First-principles Investigation Of The Thermodynamic And Mechanical Properties In The Ni-P System

Ni-P coatings have been widely used in the fields of petroleum, chemical engineering, machinery, electronics, automobiles etc., because of its outstanding performance of wear-resistance, corrosion-resistance, and water-proof. Investigating the mechanical properties of these Ni-P alloys can benefit understanding the wear-resistance etc., properties of the Ni-P coatings.In the present work, based on the stress-strain approach, first-principles calculations were utilized to investigate the mechanical properties of Ni-P alloys. First of all, the elastic constants of Ni-P alloys were calculated. Based on Vogit-Reuss-Hill approximation, the Vogit and Reuss bounds (BV, BR, GV, GR), averaged bulk modulus, averaged shear modulus, Young’s modulus, and Poisson’s ratio were calculated using the acquired elastic constants. Based on the calculated Poisson’s ratio, the brittleness and ductility of the Ni-P compounds were predicted.The Ni-P compounds are capable of forming amorphous glass. As a kind of catalytic material, the amorphous alloys show outstanding catalytic capabilities, especially the hydrogenation of unsaturated compounds. The Gibbs energies of the Ni-P phases are very crucial in evaluating the ability of forming amorphous glass for all the phases. Therefore, there is a need to obtain a complete thermodynamic description the complete database of the Ni-P system, and this will consequently benefit evaluating the ability of forming amorphous glass for all the Ni-P phases.Besides, utilizing the four-parameter Birch-Murnaghan equation of state, the ground-state properties of the Ni-P compounds were investigated, including the enthalpy of formation, bulk modulus and its first derivative versus pressure. The calculated enthalpies of formation of the Ni-P compounds were in good agreement with the experimental and theoretical values reported in the literatures. Based on frozen-phonon approach, the phonon dispersions and phonon density of states of the Ni-P compounds were calculated. Within the framework of the quasi-harmonic approach, the finite-temperature thermodynamic properties of these Ni-P compounds including the Helmholtz free energy, entropy, heat capacity at constant pressure and enthalpy are systematically predicted, by considering both the vibrational and thermal electronic contributions to the free energy.The ground-state and finite-temperature thermodynamic properties of the Ni-P compounds predicted in the present work can be combined with the phase diagram and thermodynamic data in the Ni-P system for thermodynamic modeling of this system. The modeling can be performed by means of CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) approach. In case a set of self-consistent thermodynamic parameters for the Ni-P system were obtained, the ability of forming amorphous glass for all the Ni-P alloys can be predicted, combined with the kinetic data in the Ni-P system.