Effects of the addition of SiC on the crystallization of Al 84Ni 8Co 4Y 3Zr 1 (at.%) amorphous ribbons

Abstract

Amorphous alloys present exceptional values of mechanical strength but lack any significant plasticity at room temperature. Deformation of amorphous alloys occurs in shear transformation zones that connect to form shear bands, which are easier to deform than the surrounding matrix, thus facilitating further deformation in the same location of the specimen. However, the presence of particles dispersed in the amorphous matrix can modify such strain softening behavior, resulting in real plastic deformation before fracture. Also, depending on the type of particles and how they are introduced, they can modify the crystallization behavior of the amorphous matrix by acting as heterogeneous nucleation sites. In this context, this paper reports on the effects of the addition of SiC particles on the crystallization of Al 84Ni 8Co 4Y 3Zr 1 amorphous ribbons. Pre-alloyed ingots with and without added SiC particles were melt-quenched into amorphous ribbons by the single-roller melt-spinning technique and then selectively and partially crystallized at the first and second crystallization temperatures, as determined by differential scanning calorimetry. Primary crystallization of nanometric-sized fcc-Al crystals was found to occur in both ribbons (with and without added SiC), confirming that crystallization reactions were not altered by the ceramic particles. Aluminum carbide (Al 4C 3) crystals resulting from high-temperature liquid metal/SiC reactions were observed as coatings on the SiC particles and as isolated particles dispersed in the amorphous solid matrix. In both cases, the Al 4C 3 particles also did not change the crystallization behavior of the amorphous Al 84Ni 8Co 4Y 3Zr 1 matrix, since no heterogeneous nucleation of fcc-Al crystals was observed.