Introduction to Materials Science and Engineering Cloud Gate, Millenium Park, Downtown, Chicago, Illinois, USA

Historical Perspective The most important aspect of materials is that they are ENABLING. Simply put, materials make things happen. Historically, the development and advancement of societies have been intimately tied to the ability of people to produce and manipulate materials to fill human needs.

Historical Perspective Early civilizations have been designated by the level of their materials development: –Stone Age –Bronze Age –Iron Age In today’s face-paced world, the discovery of silicon single crystals and understanding of their properties have enabled the Information Age.

Materials Science It involves the investigation of the relationships between the structures of materials and their properties.

Materials Engineering It involves designing the structure of a material to produce a predetermined set of properties, using the structure- property correlations derived from materials science.

Materials Science & Engineering From a functional perspective, the role of a material scientist is to develop or synthesize new materials, whereas a materials engineer is called upon to create new products or systems using existing materials, and/or to develop techniques for processing materials. For brevity, we will refer to Materials Science & Engineering as MSE.

A Unified Definition of MSE Materials Science and Engineering (MSE) is an interdisciplinary field of science and engineering that studies and manipulates the composition and structure of materials across length scales to control material properties through synthesis and processing.

Some More Definitions Composition –the chemical make-up of a material Structure –a description of the arrangement of atoms, as seen at different levels of detail

Some More Definitions Synthesis –refers to how materials are made from naturally occurring or man-made chemicals Processing –how materials are shaped into useful components to cause changes in the properties of different materials.

Principal Goals of MSE 1.To make existing materials better 2.To invent or discover new phenomena, materials, devices, and applications

Applications of MSE Breakthroughs in the field of MSE are applied to many other fields of study, such as –Biomedical engineering –Physics –Chemistry –Environmental engineering –Information technology

The MSE Tetrahedron The heart and soul of materials science and engineering is represented by the tetrahedron.

Application of the tetrahedron of MSE to sheet steels for automotive chassis

The Four Components of MSE With regard to the design, production, and utilization of materials, there are four elements to consider: –processing, structure, properties, and performance The performance of a material depends on its properties, which in turn are a function of its structure; furthermore, structure is determined by how the material was processed.

The Four Components of MSE Processing Structure Properties Performance

Structure The structure of a material usually relates to the arrangement of its internal components. In terms of increasing dimensionality, structural elements include: –Subatomic –Atomic –Microscopic –Macroscopic

Structure Subatomic structure involves electrons within the individual atoms and their interaction with the nuclei Atomic structure encompasses the organization of atoms or molecules relative to one another. Microscopic structure refers to large groups of atoms that normally agglomerate and is subject to direct observation using some type of microscope. Macroscopic structure refers to structural elements that can be viewed with the naked eye.

Property While in service, all materials exposed to external stimuli evoke some type of response. A property is a material trait in terms of the kind and magnitude of response to a specific imposed stimulus. –For example, a specimen subjected to forces will experience deformation. –A polished metal surface will reflect light.

Material Properties Mechanical Electrical Thermal Magnetic Optical Deteriorative

Mechanical Properties These properties relate the deformation of a material to an applied load or force. –Examples: elastic modulus (stiffness), strength, toughness

Electrical Properties These properties relate the response of a material to an electric field. –Examples: electrical conductivity, dielectric constant

Thermal Properties These properties relate the response of a material to changes in temperature. –Examples: heat capacity, thermal conductivity

Magnetic Properties These properties relate the response of a material to the application of a magnetic field.

Optical Properties These properties relate the response of a material to electromagnetic (light) radiation. –Examples: index of refraction, reflectivity

Deteriorative Properties These properties refer to the chemical reactivity of materials.

Classification of Materials There are different ways of classifying materials, such as –By traditional “groups” of materials –By function –By structure

Representative Strengths of Various Categories of Materials

Bar chart of room temperature density values for various materials

Bar chart of room temperature stiffness (i.e., elastic modulus) values for various materials

Bar chart of room temperature tensile strength values for various materials

Bar chart of room temperature resistance to fracture (i.e., fracture toughness) values for various materials

Bar chart of room temperature electrical conductivity ranges for various materials

Classification of Materials Based on Structure Crystalline –The material’s atoms are arranged in a periodic fashion. –Crystalline materials exist in the form of “single” crystals, or as polycrystalline materials Amorphous –The arrangement of the material’s atoms does not have long-range order.

Classification of Materials Based primarily on chemical makeup and atomic structure, materials can be classified as –Metals and Alloys –Ceramics –Polymers –Composites –“Advanced” Materials

Metals and Alloys Materials in this group are composed of one or more metallic elements (Fe, Al, Cu, Ti, Au, Ni, etc.) and often also non-metallic elements (C, N, O) in relatively small amounts. Atoms in metals and their alloys are arranged in a very orderly manner.

Metals and Alloys This group includes steels, aluminum, magnesium, zinc, cast iron, titanium, copper, and nickel. An alloy is a metal that contains additions of one or more metal or non-metal.

