Processing of Bulk Metallic Glass

Abstract

Bulk metallic glass (BMG) formers are multicomponent alloys that vitrify with remarkable ease during solidification. Technological interest in these materials has been generated by their unique properties, which often surpass those of conventional structural materials. The metastable nature of BMGs, however, has imposed a barrier to broad commercial adoption, particularly where the processing requirements of these alloys conflict with conventional metal processing methods. Research on the crystallization of BMG formers has uncovered novel thermoplastic forming (TPF)-based processing opportunities. Unique among metal processing methods, TPF utilizes the dramatic softening exhibited by a BMG as it approaches its glass-transition temperature and decouples the rapid cooling required to form a glass from the forming step. This article reviews crystallization processes in BMG former and summarizes and compares TPF-based processing methods. Finally, an assessment of scientific and technological advancements required for broader commercial utilization of BMGs will be made.

A thermoplastic forming map of a Zr-based bulk metallic glass

“…Bulk metallic glasses (BMGs) exhibit different flow features compared to their crystalline counterparts, due to the absence of long-range order and dislocation-like defects [1][2][3][4][5][6][7]. Dependent on temperature, stress and strain (rate), the flow of BMGs can be homogeneous or inhomogeneous not only spatially but also temporally, which is usually characterized by a deformation or flow map (a convenient means of surveying the various modes of plastic deformation of a material) [4,8].…”

“…For metallic glasses of different alloy systems, the smallest replicated features [5,31,43], the maximum plastic strain that related to the large Poisson ratio and low glass transition [41] and other parameters, such as fragility and thermal stability [37,38,[44][45][46][47], have been discovered to be associated with BMGs' formability. However, for a metallic glass with a certain composition, the temperature-dependent viscosity and long processing time [5,28,42] are regarded as the two parameters that can most significantly affect the formability of BMGs. That increasing temperature favors formability can be understood well from the viewpoint of lowering viscosity.…”

Criticality in Bulk Metallic Glass Constituent Elements

“…Early adaptation includes the use of BMGs in sporting goods, watch components, and electronic casings. 16,19,34,35 The focus of the early applications has been on the small scale, typically below 10 cm. This length scale has its origin in limited supply chains, high materials costs for most advanced BMGs, and a limited processing infrastructure.…”

“…18 Thus, BMGs can be considered high-strength metals that can be processed like plastics. 18,19 TPF-based processes for BMGs like blow-molding, 18 extrusion, 20,21 compression molding, 22,23 micro-and nano-molding, 17,24 and hot-rolling 25 permit BMGs to be formed into many complex shapes on various length scales.…”

Viscous surface flow induced on Ti-based bulk metallic glass by heavy ion irradiation

“…Because of their unique mechanical and chemical properties, such as high strength and superior resistance to corrosion, metallic glasses (MGs) have attracted great interest in recent decades [1][2][3][4][5]. Due to their inherent disordered structure, they are supposed to be ideal potential candidates for application in nuclear-irradiated environments or deep space.…”