Principle Study Iridium Alloy Toughening Mechanism-based Superalloy Primary

It was studied the toughening and embrittlement mechanisms of iridium metal based on first-principles density functional theory method in this thesis.It was calculated the electronic structure, band structure and mechanical properties of Ir, Au, Si lattice. According to metal plasticity experience criterion G/B, Cu and Au perform a good plasticity. But Ir with the face-centered cubic has a the same plastic for non-metallic Si. It was found that Cu and Au have a circle electron cloud and isotropic with the analysis of electronic structure of this materials. It was useful to the movement of atoms and the plastic deformation of the metal. Ir and Si have a similar petal-like electron cloud with serious polarization and clear direction. It was generated a great deal of resistance to plastic deformation of Ir atoms with pseudo-covalent structure. With analysis of the band structure and density of states, It was not conductive to the plastic deformation for Ir and Si with a very strong bond strength. So It was determined the ductility at room temperature for Ir intrinsic characteristics.In order to improve the brittleness of iridium, niobium was added. According to binary alloy phase diagram of Iridium-Niobium, Ir and Nb form substitutional solid solution at the content of0～15at%and form Ir and Ir3Nb two-phase region at the content of15at%-25at%. It was calculated the thermodynamic stability, mechanical properties, electronic structure and density of states of the model establishing between the two phase. The results show that the alloy design in two aspects of the thermodynamic and mechanical properties can be stably existence. The ductility was significantly improved. The polarization of the electron cloud and bond energy was reduced. It was indicated that the addition of niobium is conducive to the plastic of the iridium. It has a excellent plasticity for the content of Ir-16.67at%Nb alloy within the range of0-25at%.Ir-3.125at%Nb and Ir-15.625at%Nb was tested with SEM, XRD, HRTEM nanoindentation and observe the fracture morphology with SEM. The results show that the alloy occur a certain degree of segregation which make difference between the experimental test and the initial theoretical design, but this have no affect on the plastic improvement of iridium. The toughening mechanisms of iridium with the adding of niobium is alloying and second phase toughening.