Microstructural evolution in laser-ablation-deposited Fe–25 at.% Ge thin film

Abstract

Films with Fe–25 at.% Ge composition are deposited by the process of laser ablation on single crystal NaCl and Cu substrates at room temperature. Both the vapor and liquid droplets generated in this process are quenched on the substrate. The microstructures of the embedded droplets show size as well as composition dependence. The hierarchy of phase evolution from amorphous to body-centered cubic (bcc) to DO3 has been observed as a function of size. Some of the medium-sized droplets also show direct formation of ordered DO19 phase from the starting liquid. The evolution of disordered bcc structure in some of the droplets indicates disorder trapping during liquid to solid transformation. The microstructural evolution is analyzed on the basis of heat transfer mechanisms and continuous growth model in the solidifying droplets.

Microstructural evolution and metastable phase formation in laser ablation-deposited films of Fe-rich Fe–Ge intermetallic compounds

“…Earlier studies on diffusion couple and rapid solidification indicate complex pathways for B2 and DO 3 ordering in iron-rich germanium alloys, similar to those observed in Fe-Si systems [32,33]. Recent work by our group shows nucleation of the 2 phase during undercooling of Fe-25 at% Ge melts using an electromagnetic levitation technique [13][14][15]. The 2 phase was found to nucleate as the primary phase from the melt at all levels of undercooling studied.…”

“…Upon further cooling, this phase transforms to " (DO 19 , a ¼ 0.5169 nm, c ¼ 0.4222 nm) by a peritectic reaction with the remaining liquid at 1395 K (1122 C). However, as the peritectic reaction is diffusion-controlled it usually does not proceed to completion and, hence, leads to a phase mixture in the final microstructure [13][14][15]. Furthermore, the sluggish nature of the transformation " ! "…”

Microstructural Evolution During Laser Resolidification of Fe-25 Atom Percent Ge Alloy

“…[13] The motivation of the current work derives from our investigation of the undercooling of this alloy using the electromagnetic levitation facility. It has been found [14,15,16] that this alloy (indicated by the black arrow on the phase diagram in Figure 1) undergoes a peritectic reaction involving the ordered a 2 (B2) phase and a liquid leading to the formation of the ordered e (DO 19 ) phase. The peritectic reaction is suppressed in deeply undercooled samples, and e has been found to form from the a 2 phase via solid-state transformation.…”

“…The peritectic reaction is suppressed in deeply undercooled samples, and e has been found to form from the a 2 phase via solid-state transformation. [14][15][16] Attention can also be drawn to the eutectic reaction close to this peritectic reaction: L ! e 1 b.…”