Understanding dopants (Pt, Re, Hf, Zr, Y) on NiAl grain boundary diffusion and NiAl/Al2O3 interfacial adhesion
Yiming Jiang, Da Xue, Shuai Li, Di Huang, Zebin Bao, Jiemin Wang, Shenglong Zhu, Fuhui Wang
Abstract
• Pt, Re, Hf, Y, and Zr dopants apply certain effects in hindering Al diffusion. • Except Re, the other dopants possess a lower migration barrier than Ni. • Hf-, Zr-, Y-doping significantly increases the NiAl/Al 2 O 3 interface adhesion. • The Zr-Al and Hf-O strong bonds make main contributions to interfacial bonding. • The dopants (Hf, Y, Zr) in NiAl/ α -Al 2 O 3 interface enlarge the ionic radius of Al. The irreplaceable effects of dopants (Pt, Re, Hf, Zr, Y) on decreasing oxidation rate of high-temperature protective coatings have been proved in experimental observation, which can be attributed to reduced Al consumption or enhanced interfacial adhesion. Thereby first-principles calculations were thoroughly performed to investigate the diffusion behaviors of Al and these dopants at NiAl ∑5(310)[001] grain boundary, as well as the interfacial strengthening effect (Hf, Zr, Y). The diffusion activation energies ( Q ), composed of defect formation energy ( E d ) and migration barrier ( E m ), indicate that Hf, Zr and Y easily segregated at grain boundaries apply a blocking effect for Al diffusion relying on E m while the Pt- and Re-doping significantly increases E d occupying a high proportion in Q . The Re migration possesses the topmost E m in comparison with other dopants and is slightly higher than Ni. Then, the separation energy curve clarified the strengthening effect of Hf, Y, Zr on β -NiAl/ α -Al 2 O 3 interfacial adhesion and Hf-doping effects drastically, depending on the strong bonding with O atom. Bader analysis is utilized to predict the changes in effective atomic radius and attempts to make a connection with diffusion behavior.