Precipitation of Icosahedral Phase in Zr-Ni-Nb-Cu-Al Metallic Glasses

Abstract

The crystallization behaviors of Zr-Ni-Nb-Cu-Al metallic glasses are greatly influenced by the substitution of Ni for Zr. For the glassy Zr 71Àx Ni x Nb 3 Cu 16 Al 10 (x ¼ 7, 9, 11 at%) alloys, the onset temperature of crystallization T x increases from 717 to 748 K with increasing Ni content from 7 at% to 11 at%. The primary crystallization reaction of the studied glassy alloys corresponds to the formation of icosahedral phase from amorphous matrix. The precipitation of quasicrystalline phase with a large volume fraction in the Zr 64 Ni 7 Nb 3 Cu 16 Al 10 alloy indicates that the decrease of Ni content promotes the formation of icosahedral phase. Johnson-Mehl-Avrami analysis of isothermal transformation data suggests that the icosahedral phase precipitation proceeds by a diffusion-controlled growth mode with nearly constant nucleation rate. Furthermore, the Zr 71Àx Ni x Nb 3 Cu 16 Al 10 (x ¼ 7, 9, 11 at%) alloys possess high glass-forming ability, and the critical diameter for glass formation reaching 6 mm, 9 mm and 9 mm by copper-mould casting method, respectively.

Phason strained quasicrystalline and crystalline precipitates in Zr–Al–Ni–Cu–Nb bulk metallic glass matrix composites

“…The presence of additional alloying elements, such as Nb, Ta, V, Mo, etc., can heighten the formation of quasicrystal [16][17][18]. Besides, various crystalline precipitates are also observed during the crystallization process, for instance, tetragonal Zr 2 Ni, face-centered-cubic Zr 2 Ni, tetragonal Zr 2 Cu, tetragonal Zr 3 Al 2 , hexagonal Zr 4 Al 3 [5,[18][19][20]. Structural investigations of these precipitates, which will facilitate the understanding about the crystallization behavior and the influence on the mechanical properties of the BMGs, are highly demanded.…”

“…The appearance of icosahedral quasicrystal (IQC) as precipitation phase after isothermal annealing is widely reported [5][6][7][8], indicating the existence of the icosahedral short-range order (ISRO) structure in the amorphous matrix [9,10]. The quasicrystalline precipitate exhibits a distinct effect on glass-forming ability [1,11,12], enhanced plasticity [13,14] and the deformation behavior [15] of the BMGs.…”

Devitrification of Zr55Cu30Al15Ni5Bulk Metallic Glass under Heating and HPT Deformation

“…The processes of crystallization of Zr-based bulk amorphous alloys were investigated mainly under heat treatment. At an initial stage of the devitrification of these alloys, the formation of metastable crystalline [7,8] and quasi-crystalline [9,10] phases was observed. Under heating or annealing, after the completion of the first crystallization stage alloys have an amorphous-nanocrystalline structure, with the fraction of the crystalline phase depending on heat treatment conditions.…”