Super Metallic Glass Created

Slowlybut surely we have continued to improve on past performance.  Yet I suspect that it will take a fundamentalbreakthrough to go much further.  We havelong since passed the point of diminishing returns for most of this.  After all, we still use steel for a greatreason! It is cheap.

I see this stuff been used intime to form thin shinned craft needing to be very light.  Even an airship could become huge usingmaterial such as this, and since the sole limitation there to real gigantism ismaterial strength, a super strong light material is necessarily useful. Recallperformance improves as a cube to strength performance increases.

Of course, my interest is inMagnetic Field Exclusion Vessels which also need to be large and light to beinitially space worthy during the early development.

JANUARY 10, 2011

Ashby map of damage tolerance (toughness versus strength) of materials. 

Glass stronger and tougher than steel? A new type of damage-tolerantmetallic glass, demonstrating a strength and toughness beyond that of any knownmaterial, has been developed and tested by a collaboration ofresearchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory(Berkeley Lab)and the California Institute of Technology. What’s more, evenbetter versions of this new glass may be on the way.

The new metallic glass is a microalloy featuring palladium, a metal with a high“bulk-to-shear” stiffness ratio that counteracts the intrinsic brittleness ofglassy materials.

Micrograph of deformed notch in palladium-based metallic glass shows extensive plastic shielding of an initiallysharp crack. Inset is a magnified view of a shear offset (arrow) developedduring plastic sliding before the crack opened. (Image courtesy of Ritchie andDemetriou)

“Because of the high bulk-to-shear modulus ratio ofpalladium-containing material, the energy needed to form shear bands is much lower than the energy required to turnthese shear bands into cracks,” Ritchie says. “The result is that glassundergoes extensive plasticity in response to stress, allowing it to bendrather than crack.”

In earlier work, the Berkeley-Cal Tech collaboration fabricated ametallic glass, dubbed “DH3,” in which the propagation of cracks was blocked bythe introduction of a second, crystalline phase of the metal. This crystallinephase, which took the form of dendritic patterns permeating the amorphousstructure of the glass, erected microstructural barriers to prevent an openedcrack from spreading. In this new work, the collaboration has produced a pureglass material whose unique chemical composition acts to promote extensiveplasticity through the formation of multiple shear bands before the bands turn into cracks.

“The rule of thumb is that to make a metallic glass we need to have at leastfive elements so that when we quench the material, it doesn’t know what crystalstructure to form and defaults to amorphous,” Ritchie says.

Owing to a lack of microstructure, glassy materials are inherentlystrong but brittle, and often demonstrate extreme sensitivity to flaws.Accordingly, their macroscopic failure is often not initiated by plasticyielding, and almost always terminated by brittle fracture. Unlike conventionalbrittle glasses, metallic glasses are generally capable of limited plasticyielding by shear-band sliding in the presence of a flaw, and thus exhibittoughness–strength relationships that lie between those of brittle ceramics andmarginally tough metals. Here, a bulk glassy palladium alloy is introduced,demonstrating an unusual capacity for shielding an opening crack accommodatedby an extensive shear-band sliding process, which promotes a fracture toughnesscomparable to those of the toughest materials known. This result demonstratesthat the combination of toughness and strength (that is, damage tolerance)accessible to amorphous materials extends beyond the benchmark rangesestablished by the toughest and strongest materials known, thereby pushing theenvelope of damage tolerance accessible to a structural metal.

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