Effect of sample diameter on primary and secondary dendrite arm spacings during directional solidification of Pb-26wt.%Bi hypo-peritectic alloy

Abstract

The microstructure scales of dendrites, such as primary and secondary dendrite arm spacings, control the segregation profiles and the formation of secondary phases within interdendritic regions, which determine the properties of solidified structures. Investigations on primary and secondary dendrite arm spacings of primary α-phase during directionally solidified Pb-26wt%Bi hypo-peritectic alloy were carried out in this research, and systematic studies were conducted using cylindrical samples with different diameters (Φ = 1.8 and 7.0 mm) in order to analyze the effects of sample diameter on the primary and secondary dendrite arm spacings. In this work, the dependence of dendrite arm spacings on growth velocity was established. In addition, the experimental data concerning the primary and secondary dendrite arm spacings were compared with the main predictive dendritic models from the literatures. A comparison between experimental results for dendrite arm spacings of the 1.8-mm-diameter sample and 7.0-mm-diameter sample was also conducted.

Steady and unsteady state peritectic solidification

“…the theoretical predictions are in good agreement with the experimental scatters of both hypoperitectic and hyperperitectic alloys. However, Hu et al 26 examined the growth of a Pb–26 wt- Bi hypoperitectic alloy under steady state DS solidification (Bridgman growth) for a wide range of growth rates (5×10 −3 to 5×10 −1 mm s −1 ) and have concluded that the predictions of the Hunt–Lu model are smaller and very far from the experimental evolution of λ 1 . Hu et al 25 have also carried out experiments of Bridgman growth with two hypoperitectic and two hyperperitectic Pb–Bi alloys and checked the experimental scatters of λ 1 against the theoretical predictions of the main steady state growth models from the literature: Hunt, 37 Kurz–Fisher 38 and Trivedi 39 models.…”

“…, the microstructure consisted of branched dendrites of a in a matrix of b, for intermediate values of G L .V L 21 aligned rods of a in a matrix of b, and for high values of G L .V L 21 , the microstructure was formed only by the phase b. Hu et al 15,[23][24][25][26] investigated the growth of Pb-Bi alloys having 26, 28 30 and 34 wt-% Bi using a Bridgman vertical apparatus with V L ranging from 5 to 500 mm s 21 at a constant G L of 20 K mm 21 . The observed microstructure is reported to be formed by dendrites of the primary a in a complex matrix of b.…”

“…25,26 ) experiments a Pb-9?5 wt-% Bi; b Pb-20?5 wt-% Bi; c Pb-25 wt-% Bi; d Pb-32 wt-% Bi 6 Comparison of experimental and theoretical (Hunt-Lu model 41 ) primary dendrite arm spacings as function of cooling rate for Pb-Bi alloys in unsteady state DS Castanho et al Steady and unsteady state peritectic solidification…”

Interconnection of thermal parameters, microstructure, macrosegregation and microhardness of unidirectionally solidified Zn-rich Zn–Ag peritectic alloys

“…However, a variety of microstructures can be obtained from during solidification of peritectic alloys under non-equilibrium conditions, which depend mainly on the thermal parameters during solidification (thermal gradient, G L , growth rate, V L , and cooling rate, _ T) and the nucleation conditions. Possible microstructures include: cellular [4], bands [5,6], lamellar [7], eutectic type structures [8], and dendritic structures [9].…”

Secondary dendrite arm migration caused by temperature gradient zone melting in the directionally solidified Sn–40 at.% Mn peritectic alloy

“…Both experimental and theoretical studies [1][2][3][4][5] have been carried out on peritectic solidification since many technologically important materials have been observed in peritectic systems. Recently, many studies on peritectic solidification have been carried out, and complex microstructures have been obtained, such as the dendritic/cellular growth of primary phase in the matrix of peritectic phase, coupled growth, 6,7 and banded structure.…”