1.Department of Mechanical Engineering,Dalian University,Dalian,Liaoning 1 16622,China;2. Department of Materials Engineering,Dalian University of Technology,Dalian,King, Liaoning,China. The principle of formation is summarized. Performance characteristics and applications are summarized.
Amorphous alloy refers to a metal alloy with short-range order and long-range disorder in the solid state, also known as metallic glass. Under the normal cooling rate, metals and alloys exist in a stable crystalline state, amorphous state. Alloys can only form under non-equilibrium conditions. Since amorphous alloys have some excellent properties that are not possessed by crystalline alloys, they have led people to continue to explore and research in this field. 1 History and Current Status of Amorphous Alloys The earliest successful preparation of amorphous alloys was reported in 1934. An amorphous film was obtained by evaporative deposition using a ruler; in 1950, Brenner21 et al. used an electrodeposition method to prepare an amorphous NiP film; in 1960, 63 et al. used a rapid solidification method in a 5-alloy system. 130 amorphous alloy films were successfully prepared; in 1969, breakthroughs were made in the preparation of amorphous alloys, and the amorphous seventies that were tens of meters long were prepared by 4 others using the roll method. In the decade, a great deal of research was conducted on amorphous alloys. Amorphous alloys were found in many metal alloys. However, these amorphous alloys must be formed at a cooling rate greater than 4 ft 3 and amorphous films were obtained. The thickness of the PdNiP and PtNiP alloys is less than 50μm, and the critical cooling rate is also on the order of 103-36. Under these conditions, amorphous alloys can only produce ribbon flakes and powder shapes. Due to the influence of shape and size, the application range of amorphous alloys is limited.
In the 1990s, the size of amorphous alloys has made a breakthrough. Due to the discovery of alloys with a strong ability to form amorphous alloys, it is possible to obtain dimensional dimensions on the order of millimeters using a general process such as a copper mold casting method with a critical cooling rate of less than 102 ft 3 . Bulk amorphous alloy. It has been reported that in the bulk amorphous alloys that have been obtained, the minimum critical cooling rate is as low as 0.1 ft 3, and the maximum amorphous alloy thickness is 100. The multicomponent alloys capable of forming bulk amorphous materials discovered in the past decade have MgLnTM81LnATMmZrAlTMU received a 200-year faculty of material engineering and doctoral tutor.
TiZrAlTMlllPdNiFeP2 and so on TM transition group metal elements, Ln lanthanides, are closely related to the preparation of bulk amorphous alloy is its preparation method, in the currently reported methods can be exemplified by the following arc melting method 7 using arc melting alloy, in water cooling Copper sulphate quickly condenses.
The copper mold casting method 7 casts the alloy melted under a high vacuum and uniformly mixed into a water-cooled copper mold.
The quartz tube melt quenching method 13 puts the pre-prepared mother alloy in a quartz tube, which is heated and melted, quenched and cooled together with the quartz tube to release the flowing water.
The suction casting method 14 sucks the molten alloy into a copper mold for cooling by suction generated by different pressures between the melting chamber and the copper mold.
The directional region melting method 5 employs an arc electrode as a heat source, and the amorphous alloy rod can be continuously produced by the movement of the electrode.
The high-pressure die-casting method 7 rapidly presses the melted alloy in the melting chamber into the water-cooled copper mold at a relatively high pressure.
The glass powder extrusion method 16 press-forms a previously prepared spherical metallic glass powder at a temperature lower than the crystallization temperature.
2 Bulk Amorphous Forming Ability The composition of the amorphous alloy with high glass forming ability is selected according to the following empirical rule 17 of one or more elements; there is a large atomic size difference between the elements constituting the alloy, wherein The atomic size ratio between the main constituent elements should be negative for the heat of mixing between the constituent elements.
The evaluation of the glass forming ability of amorphous alloys is currently described by the size of the supercooled liquid phase region of the amorphous alloy and the reduced glass temperature 7 , 7; = 77 = 7 where B is the crystallization temperature , is the glass transition temperature, 7; melting point. In general, the larger the value of 41 is, the larger the value of 7 is, the smaller the critical cooling rate is, and the greater the glass forming ability, that is, when the 4 and 7 values ​​reach a large value at the same time, it is possible to achieve a large glass forming ability. . But there are also reports that Moses and 7 are not in the same situation.
The series of alloys discovered in recent years have relatively large glass forming ability, and many of them have a value of more than 80 feet, especially 65 inches. wind. To 75, Mo 7; = 127 feet 19. Attached to 2 from the alloy system in the part of the large feeding size and preparation methods.
