26.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB
2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB
2and(1-100)NbB
2surface can be substituted by Al to form(Al,Nb)B
2intermedia layers.In addition,a layer of NbAl
3-like compound(NbAl
3')can cover the surface of NbB
2with the orientation relation of(1-100)[11-20]NbB
2//(110)[110]NbAl
3'.Both of the(Al,Nb)B
2and NbAl
3'intermedia layers contribute to enhancing the nucleation potency of NbB
2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys.
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