Analysis on the growth and growth-dependent microhardness of Ni3Sn4 intermetallic compound phase in directionally solidified Sn–Ni alloy

Abstract

The growth morphologies and growth-dependent microhardness of the Ni3Sn4 intermetallic phases were investigated in directionally solidified Sn-15at.%Ni alloy through acid corrosion. To better characterize the growth of Ni3Sn4 phase, the dependences of the inter-phase spacing λ and thickness l on growth velocity v are also presented. The non-linear fit of the experimental results shows λ = 141.93v−0.19 and l = 43.45v−0.32. Comparison between the models describing the variation of primary dendrite arm spacing λ1 as a function of growth velocity and the experiments shows that these models are not appropriate for describing the growth of solidified Ni3Sn4 phase with faceted morphology. In addition, the variation of the microhardness (Hv) of Ni3Sn4 phase on the inter-phase spacing of it λ was measured as a function of growth velocity. The obvious dependence of microhardness on this solidification processing parameter shows that the microhardness (Hv) of Ni3Sn4 phase is obviously influenced by the growth mechanism of Ni3Sn4 phase in this Sn–Ni alloy. The local morphology of Ni3Sn4 phase shows that this lath-shaped phase is composed of sub-structures with faceted morphology. In addition, not only the faceted to non-faceted transition in growth morphology, but also the variation in morphology of the faceted sub-structure with increasing growth velocity can be confirmed through both directionally solidified microstructures with/without acid corrosion. This indicates that the variation in the sub-structure can lead to the change in growth morphology of Ni3Sn4 phase, thus the dependence of Hv on the growth velocity.