Metals and Alloys These materials are relatively stiff and strong, yet ductile (“formable”) and are resistant to fracture. –This accounts for their widespread use in structural and load-bearing applications.

Metals and Alloys Metals are extremely good conductors of electricity and heat. They are not transparent to visible light. Polished metal surface has a lustrous appearance. Some metals (i.e., Fe, Co, Ni) possess magnetic properties.

Metals and Alloys Although pure metals are occasionally used, alloys provide improvement in a particular desirable property or permit better combinations of properties.

Metals and Alloys Familiar objects made of metals and metal alloys (from left to right): silverware (fork and knife), scissors, coins, a gear, a wedding ring, and a nut and bolt.

Ceramics Ceramics can be defined as inorganic crystalline materials. Beach sand and rocks are examples of naturally occurring ceramics. Advanced ceramics are materials made by refining naturally occurring ceramics and other special processes.

Ceramics Ceramics are compounds between metallic and nonmetallic elements. They are most frequently oxides, nitrides, and carbides.

Ceramics Common ceramic materials include Aluminum oxide (or alumina, Al 2 O 3 ) Silicon dioxide (or silica, SiO 2 ) Silicon carbide (SiC) Silicon nitride (Si 3 N 4 ) Porcelain Cement Glass

Ceramics Ceramic materials are relatively stiff and strong in compression –Stiffness and compressive strength are comparable to those of metals. These materials are also typically hard. Traditional ceramics exhibit extreme brittleness (lack of ductility) and are highly susceptible to fracture.

Ceramics Ceramics are typically insulative to the passage of heat and electricity. They are more resistant to high temperatures and harsh environments than metals and polymers. Some ceramics (e.g., Fe 3 O 4 ) exhibit magnetic behavior.

Ceramics They can be transparent, translucent, or opaque.

Ceramics Three thin disk specimens of aluminum oxide that have been placed over a printed page in order to demonstrate their differences in light-transmittance characteristics. Left: transparent; Center: translucent; Right: opaque.

Ceramics Common objects made of ceramic materials: scissors, a china teacup, a building brick, a floor tile, and a glass vase.

Polymers Polymers include the familiar plastic and rubber materials. Many of them are organic compounds that are chemically based on carbon, hydrogen and other non-metallic elements (i.e., O, N, and Si). They have very large molecular structures, often chainlike in nature, that often have a backbone of carbon atoms.

Polymers Some of the common and familiar polymers are –Polyethylene (PE) –Nylon –Polyvinyl chloride (PVC) –Polycarbonate (PC) –Polystyrene (PS) –Silicone rubber –Polyether ether ketone (PEEK)

Polymers They typically have low densities (i.e., lightweight). Many are extremely ductile and pliable, which means they are easily formed into complex shapes. They are mostly chemically inert and unreactive in a large number of environments.

Polymers One major drawback to the polymers is their tendency to soften and/or decompose at modest temperatures, thus limiting their use in some instances. Furthermore, they have low electrical conductivities and are non-magnetic.

Polymers Several common objects made of polymeric materials: plastic tableware (spoon, fork, and knife), billiard balls, a bicycle helmet, two dice, a lawn mower wheel (plastic hub and rubber tire), and a plastic milk carton.

Coke in Glass, Plastic and Metal Containers

Composites A composite is composed of two or more individual materials belonging to either the metals, ceramics, or polymers category. The design goal of a composite is to achieve a combination of properties that is not displayed by any single material, and also to incorporate the best characteristics of each of the component materials.

Composites One of the most common and familiar composites is fiberglass, in which glass fibers are embedded within a polymeric material (normally an epoxy or polyester). –The glass fibers are relatively strong and stiff (but also brittle), whereas the polymer is more flexible. –Thus, fiberglass is relatively stiff, strong, and flexible. In addition, it has a low density.

Composites Fiberglass

Composites Another important composite is the carbon fiber reinforced polymer (CFRP). –Carbon fibers are embedded within a polymer. –These materials are stiffer and stronger than fiberglass, but more expensive. –They are used in some aircraft and aerospace applications, in sporting equipment (e.g., bikes, golf clubs, rackets, etc.), and in automobile bumpers.

Composites Carbon Fiber Reinforced Polymer (CFRP).

Composites

Advanced Materials Advanced materials are used in high-tech applications, such as –electronic equipment (camcorders, DVD players, etc) –computers –fiber-optic systems –spacecraft and aircraft –military rocketry –lasers

Advanced Materials Semiconductors Biomaterials Smart materials Nanomaterials

Semiconductors Electrical conductivities intermediate between conductors (metals) and insulators (ceramics, polymers). The electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms.

Semiconductors

Biomaterials These are employed in components implanted into the human body to replace diseased or damaged body parts. They must not produce toxic substances and must be compatible with body tissues (i.e., must not cause adverse biological reactions).

Biomaterials BIOMATERIAL FOR ARTERY AND KNEE CARTILAGE REPLACEMENT

Smart Materials Smart materials are a group of new and state-of-the-art materials now being developed. They sense and respond to changes in their environments in predetermined manners – traits that are also found in living organisms.

