Investigation on elastic properties and electronic structure of dilute Ir-based alloys by first-principles calculations

Abstract As the potential ultrahigh temperature alloy, the brittle fracture of iridium (Ir) has puzzled people for a long time as a challenge. In this work, thirty-three alloying elements are employed to enhance the ductility of dilute Ir-based alloys by first principles calculations based on density functional theory (DFT). The results show that dilute Ir-based alloys has negative mixing enthalpy except four alloying elements (Cd, Ag, La and Au) and the four Ir-X binary alloys (X = Cd, Ag, La and Au) have positive zero-order interaction parameters, indicating the four alloying elements are not lightly dissolved in Ir matrix. The elastic properties of Ir are consistent with available experiment and other theory studies. The bulk modulus of dilute Ir-based alloys decreases with increasing of atomic radius of solute in full relaxing strategy, while the bulk modulus has a revered trend in atom relaxing strategy. Ir31Th has the best ductility and Ir31Tc has the highest hardness in full relaxing strategy. Nonetheless, the most Ir31X are brittleness after doping alloying elements. Through electronic structure analysis in full relaxing strategy, the reason why Ir31Th has the best ductility is that the electron cloud shows spherical distribution after Th doped in (100) plan and there are the lowest mean bond population and longest mean bond length between Th and Ir, While the reason why Ir31Tc has the highest hardness is that the degree of delocalization of electron cloud is the largest around Tc and there is the shortest mean bond length between Tc and Ir, indicating the stronger ionic between Tc and Ir. Besides, calculation of phase diagrams (CALPHAD) is employed to construct the composition-dependent elastic properties model for Ir-X binary alloys. which can be employed to describe the properties of Ir-based multicomponent alloys.