Surface compositions of the two phases of differently prepared Ni-Cr-Al and Ni-Cr-Al-Zr samples

Abstract

The surface compositions of the α/β and γ/γ' phases of different metallographic preparations of Ni-15Cr-24Al and Ni-15Cr-24Al-0.3Zr (at%) alloys are presented. Surfaces investigated include a mechanically polished surface for both alloys, a mechanically polished acid etched surface of the Ni-Cr-Al-Zr both before heating and after heating to 600°C for several hours, and the underlying surface of this latter sample exposed by ball cratering. Both phases of all surfaces considered show depletion of Al. It is concluded that the Al depletion is not an artefact of the sample metallographic preparation or the analytical procedure. This is supported by analysis of the composition of a sample scratched in situ under UHV. It is further concluded that the Al depletion is due to oxidation during bakeout. Cr-rich features in both the α/β and γ/γ' phases are reported. An optimal two dimensionally smoothed Cr Auger image is presented showing these features which are considered to be due to the αCr solid solution particles or clustering of these particles in the α/β phase and the Ni solid solution component in the γ/γ' phase.