EFFECT OF PLASMA ACTIVATION ON THE PHASE-TRANSFORMATIONS OF ALUMINUM-OXIDE

The deposition of protective, anticorrosive and wear resistant layers onto large-area metal substrates by physical vapor deposition techniqu es is gaining increasingly in industrial significance. This contributi on deals with the deposition of aluminum oxide onto stainless steel. T he aluminum oxide was deposited by reactive high-rate electron beam ev aporation. Plasma activation of the vapor took place via a hollow-cath ode plasma. The substrates were coated at a temperature of 500 and 700 degrees C and subsequently postannealed in vacuo at 600, 800, 1000 an d 1200 degrees C. At a substrate temperature of 500 degrees C with and without plasma activation Al2O3 is deposited with different densities and amorphous to X-rays. At 700 degrees C without plasma activation, however, gamma-Al2O3 is found in an amorphous matrix whereas plasma ac tivation results in alpha-Al2O3 in an amorphous matrix. The effects of plasma activation and post-annealing temperature on the sequence of A l2O3 phase transformations were investigated. The hardness of the laye rs increases noticeably with plasma activation and post-annealing temp erature. In addition, layers deposited under plasma activation exhibit better thermal stability with respect to volume contraction. Phase id entification was done using X-ray diffraction, and transmission electr on microscopy with selected area diffraction. The morphology of the la yers was investigated by scanning electron microscopy and the hardness was measured by nanoindentation.