Microstructure, Mechanical And Tribological Properties Of Chromium Boride-Based Coatings In Aqueous Environment

The CrB2 films, CrBN films and CrBCN films were deposited on the 316 L stainless steels and Si(100) wafers by unbalanced magnetron sputtering system and DC and RF magnetron co-sputtering system respectively. The morphorlogies, microstructures and components of the coatings were analyzed using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The adhesion strength, surface roughness, hardness and elastic module were measured by using scratch tester, light interferometric three dimensional profilometer and nano-indentation tester, respectively. The influences of deposited parameters and tribological conditions on frictional property of the coatings in water lubrication were also investigated. Then the wear mechanism was discussed through tribopairs morphology after friction test. The results showed that:1) The CrB2 coatings with different deposited parameters were deposited using unbalanced magnetron sputtering. The presence of Cr adhesive layer effectively enhanced the adhesion strength between the coatings and substrates; it also improved the bearing capacity of the film, which increased the hardness of the coatings to some extent. The friction coefficients of all the tribopairs ranged from 0.1 to 0.2. With the normal load increasing, the friction coefficients decreased gradually. The lowest friction coefficient in the system was 0.11 for CrB2-2/SiC at the normal load of 2N and the lowest wear rate of coatings was 3.6×10-7mm3/Nm at the load of 5N.2) The Cr(B)N coatings with different deposited parameters were deposited using unbalanced magnetron sputtering. The highest hardness of the coatings was 28.9GPa when the current of CrB2 target was 2A. The low concentration B doping into CrN coating improved the hardness of the coatings and lowered the wear rate of the tribopairs. But when the currents of CrB2 target varied in the range of 3A to 4A, the hardness and elastic modulus gradually decreased because of the large amount of the soft BN phase. However, the formation of amorphous BN phase had no obvious effect on reducing the friction coefficient. The CrBN-2/SiC tribopairs showed better tribological property with varied normal loads. The friction coefficients changed from 0.14 to 0.17 and the wear rate of coatings varied in the range of 8.4×10-8mm3/Nm to 1.8×10-7mm3/Nm.3) The CrBCN coatings were deposited by adjusting N2 flow, target powers and bias voltages using DC and RF magnetron co-sputtering. The change of N2 flow and target powers had no obvious effects on the hardness of CrBCN coatings. However, the increase of bias voltages was beneficial to improve the hardness of coatings in some ways. The lower friction coefficient and wear rate of CrBCN coating were obtained at N2 flow of 4sccm, sputtering power of 100 W and bias voltage of-80 V.