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Characteristics of amorphous materials

Characteristics of amorphous materials

2021-09-17

As a kind of rigid solid with special structure, metallic glass has higher strength than general metal (for example, amorphous Fe80B20, fracture strength σF reaches 37kgf/mm, which is more than seven times that of general structural steel); and the size effect of strength is very large. small. Its elasticity is also better than that of ordinary metals, and its bending deformation can reach more than 50%. Hardness and toughness are also high (Vickers hardness HV is generally around 1000-2000).


The corrosion resistance of iron-based metallic glass with low chromium content (such as Fe27Cr8P13C7) is far better than that of stainless steel. Due to the long-range disorder of the atomic arrangement, the contribution of phonons to the scattering of conducted electrons is very small, making the resistivity very high, generally above 100μΩ·cm at room temperature, and the temperature coefficient of resistivity is very small (less than ±10K); At 0K, there is a high residual resistance. In some amorphous alloys (such as PdSiCr), the resistance has a minimum value when the resistance temperature curve T=Tm. When T<Tm, the resistance increases with the decrease of temperature, similar to that in crystalline diluted alloys. The mechanism of the Kondo effect is unclear.


There are 15 kinds of amorphous quenched superconducting alloys that have been reported. Their superconducting transition temperature is 1.5~8.71K, which is lower than that of crystalline superconductors. It is characterized by far stronger radiation resistance than crystalline superconductors. The metallic glass based on transition metals (iron, cobalt, nickel) has excellent soft magnetic properties (see magnetic materials), high magnetic permeability and low AC loss, far better than commercial silicon steel sheets, and can be compared with permalloy. For example, (Fe4Co96)(P16B6Al3) amorphous alloy has coercivity Hc≈0.13Oe and remanence Br≈4500G, which may be widely used in high and low frequency transformers (partially replacing silicon steel sheets and permalloy), magnetic sensors, and recording Magnetic heads, magnetic shielding materials, etc.


After research, the internal structure of the glass has no "spatial lattice" feature, but is similar to the liquid structure. It's just that the "quasi-crystal regions" cannot move with each other, causing the glass to have no fluidity. We call this state "amorphous state". Strictly speaking, "amorphous solids" do not belong to solids, because solids refer exclusively to crystals; it can be regarded as a very viscous liquid. Therefore, "amorphous state" can be proposed as another state of matter. In addition to ordinary glass, there are many "amorphous" solids, such as rubber, paraffin, natural resin, asphalt, and polymer plastics.

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