464466 High Throughput Analysis of Alloy Corrosion Across Composition Space: AlxFeyNi1-X-Y (x = 0 → 1, y = 0 → 1-x)

Tuesday, November 15, 2016: 3:15 PM
Golden Gate 4 (Hilton San Francisco Union Square)
Andrew J. Gellman, Matthew Payne and James B. Miller, Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA

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.


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