Microstructural length scales in directionally solidified Sn-40 at.%Mn peritectic alloy containing intermetallic compounds

Sn-40 at.%Mn peritectic alloys in which both primary and peritectic phase are intermetallic compounds were directionally solidified at different growth rates (1 μm/s∼100 μm/s). Dendritic growth of primary phase has been observed even at low growth rate, and dependence of microstructural characteristic length scales on growth rate has been investigated. Liquidus slope is the dominating factor in determining non-faceted/faceted solid/liquid morphology. Experimental results show that: λ₁ = 229.64v ^-0.20, λ₂ = 33.337v^-0.34, λ₃ = 39.90v^-0.378, R = 16.90v^-0.384. Besides, both λ₁/λ₂ and λ ₁/λ₃ vary greatly with increasing growth rates while λ₂/R ranges from 2 to 2.3 with increasing growth rate. Both the peritectic reaction and solute distribution of intermetallic compounds during solidification influence these length scales. A modified solute distribution coefficient which is appropriate for intermetallic compounds makes calculation agree reasonably well with experimental results. The value of λ₁ is influenced more by solute distribution of intermetallic compounds, while growth of λ₂, λ₃ and R are more significantly influenced by the peritectic reaction.