Effect of TiB2 on the second Bi-rich phase in immiscible Al-Bi alloy

Immiscible alloys are easy to form segregation due to their liquid phase separation characteristics. Refractory solid particles have been proved can inhibit the segregation of the second phase in this type of alloy during solidification process by either promoting nucleation or preventing the coagulation of the second phase. However, it is not clear that whether the solid particle could provide a steric hindrance effect after serving as nucleation particles. In the present work, the refining mechanism of TiB2 solid particles on the second Bi-rich phase in Al92Bi8 alloy was disclosed in both the terms of heterogeneous nucleation and steric hindrance effect. The results showed that TiB2 particles have remarkable refining effect on the second Bi-rich phase in Al92Bi8 alloy. TiB2 particles first act as nucleation particles to promote nucleation of the liquid Bi-rich phase, then migrate to and self-assemble on the interface between the liquid Bi-rich phase and the Al matrix to reduce the system interfacial energy, furtherly providing steric hindrance effect to prevent the collision and coagulation of the liquid Bi-rich phase.