China has achieved large-scale commercial production in the field of Amorphous metal/Alloy, and the products have been applied to Tesla, Huawei, and Apple phones…
Bulk metallic glass composites (English: Bulk metallic glass composites, abbreviation: BMGCs), also known as amorphous metals (English: Amorphous metal), refers to a metal material with disordered structure on the atomic scale. Most metal materials have a highly ordered structure, and the atoms exhibit a periodic crystal arrangement. On the contrary, the bulk metallic glass composite material does not have any long-range order structure, but has short-range order and medium-range order.
Generally speaking, a material with such a disordered structure can be directly cooled from its liquid state, so it is also called "glass state". Therefore, it is also called "Glassy metal" (Glassy metal, Metallic Glass), "Glass metal", "Liquid metal" (Liquid metal).
The basic and theoretical research of Chinese scientists in the field of Bulk metallic glass composites/Amorphous metal/Alloy has risen to a new level.
Bulk metallic glass composites containing β-Ti dendrites formed in situ are promising in many applications. However, it is still challenging to effectively adjust its microstructure and mechanical properties for application.
Recently, the research team of Professor Zhang Haifeng from the Institute of Metal Research of the Chinese Academy of Sciences found that when the in-situ β-Ti has marginal metastable properties, the bulk metallic glass composite material exhibits an obvious stress-strain curve in the metal. Jagged. This is very different from the previously reported tensile behavior of the material, but similar to the compression behavior of the overall material. These findings were published in the recent Physical Review Letters.
The uniaxial tensile test showed that the material fractured in shear mode. In the microstructure of the fractured sample, the deformation zone penetrated both the β-Ti dendrites and the local glassy matrix.
TEM characterization showed that the deformation band with a thickness of about 10n nanometers in the β-Ti dendrites was mainly composed of ω-Ti, indicating that the β phase was transferred to the ω phase during the deformation process.
The thickness of the ω band is similar to the thickness of the shear band in the glass-like matrix, which means continuous transmission of strain between the shear band and the ω-Ti band.
Therefore, under this new plastic deformation mechanism, the zigzag behavior of the material under tension is observed: the cooperative shearing mechanism includes the shear band in the glassy matrix and the ω in the metastable β-Ti dendrites. -Ti belt.
The slip of the three partial dislocations on the three consecutive {112} planes transforms the β phase into the ω phase, because the free energy of the ω phase is lower compared to the metastable β phase. Therefore, this cooperative shearing mechanism is closely related to the metastability of β phase.
The coordinated shearing event including the shear band and the ω-Ti band triggered a shear avalanche in the local area of a single dendrite (with a scale of tens of microns), but was prevented by adjacent β-Ti dendrites with different strengths Crystal orientation. This is because higher stress is required to penetrate other β-Ti dendrites with different orientations. Repeated activation and deactivation of coordinated shear events will cause the material to appear jagged under tension.
The discovery of the co-shearing of shear bands in the glassy matrix and inclusion of ω bands in β-Ti dendrites not only enriches the deformation mechanism of the material, but also develops high-energy release blocks with tensile plasticity and fracture modes Shaped metallic glass composite material provides the basis.