In-situ observation of unsteady peritectic growth modes

Abstract

A transparent non-facetted/non-facetted peritectic system was used for in-situ studies of peritectic growth morphologies above and below the limit of constitutional undercooling. For a hypo-peritectic alloy with near peritectic composition an oscillatory growth mode was found for velocities in the cellular/dendritic regime. It is demonstrated that the co-existence of two distinct cellular/dendritic solid/liquid interfaces which try to reach stable growth conditions causes this oscillations. Additionally, it is shown that on reducing the withdrawal speed the two distinct interfaces arrange into an isothermal coupled peritectic growth mode.

The Effect of Growth Kinetics on the Formation of Peritectic Microstructures in a Sr(NO3)2–H2O System

“…This is because the supersaturation for the former is higher than that for the latter owing to the nature of the peritectic equilibrium. As a result of growth competition, it is possible to form the peritectic microstructures with the stable phases enclosing the metastable phases symmetrically above and below the T p . ,− However, this is not the case for the faceted crystal growth where the surface kinetic process is rate-determining. Conversely, the effect of growth kinetics on the formation of peritectic microstructures can be examined by comparing the behavior of faceted crystals of the two phases above and below the peritectic temperature.…”

Investigation of Peritectic Solidification Morphologies by Using the Binary Organic Model System TRIS-NPG

“…For cellular/dendritic growth conditions, observations indicated that the primary α-phase grew continuously in a cellular/dendritic pattern, as expected. In contrast, the peritectic β-phase solidified dendritically and discontinuously within the intercellular/dendritic liquid [23] or both phases solidify in a dendritic/cellular manner in the form of an oscillating coupled growth [24]. For process conditions that had both phases solidified in a planar, the main findings were that a layered peritectic solidification pattern, in the form of island bands, later transform into unstable PCG or nucleation events of the β-phase at the s/l interface and were directly overgrown.…”

“…It is especially the case that all findings are based on post mortem analyses of metal samples, which has drawn attention by the authors to use the transparent, organic non-faceted/non-faceted (nf/nf) components TRIS (Tris-(hydroxylmenthyl) aminomethane) and NPG (Neopentylglycol) [20] as a model system for peritectic solidification [21][22][23][24][25][26]. Thus, it became possible to observe, in situ, the mechanisms that lead to bands, island bands, and isothermal PCG [21].…”

In-situ observation of coupled growth morphologies in organic peritectics

“…It has become obvious from investigations of directional solidified peritectic alloys (Zn-Ag [1], Sn-Cd [2][3][4][5], Cu-Sn [6], Pb-Bi [7][8][9][10][11], Zn-Cu [12][13][14], Sn-Sb [15][16], Ti-Al [17][18], Fe-Ni [19][20][21][22][23][24][25][26][27][28], Ni-Al [29], YBCO [30], Nd-Fe-B [31] and TRIS-NPG [32][33][34]) that peritectic systems show a variety of complex microstructures. Close or below the limit of constitutional undercooling of both solid phases isothermal peritectic coupled growth (PCG), cellular peritectic coupled growth, discrete bands, island bands, and oscillatory tree-like structures were found [35][36][37][38].…”

“…In the present work, the organic non-faceted/non-faceted (nf/nf) peritectic system TRIS (Tris-(hydroxylmenthyl)aminomethane)-NPG (Neopentylglycol) [41] is used as a model substance for metallic solidification by performing in-situ observations of peritectic solidification morphologies which occur close to the critical value for morphological stability [32][33][34]. Both organic substances show a low temperature faceted phase and a transparent non-faceted high temperature phase, which forms in an intermediate concentration range of the peritectic equilibrium, see Figure 1.…”