(388a) High Throughput Analysis of Alloy Corrosion Across Composition Space: AlxFeyNi1-X-Y (x = 0 → 1, y = 0 → 1-x)

Gellman, A. J., Carnegie Mellon University
Payne, M., Carnegie Mellon University
Miller, J. B., Carnegie Mellon University

Improving our fundamental understanding of
the oxidation of multicomponent alumina-forming alloys is crucial to their
ongoing development.  In this work, high-throughput methods were developed to
study oxidation of AlxFeyNi1-x-y
alloys in dry air at 427 °C using composition spread alloy films (CSAFs) as
combinatorial libraries (x = 0 → 1, y = 0 → [1-x]). 
CSAFs were deposited under ultra-high vacuum conditions using a rotating shadow
mask, electron beam evaporation tool.  The AlxFeyNi1-x-y
CSAFs we first analysed using EDX to map their local compositions across the
library, then exposed to oxidation conditions, before subsequent analysis using
spatially resolved EDX, Raman spectroscopy, and XPS depth profiling.  These
allowing mapping of the oxygen uptake (Figure 1), the local phases formed and
the distribution of the metal and oxide phases into the depth of the CSAF.  This
work used AlxFeyNi1-x-y
CSAFs to determine the critical Al concentration, NAl*(x,
y), for establishment of a passivating Al2O3 scale
continuously across AlxFeyNi1-x-y
composition space (x = 0 → 1, y = 0 → [1-x])
in both dry air and a 10% H2O/air mixture at 427 °C.  The results
divide the AlxFeyNi1-x-y
composition space into four regions of phenomenologically distinct oxidation
behaviour.  At high an Al fraction, the alloy is passivated by either a surface
Al2O3 scale or a subsurface Al2O3
scale.  The boundary defining NAl*(x,
y) was determined across the entire continuous AlxFeyNi1-x-y
composition space.  The presence of H2O vapour in an oxidizing
environment increases the value of NAl*
required to establish a passivating Al2O3 scale in
multicomponent alumina-forming alloys.  The NAl*(x,
y) in this environment was significantly higher across much of
composition space than that measured in dry air.  Physical insights from the
observed differences between passivation in dry and humid air have been
considered using a modified Wagner-Maak model. 

Figure 1.  Map of oxygen uptake
into a AlxFeyNi1-x-y
CSAF following exposure to dry air at 427 oC for 4 hrs.