Structural origin underlying poor glass forming ability of Al metallic glass

Abstract

We performed molecular dynamics simulations to study the glass formation and local atomic structure of rapidly quenched Al. Both potential energy and structural parameters indicate that the glass transition temperature of amorphous Al is as low as 300 K, which may lead to the poor thermal stability of the amorphous Al as it is prone to crystallize even at room temperature. Voronoi polyhedra analysis reveals that the most popular polyhedron is the deformed body-centered cubic (bcc) cluster characterized by the index < 0, 3, 6, 4 > in the amorphous Al, while the icosahedron with the index < 0, 0, 12, 0 > is always predominant in bulk metallic glass formers with excellent glass forming ability (GFA). Moreover, these deformed-bcc short-range orders can make up medium-range orders via the linkage of vertex-, edge-, face-, intercrossed-shared atoms, which are believed to more easily transform into face-centered cubic (fcc) Al nanocrystal compared with the icosahedral clusters in terms of the symmetrical similarity between bcc and fcc structures. This finding could unveil the structural origin of poor GFA of Al-based alloys.

Correlation between medium-range order structure and glass-forming ability for Al-based metallic glasses

“…[10][11][12] Recently, Li et al proposed that abundant deformed-bcc clusters existing in the amorphous structure could be the reason for the poor GFA of the amorphous Al. 13 However, for Al 75 Co 25 MG with better GFA, the most popular polyhedron is full icosahedron with Voronoi index h0,0,12,0i, which is always predominant in the BMGs formers with excellent GFA. 14 The other route is based upon the experimental analyses using synchrotron radiation x-ray diffraction (XRD) 15 and fluctuation electron microscopy 16 to provide key information of short range order (SRO) and medium range order (MRO).…”

Different Connection Models of Icosahedral Structures in TiAl Alloy Caused by the Cooling Rates

“…The Wendt–Abraham parameter emphasizes the local character of g(r) , permitting a direct comparison between different structures and leading to a better estimate of the glass transition temperature ( T g ). [ 36,37 ]…”

Formation of highly thermal stable Al88Ni6Y6 amorphous composite by graphene addition design

“…At present, the study on molecular-dynamics simulations has shown that the Al-based amorphous alloys had a low T g and contained a large amount of deformed body-centered cubic (bcc) short-range orders, while the icosahedron is always predominant in the amorphous matrix [41]. Moreover, these deformed-bcc short-range orders could make up medium-range orders via some linkages, such as edge-, face-, intercrossed-shared atoms, which were believed to more easily transform into the fcc nanocrystals, compared with the icosahedral clusters due to the symmetrical similarity between bcc and fcc structures.…”