The Three-Dimensional Structure of Mg-Rich Plates in As-Cast Mg-Based Bulk Metallic Glass Composites

Abstract

The three-dimensional morphology of crystalline plates that form in as-cast Mg 65+x (Cu 0.667 Y 0.333 ) 30-x Zn 5 (x = 6, 12, 14, and 16) bulk metallic glass (BMG) composites was investigated by focused ion beam (FIB) tomography. The size, shape, and distribution of the plates were found to be dependent both on alloy composition and cooling rate of the melt, whereby rapid cooling and lower x values generated a lower volume fraction of plates due to a decreased propensity for crystallization. Using FIB tomography, it was demonstrated that these plates may nucleate at micron-sized cuboidal, spherical, and irregularly shaped particles that form first during the casting process. The plates subsequently grow in preferential directions during cooling of the alloy to below the glass transition temperature to ultimately generate a multivariant, interwoven crystalline structure throughout the amorphous matrix. This complex structure is argued to contribute to the improved toughness of the alloy by hindering the propagation of gross shear bands and promoting the formation of multiple shear bands.

Recent developments in ductile bulk metallic glass composites

“…[1] A major advantage of in situ BMGCs is that they potentially produce better interfacial bonding of the particle and matrix leading to superior mechanical properties. [1] There are at least three primary methods for producing in situ BMGCs (see e.g., [13][14][15][16][17][27][28][41][42][43][44][45][46][47][48][49][50] ):…”

“…9). When viewed in 3D, [45] this generated a multivariant, interwoven crystalline structure throughout the glassy matrix.…”

Heterogeneous nucleation at inoculant particles in a glass forming alloy: An ab initio molecular dynamics investigation of interfacial properties and local chemical bonding

“…This field of research is significant as the addition of inoculant particles into the melt of a glass forming alloy composition generates an in situ bulk metallic glass composite (BMGC) with the inoculant phase affecting an alloy's physical and dynamic properties such as the critical cooling rate [17] and glass forming ability [18]. An understanding of the effectiveness of an inoculant phase on nucleating a crystalline phase is also important as it provides a fundamental approach to controlling the final size, shape and distribution of the crystalline phase leading to high strength BMGCs [19] with desired ductility [20].…”

Uncovering the true nature of deformation microstructures using 3D analysis methods

“…Over the past few years, considerable progress has been made in the development of another 3D technique, termed 3D electron backscatter diffraction (3D EBSD), for understanding various metallurgical phenomena [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Using a typical DualBeam™ or similar platform, sub-100 nm thick layers of a material can be milled sequentially by the focused ion beam (FIB) and each surface mapped by EBSD (figure 1a).…”