A brief introduction to metallic glasses (amorphous alloys) Sheng Guo Assistant Professor Materials and Manufacturing Technology Department E-mail: sheng.guo@chalmers.se
Outline What are metallic glasses H istorical development A lloy(composition) design strategy Unique properties Typical applications Scientific and technical challenges
Amorphous alloys/ metallic glasses An amorphous metal, also known metallic glass or glassy metal, is a solid metallic material, usually an alloy, with a disordered atomic-scale structure. (Cambridge Univ. TLP library) (Telford, Mater Today, 2014) Amorphous materials, like window glass o have no long-range order, so no translational symmetry o not truly random, have short-range order (Kaban et al., Acta Mater, 2013)
Si gns f or amorphism (Li et al., J Alloy Compd, 2010) amorphous (Lacasse et al., Pfonline.com) crystalline crystalline amorphous High-resolution TEM (halo) amorphous o o X-ray diffraction (hump) have no long-range order/translational symmetry shows the glass transition behavior Differential scanning calorimetry (Tg) (Karpukhina et al., Chem Soc Rev, 2014)
Some concepts (Zhang et al., Mater Trans, 1990) (Debenedetti et al., Nature, 2001) (Cornell web page) * Critical cooling rate * Glass transition * Supercooled liquid region: T=Tx-Tg A gauge of thermal stability of metallic glasses, also quite often characterizes the glass forming ability
Some histories Au75Si25 P Duwez W Klement, R Willens, P Duwez, Non-crystalline Structure in Solidified Gold-Silicon Alloys, Nature, 1960, 187: 869
MGs Bulk Metallic Glasses (BMGs) melt spinning suction casting (Survanarayana, Bulk Metallic Glasses) BMGs: the smallest dimension of MGs>1mm Φ80*85 mm (Wikipedia) (Telford, Mater Today, 2014) Pd 42.5 Cu 30 Ni 7.5 P 20 BMG 3.4 Kg! (Nishiyama et al, Intermetallics, 2012)
Alloy design strategy for BMGs A Inoue (1990) Inoue s three empirical rules to prepare BMGs at least 3 alloying elements; large mismatching atomic sizes of constituent elements large negative heat of mixing among major alloying elements atomic size distribution heat of mixing (Lu et al., J Mater Sci, 2004) (Guo et al., Intermetallics, 2013) (Greer, Mater Today, 2009)
Attractive properties of BMGs High strength : >2000 MPa High hardness: 600-1300 DPH High fracture toughness: >70 MPa. m 1/2 High elastic strain: ~ 2% elastic strain Good formability: >1000% elongation Superior aqueous corrosion resistance Good wear resistance Excellent soft magnetic properties: Fe-base MGs Other interesting optical and physical properties (Demetriou et al, Nat Mater, 2011)
Bulk Metallic Glasses Structural From Liquidmetal Technologies
Micro-devices: micro-gears made of MGs Only one casting process 100µm Super-precision gear mold Super-precision gear parts made of glassy alloy Conventional machined gear Diameter = 647 mm Teeth = 14 p Module = 40 mm Newly developed gear Diameter = 288 µm Teeth = 9 p Module = 25 µm Human hair (d= 80 µm ) (Nishiyama et al, 2005)
Blow moulding of BMGs (Yale Schroers Lab)
BMGs and Apple products SIM tray tool
Soft magnetic properties Soft magnetic materials: High saturation magnetization Low coercivity High electrical resistivity amorphous transformer core (Survanarayana, Bulk Metallic Glasses)
Seeing is believing I: high elastic strain (Telford, Mater Today, 2014)
Seeing is believing II: excellent formability (Kumar et al., Nature, 2009) upon crystallization
Achilles heel: (Tension) Brittleness shear banding (Inoue et al., Nat Mater, 2003) (Cambridge web page)
(Debenedetti et al., Nature, 2001) Glass transition is still a mystery What is the nature of glassy state? was selected as one of the most important 125 scientific questions to be resolved this century--- Science, 2005 Glass transition is one of the deepest and most important unsolved problems in condensed matter physics ---- Nature Materials, 2008