AEM 338 Engineered Materials Testing

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

2. 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.

3. 1.1 Introduction • Materials Technology • Specifications, properties, selection, and testing of engineering materials • Engineering Materials • Primarily used in construction of various structures, machines, etc.

4. 1.2 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

5. 1.2 Atomic theory • Classification into one of the following: • Elements • Compounds • mixtures

6. 1.2 Atomic theory • By studying elements, scientists discovered • Repetitive patterns • Allowed them to predict nature and properties of elements not discovered until much later

7. 1.2 Atomic Theory

8. 1.2 Atomic theory • An atom consists of

9. 1.2 Atomic theory • The number of PROTONS in the nucleus determines what element the atom represents

10. 1.2 Atomic theory Atoms are held together in molecules by various types of bonds • Primary bonds - generally associated with formation of molecules • Secondary bonds - generally associated with attraction between molecules • Primary bonds are much stronger than secondary bonds

11. 1.2 Atomic theory PRIMARY BONDS Characterized by strong atom‑to‑atom attractions that involve exchange of valence electrons • Following forms: • Ionic • Covalent • Metallic

12. 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 1.2 Atomic theory: Ionic Bonding

13. Electrons are shared (as opposed to transferred) between atoms in their outermost shells to achieve a stable set of eight 1.2 Atomic theory: Covalent Bonding

14. Sharing of outer shell electrons by all atoms to form a general electron cloud that permeates the entire block 1.2 Atomic theory: Metallic Bonding

15. 1.2 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: • Dipole forces • London forces • Hydrogen bonding

16. Arise in a molecule comprised of two atoms with equal and opposite electrical charges Each molecule therefore forms a dipole that attracts other molecules 1.2 Atomic theory: Dipole Forces

17. 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 1.2 Atomic theory: London Forces

18. Occurs in molecules containing hydrogen atoms covalently bonded to another atom (e.g., H2O) 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 1.2 Atomic theory: Hydrogen Bonding

19. 1.2 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

20. 1.4 Crystalline structures • Crystalline structures • Simple, body-centered cubic (bcc), face-centered cubic (fcc), close-packed hexagonal

21. 1.2 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

22. Progression of crystal structures • Illustration of the BCC

23. 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

24. Supercooling process • 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

25. 1.5 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

26. 1.6 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)

27. REVIEW • Questions?