Bulk Metallic Glasses Processability


Bulk Metallic Glasses (BMGs), even called bulk amorphous alloys, are a category of new advanced materials with a disordered atomic-scale structure. Their unique microstructure imparts outstanding physical and chemical properties (Huang et al., 2016) to the manufacts (Schroers, 2010b; Schroers et al., 1999; Mirsayar et al., 2016, 2017).

The absence of long-range atomic order lead to unique, physical, chemical and mechanical properties of bulk metallic glasses, that have found pilot applications in a wide range of field from sporting goods to precision mechanical components, electronics and biomedicine (Wang et al., 2004; Schroers, 2010a; Kumar et al., 2009; Inoue and Takeuchi, 2011).

 Zr-based BMGs are technologically attracting since they can be processed in larger parts due to their broad super-cooled liquid region and high glass-forming ability. Among the Zr-based alloy systems recently developed, containing different combination of Cu, Al, Ti, Ni (Wang, 2007; Shen et al., 2005; Jiang et al., 2008; Liu et al., 2007; Mattern et al., 2002), we investigate a commercial BMG containing the same atoms but with the addition of Be. In the last few years Zr-based bulk materials have been deeply explored for their superior Glass Forming Ability (GFA). The properties advantage ranges from high mechanical strength, high fracture strength, superior elastic limit to good and precise deformability, good ductility, low coefficient of thermal expansion and excellent corrosion/wear resistance (Aversa et al., 2016a; 2016b; 2016c; 2016d; 2016e; 2016f; 2016g; 2016h; 2016i; 2016j; 2016k; 2016l).

BMGs multicomponent alloys based on Zr have superior GFA and they can be produced into parts with thickness larger than a few centimeters by conventional melting and casting techniques (Liu et al., 2002).

Among the other advantage, BMGs utilization offers reduced process costs and it gives the possibility to manufacture a variety of industrial products (Morito and Egami, 1984; Aversa et al., 2016 a-o, 2017 a-e).

The microstructure of BMGs compared to the other conventional metals holds the advantage of not presenting a long-range order crystalline structure. Conversely, their microstructure has a short-range organized amorphous arrangement, which is characteristic of all glassy materials, such as those found in ceramics and polymers (Busch, 2000; Petrescu et al., 2016 a-e).

An important issue in the processing of glass forming materials is, therefore, the rheology of the melt during the cooling procedures.

This issue is particularly critical for thermodynamically favored crystal forming materials. For these materials, such are metals, sufficiently high cooling rates are necessary to avoid crystallization from the melt and to preserve the liquid amorphous microstructure (Huang et al., 2016) in the solidified glass (Debenedetti and Stillinger, 2001; Eckert et al., 1998). insert molding