| Chromium nitride is widely used in die casting and tool machining applications, because CrN coating has high hardness, good wear resistance and corrosion resistance. Addition of small amounts of Al into the face-centered cubic (fcc) structure of CrN results in the formation of a metastable ternary solid solution CrAlN, which can further improve the mechanical performance of CrN coating.In this paper, CrAlN coatings were deposited by gaseous ion source enhanced closed field unbalanced magnetron sputtering from Cr and Al elemental targets in an Ar+N2 mixture atmosphere. The effects of bias voltage and targets power on coating microstructure, hardness and adhesion were investigated. The repeated impact resistance and high-temperature oxidation resistance of CrAlN coatings were studied. To further explore the potential of the coating system for more industrial applications, corrosion resistance and wear resistance at room temperature and 600℃of CrAlN coatings deposited on the nitrided and unnitrided H13 steel were studied. The results in this paper are concluded as follows: (1) The substrate bias voltage greatly affected the microstructure and hardness of CrAlN coatings. At the same Al/Cr target power ratio, with increasing substrate bias voltage, the CrAlN coatings became more compact and denser, the microhardness increased, the ability to restrict the crack expansion enhanced, and coating adhesion increased. The (111) diffraction peak decreased in intensity and broadened in width as the bias voltage increased, which is attributed to the variation in the grain size and microstrain. At the same substrate bias, coating density and hardness increased with an increase of Al/Cr target power ratio.(2) The repeated impact resistance of the CrAlN coatings was improved with the increase of coating density, coating hardness and fracture toughness. The coatings prepared at substrate bias voltage of -120V showed the best performance with high hardness, good adhesion and excellent resistance under repeated impact.(3) The results of the cyclic oxidation tests show that the oxidation resistance of the CrAlN coatings increased as the bias voltage increased. The main reason is that more mixture of Cr and Al oxides formed with the increase of the bias voltage, this oxide mixture layer acted as an effective diffusion barrier slowing down the inward diffusion of oxygen at high temperatures. On the other hand, Al and N atoms were covalently bonded, which improved the thermal stability of the coatings.(4) The CrAlN-coated samples exhibited superior corrosion resistance when compared with untreated AISI H13 steel. And with increasing substrate bias voltage, the corrosion resistance of the CrAlN-coated AISI H13 samples increased, which was attributed to the decreased grain size and roughness of the CrAlN coatings and the formation of dense microstructure. The duplex systems CrAlN coating/nitrided steel exhibited superior corrosion resistance because the layers of the dense passivated iron nitride formed during nitriding effectively prevented the invasion of corrosion medium into substrate.(5) The results of wear test at room temperature show that the wear resistance of CrAlN coatings deposited on the H13 steel was improved when compared with untreated AISI H13 steel. The wear resistance of the CrAlN coaitngs increased with increasing substrate bias voltage. During the wear test at 600℃, the friction coefficient of the H13 steel substrate coated with CrAlN coating increased, but the wear resistance increased. The increase in the friction coefficient value is because that the hard mixture of Cr and Al oxides formed during wear brought abrasive wear, but the increased hardness and fracture toughness in CrAlN coaitngs contributed to the increased wear resistance of the CrAlN coaitngs. The study show that the wear resistance of the nitrided H13 steel/(CrAl)N PVD duplex coating was not increased, because the compound layer formed during the nitriding process impaired the adhesion of the CrAlN coating deposited on a nitrided steel, with the fracture and subsequent removal of the coating from the substrate after a period of friction, and thus the disappearance of the effect of the improvement of wear resistance by coating.
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