Nucleation and growth during reactions in multilayer Al/Ni films: The early stage of Al3Ni formation

Abstract

Solid-state interdiffusion reactions at Al/Ni interfaces in multilayer films have been studied using differential scanning calorimetry, cross-sectional transmission electron microscopy/microanalysis, and thin-film x-ray diffraction. Multilayer films with various modulation periods and an overall atomic concentration ratio of three Al to one Ni were prepared by alternate electron-beam evaporation in high- and ultrahigh-vacuum systems. We show calorimetric, microstructural, and compositional evidence that interdiffusion of Al and Ni leading to solid solutions precedes the formation of intermetallic crystalline compounds. Isothermal calorimetry indicates that Al3Ni subsequently nucleates in the interdiffused region at preferred sites. Calorimetric analyses also suggest that nucleation sites quickly saturate in the early stage of Al3Ni formation and that the nucleation site density strongly depends on the grain sizes of the deposited films. After coalescence into a continuous layer at the interface, Al3Ni thickens through a diffusion-limited process, in agreement with previous reports. A kinetic model is developed which yields calculated calorimetric traces in good agreement with experimental data. Our results suggest the importance of prenucleation interdiffusion, in addition to nucleation, in the selection of the first phase during thin-film reactions.

Non-equilibrium intermixing and phase transformation in severely deformed Al/Ni multilayers

“…The observed nucleation of the Al 3 Ni phase during short time annealing is consistent with published data showing that this phase is the first to grow in annealed Al/Ni multilayers [11,12,14,17,18,22,23]. It is however recognised that intermixing is a necessary initial process that needs to occur before any phase formation can proceed [17,21]. In cold rolled multilayers, this first step is not thermally activated but induced by the severe plastic deformation prior to annealing.…”

“…The Al-Ni system was chosen as a model system since it is both attractive for applications, e.g. in superalloys or as coatings of III-V semiconductors, and has also been studied thoroughly concerning the microstructure-and the phase evolution [10,11,[13][14][15][16][17][18][19][20][21]. In the studies reported so far, thin Al/Ni multilayers have mostly been deposited by sputtering [17,19,20] or electron-beam evaporation [16,[19][20][21], while repeated folding and cold rolling of Al and Ni foils was also applied as an alternative process to synthesize Al-Ni multilayer foils [10-12, 14, 18].…”

Thermal stability and crystallization kinetics of mechanically alloyed TiC∕Ti-based metallic glass matrix composite

“…It should be noted that a very close Avrami exponent n = 2.6± 0.1 was also reported in the Al/ Ni multiplayer films prepared by solid-state interdiffusion reaction. 44 It is assumed that the nucleated Al 3 Ni grows and coalesces into a continuous layer and then thickens by diffusion-limited process with kinetic characteristics and the presence of a significant amount of interfacial impurities has a strong influence on the nucleation and growth of the intermetallic Al 3 Ni phase. This scenario is very similar to the current work that there are also a mount of interfaces between the TiC particle and the glassy matrix phase in the composite, resulting in that the preexisting TiC particles might serve as potential nucleation sites of crystals during crystallization.…”

Air blast characteristics of laminated al and NI-AL casings

“…Ni-Al reaction seems to be associated with bimetallic diffusion that largely depends on Al melting [3][4]. At the atmospheric condition, Al has a melting point of 933 K while the Ni melting point is 1726 K. To understand the heating behavior of Al, a 1D hydrocode (Chinook from Martec Ltd.) simulation was conducted for the early shock reverberating compression of Ni-Al laminated layers driven by the C4 detonation.…”

“…The heat of reaction for the NiAl product is 1.380 kJ/g; for the Ni 3 Al product, it is 0.4419 kJ/g in liquid phase and 0.7647 kJ/g in solid phase. Reaction of nanometric laminated Ni-Al can be found in a number of studies where ignition occurs at 450-900 K depending on the layer thickness/spacing [3][4]. This reaction threshold temperature is near the Al melting to facilitate diffusion mixing of Al and Ni.…”