Alloying Control Of TiB₂ Toughness And Fracture Mechanism Of α-Fe/TiB₂ Interfac

The development of lightweight materials that possess high strength,high ductility,low density,and high modulus is crucial for the automotive and aviation industries.In-situ Ti B₂/Fe-based composite materials have the potential to achieve these goals.While the Fe matrix has good toughness and impact resistance,it lacks strength.The Ti B₂reinforcement phase has advantages such as high strength,high hardness,high modulus,and high-temperature resistance.However,Ti B₂of initial particles are coarse,and the eutectic particles are sharp,leading to local stress concentration during loading.Cracks can originate from inside the particles or sharp edges,leading to brittle fractures,and limiting the material’s application.To address these issues,alloying methods are employed to introduce new alloying elements to improve the strength of the Fe matrix and the ductility of the Ti B₂reinforcement phase,thereby enhancing the composite material’s strength and toughness.This paper is based on the first-principles calculations,screening effective alloying elements and their concentrations by calculating the mixing enthalpy,elastic properties,and generalized stacking fault energy of Ti B₂doped with different alloying elements.The micro-mechanisms are revealed by electronic structure analysis.Then,the interface model of the in-situ Ti B₂/Fe composite material is established to investigate the influence mechanism of alloying elements on interface bonding and reveal the micro-mechanism of interface fracture through tension simulation.Finally,the composite material is experimentally verified by preparing it using a vacuum arc furnace.The main research contents are as follows:（1）29 alloying elements are introduced into Ti B₂to form a dilute solid solution,and their influence on mixing enthalpy and elastic properties is studied.According to the screening results,Mo,Nb,and Ta are the most effective alloying elements because they improve the material’s stability and ductility without significantly reducing its hardness.The plasticity of alloyed Ti B₂increases with increasing Ti element concentration.At a concentration of 0.5,the generalized stacking fault energy of(Ti_0.5Nb_0.5)B₂and(Ti_0.5Ta_0.5)B₂is lower than that of pure Ti B₂,once again proving that alloying can improve its ductility.（2）The effects of nine typical elements on theα-Fe（001）/Ti B₂（001）interface are studied.Compared with other elements,Nb is more likely to occupy the position of Ti atoms;compared with other elements,Al is the least likely to occupy the position of Fe atoms.According to the results of adhesion work and interface energy,all elements that replace Fe atoms can improve interface stability.The maximum stress of the interface of the Nb-occupied Fe atom position（24.19GPa）is higher than that of the Ti-occupied position（23.36GPa）in the interface theoretical tensile calculation.Compared with the pure interface,the Nb-doped interface has higher tensile strength and stability.Through differential charge density analysis,the reason for fracture is mainly due to the transfer of valence electrons from the interior of the bulk material to the interface.Finally,the Fe-Fe bond and Fe-B bond rupture,leading to interface failure.（4）A Fe-10Ti-4B-4M（wt%）composite material with a eutectic structure is prepared using a vacuum arc melting method.Element segregation in Ti B₂particles is confirmed by electron probe microanalysis（EPMA）,which is consistent with the calculation of mixing enthalpy.The fracture toughness is tested by indentation,and it is found that the addition of the Nb、Ta elements increases both the hardness and fracture toughness of the material.Finally,Nb and Ta are selected as effective alloy elements,which can improve the strength and toughness of in-situ Ti B₂/Fe matrix composites.At the same time,it also provides certain guiding significance for the subsequent research of composite materials.