Scanning Kelvin Probe Force Microscopy and Density Functional Theory Studies on the Surface Potential of the Intermetall
- PDF / 2,903,317 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 25 Downloads / 229 Views
JMEPEG https://doi.org/10.1007/s11665-019-04160-6
Scanning Kelvin Probe Force Microscopy and Density Functional Theory Studies on the Surface Potential of the Intermetallics in AA7075-T6 Alloys Ni Li, Chaofang Dong, Xin Wei, Chen Man, Jizheng Yao, Jiangli Cao, and Xiaogang Li (Submitted June 20, 2018; in revised form February 26, 2019) The surface potentials of Mg2Si and Al7Cu2Fe intermetallic particles in AA7075-T6 alloys were investigated by scanning Kelvin probe force microscopy (SKPFM) technique. The experimental surface potentials of Mg2Si and Al7Cu2Fe intermetallic particles relative to Al matrix were ranging from 2 368 to 2 265 mV and 480–500 mV, respectively. A theoretical method for assessing relative nobility of intermetallics in Al alloys was discussed through first principle calculation. The work functions and surface energies of Mg2Si and Al7Cu2Fe surfaces were calculated by using density functional theory (DFT) method. The results showed that work functions and surface energies of Mg2Si and Al7Cu2Fe intermetallics were influenced by the orientations of crystal face and terminal types. At the oxygen coverage of 1/4 ML and 1 ML, the theoretical surface potential differences between Mg2Si intermetallics and Al matrix were increased by 10– 560 mV and 0–620 mV, while those between Al7Cu2Fe intermetallics and Al matrix were increased by 62– 360 mV and 102–331 mV. For the adsorption of oxygen atom, theoretical surface potentials of Mg2Si and Al7Cu2Fe intermetallics relative to Al matrix had a close agreement with the experimental surface potentials. It was verified that DFT method was a valuable theoretical approach to assess the relative nobility of different phases in alloys. Keywords
density functional theory (DFT), intermetallics, scanning Kelvin probe force microscopy (SKPFM), surface energy, work function
1. Introduction Aluminum (Al) alloys are widely used in aerospace industry owing to the properties of low density, high strength and high stiffness. Various alloying elements such as Zn, Mg, Cu and Si were added into Al matrix to achieve high mechanical properties (Ref 1, 2). However, the intermetallic particles (IMPs), which were precipitated if the concentration of alloying elements reached a particular level, had a negative effect on corrosion resistance of Al alloys (Ref 3, 4). For example, pits were observed to initiate most commonly at the interface of intermetallics and Al matrix, due to micro-galvanic interactions (Ref 5). Previous studies found that such localized damaging might trigger other forms of localized corrosion, such as intergranular corrosion (Ref 6) and stress corrosion cracking (SCC) (Ref 7). Therefore, it is important to investigate the electrochemical behavior of intermetallics in Al alloys.
Ni Li, Chaofang Dong, Xin Wei, Chen Man, Jizheng Yao, Jiangli Cao, and Xiaogang Li, Corrosion and Protection Center, Key Laboratory for Corrosion and Protection (MOE), University of Science and Technology Beijing, Beijing 100083, Peoples Republic of China. Contact e-mail: [email protected]
Data Loading...
