The basic oxygen furnace used in the production of steel was just illustrated. Is this the process by which all metals and alloys are created? Not necessarily. This page will discuss some alternative materials processes.
Before we discuss alternative processes to the melt-and-pour approach, let us consider a method of melting which does not involve a container to hold the liquid metal. Why is this an issue? Because many defects are introduced into metals and alloys by various interactions between the molten mass and the crucible used to contain it. For example, part of the crucible could break off and become included in the the final product. Such particles are called inclusion particles and can greatly affect the mechanical integrity of a manufactured part. Also, the crucible material may actually interact with the molten metal. For example, liquid aluminum can interact with a steel crucible to make iron-aluminide(s), unique chemical compounds. Additionally, when the liquid metal solidifies, the process of solidification begins at the crucible wall. The properties of the final casting are considerable influenced by this occurrence. It would be highly desirable to melt and solidify metals and alloys without interaction with a crucible.
The image below shows a sample of molten aluminum (the glowing sphere) levitated in an RF (Radio-Frequency) coil. Water-cooled copper tubing carries the RF induction power to the specimen. The crucible here can be vacuum or an inert gas. Research in levitation melting have been conducted on planet Earth at the Institute for Materials Research, at the University of Leeds . . For more information on this technique, visit the Ameritherm web pages. NASA has conducted much research on making metals and alloys in the vacuum of space where one can not only take advantage of RF (or laser) heating: but one can eliminate the influence of gravity and atmosphere in the solidification process. For information about micro-gravity materials research, link to the following pages.
The traditional process for making metallic components begins with melting of the metal or alloy. If the molten mass is poured into a mold of some type and solidified, the process is called casting. But metals and alloys do not have to begin their service to society through the casting process. Let us consider some alternatives.
Below are parts made from metal powders by a company in Korea called the Daedong Brake Manufacturing Co [unfortunately, no longer on the Internet]. That is right: these parts are produced from small powder particles, packed in a can (or placed in a die), then heated and pressurized below the melting temperature of the metal until consolidation of the powder particles occurs. The consolidation process is called 'sintering'. The finished pieces are more or less fully dense as would be a cast metal part. The same situation can occur if one starts with metal "pastes" in the metal injection molding process (MIM). A basic overview of the powder metallurgy process is offered in the EPMA [European Powder Metallurgy Association] web pages.
Are you curious as to what the compacted powders look like before sintering? Here is a SEM (Scanning Electron Microscope) image of them taken from the pages of Remington Arms, Inc. The following two links will provide you another view of the powder metallurgy and metal injection molding processes.
Sometimes, it is desireable to deposit only a very thin metal film to achieve some end. For example, one may want to deposit a thin aluminum film on glass to make a mirror; or a thin gold film on a bathroom faucet to impress guests; or thin-metal lines on an integrated circuit to connect different electrical regions. Casting or powder metallurgy processes cannot be used for this purpose.
One process to deposit thin material films is
Here PVD Team member, Jennifer Roper, prepares an ion-beam sputtering chamber for thin-film deposition. Ions are created and caused to impinge on a target material, thus sputtering-off atoms present in the target. These atoms find their way to a substrate and coat it. The coating material may provide better wear or corrosion resistance: or protection during high temperature exposure. Sputtering (ie, physical vapor deposition) is a powerful tool to create and modify material products useful to society, is it not? You are encouraged to look over the web pages for the Materials Science and Technology Division at LANL to get a good idea of a leading-edge academic or National laboratory where materials research might be done.
Would it not be interesting to know how many of these people consider themselves to be materials scientists? Or, are they physicists? Or, do they consider themselves to be polymers scientists? Too, it would be interesting to know how many of these individuals have had advanced materials education (ie, M.S. or PhD in Materials Science and Engineering). In other words, how do you get there from here? For more about this issue, click on "opportunities" on any of the World of Materials pages.
Molecular Beam Epitaxy (MBE) is used to grow materials one atomic layer at a time. Mixing and alternating various kinds of atoms can result in new materials with exotic and useful properties. The system you see below is used by the the Imperial College of London for growing atomic-layers to be used in the fabrication of GaAs based integrated circuits, for example; but, it can be used to grow metallic films as well. Metallic films for use in magnetic recording is one application of the MBE technique for thin-film deposition. For further information about this surface deposition technique, visit the Laboratory for Surface Science and Technology at the University of Maine.
This has been an overview of a few processing methods available to the materials scientist and engineer to create new and unique materials. Each year, these methods are further improved and new ones evolve. You too can participate. Materials processing is an excellent career opportunity which will always be in demand.
Opportunities
Metals and Alloys
Ceramics
Polymers
Composites
Semiconductors
Biomaterials
Materials Characterization
Concept of Structure
Failure Analysis
Return to the Chemical and Materials Engineering Department Home Page at San Jose State University.