• Research highlights of the present work are listed as follows: • The oxidation behavior of Ni-17Cr-xAl model alloys in 650°C/1 atm CO 2 is studied; • Al addition minishes Cr/Al depletion zones at passivated boundary; • Al addition effectively retards or prevents preferential oxidation; • Intragranular oxide platelets exhibit Al 2 O 3 at core and Cr 2 O 3 distributed laterally; • Intragranular Al 2 O 3 platelets have greater lengths than Cr 2 O 3 platelets. The oxidation behavior of Ni-17Cr- x Al ( x =0, 1.5 wt.%, 3 wt.%) model alloys under 650°C/1 atm (1.01325 bar) CO 2 condition was systematically investigated. Following vibratory polishing, all three alloys exhibit passivation at random high angle grain boundaries (RHABs) and some low angle grain boundaries (LAGBs). Al-containing oxide markedly reduces Cr outward diffusion and O inward diffusion, significantly shrinking the Cr/Al depletion zones ahead of the oxidation front. Preferential oxidation occurred at some twin boundaries (TBs), other coincident site lattice boundaries (CSLBs, ∑>3) and LAGBs. Al-rich oxide effectively retards or prevents preferential oxidation therein. Some TBs and LAGBs exhibit the same oxidation rate as the matrix. The higher diffusivity of Al, coupled with the low oxygen partial pressure required for Al 2 O 3 nucleation, drives the accelerated longitudinal growth of intragranular Al 2 O 3 platelets, resulting in greater lengths than Cr 2 O 3 platelets. In Al-containing alloys, Cr 2 O 3 subsequently grows along both sides of Al 2 O 3 , ultimately forming a platelet structure with Al 2 O 3 at the core and Cr 2 O 3 distributed laterally.
Xue et al. (Wed,) studied this question.