Abstract
Bulk Metallic Glasses (BMG) are metallic alloys that have the ability to solidify in an amorphous state. BMGs show enhanced properties, for instance, high hardness, strength, and excellent corrosion and wear resistance. BMGs produced by conventional methods are limited in size due to the high cooling rates required to avoid crystallization and the associated detrimental mechanical properties. Additive manufacturing (AM) techniques are a potential solution to this problem as the interaction between the heat source, e.g., laser, and the feedstock, e.g., powder, is short and confined to a small volume. However, producing amorphous parts with AM techniques with mechanical properties comparable to as-cast samples remains a challenge for most BMGs, and a complete understanding of the crystallization mechanisms is missing. This review paper tries to cover recent progress in this field and develop a thorough understanding of the correlation between different aspects of the topic. The following subjects are addressed: (i) AM techniques used for the fabrication of BMGs, (ii) particular BMGs used in AM, (iii) specific challenges in AM of BMGs such as the control of defects and crystallization, (iv) process optimization of mechanical properties, and (v) future trends.
Highlights
Bulk metallic glasses (BMGs) have the ability to solidify in an amorphous structure, which provides them with high strength and elasticity, hardness, and wear and corrosion resistance, due to the absence of structural defects usually found in crystalline materials such as dislocations, grain boundaries, and chemical segregation
We identified seven Additive manufacturing (AM) techniques for the production of BMGs: laser powder-bed fusion (LPBF), selective laser sintering (SLS), laser solid forming (LSF), direct energy deposition (DED), laser foil printing (LFP), ultrasonic AM (UAM), and fused filament fabrication (FFF)
Sohrabi et al [73] showed that 0.4% of porosity in a Pd-based BMG sample fabricated via LPBF resulted in a compressive strength 14% lower than the as-cast material
Summary
Bulk metallic glasses (BMGs) have the ability to solidify in an amorphous structure, which provides them with high strength and elasticity, hardness, and wear and corrosion resistance, due to the absence of structural defects usually found in crystalline materials such as dislocations, grain boundaries, and chemical segregation. BMGs are commonly processed by direct casting and melt spinning with rapid quenching from the melt to avoid crystallization [1,2] It is a convenient one-step process where cooling and forming take place simultaneously, it is difficult to achieve intricate shapes in the final products due to the limitations posed by required high cooling rates. Halim et al [26] included a section about AM of BMGs in a review related to processing methods of BMGs. Liu et al [18] focused mainly on the crystallization of BMGs fabricated via laser powder-bed fusion (LPBF). We identified seven AM techniques for the production of BMGs: laser powder-bed fusion (LPBF), selective laser sintering (SLS), laser solid forming (LSF), direct energy deposition (DED), laser foil printing (LFP), ultrasonic AM (UAM), and fused filament fabrication (FFF).
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