Effect of Zr modification on solidification structure of Fe-Ni base invar expansion alloy

Effect of Zr modification on solidification structure of Fe-Ni base invar expansion alloy was researched. The results show that great amount of high-melting compound with the size of 1.0~3.0μm are formed in the Zr-modified Fe-Ni base invar expansion alloy. Based on the theory of lattice misfit, the lattice misfit of low-index plane between ZrO2and Fe-Ni base invar expansion alloy is 8.6%, which is relatively low. Because of the heterogeneous nucleation of ZrO2, the solidification structure of the alloy is changed from columnar grain to equiaxed grain + columnar grain, the ratio of equiaxed grain on cross-section of the sample is 55%. Furthermore, ZrO2, ZrC and ZrN are distributed at grain boundaries of the columnar and equiaxed grains, pinning grain boundary and thus refining grain.