Effect of Alloy Nanocrystallization and Cr Distribution on the Development of a Chromia Scale

Abstract

Nanocrystallization, an alternative method for improving the high-temperature oxidation resistance of alloys by increasing the supply of the protective oxide-forming element such as Cr or Al, has received considerable attention. However, for nanocrystalline ͑NC͒ alloys containing two phases, the effect of spatial distribution uniformity of the oxide-forming element on oxidation has not been studied. In this contribution, three compositionally similar Cu-Ni-Cr NC alloys, with corresponding Cr distribution in atomic, nano-, and micrometer length scale, have been specifically designed and fabricated using direct current magnetron sputtering ͑DCMS͒, nanocomposite electrodeposition ͑NCE͒, and surface mechanical attrition treatment ͑SMAT͒, respectively. These NC alloys, in comparison to the conventional coarse-grained alloy counterpart during oxidation in air at 800°C, exhibited dramatically increased ability to develop a continuous chromia scale, causing a considerable decrease in the oxidation kinetics. The change in oxidation behavior is associated not only with the small grain size of the alloys, but also with the refined distribution of the Cr-rich phases. Among the three methods, microstructures developed by DCMS and NCE were more effective than that from SMAT. The formation of these processing-dependent microstructures and their relationship with the Cr-selective oxidation process are discussed.

Role of Nanostructure in Electrochemical Corrosion and High Temperature Oxidation: A Review

“…14-Cross-sections of (a) Ni 3 (AlCr) nanocrystalline coating after oxidation at 1173 K (900°C) for 200-h, [181] and (b) microcrystalline Fe 3 Al-Y alloy after oxidation at 1373 K (1100°C) for 120-h, [213] showing the formation of micro-pegs. Huang et al [199] studied the effect of nanocrystalline structure and the spatial Cr distribution on the development of a chromia scale. The study compared three compositionally same Cu-30Ni-20Cr alloys fabricated using different synthesis routes, namely, DCMS, nanocomposite electrodeposition (NCE) and SMAT.…”

“…16-(a-1 through c-1) Cross-sectional SEM and (a-2 through c-2) corresponding TEM images of Cu-30Ni-20Cr nanocrystalline alloys fabricated using DCMS (a-1, 2), NCE (b-1, 2), and SMAT (c-1, 2), respectively. [199] a protective oxide film of Cr 2 O 3 . The parabolic rate constants in case of DCMS and NCE alloys were very close to that of pure Cr which indicates that these alloys formed a Cr 2 O 3 layer.…”