Nb-Driven Modification of TiB2(10-10) and (0001) Surfaces for Improved Si-Poisoning Resistance and Grain Refinement in Al-Si Alloys

Abstract

Al-Nb-Ti-B has the potential to address the Si-poisoning issue; however, the relatively high atomic weight and cost of Nb result in limited anti-fading performance and economic feasibility for industrial application. In this study, a novel Al-4Ti-1Nb-B grain refiner was developed by introducing a small amount of Nb into the Al-Ti-B melt. The resulting TiB2 forms a unique structure, with 1.45-1.74 at.% Nb segregating on the TiB2(10-10) and (0001) surfaces, which not only ensures the anti-fading properties but also provides enhanced resistance to Si-poisoning. An unprecedented orientation relationship between TiB2 and Al is discovered: Al(111) // TiB2(10-10), Al(1-1-1) 2° from TiB2(-1101). Experimental analyses, supported by first-principles calculations, indicate that Nb atoms preferentially substituted on the TiB2(10-10) and (0001) surfaces. Nb adsorption activates new crystallographic planes, TiB2(10-10), allowing both TiB2(10-10) and TiB2(0001) to serve as effective nucleation substrates for α-Al, thereby enhancing the chemical affinity between Al and TiB2. Furthermore, the Nb adsorption layer exhibits significant resistance to Si intrusion. Consequently, the Al-4Ti-1Nb-B grain refiner demonstrates both superior refinement efficacy and excellent anti-fading properties. These findings highlight the pivotal role of Nb-modified TiB2 particles in enhancing grain refinement and provide a novel approach for advancing grain refiner technologies in Al-Si alloys.

Keywords: Si-poisoning, grain refinement, nucleation mechanism, Nb adsorption, Ab initio calculations