Early stage SCC initiation analysis of fcc Fe-Cr-Ni ternary alloy at 288 °C: A quantum chemical molecular dynamics approach

The initiation of stress corrosion cracking in fcc Fe-Cr-Ni ternary alloys was studied by means of quantum chemical molecular dynamics at 288 degrees C. This study showed that the iron and chromium atoms segregate faster than nickel atoms at the surfaces. The atomic model showed that nickel enrichment occurred at the inner oxide layer. The binding energy helps reduce the mobility of the nickel atoms. The surface morphology showed that Fe, Cr, and O accumulate on the very top surface while Fe, Cr, Ni, and 0 bonding takes place beneath this revealing the formation of an outer and inner oxide film. The diffusion of oxygen and hydrogen into the surface increases when it is under strain. The deeply diffused hydrogen becomes negatively charged by taking electron from metal atoms. Consequently, the process weakens the metallic bonds following with the result that oxygen can diffuse easily into the surface. It seems that hydrogen effectively functions as an oxygen carrier. This kind of reaction process can take place in the molecular domain of a crack tip and thus play a vital role in initiating the SCC process. (C) 2009 Elsevier Ltd. All rights reserved.