Improved Cr 2O 3 adhesion by Ce ion implantation in the presence of interfacial sulfur segregation

Abstract

As-polished and preoxidized Ni–20Cr alloys were Ce-implanted with a dosage of 1 × 10 17 ions/cm 2, then subsequently oxidized at 1050 °C in air. The oxide adhesion and the extent of sulfur segregation at the oxide–alloy interface were determined, respectively, using tensile pull testing and scanning Auger microscopy with an in situ scratch device. The critical load for oxide failure was the lowest on the unimplanted Ni–20Cr, and was slightly higher on those with implantation made into a preformed oxide. Oxides that formed directly on Ce-implanted Ni–20Cr never failed under the pull test, which showed the strongest scale adhesion; however, similar amounts of interfacial sulfur, which segregated from the alloy during oxidation, were found at all interfaces. Ce additions were also found to reduce the oxidation rate and affect the extent of voids at the scale–alloy interface. It is suggested that the change in the oxide growth mechanism reduces the number of interfacial voids and, unlike Al 2O 3, these factors are more important for Cr 2O 3 scale adhesion than sulfur segregation to the scale–alloy interface.