Smart Materials Components of a smart material include some type of sensor (that detects an input signal) and an actuator (that performs a responsive and adaptive function). –Actuators may be called upon to change shape, position, natural frequency, or mechanical characteristics in response to changes in temperature, electric fields, and/or magnetic fields.

Smart Materials

Nanomaterials Nanomaterials may be any one of the four basic types of materials – metals, ceramics, polymers, and composites. Nanomaterials are distinguished by their size: the dimensions of these structural entities are on the order of nanometers; as a rule, less than 100 nanometers (i.e., atomic and molecular level).

Nanomaterials Prior to the advent of nanomaterials, the general procedure scientists use to understand the chemistry and physics of materials was to begin by studying large and complex structures, and then to investigate the fundamental building blocks of these structures that are smaller and simpler. –This approach is sometimes termed “top- down” science.

Nanomaterials With the development of scanning probe microscopes, which permit observation of individual atoms and molecules, it has become possible to design and build new structures from their atomic level constituents, one atom or molecule at a time. –This ability to carefully arrange atoms provides opportunities to develop material properties that are not otherwise possible. –We call this the “bottom-up” approach.

Nanomaterials Some of the physical and chemical characteristics exhibited by matter may experience dramatic changes as particle size approaches atomic dimensions. For example: –materials that are opaque in the macroscopic domain may become transparent on the nanoscale –some solids become liquids –chemically stable materials become combustible –electrical insulators become conductors

Nanomaterials (continued) Some of the physical and chemical characteristics exhibited by matter may experience dramatic changes as particle size approaches atomic dimensions. –Properties may depend on size in the nanoscale domain. –Some of these effects are quantum mechanical in origin; others related to surface phenomena.

Nanomaterials Whenever a new material is developed, its potential for harmful and toxicological interactions with humans and animals must be considered. Small nanoparticles have exceedingly large surface area to volume ratios, which can lead to high chemical reactivities.

Nanomaterials Although the safety of nanomaterials is relatively unexplored, there are concerns that they may be absorbed into the body through the skin, lungs, and digestive tract at relatively high rates, and that some, if present in sufficient concentrations, will pose health risks – such as damage to DNA or promotion of lung cancer.

Nanomaterials

Materials Selection Criteria When selecting materials for engineering applications, we consider the following criteria or factors: –In-service conditions to which the material will be subjected to –Any deterioration of material properties during operation –Economics or cost of the fabricated piece

Challenges for the Future Technological challenges remain, such as –the development of even more sophisticated and specialized materials, and –Consideration of the environmental impact of materials production. Nuclear energy –Safety issues like containment structures –Facilities for disposal of radioactive waste

Challenges for the Future Transportation challenges –reducing the weight of transportation vehicles (cars, aircraft, trains, etc) –Increasing engine operating temperatures to enhance fuel efficiency –New high-strength, low-density structural materials remain to be developed, as well as materials that have higher-temperature capabilities for use in engine components.

Challenges for the Future Economic challenges –There’s a need to find new, economical sources of energy and to use present resources more efficiently For example, direct conversion of solar power into electrical energy has been demonstrated. However, solar cells employ complex and expensive materials. To ensure a viable technology, materials that are highly efficient in this conversion process yet less costly must be developed.

Challenges for the Future Hydrogen Power –The hydrogen fuel cell is another very attractive and feasible energy-conversion technology that has the advantage of being nonpolluting. –It is just beginning to be implemented in batteries for electronic devices and holds promise as a powering agent for automobiles. –New materials need to be developed for more efficient fuel cells and also for better catalysts to be used in the production of hydrogen.

Challenges for the Future

Environmental Quality –This depends on our ability to control air and water pollution. –Pollution control techniques employ various materials. –In addition, materials processing and refinement methods need to be improved so that they produce less environmental degradation—that is, less pollution and less despoilage of the landscape from the mining of raw materials.

Challenges for the Future Environmental Quality –Also, in some materials manufacturing processes, toxic substances are produced, and the ecological impact of their disposal must be considered.

Challenges for the Future Non-renewable resources –Many materials that we use are derived from non-renewable resources, such as polymers, for which the prime raw material is oil, and some metals.

Challenges for the Future Non-renewable resources are gradually becoming depleted, necessitating –the discovery of additional reserves –the development of new materials having comparable properties with less adverse environmental impact –increased recycling efforts and the development of new recycling technologies.

Challenges for the Future As a consequence of the economics of not only production but also environmental impact and ecological factors, it is becoming increasingly important to consider the “cradle-to-grave” life cycle of materials relative to the overall manufacturing process.

Schematic representation of the total materials cycle.

Schematic representation of an input/output inventory for the life-cycle assessment of a product

Challenges for the Future It has been estimated that worldwide, about 15 billion tons of raw materials are extracted from the Earth every year; some of these are renewable and some are not. Over time, it is becoming more apparent that the Earth is virtually a closed system relative to its constituent materials and that its resources are finite. In addition, as societies mature and populations increase, the available resources become scarcer, and greater attention must be paid to more effective use of these resources relative to the materials cycle.