Why alloys of certain components can form bulk amorphous can be explained in terms of structural thermodynamics. First of all, from the structural point of view, as described in the previous empirical rule, it is possible to form a bulk amorphous alloy, its attached 1 series of bulk amorphous alloys, the alloy composition size must be mm preparation process quartz tube melt quenching method suction casting method The atomic size ratio between main constituent elements of not less than 6.5 arc melting is greater than 13 and there is a negative heat of mixing between the main constituent elements, which will lead to a high dense packing disordered stacking structure of the alloy. The disordered stacking structure increases the liquid-solid interfacial energy, thereby inhibiting the nucleation of the body phase. On the other hand, the long-range diffusion of the atoms is hindered, which is necessary for crystallographic phase nucleation and growth. It also inhibits the growth of crystallographic phases. Secondly, from a thermodynamic point of view, Gibbs free energy 0 = where 5, where 0 is free energy, where 5 and 5 are the enthalpy and entropy when the liquid phase is transformed into the solid phase. Only under very low conditions, it is easy to form amorphous, so only a small 4 Dan, and a large amount of ability to reduce 46, from the thermodynamic we know that 4 is proportional to the number of microscopic state of the system, and more The increase of the component will lead to an increase in the density of the system's close-packed disorder, and this close-packed stack structure is advantageous for reducing the value and increasing the liquid-solid interfacial energy. Therefore, bulk amorphous materials require more than one elemental element to meet thermodynamic requirements. Finally, from the kinetic point of view, if the nucleation and growth of the crystallographic phase can be inhibited, it will be beneficial to the formation of amorphous. The nucleation rate and linear growth of the crystallization process are known. Can be given by
Melting point; Minhe is the kinetic constant of the nucleation rate and the kinetic constant of the growth rate; 6 is the geometric factor. In the equation, the important parameter is the viscosity coefficient 1 to reduce the surface tension, and the reduction and reduction of the equilibrium between the zero and the zero, respectively, from the next two equations will increase the value of 0, which will lead to the decrease of the sum value, and the value of the formula from the 34 Increasing and decreasing the value will increase the sum value, that is, increase the glass forming ability of the alloy, which is due to the thermodynamic explanation.
3 Bulk Amorphous Performance Characteristics and Applications Bulk amorphous alloys have distinctly different mechanical properties from conventional crystalline alloys. These have been confirmed in Mg-based La-based Pd-based Zr-value Ti-based and Fe-based alloys. Crystalline alloys have higher tensile strength and lower Young's modulus than conventional crystalline alloys. 71. For example, in Alloy 25, the tensile strength is as high as 1 850, and the Young's modulus is 90,18. In addition, amorphous alloys also have an advantage in terms of properties such as yield strength fatigue strength.
It has been proved that 2! The base bulk amorphous alloy is an alloy having a combination of various high mechanical properties. It also has high tensile strength, high yield strength, high fracture toughness, high fracture energy, high fatigue strength, good casting performance, and good cutting performance. Processing performance and high corrosion resistance
The other property characteristic of bulk amorphous is its superplasticity, which has a high deformability in the supercooled liquid region. The existence of Newtonian flow in the supercooled liquid region has been confirmed in experiments of 21-base amorphous alloys, ie, there is an ideal superplasticity. Thus, the elongation of some bulk amorphous alloys can reach 4612.
Amorphous alloys have very good soft magnetic properties. Because there are no grains in the amorphous alloy, there is no magnetic anisotropy. Compared with crystalline alloys, amorphous alloys have high magnetization and high magnetic permeability and low magnetic losses. In recent years, bulk amorphous alloys with good hard magnetic properties have also been discovered, in addition to the above-mentioned properties. In addition, amorphous alloys have several other excellent properties. Therefore, amorphous alloys have a very wide range of applications. They can be used as mechanical materials, structural materials, magnetic materials, optical materials, acoustic materials, electronic materials, sports materials, etc. In addition, 1 and 2 Ding Yifan bulk amorphous alloys such as Chen Weirong and other bulk amorphous alloys have been used in the production of golf clubs.
Because of the excellent mechanical, physical and chemical properties of amorphous alloys, its application prospects are very broad. However, the composition of amorphous alloys is very complicated, which limits the introduction of new materials. Therefore, it has been found that the formation of large amorphous alloys can be formed more easily. Large-sized amorphous alloys and alloy components are goals for the future.
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