Si-TaSi_2 eutectic in situ composite is a promising field emission material due to the relatively low work function,high melting point,good electron conductivity and good combination capability with Si of the refractory disilicide TaSi_2.

The directionally solidified Si-TaSi_2 eutectic in situ composite for field emission was pre- pared with the electron beam floating zone melting (EBFZM) technique.

The effect of the solidified rate on the morphology of eutectic Si and α-Al dendrite was studied by mean of scanning electron microscope(SEM).

The results show that with the increase of superheat treatment temperature, the undercooling increases, and the superheat treatment results in remarkable refinement of the α-Al dendrite and the particle or fibre transition of the eutectic Si.

The results show that,without magnetic field,the plate-like primary Si concentrates at the edge of the sample,and the center is concentrated with the eutectic Si;exerting rotary magnetic field on the P-Salt modified hypereutectic Al-18%Si alloy,the primary Si is thick and block-like and concentrates at the edge of the sample,and the center concentrates with the eutectic Si;exerting static mag.

It is found that the sample modified by Na-salt was kept 720℃ for 20 minutes under the condition without high magnetic filed,coarse plate-like or acicular eutectic Si appear on section of the sample and distribution of eutectic Si is unevenly;but under the condition with high magnetic filed,Eutectic Si become fine.

With studying on the eutectic Si modification, many new evidences were found one after the other and hence some new mechanisms were put forward.

In this paper it was investigated that the growth rate (v) affects the morphology of graphite flakes and the longitudinal mechanical properties of the unidirectionally solidified Fe-C-Si eutectic alloy.