Laser cladding of quasi-crystal-forming Al-Cu-Fe-Bi on an Al-Si alloy substrate

Abstract

We report here the results of an investigation aimed at producing coatings containing phases closely related to the quasi-crystalline phase with dispersions of soft Bi particles using an Al-Cu-Fe-Bi elemental powder mixture on Al-10.5 at. pct Si substrates. A two-step process of cladding followed by remelting is used to fine-tune the alloying, phase distribution, and microstructure. A powder mix of Al 64 Cu 22.3 Fe 11.7 Bi 2 has been used to form the clads. The basic reason for choosing Bi lies in the fact that it is immiscible with each of the constituent elements. Therefore, it is expected that Bi will solidify in the form of dispersoids during the rapid solidification. A detailed microstructural analysis has been carried out by using the backscattered imaging mode in a scanning electron microscope (SEM) and transmission electron microscope (TEM). The microstructural features are described in terms of layers of different phases. Contrary to our expectation, the quasi-crystalline phase could not form on the Al-Si substrate. The bottom of the clad and remelted layers shows the regrowth of aluminum. The formation of phases such as blocky hexagonal Al-Fe-Si and a ternary eutectic (Al ϩ CuAl 2 ϩ Si) have been found in this layer. The middle layer shows the formation of long plate-shaped Al 13 Fe 4 along with hexagonal Al-Fe-Si phase growing at the periphery of the former. The formation of metastable Al-Al 6 Fe eutectic has also been found in this layer. The top layer, in the case of the as-clad track, shows the presence of plate-shaped Al 13 Fe 4 along with a 1/1 cubic rational approximant of a quasi-crystal. The top layer of the remelted track shows the presence of a significant amount of a 1/1 cubic rational approximant. In addition, the as-clad and remelted microstructures show a fine-scale dispersion of Bi particles of different sizes formed during monotectic solidification. The remelting is found to have a strong effect on the size and distribution of Bi particles. The dry-sliding wear properties of the samples show the improvement of wear properties for Bi-containing clads. The best tribological properties are observed in the as-clad state, and remelting deteriorates the wear properties. The low coefficient of friction of the as-clad and remelted track is due to the presence of approximant phases. There is evidence of severe subsurface deformation during the wear process leading to cracking of hard phases and a change in the size and shape of soft Bi particles. Using these observations, we have rationalized possible wear mechanisms in the Bi-containing surface-alloyed layers.

Formation and Stability of Pb-Sn Embedded Multiphase Alloy Nanoparticles via Mechanical Alloying

“…It has already been reported that Al and Pb have been found to form supersaturated Al(Pb) solid solution during high-energy mechanical milling even though they have positive heat of mixing. [38][39][40] In addition, it has also been reported that the sizes of the embedded Pb nanoparticles in Al [41] and embedded Bi nanoparticles in Al-Cu-Fe, [42] which are well-known immiscible systems, have also been found to be increased during fretting wear test. These are reported to be due to pipe diffusion, i.e., particles are interconnected by dislocations and they can have diffusion through dislocations.…”

Rapid Solidification Processing and Bulk Metallic Glass Casting

“…Some examples of nanoquasicrystalline materials developed recently are Al-Cu-Fe-Bi, Al-Si, and Fe 48 Cr 15 Mo 14 C 15 B 6 Tm 2 (79,80). Because of the need for a high cooling rate of at least 106 K s À1 , the nanostructured quasicrystals are produced on different substrates via laser processing (79). Because of the need for a high cooling rate of at least 106 K s À1 , the nanostructured quasicrystals are produced on different substrates via laser processing (79).…”