Unveiling the atomistic mechanism of oxide scale spalling in heat-resistant alloys
Congcong Li, Wenjin Zheng, Haonan Zhong, Xiongjun Liu, Huihui Zhu, Hui Wang, Yuan Wu, Xiaobin Zhang, Zhiyang Yu, Suihe Jiang, Zhaoping Lü
Abstract
An intact oxide scale adhering well to the matrix is crucial for the safe service of metallic materials at high temperatures. However, premature failure is usually caused by spallation of scales from the matrix. Although few mechanisms have been proposed to understand this phenomenon, consensus has not yet been reached. In this study, we reveal that trace sulfur impurities contaminated in high-purity raw materials prominently segregate to the interface and form a thin intermediate amorphous-like layer between the oxide scale and alloy matrix during the oxidation process. Subsequently, cracking and spallation occur preferentially between the sulfur-rich layer and alumina scale due to the weak bonding between sulfur and alumina atoms. We validate the revealed atomistic spalling mechanism by successfully eliminating the detrimental effect of sulfur via microalloying. Our findings are useful for improving adhesion of oxide scales and enhancing heat-resistant properties of other high-temperature alloys. The good adhesion of scales is crucial for safe service of alloys. This study reveals that trace sulfur impurities can cause severe interface segregation and premature cracking, and such a detrimental effect can be prevented by micro alloying.