Effects of alloying elements on the electronic structure and ductility of NiAl compounds investigated by X-ray absorption fine structure

Abstract

The Ni L_3,2-edge spectra of the pure Ni, pure NiAl and alloying-element-doped NiAl compounds were obtained by synchrotron radiation X-ray absorption fine structure (XAFS). Due to orbital hybridization effect, directional covalent-type bonds formed and decreased the ductility during forming NiAl. Combining the XAFS spectra analysis and electronegativity comparison, the effects of alloying elements on the electronic structure and then the ductility of the NiAl compounds were obtained. The results showed that Cr, Co, Mo, Ru and W doping could be beneficial to the ductility by both weakening the directional bonds along the <111> direction and enhancing the d–d interactions of the transition metals–Ni atom pair, namely by the transition from covalent bonds to metallic bonds which was beneficial for dislocation to migrate. The results agreed well with the available experimental data and other theoretical results, proving that the model linking the electronic structure and ductility is reliable and can be used as guidance for alloy design.

Keywords:

• NiAl system
• electronic structure
• X-ray absorption fine structure
• ductility

Acknowledgements

This work was supported by a grant from the Major State Basic Research Development Program (973 Program) of China under Grant No. 2010CB631200 (2010CB631206) and from the National Natural Science Foundation of China (NSFC) (Nos. 50931004, 51071164 and 50671102). We would like to thank the National Synchrotron Radiation Laboratory, University of Science and Technology of China for XAFS measurements and data analysis.