Mechanical properties, electrochemical performance and interfacial contact resistance of as-deposited and annealed NbxAlyC and CrxAlyC coatings on stainless steel 316L substrates

Abstract

NbxAlyC and CrxAlyC coatings (where x is the Nb or Cr target current and y is the Al target current) were deposited on stainless steel 316L substrates using a radio frequency unbalanced magnetron sputtering system. The sputtered NbxAlyC and CrxAlyC coatings were vacuum annealed at 800°C and 750°C for 1 h, respectively. The cross-sectional and surface morphologies of the as-deposited coatings showed a columnar structure and a loose surface, respectively. The X-ray diffraction results showed that the annealed NbxAlyC and CrxAlyC coatings contained Nb2AlC and Cr2AlC MAX crystalline phases, respectively, The MAX crystalline phase improved the hardness, corrosion resistance, and electrical conductivity of the coatings. The annealed coatings also formed an Al2O3 layer with a small cluster size and a dense surface, which significantly improved the corrosion resistance compared to that of the as-deposited coatings. The electrochemical test results showed that the corrosion current density (Icorr) and interfacial contact resistance (ICR) values of all the annealed coatings were lower than those of the as-deposited coatings and were consistent with the standard for the bipolar plates in commercial proton exchange membrane fuel cells. Among all the coatings, the annealed Nb2.5Al0.5C-H coating showed the lowest Icorr and ICR values.