Abstract
Composition Spread Alloy Films (CSAFs) were used to study the resistance to oxidative corrosion of CrxFeyNi1-x-y alloys in dry air and determine the critical Cr composition, xCr∗, necessary to prevent bulk oxidation. CrxFeyNi1-x-y CSAFs were made using physical vapor deposition (PVD) and then oxidized in dry air between 100 – 500 °C for periods of 1 h. A sharp passivation boundary was observed at 300 °C separating alloys showing evidence of heavy oxidation from Cr-rich alloys that were passivated. X-ray photoelectron spectroscopy (XPS) depth profiling was used to measure the extent of oxidation and penetration depth of the oxide layer on either side of the passivation boundary. XPS measurements confirmed the presence of a critical Cr composition, xCr∗, ranging from 18 to 26 at.%. For alloys with xCr≥xCr∗, a sufficiently thick passivating layer of oxidized Cr, Cr(ox), had formed on the top surface preventing the oxidative corrosion of either Fe or Ni. On the other hand, when xCr<xCr∗, bulk oxidation was observed, with appreciable Fe(ox) and/or Ni(ox) measured on the surface and often penetrating through the entire alloy film thickness. The trajectory of xCr∗ plotted within CrxFeyNi1-x-y composition space supports the trend towards using higher Cr-content stainless steel grades in harsh oxidative environments.
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