granular structure with the increase of argon gas pressure. The morphology of the films depended not only on argon gas pressure but also bias voltage; i.e., the effect of increasing bias voltage was similar to that of decreasing argon gas pressure. The Al films which exhibited the (200) preferred orientation and the granular structure showed good corrosion resistance. Especially, the corrosion resistance of the film prepared with the bias voltage of -2.0 kV and the argon gas pressure of 7.3 x 10(-1) Pa was better than a rolled plate of 99.99%Al. That is, this showed that the corrosion resistance of the Al thin films can be changed by controlling the crystal orientation and morphology. It appears well established that the properties of the Al films prepared by the thermo-electron activation ion plating process depend on the deposition conditions.