Characterization Of Growth And Mechanical Properties Of Chromium Oxide Coating Deposited By RF Magnetron Sputtering

Chromium oxide coatings were deposited by radio frequency reactive magnetron sputtering. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope and high resolution transmission electron micoscopy were used to investigate the microstructure and mechanism of growth of chromium oxide coatings. Hardness, elastic modulus, wear resistance, fracture toughness of the scale and the adhesion strength between the coating and substrate were determined by nanoindentation and universal mechanical test system, respectively. The main results are as follow:(1) A uniform, dense and less defects chromium oxide coating was deposited by RF magnetron sputtering. A chromium interlayer was introduced between the coating and substrate to decrease the residual stress and achieve thicker coatings.(2) The microstructure of the coating deeply depends on the deposition parameters. Amorphous structure was achieved at low oxygen flow rate (oxygen partial pressure) but columnar structure was detected when the oxygen flow rate increased. With increasing the coating thickness, the size of the columnar crystalline, hardness, elastic modulus and wear resistance increased but the adhesion showed a little bit lower than that at low oxygen flow rate.(3) A 50-120 nm thickness amorphous layer was detected not only on the interface between substrate and interlayer but also on the interface between interlayer and chromium oxide coating, which plays a role on the mechanical properties of chromium oxide coating. It can block the growth of columnar crystalline and decrease the surface roughness of the coating.(4) The amorphous chromium oxide coatings could transform to crystal when the annealing temperature went up to 480℃. The hardness, elastic modulus, wear resistance increased after phase transformation. The adhesion was also improved.(5) Investigations of single and multi-layer Cr/Cr2O3 coatings show that although there are not too much difference on the microstructure of each layer, the mechanical properties of the multi-layer coating are better than that of the single layer coating. (6) The quantitative measurements through scratch and indentation test in dry and wet condition show that water affects the adhesion between the coating and substrate significantly.