Adhesion in NiAl-Cr from first principles

Energy investigation of effects of O on mechanical properties of NiAl intermetallics

We have investigated effects of O on mechanical properties of NiAl by calculating the cleavage energy (γ(C)) and the unstable stacking fault energy (γ(us)) using a first-principles method. O is shown to reduce γ(C)/γ(us) for the [001](110) and [100](001) slip systems, indicating that the presence of O should be associated with the ductility reduction of NiAl. Further, γ(C)/γ(us) of the NiAl-O system can be increased by Cr, suggesting the possibility to suppress the negative effect of O via alloying elements.

Atomic structure and adhesion of the Nb(001)/α-Nb5Si3(001) interface: a first-principles study

The density functional calculations have been performed to study the Nb(001) and α-Nb5Si3(001) surfaces as well as the interface properties of Nb(001)/α-Nb5Si3(001). The surface energy of the Nb(001) surface is about 2.25 J m (- 2). The calculated cleavage energies of bulk Nb5Si3 are 5.103 J m (- 2) and 5.787 J m (- 2) along (001) planes with the breaking of Nb-Si and Nb-NbSi bonds, respectively. For the Nb(001)/α-Nb5Si3(001) models, the Nb atoms in the interface region initially belonging to body centered cubic metal Nb are twisted to the position of the Nb atom layer in Nb5Si3 and the interlayer distance is similar to that of bulk Nb5Si3 after being fully relaxed. The ideal work of adhesion of the Nb(001)/Nb5Si3(001) interface is calculated and compared to those of bulk Nb and Nb5Si3. The results show that the bulk Nb5Si3 has the largest work of adhesion, the bcc Nb ranks second and the interface ranks last. Moreover, the Nb-Si bond is weaker than Nb-NbSi and Nb-Nb bonds in the interface, which means that the Nb-Si bond in the interface is the most possible site for the micro-crack generation when the stress is applied quasi-statically along the [001] direction. The densities of states, Mulliken population and overlap population of the Nb(001)/α-Nb5Si3(001) interface are also analyzed.

Bonding characteristics in NiAl intermetallics with O impurity: a first-principles computational tensile test

We have performed a first-principles computational tensile test on NiAl intermetallics with O impurity along the [001] crystalline direction on the (110) plane to investigate the tensile strength and the bonding characteristics of the NiAl-O system. We show that the ideal tensile strength is largely reduced due to the presence of O impurity in comparison with pure NiAl. The investigations of the atomic configuration and bond-length evolution show that O prefers to bond with Al, forming an O-Al cluster finally with the break of O-Ni bonds. The O-Ni bonds are demonstrated to be weaker than the O-Al bonds, and the reduced tensile strength originates from such weaker O-Ni bonds. A void-like structure forms after the break of the O-Ni and some Ni-Al bonds. Such a void-like structure can act as the initial nucleation or the propagation path of the crack, and thus produce large effects on the mechanical properties of NiAl.