Alloy Materials and Their Allied Applications provides an in-depth overview of alloy materials and applications. The 11 chapters focus on the fabrication methods and design of corrosion-resistant, magnetic, biodegradable, and shape memory alloys. The industrial applications in the allied areas, such as biomedical, dental implants, abrasive finishing, surface treatments, photocatalysis, water treatment, and batteries, are discussed in detail. This book will help readers solve fundamental and applied problems faced in the field of allied alloys applications.
Inamuddin, PhD, is an assistant professor at King Abdulaziz University, Jeddah, Saudi Arabia and is also an assistant professor in the Department of Applied Chemistry, Aligarh Muslim University, Aligarh, India. He has extensive research experience in multidisciplinary fields of analytical chemistry, materials chemistry, electrochemistry, renewable energy and environmental science. He has published about 150 research articles in various international scientific journals, 18 book chapters, and 60 edited books with multiple well-known publishers.
Rajender Boddula, PdD, is currently working for the Chinese Academy of Sciences President's International Fellowship Initiative (CAS-PIFI) at the National Center for Nanoscience and Technology (NCNST, Beijing). His academic honors include multiple fellowships and scholarships, and he has published many scientific articles in international peer-reviewed journals, edited books with numerous publishers and has authored twenty book chapters.
Mohd Imran Ahamed received his Ph.D on the topic "Synthesis and characterization of inorganic-organic composite heavy metals selective cation-exchangers and their analytical applications", from Aligarh Muslim University, India in 2019. He has published several research and review articles in SCI journals. His research focusses on ion-exchange chromatography, wastewater treatment and analysis, actuators and electrospinning.
Abdullah M. Asiri is the Head of the Chemistry Department at King Abdulaziz University and the founder and Director of the Center of Excellence for Advanced Materials Research (CEAMR). He is the Editor-in-Chief of the King Abdulaziz University Journal of Science. He has received numerous awards, including the first prize for distinction in science from the Saudi Chemical Society in 2012. He holds multiple patents, has authored ten books and more than one thousand publications in international journals.
Fabrication Methods for Bulk Amorphous Alloys
Institute of Physics, Faculty of Production Engineering and Materials Technology, Czestochowa University of Technology, Czestochowa, Poland
Amorphous alloys are one of the newer groups of functional materials that are widely used in many industries. Their properties are much better than materials with the same chemical composition and crystal structure. Amorphous alloys are produced by rapid cooling techniques. The most popular methods are: melt-spinning method, injection method, suction method, centrifugal method. Using these methods, products of various shapes can be produced. There are two groups of amorphous materials: conventional in the form of a thin tape and bulk amorphous materials with a thickness of more than 100 µm and various shapes, e.g. rods, tubes, plates, etc. The era of bulk amorphous material began when A. Inoue of Tohoku University in Japan developed three criteria. These criteria make it possible to systematically manufacture massive amorphous materials. Of course, there are many restrictions on their production, but the date 1989 is the date of birth of a new group of materials, i.e. bulk amorphous alloys. Material engineers need such materials and their development is continuous, as evidenced by numerous scientific publications in this field. It should be assumed that the growing demands on modern materials will promote the development of this group of materials.
Keywords: Bulk amorphous materials, injection casing, suction casting, application of amorphous materials
1.1 Production Methods of Amorphous Materials
1.1.1 Initial Preparation for the Production of Amorphous Materials
Initial preparation of the specific chemical composition of the alloying components-prior to the main melting process-is a fundamental operation in the production process of amorphous materials. The results of many years of the Author's own research corroborate the fact that the initial ingot preparation, or even the material used to make the ingots in the first place, defines the quality of the amorphous materials. The most important criterion for success is to determine the correct weights of the alloying elements for the ingot. For example, in the case of rare-earth metal elements, the redundant mass of these elements has to be taken into account. The weight of the other alloying elements should be determined to an accuracy of ±0,001 g. For the initial ingot preparation, high-purity elements should be used, as this gives a higher probability that the resultant alloy will have an amorphous structure. However, this increases the production cost of this type of material. Therefore, alloying elements with a purity of 99.99% are used only for the first test samples.
Generally, two alternative methods are utilized for the production of the ingots: using an induction furnace (Figure 1.1) or by arc-melting (Figure 1.2). The production process of a polycrystalline ingot, using an induction furnace, is a very long and labor-intensive process. The alloying components are usually placed in quartz capsules and re-melted several times using the induction (eddy-current) heating process. Each subsequent re-melting of the components results in improved homogeneity of the final ingot. However, this method struggles when it comes to some of the "hard to melt" metals. The presence of non-melted alloying components can be observed by various microscopy methods. In the case of the second ingot production method, using a plasma arc, a much higher degree of mixing of the elements in the alloy can be obtained, than by using the induction method. The temperature of the electric arc depends on the current and can reach up to several thousand Kelvin. The ingot material is melted on one side; then, after allowing a few seconds for solidification to occur, it is turned over using a manipulator and melted again. The production of the ingot, using the arc-melting method, is a single-step process-which reduces the cost and time of the production process, in comparison to the induction method.
