Abstract
We use in situ scanning probe microscopy (SPM) to investigate the high temperature oxidation of Ni-based single crystal alloys at the micro-/nanoscale. SiO2 micro-pillar arrays were pre-fabricated on the alloy surface as markers before the oxidation experiment. The SPM measurement of the oxidized surface in the vicinity of SiO2 micro-pillars was conducted real time at temperatures from 300 °C to 800 °C. The full-field evolution of oxide film thickness is quantitatively characterized by using the height of SiO2 micro-pillars as reference. The results reveal the non-uniform oxide growth featuring the nucleation and coalescence of oxide islands on the alloy surface. The outward diffusion of Ni and Co is responsible for the formation and coalescence of first-stage single-grain oxide islands. The second-stage of oxidation involves the formation and coalescence of poly-grain oxide islands.
Highlights
Due to their excellent high temperature mechanical properties, corrosion resistance and high strength-to-weight ratio, Ni-based alloys have been widely used and extensively investigated over the past few decades[1,2,3]
Recent studies via in situ high resolution transmission X-ray microscope[22,23] and in situ transmission electron microscope[24,25] have focused on the oxidation at the nano/atomic-scale and revealed a locally inhomogeneous oxidation behavior during the early stage of oxidation. These studies are limited to the incipient oxidation process without sufficient attention to oxide evolution as the oxide film is accumulated with time
As the time increased to 80 min and the temperature remained at 300 °C, no obvious surface oxide was detected (Fig. 2(b))
Summary
Due to their excellent high temperature mechanical properties, corrosion resistance and high strength-to-weight ratio, Ni-based alloys have been widely used and extensively investigated over the past few decades[1,2,3]. Several conventional experimental methods have been used to study the oxidation of Ni-based alloys, including mass gain/loss method, oxygen uptake measurement, accelerated life test, etc[12,13,17,18,19,20,21] These experimental methods have provided strong support for the investigations of oxidation kinetics, few of them have the ability of providing the important information of spatial variation of growing oxides, since the results are usually obtained by smearing out the regional difference of oxidation evolution. Recent studies via in situ high resolution transmission X-ray microscope[22,23] and in situ transmission electron microscope[24,25] have focused on the oxidation at the nano/atomic-scale and revealed a locally inhomogeneous oxidation behavior during the early stage of oxidation These studies are limited to the incipient oxidation process without sufficient attention to oxide evolution as the oxide film is accumulated with time. Our results provide new insights into the formation and growth of oxide islands on the alloy surface
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