Amorphous layer formation in Al86.0Co7.6Ce6.4 glass-forming alloy by large-area electron beam irradiation

Abstract

Amorphous Al-Co-Ce alloys are of interest because of their resistance to corrosion, but high cooling rates are generally required to suppress the formation of crystalline phases. In this study, the surface of a bulk crystalline Al-Co-Ce alloy of a glass-forming composition was treated using large area electron beam (LAEB) irradiation. Scanning electron microscopy shows that, compared to the microstructure of the original crystalline material, the treated surface exhibits greatly improved microstructural and compositional uniformity. Glancing angle X-ray diffraction conducted on the surface of treated samples indicates the formation of the amorphous phase following 25 and 50 pulses at 35 kV cathode voltage. However, when the samples are treated with 100 and 150 pulses at 35 kV cathode voltage of electron beam irradiation, the treated layer comprises localised crystalline regions in an amorphous matrix.In addition, the formation of cracks in the treated layer is found to be localised around the Al 8 Co 2 Ce phase in the bulk material. Overall, crack length per unit area had no clear change with an increase in the number of pulses.

Effect of prior laser microstructural refinement on the formation of amorphous layer in an Al86Co7.6Ce6.4 alloy

“…This is due to the brittleness characteristic of this phase [10]. These large and brittle Al 8 Co 2 Ce phase particles act as easy crack initiation sites in the as-cast material, these particles also provide easy growth paths for the crack propagation, as shown in Figure 9a.…”

“…This needs a sufficiently high temperature and enough time for the melting and diffusion. Therefore, when low cathode voltage or small number of pulses was used, the alloy cannot be transformed to amorphous state [10]. Second, upon obtaining a homogeneous composition, a fast enough cooling rate is a crucial condition for the alloy to form amorphous phase.…”

“…The crystallisation may result from reduced cooling rates due to progressive temperature increase of the substrate with additional pulses [10].…”

“…Large-area electron beam (LAEB) irradiation, a recent variant of electron beam treatment, has several advantages such as a large beam size (~60 mm in diameter) which decreases processing time by decreasing the need for overlapping tracks. It has been used to polish mould surfaces [7], increase hardness and wear resistance [8], lower surface roughness, reduce the porosity of sprayed coatings [9] and, as demonstrated in our previous paper [10], generate an amorphous layer when used to melt the surface of a cast Al-Co-Ce alloy. However, cracking of the amorphous layers was found to occur around large, pre-existing particles of the Al 8 Co 2 Ce phase.…”

Magnetic properties and crystallization behavior of Al–Co–Ce(Dy) amorphous ribbons

“…Al-TM-REM amorphous alloys exhibit good mechanical characteristics combining high strength and plasticity [1][2][3][4][5]. An important feature of these alloys is the excellent corrosion resistance and heat resistance, which enable one to consider them for use as protective coating materials in aviation and space industry [6,7]. Further improvement in the mechanical properties has been reached by partial crystallization of amorphous structures, forming a precipitation of nanometer-sized fcc-Al phase in the amorphous matrix [8,9].…”