AEM 338 Engineered Materials Testing Introduction to Materials Technology Sergio Sgro Eastern Kentucky University

INT 238 Lecture Objectives State reasons for studying materials List and describe common terms related to the study of materials Describe and define terms and conditions associated with atomic structure and atomic theory Recognize and describe how the periodic table of elements is used and the structure of the table List and describe how the various bonding forces act to hold atoms together Define the various structures of materials in crystal lattice formation Describe the solidification process List and recognize various organizations and their purposes.

Eastern Kentucky University INT Introduction Materials Technology  Specifications, properties, selection, and testing of engineering materials Engineering Materials  Primarily used in construction of various structures, machines, etc.

Eastern Kentucky University INT Atomic theory Why study engineering materials  To understand the characteristics of materials and their structures Categories (ways to classify)  Chemical composition  Material’s natural state  Manufacturing/refining to bring to useful state  Atomic structure

Eastern Kentucky University INT Atomic theory Classification into one of the following:  Elements  Compounds  mixtures

Eastern Kentucky University INT Atomic theory By studying elements, scientists discovered  Repetitive patterns  Allowed them to predict nature and properties of elements not discovered until much later

Eastern Kentucky University INT Atomic Theory

Eastern Kentucky University INT Atomic theory An atom consists of

Eastern Kentucky University INT Atomic theory The number of PROTONS in the nucleus determines what element the atom represents

Eastern Kentucky University INT Atomic theory Atoms are held together in molecules by various types of bonds 1. Primary bonds - generally associated with formation of molecules 2. Secondary bonds - generally associated with attraction between molecules Primary bonds are much stronger than secondary bonds

Eastern Kentucky University INT Atomic theory PRIMARY BONDS Characterized by strong atom ‑ to ‑ atom attractions that involve exchange of valence electrons Following forms:  Ionic  Covalent  Metallic

Eastern Kentucky University INT Atomic theory: Ionic Bonding Atoms of one element give up their outer electron(s), which are in turn attracted to atoms of some other element to increase electron count in the outermost shell to eight

Eastern Kentucky University INT Atomic theory: Covalent Bonding Electrons are shared (as opposed to transferred) between atoms in their outermost shells to achieve a stable set of eight

Eastern Kentucky University INT Atomic theory: Metallic Bonding Sharing of outer shell electrons by all atoms to form a general electron cloud that permeates the entire block

Eastern Kentucky University INT Atomic theory: Secondary Bonds Whereas primary bonds involve atom ‑ to ‑ atom attractive forces, secondary bonds involve attraction forces between molecules  No transfer or sharing of electrons in secondary bonding  Bonds are weaker than primary bonds  Three forms: 1. Dipole forces 2. London forces 3. Hydrogen bonding

Eastern Kentucky University INT Atomic theory: Dipole Forces Arise in a molecule comprised of two atoms with equal and opposite electrical charges Each molecule therefore forms a dipole that attracts other molecules

Eastern Kentucky University INT Atomic theory: London Forces Attractive force between nonpolar molecules, i.e., atoms in molecule do not form dipoles However, due to rapid motion of electrons in orbit, temporary dipoles form when more electrons are on one side

Eastern Kentucky University INT Atomic theory: Hydrogen Bonding Occurs in molecules containing hydrogen atoms covalently bonded to another atom (e.g., H 2 O) Since electrons to complete shell of hydrogen atom are aligned on one side of nucleus, opposite side has a net positive charge that attracts electrons in other molecules

Eastern Kentucky University INT Atomic theory: Macroscopic Structures of Matter Atoms and molecules are the building blocks of more macroscopic structure of matter When materials solidify from the molten state, they tend to close ranks and pack tightly, arranging themselves into one of two structures:  Crystalline  Noncrystalline

Eastern Kentucky University INT Crystalline structures Crystalline structures  Simple, body-centered cubic (bcc), face-centered cubic (fcc), close-packed hexagonal

Eastern Kentucky University INT Atomic theory: Crystalline Structure Structure in which atoms are located at regular and recurring positions in three dimensions Unit cell - basic geometric grouping of atoms that is repeated The pattern may be replicated millions of times within a given crystal Characteristic structure of virtually all metals, as well as many ceramics and some polymers

Eastern Kentucky University INT 238 Progression of crystal structures Illustration of the BCC

Eastern Kentucky University INT 238 Metal lattices Some metals undergo a change in structure at different temperatures IRON  BCC at room temperature  Changes to FCC 1674 F (912 C)  Back to BCC above 2550 F (1400 C) Referred to as ALLOTROPIC or polymorphs

Eastern Kentucky University INT 238 Supercooling process VERY HOT Metals in liquid state (VERY HOT) As heat decreases  Primary and secondary forces develop in distinct patterns characteristic for that material (lattices) – this is called the FREEZING POINT  Lattice formation creates heat, grows until stopped by another lattice or container  Where lattice structures collide, it is a grain boundary GRAIN BOUNDARY: Bounding surfaces between crystals

Eastern Kentucky University INT Specification of material What and why?  Clear and accurate descriptions of technical requirements of materials, products, or services. They may state requirements for quality, use of material and methods to produce a desired product, system, application, or finish

Eastern Kentucky University INT standards What are they?  A consortium or group of people defining common definitions and procedures  Only work when people adopt and use them properly ASTM standards  American Society for Testing Materials (ASTM)ASTM

Eastern Kentucky University INT 238 REVIEW Questions?