Corrosion resistance, wear behavior and residual stress for Ti/TiN coatings deposited on nitrided AISI 316L by cathodic arc

L. VACA; J. P. QUINTANA; A. MARQUEZ; S. BRÜHL; D. VEGA

Congreso; Materials Science and Engineering Congress 2018; 2018

Cathodic arc deposition (CAD) allows obtaining dense compound coatings with high deposition rates and good adhesion, making it attractive for applications that require hard and wear-resistant coatings.Combining CAD with plasma assisted nitriding, results in an improvement of the load capacity of the treated surface. The high temperature( 500ºC) usually employed in industrial CAD equipmentsto improve the film adhesion prevents its application in nitrided austenitic stainless steels, because the precipitation of chromium nitrides occurs and thus, the degradationof the anticorrosive properties.Biasing the substrate with high voltages pulses during CAD? called plasma based ion implantation and deposition (PBII&D) process-generally leads to more compact coatings and reduce residual stresses, thus improving the adhesion at lower temperatures.This work presents a comparative study of Ti/TiN films grown by PBII&D and CAD onnitrided AISI 316L stainless steelsubstrates. The samples were nitrided in a commercial facility at 420º C for 20 hours in a mixture H2-N2.Hardness increased up to 800 HV, and the nitrided layer or S phase consisted only of nitrogen in solution, free of nitrides and was about 7-8 m thick. TheTi arc was run at a 100A current. The Ti interlayers were deposited in the base vacuum at 10-5 mbar, while the TiN films were obtained in a N2 atmosphere at 10-4 mbar. The substrates temperature was maintained constant at 300 ºC during the growth process. Some of the samples were biased with negative pulses of 6 kV at 200 Hz with 30 μs duration.Morphology, microstructure, adhesion, corrosion resistance, residual stress and wear behavior of the films were characterized. The coating morphology was studied through optical and scanning electron microscopy. The film structure was analyzed by X-ray diffraction in the Bragg-Brentano geometry. The residual stress was determined from diffractograms registered with grazing incidence. The filmadhesion was evaluated with Rockwell-C testandScratch Test.Corrosion response was studied with the passivation test and by Salt Spray Fog Test during 100 hours. The wear resistance was determined with the pin-on-disk test.Compact films were observed. The coatings thickness varied between 1.5 µm to 2.5 µm. In all cases the main peaks of TiN and Ti were detected by XRD. No significant differences on residual stress were noticed. The better adhesion was obtainedfor films grown by PBII&D.