Figure 1.1 Schematic view of the induction method for the production of crystalline ingots.
Figure 1.2 Schematic views of the arc-melting method for the production of crystalline ingots: (a) side view, (b) plan view.
Figure 1.3 The surface of a crystalline ingot-arc-melting method: (a) after cleaning and (b) before cleaning.
The initial preparation of ingots that are made from metallic materials is carried out in a vacuum, or under the protective atmosphere of a neutral gas (usually argon). This measure prevents the creation of oxides on the metal surfaces-heterogeneous "embryos", which could become centers for crystallization, later in the production process.
The manufactured ingots are cleaned by abrasion and by an ultrasonic cleaner (Figure 1.3).
1.1.2 The Single-Wheel Melt-Spinning Method
The unidirectional cooling of liquid alloy at high speed on a rotating copper cylinder was one of the first methods used for the production of solid, metallic amorphous materials in the form of tapes (ribbons) [1, 2]. By the 1970s, this method had been used on an industrial scale for the production of materials for the electrical and electronic industries by the companies Metglas and Vacuumschmelze [3, 4]. The production process involves forcing the liquid alloy through an opening of small diameter, situated in the lower part of the melting crucible, onto a copper cylinder which is rotating at high speed (Figure 1.4).
On contact with the surface of the cylinder, the liquid alloy is cooled rapidly and solidifies at a rate of up to 106 K/s. Therefore, this method is often referred to as ultrafast (rapid) quenching. It has been concluded that the rate of cooling of the liquid alloy is determined by the linear velocity at the surface of the copper cylinder (Figure 1.5) [5, 6].
The pressure of the liquid alloy in the melting crucible is of lower importance. The shape (form) of the amorphous materials, obtained using this method, was in most cases ribbons of approximate dimensions: width = 3-5 mm and thickness = 35-60 µm (Figure 1.6).
Figure 1.4 Schematic diagram of the continuous casting process for amorphous ribbons-high speed of quenching on the rotating, copper cylinder (side view).
Figure 1.5 Relationship between the rotational speed of the cylinder with over pressure .
Figure 1.6 Amorphous ribbons [8-10].
This method allows the production of samples with thicknesses of greater than 100 µm, which, by definition, could be classified as bulk amorphous alloys. However, the samples are produced in the form of flakes, and require detailed segregation, as over 70% fail to achieve an amorphous structure. Therefore, this method is not satisfactory for the production of bulk amorphous alloys.
Amorphous and nanocrystalline ribbons are used as materials for transformer cores with higher efficiencies when compared with ribbons made from transformer steel . In Poland, since the 1970s, several scientific institutions have carried out research into the properties of amorphous and nanocrystalline ribbons (e.g., Finemet, Metglas, Nanoperm, and Hitperm), and also into the influence of thermal treatment on their microstructure and properties [11-16]. The specific thermal treatment of the amorphous ribbons allows their nanocrystallization. Usually, annealing of the material is performed at a certain temperature, and over a certain time, in the vacuum resistance furnace. The nanocrystalline ribbons could also be made directly, using a melt-spinning method. The advantages of amorphous ribbons, exhibiting soft magnetic properties, are very low magnetic hysteresis losses and near-zero magnetostriction. The lower hysteresis losses mean lower applied-energy costs, and the almost zero magnetostriction is an ecological factor which reduces the noise ("hum"), which accompanies transformers based on FeSi steel. Currently, amorphous ribbons are used, for example, in the reinforcement of the foundations of skyscrapers exposed to seismic stresses, and for multilayer tank armour. Ribbons of small width (narrow) are obtained by using melting crucibles with small single holes (Figure 1.7a).
Developments in electronic equipment, and enhanced requirements from Industry, have been major drivers in the increased interest in amorphous materials-in particular, wider and thicker amorphous ribbons. This has resulted in modifications to the original melt-spinning method, and a technique allowing the production of amorphous ribbons of width up to a few centimeters has been developed (Figure 1.6 and 1.7b); several parallel nozzles apply the liquid alloy to the surface of the rotating copper cylinder. The "sprayed" metallic liquid meets the cylinder near its surface on a so-called "air bag" and, as a result, is solidified in the form of a wide ribbon. The thickness of the ribbon depends on its chemical composition. Unfortunately, even when using alloys with very good glass-forming ability, this method is not suitable for the production of bulk amorphous alloys.