Metal glass

Introduction

For scientists, glass is any material that can cool into a solid from the liquid without crystallization. Most metallic cooling is crystallized, and atoms are arranged in a regular form called lattice. If crystalline is not crystallized and atoms still arrange irregularities, a metal glass is formed. Unlike glass plates, metal glass is opaque or unflavored, and their rare atomic structure has special mechanical properties and magnetic properties. Ordinary metals are easily deformable due to their lattice defects, resulting in permanent deactivation. In contrast, the metal glass is easier to play back to its initial shape after deformation. The lack of crystallization defects make the metal glass of the original iron water into an effective magnetic material.

Metal glass is a new material invented in 1960, and has been studied by scientists in various countries for many years. This material exhibits very unique mechanical and physical properties compared to the corresponding crystalline alloys, making it broad application prospects in multiple fields. At the same time, metal glass is a relatively simple representative system in structural disorder materials, and is a more desirable material model for studying amorphous physics. Solve basic scientific issues in metal glass, such as its structural characterization, deformation mechanism, glass transformation, glass forming ability, etc., not only can promote the application of metal glass itself, but will also promote the development of the entire coagular physics.

Development brief history

The emergence of metal glass can be traced back to the 1930s, Kramer's first report uses a vapor deposition method to prepare metal glass in 1950, metallurgist Learn to remove crystals by mixing a certain amount of metal-such as nickel and zirconia, Klement and Duwez et al., The US California Institute of Technology have prepared metal glass by quenching techniques. When the thin layer of the alloy is cooled at a rate of one hundred degrees of cascade per second, they form a metal glass. However, because the requirements are quickly cooled, they can only be made into thin strips, wires or powders.

Recently, scientists form a variety of metal glass such as strips by mixing four to five elements of different sizes atoms. The change atom size makes it mixed to form a glass, which is more tough. One of these new alloys is in commercial use to make a head of a golf bar.

ingredients

Most of the metal crystallizes when cooling, and the atoms are arranged as a regular pattern called lattice. However, if the crystal does not appear, the atom will randomly arrange the metal glass.

The atom of ordinary glass is also randomly arranged, but it is not a metal. Metal glass is not transparent, it has unique mechanical and magnetic traits, not easy to break and not deform. It is an ideal material for manufacturing transformers, golf bats and other products.

The metal glass currently produced is thinner and finer because the metal cools will be crystallized, so it takes very fast frozen. He Nacho, a researcher at the University of Johnsti, USA, is working on how to produce super powerful, elasticity and magnetic traits, but a large metal glass. This new metal will keep the solid without crystallization at high temperatures, which will be suitable for manufacturing engine parts and military weapons.

It is a good magnetic substance with iron, and since it becomes soft after heating, it is easy to cast a finished product of different shapes.

Figure "Metal Glass Scientist" see He Nago uses the induction furnace, and quickly dissolves the metal mixture and becomes a metal glass.

Production Process

With the support of the State Science Foundation and the US Army Research Administration, Hufnagel has established a laboratory of testing new alloys. He attempted to create a metal glass that would remain in a high temperature and not crystallized, so that it can be a material useful in engine parts. This material can also be used in military situations such as armor. It is not like most crystalline metal shells, which becomes a mushroom shape after the impact, Hufnagel believes; each side of the metal glass warhead will turn and give the best penetrating score.

Metal glass manufactured, bulky shape is difficult, because most metals suddenly appear crystalline during cooling, manufacturing glass, metal must be hard, because the lattice formation will change, From pure metal - such as copper, nickel to create glass, it will cool at a rate of one trillion degrees Celsius per second.

Deformation

conventional crystal material, its atom is periodically arranged in a lattice, while the lattice is defective, such as dislocation, layer error, etc. The energy required for these defective movements is relatively low, making the macroscopic deformation of the crystals easily realized. So what is its plastic deformation mechanism for a metal glass without a lattice structure?

macro view, the deformation characteristics of metal glass have close relationships with temperature. When the temperature is close to the glass transition point and even higher, the material is partially participated in the deformation, and is manifested as a homogeneous flow, referred to as uniform deformation. When the temperature is much lower than the glass transition point, the metal glass is often manifested as non-uniform deformed, and the deformed area is only concentrated in a small area, which is a scaner of 10 to 50 nm, which is referred to as a shear belt. Since the glass transition temperature of general metal glass is much higher than room temperature, the deformation localization is the main feature of the metallic glass deformation at room temperature, and has been widely concerned. The highly localized deformation occurs only in the shear belt, and the shear belt will be quickly expanded under the condition that there is no constraint, eventually leading to the brittle fracture of the material. This is the reason why there is no macroscopic plastic in the room temperature, and this problem is to promote the key ring of metal glass applications, and many researchers have made a hard effort in this direction. In order to increase plastics, some people use methods for preparing composites, and some people use the introduction of residual stress or other processing methods. In 2007, Liu Yanhui, the Physics Research Institute of the Chinese Academy of Sciences, reported on "Science", developing a metal glass with oversized compressed plastic properties at room temperature, and can be bent as pure copper, pure aluminum is bent into a certain shape, thereby further leading a large number of related related Research work. However, the problem of metal glass room temperature macro-plasticity is not solved, especially those expected stretch plasticity, and the academic community look forward to new progress.

From a micro-view, the deformation involves local atomic rearrangement of the material. From this perspective to study the origin of the deformation, there are currently two mainstream theoretical models, namely the "free volume" model and "shear transition zone" model. The free volume model was originally proposed by Cohen and Turnbull, which was used to explain the glass transition, and later was used by spaepen to understand the deformation of the glass. This model believes that the deformation of the metal glass is achieved by the transition movement of a single atom, and each atom has a certain proportion of free volume in any position, with a wide range of free volume, the atomic transition movement is easy to implement; with a small amount of free volume Where the atomic transition movement is not easy to achieve. In the absence of external force, the atom is equal to the chance of jump in each direction, and atoms tend to transition to a certain direction, thereby causing a deformation in the stress direction. However, since the free volume itself is a blurred concept, it is difficult to imagine a single atom's transition to comply with the stress given by the outside, so the basis of the free volume model is very unresolved. However, it provides a very intuitive concept to understand, and it is very simple, so workers in the glass are very widely affected. The shear transition zone model is a more classic and well-known model, which is developed from the ratio of Argon et al. They believe that the deformation of the metal glass is not caused by the transition of a single atom, but causes the shear movement of the matrix relative to the shear movement of several atoms. The atomic cluster of this shear movement occurs. The "shear transition zone" is called "shear transition zone", and the accumulation of local plastic deformation generated by the shear transition zone ultimately leads to macroscopic deformation. Based on the above model, many deformation phenomenon of metal glass can be explained, such as localization of shear belts at low temperatures, uniform flow rates at high temperatures, and the like. However, since the shear transition model is used as a single event as a single event, that is to say that this processing method ignores the interaction between the basic units of different deformation, there is also some experimental phenomenon that it cannot be explained, such as stress The sawtooth wave phenomenon on the strain curve. Recent research work has analyzed detailed analysis of this zigzag wave behavior, and found that the shear driving force of brittle metal glass has characteristics of chaotic behavior, and the tough metal glass can evolve into self-organized critical state. These results indicate that amorphous alloys are more complicated in the process of deformation, and their shear belt movement is complicated, and the interaction between multiple shear belts is required and synergistic.