Growth velocity and microhardness dependences of intermetallic compound phases on solubility range during peritectic solidification

Abstract

It is well known that the growth of solid phases are determined by both the external solidification growth conditions and the solidification characteristics of themselves. The growth of intermetallic compound phases (IMCs) has been analyzed in two peritectic systems containing IMCs: Sn-Ni and Sn-Mn through secondary dendrite, indicating that the solidification characteristics of them are closely related to the growth of IMCs in these alloys. However, the relationship between the solidification characteristics of IMCs and the growth of secondary branch has not been discussed yet. The IMCs can be classified to be different types according to whether their solubility ranges are nil. Thus, the solubility ranges of IMCs are chosen as the representative solidification characteristics. In this work, through a morphology parameter φ characterizing the morphology of secondary branch, the quantitative relationship between the growth behaviors of secondary dendrite arm of IMCs and their solubility ranges has been established. Comparison in both the theoretical prediction of this work and the experimental measurement between these two peritectic systems demonstrated that the solid phases whose solubility range are larger should have a larger growth velocity vtip of secondary branch in the same growth conditions. In addition, the growth-dependent microhardness of the intermetallic compound phases were investigated, which also shows that the microhardness of intermetallic compound phases are also dependent on the growth velocity, thus the solubility range of themselves. It is commonly assumed that the microhardness of the solidified phase is nearly constant in steady state directional solidification. However, the microhardness of the IMCs at the tips of secondary branches gradually decrease during directional solidification, which is consistent with the gradual reduction in vtip. In addition, the variation of the microhardness is more obvious in IMC with larger solubility range.