First-Principles Calculation Of The Diffusion Behavior Of Alloy Elements In Nb And Modification Of Nb-Based Alloys

Niobium alloy is considered one of the high-temperature alloys with potential applications in the manufacturing of hot-end components due to its excellent high-temperature strength and low-temperature plasticity.In addition,among numerous niobium-based alloys,niobium silicon high-temperature alloys have prominent characteristics such as high melting point and low density,which stand out among high-temperature materials and are expected to become alternative materials to replace nickel-based alloys.However,due to room temperature brittleness,their further applications are limited,and alloying is an effective way to improve the mechanical properties of materials.This article uses first principles calculations to investigate the diffusion behavior of ten elements（Si,Ti,V,Ta,Ru,Cr,Te,Tc,Ir,and Y）in Nb.Secondly,the basic properties of Nb-Si intermetallic compounds are calculated.Finally,the influence of alloy elements（Cr,Ti,Ta,Zr,Y,Ir,Re,Rh,Ru,Te）on the mechanical properties of Nb₅Si₃ is calculated.The main results obtained are as follows:（1）The diffusion behavior of ten alloy elements（Si,Ti,V,Ta,Ru,Cr,Te,Tc,Ir,and Y）in Nb was studied using first-principles calculations combined with the BCC lattice nine frequency model.The calculated diffusion coefficients of Si,Ti,Ru,V,and Ta in BCC-Nb are very consistent with the experimental results,confirming the reliability of the calculated results.The calculated diffusion coefficients of Cr,Tc,Te,Ir,and Y,as there is no corresponding experimental data,can be used as the basic kinetic data.（2）The basic properties of Nb-Si intermetallic compounds were calculated and it was found that among the three structures of Nb₅Si₃,α-Nb₅Si₃ has the lowest formation energy and the best thermodynamic stability,followed byβ-Nb₅Si₃ andγ-Nb₅Si₃.The calculation results of mechanical properties indicate thatα-Nb₅Si₃ has the maximum shear modulus,bulk modulus,and Young’s modulus,but its brittleness is relatively high.The calculation results for three types of Nb₃Si compounds indicate that they all have thermodynamic stability.The toughness of Nb₃Si with Pm-3n type structure is the best,followed by P4₂/n type and Pm-3m type.The calculation results of Nb Si₂ show that it also meets the mechanical stability conditions.The mechanical properties calculation results of Nb Si₂ indicate that it has poor toughness.（3）Explored the effects of adding ten elements（Cr,Ti,Ta,Zr,Y,Ir,Re,Ru,Te,Rh）on the influence of structural stability and mechanical properties ofα-Nb₅Si₃.The results indicate that Ta,Re,Cr,Ir,Ti,Ru,and Rh tend to occupy the Nb1 position,while Zr and Y preferentially occupy the Nb2 position,while Te tends to occupy the Si1 position.All alloying compound structures are mechanically stable,with the addition of Ir and Te elementsα-Nb₅Si₃ has the best toughness,followed by Ru,Rh,Re,Y,Cr and Zr elements.