Investigation of the early stage of reactive interdiffusion in the Cu-Al system by in-situ transmission electron microscopy

Abstract

The early stage of the reactive interdiffusion in the Cu-Al system was investigated at 350°C and 300°C thanks to in-situ transmission electron microscopy. A special care was given to find conditions where the electron beam and the sample free surface do not affect significantly the reaction. A special emphasis was then given on the influence of grain boundaries that are fast diffusion paths, and on nanoscaled particles that may interact with the transformation front. It was found that there is a transient state followed by a steady state where the mean growth rates of intermetallic compounds follow a parabolic law indicating that the kinetics is diffusion controlled. Thanks to the in-situ observations at the nanoscale, it was also possible to track the local velocity of interfaces between the different phases. Strong fluctuations were exhibited within length scales smaller than 100nm and they are partly attributed to interface pinning by nanoscaled particles. Last, considering thermodynamic and kinetic arguments, it is shown that it is mainly an indirect effect induced by a local change of solute fluxes and of concentration gradients.

Microstructure and mechanical properties characterization of architectured copper aluminum composites manufactured by cold-drawing

“…A fiber texture with major <111 > and minor <001> orientations, was characterized for both phases, in agreement with the results from previous researchs on the influence of cold drawing on the texture of pure Cu [17,18] and pure Al [19]. vious papers for the same samples [14,16], in agreement with literature [21,22,23,24]. For short heat treatment conditions (300 • C during 15 min to enable the TEM observation of the IMC interface), the bright field TEM image of a 1.7 mm diameter ACCA (figure 4(a)) reveals that the AlCu layer is the thinnest one.…”

“…Figure 2(b) shows at higher magnification, in bright field STEM mode, of a typical Cu/Al interface. As reported in a previous article[16], no IMC could be detected along such an interface, except for a small fraction of nanoscaled Al 2 O 3 resulting from the cold-drawing process. The grains are mostly dislocation-free, however, few grains also exhibit dislocation walls/cells (encircled in the figure2(b)).…”

“…In this case, the thickness of the IMCs layer is about 25 µm. More details about the IMCs characterization can be found in a previous article [16]. Table 1 summarizes the following characteristics of each ACCA sample: final diameter, average plastic strain during the process (estimated from eq.1), Grain Size (GS) of the Cu and Al phases, alongside their corresponding maximal density pole (indicating the texture intensity, I).…”

“…Table 1 summarizes the following characteristics of each ACCA sample: final diameter, average plastic strain during the process (estimated from eq.1), Grain Size (GS) of the Cu and Al phases, alongside their corresponding maximal density pole (indicating the texture intensity, I). The volume fractions ( f w ) of Al, Cu, Al 4 Cu 9 , AlCu and Al 2 Cu are also estimated using the average aluminum area and the growth kinetics of the intermetallic compounds reported in previously published papers for the same materials [14,16]. The same microstructural characteristics for the conventional CCA wires are also included in this table.…”

Intrinsic Diffusivities Ratio Analysis in the Al-Cu System

“…Authors [16] didn't calculate diffusion activation energies and the pre-exponential factors, so we can do it using calculated data by k. p. gurov's and a. m. gusak's method or "constant flux method" [3,4,[18][19][20][21][22][23] (Table 2) and eqs. 27:…”