Quasicrystal is a solid between crystalline and amorphous. Quasicrystals have a long-range ordered atomic arrangement similar to crystals, but do not possess the translational symmetry of crystals, so they can have macro symmetry that crystals do not allow. Quasicrystals are characterized by low surface energy, low friction factor, wear resistance, excellent dispersion, high hardness, high temperature plasticity, high thermal resistance, corrosion resistance and high resistance. At present, the application of quasicrystals lies in composite materials, surface coatings, bulk quasicrystal preparation, hydrogen storage materials, optical materials, etc.
Figure 1. Quasicrystal diffraction pattern
Due to its good physical and chemical properties, diverse preparation methods and great application value, quasicrystals play an important role in surface coating materials, composite materials and other fields.
- Surface coating materials: The low surface wettability and high hardness of quasi-crystals cause their strong wear resistance and low friction factor, and allow quasi-crystals to be used as a potential anti-friction coating material that can be used in the preparation of non-stick pans in kitchenware. Compared with the traditional non-stick pan material Teflon, the quasi-crystalline non-stick pan coating material has the characteristics of scratch resistance and high temperature stability. Currently, non-stick pans based on quasicrystals have patents. In addition, quasi-crystalline coating materials can also be used for the preparation of some mechanical parts in industry. For example, Al-Cu-Fe and other quasicrystals have a thermal conductivity similar to the traditional thermal insulation coating material ZrO2. Unlike ZrO2, the Al-Cu-Fe quasicrystalline coating has a similar volume expansion coefficient to the metal substrate. This feature reduces the stress between the coating and the substrate, but makes the quasicrystal restricted by the generally low melting point of the aluminum-based alloy and causes the usable temperature of the Al-Cu-Fe quasicrystal to be lower than ZrO2. As a result, Al-Cu-Fe quasicrystalline coatings are suitable for small engine blades.
Figure 2. Quasicrystals are used as non-stick coating materials
- Reinforced phase of composite materials: Bulk quasicrystals present a relatively high brittleness which limits their use as structural materials. However, using bulk quasicrystals as the dispersion-enhancement phase of the composite material can not only maintain its own high strength, but also significantly increase the toughness of the composite material, and also make the composite material have a lower friction factor and wear rate. For example, 12%Cr-9%Ni-4%Mo-2%Cu-1%Ti of martensitic aging steel containing quasicrystal phase precipitation can be presented as composite material with good reinforcing phase, and its application to composite materials can significantly enhance the surface properties of composite materials.
According to different criteria, quasicrystals can be classified in many ways. There are currently four main categories: the number of rotational symmetry, alloy components, thermodynamic stability, and quasi-periodic dimension. According to the different times of rotational symmetry, quasicrystals can be divided into five quasicrystals, eight quasicrystals, ten quasicrystals and twelve quasicrystals. According to different alloy components, quasicrystals can be divided into aluminum reference crystal, magnesium reference crystal, zinc reference crystal, zirconium reference crystal, titanium reference crystal, gallium reference crystal, cadmium reference crystal and palladium reference crystal. According to different thermodynamic stability, quasicrystals can be divided into metastable quasicrystals and stable quasicrystals. According to the different quasi-periodic dimensions, quasi-crystals can be divided into one-dimensional quasi-crystals, two-dimensional quasi-crystals and three-dimensional quasi-crystals. Among them, classification according to the period dimension is the most commonly used classification method for quasicrystals.
Commonly used methods for quasicrystals preparation include rapid condensation method, physical and chemical method, mechanical alloying method, meteorological deposition method, electron beam surface rapid melting method, electrodeposition and evaporation condensation method, etc.
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