Abstract

Nickel and cobalt-based superalloys are extensively used in various industrial turbomachinery. In the aerospace industry, these alloys are employed as outstanding materials and quality coatings, exhibiting exceptional mechanical performance within the severe environments of gas turbine engines. The formation of nickel oxide (NiO) and cobalt oxide (CoO) during sliding contributes to lubricious tribofilms reducing friction and wear rates at contact interfaces. Despite their similar rock salt crystal structure with ionic bonds, NiO and CoO display distinct behaviors in mechanical and tribological terms. Experimental studies reveal the superior performance of the third body formed on Co-based alloys compared to that of Ni-based materials. However, computational investigations at the nanoscale are essential to analyze the different behaviors of these metal oxides.

In this dissertation, molecular dynamics (MD) simulations were carried out to evaluate the mechanical behavior of NiO and CoO under uniaxial compressive and tensile loading at room temperature (300 K). The combination of the Second Nearest-Neighbor Modified Embedded-Atom Method and the Charge Equilibration method (2NNMEAM+Qeq) potential was employed for each oxide to accurately present the interatomic forces and interactions within the ionic crystal structure. The compressive and tensile engineering stress-strain findings of the present study highlight the remarkable ability of CoO for high-strength applications where structural stability and resistance to permanent deformation are critical. CoO exhibits stronger performance compared to NiO under higher stress conditions. The use of durable materials and excellent oxide-based coatings could significantly enhance equipment efficiency, leading to fuel consumption reductions in aerospace applications.