First-Principles Study on Si Atom Diffusion Behavior in Ni-Based Superalloys

The Si atom diffusion behavior in Ni-based superalloys was evaluated based on first-principles calculations. Also, the site occupation of Si atoms as the melting point depressant elements in Cr, Mo, and W atom doped & gamma;-Ni and & gamma;& PRIME;-Ni3Fe supercells was discussed and Si atom diffusion behaviors between both adjacent octahedral interstices were analyzed. Calculation results indicated that formation enthalpy ( increment Hf) was decreased, stability was improved by doping alloying elements Cr, Mo, and W in & gamma;-Ni and & gamma;& PRIME;-Ni3Fe supercells, Si atoms were more inclined to occupy octahedral interstices and the diffusion energy barrier was increased by increasing the radius of the doped alloy element. Especially, two diffusion paths were available for Si atoms in the & gamma;& PRIME;-Ni3Fe and Si diffusion energy barrier around the shared Fe atoms between adjacent octahedral interstices and was significantly lower than that around the shared Ni atoms. The increase of interaction strength between the doped M atom/octahedron constituent atom and Si atom increased Si atom diffusion and decreased the diffusion energy barrier. The Si atom diffusion behavior provides a theoretical basis for the phase structure evolution in wide-gap brazed joints.

Automated summary

The diffusion behavior of Si atoms in Ni-based superalloys was evaluated using first-principles calculations. The occupation of Si atoms as melting point depressants in Cr, Mo, and W doped γ-Ni and γ'-Ni3Fe supercells was discussed, and the diffusion behavior of Si atoms in adjacent octahedral interstices was analyzed. The results show that the addition of alloying elements Cr, Mo, and W decreases the formation enthalpy and improves stability, leading to a higher inclination of Si atoms to occupy octahedral interstices. Increasing the radius of the doped alloy element increases the diffusion energy barrier. Moreover, Si atoms in γ'-Ni3Fe exhibit two diffusion paths, with the diffusion energy barrier around shared Fe atoms being significantly lower than that around shared Ni atoms. The increase in interaction strength between the doped M atom/octahedron constituent atom and Si atom promotes Si atom diffusion and lowers the diffusion energy barrier. The diffusion behavior of Si atoms provides a theoretical basis for the phase structure evolution in wide-gap brazed joints.