MATERIAL SCIENCE Module 1 Structure of Metals

1 MATERIAL SCIENCEM odule 1 Structure of MetalsTABLE OF CONTENTSLIST OF iiLIST OF 1 Atomic 1 Order in 5 COMMON LATTICE 6 Common Crystal 8 GRAIN Structure AND 9 Grain Structure and 12 Polymorphism 15 Common Characteristics of 15 Type 304 Stainless 16 Composition of Common Engineering 17 IMPERFECTIONS IN 18 Microscopic 18 Macroscopic 22 Rev. 0 Page iMS-01 LIST OF FIGURESF igure 1 Bonding 3 Figure 2 Common Lattice 7 Figure 3 Grains and 10 Figure 4 Grain 10 Figure 5 Cooling Curve for Unalloyed 12 Figure 6 Change in Alpha Uranium Upon Heating From 0 to 300 13 Figure 7 Point 19 Figure 8 Line Defects (Dislocations).. 19 Figure 9 20MS-01 Page iiRev.

2 0 LIST OF TABLEST able 1 Examples of Materials and Their 2 Table 2 Typical Composition of Common Engineering 16 Rev. 0 Page iiiMS-01 REFERENCES Academic Program for Nuclear Power Plant Personnel, Volume III, Columbia, MD, General Physics Corporation, Library of Congress Card #A 326517, 1982. Foster and Wright, Basic Nuclear Engineering, Fourth Edition, Allyn and Bacon, Inc.,1983. Glasstone and Sesonske, Nuclear Reactor Engineering, Third Edition, Van NostrandReinhold Company, 1981. Metcalfe, Williams, and Castka, Modern Chemistry, Holt, Rinehart, and Winston, NewYork, NY, 1982. Reactor Plant Materials, General Physics Corporation, Columbia Maryland, 1982. Savannah River Site, MATERIAL SCIENCE Course, CS-CRO-IT-FUND-10, Rev.

3 0, 1991. Tweeddale, , The Mechanical Properties of Metals Assessment and Significance,American Elsevier Publishing Company, 1964. Weisman, Elements of Nuclear Reactor Design, Elsevier Scientific Publishing Company, ivRev. 0 TERMINAL references, DESCRIBE the bonding and patterns that effect the Structure of the five types of bonding that occur in materials and their the following cubic cubic close-packed the three lattice-type structures in a description or drawing, DISTINGUISH between the three most common typesof crystalline the crystalline Structure possessed by a the following the term the ranges and names for the polymorphism phases associated with the polymorphism phase that prevents pure uranium from being used as 0 Page vMS-01 ENABLING OBJECTIVES (Cont.)

4 The term an alloy as to the three possible microstructures and the two generalcharacteristics as compared to pure the two desirable properties of type 304 stainless the three types of microscopic imperfections found in crystalline how slip occurs in the four types of bulk viRev. 0 BONDINGThe arrangement of atoms in a MATERIAL determines the behavior and propertiesof that MATERIAL . Most of the materials used in the construction of a nuclearreactor facility are Metals . In this chapter, we will discuss the various types ofbonding that occurs in MATERIAL selected for use in a reactor facility. TheChemistry Handbook discusses the bonding types in more detail. EO the five types of bonding that occur in materials andtheir , as we know it, exists in three common states.

5 These three states are solid, liquid, andgas. The atomic or molecular interactions that occur within a substance determine its state. Inthis chapter, we will deal primarily with solids because solids are of the most concern inengineering applications of materials. Liquids and gases will be mentioned for comparativepurposes matter is held together by forces originating between neighboring atoms or forces arise because of differences in the electron clouds of atoms. In other words, thevalence electrons, or those in the outer shell, of atoms determine their attraction for theirneighbors. When physical attraction between molecules or atoms of a MATERIAL is great, thematerial is held tightly together. Molecules in solids are bound tightly together.

6 When theattractions are weaker, the substance may be in a liquid form and free to flow. Gases exhibitvirtually no attractive forces between atoms or molecules, and their particles are free to moveindependently of each types of bonds in a MATERIAL are determined by the manner in which forces hold mattertogether. Figure 1 illustrates several types of bonds and their characteristics are listed bond - In this type of bond, one or more electrons are wholly transferredfrom an atom of one element to the atom of the other, and the elements are heldtogether by the force of attraction due to the opposite polarity of the bond - A bond formed by shared electrons. Electrons are shared whenan atom needs electrons to complete its outer shell and can share those electronswith its neighbor.

7 The electrons are then part of both atoms and both shells 0 Page bond - In this type of bond, the atoms do not share or exchange electronsto bond together. Instead, many electrons (roughly one for each atom) are moreor less free to move throughout the metal , so that each electron can interact withmany of the fixed bond - When the electrons of neutral atoms spend more time in oneregion of their orbit, a temporary weak charge will exist. The molecule willweakly attract other molecules. This is sometimes called the van der Waals ormolecular bond - This bond is similar to the molecular bond and occurs due to theease with which hydrogen atoms are willing to give up an electron to atoms ofoxygen, fluorine, or examples of materials and their bonds are identified in Table chlorideIonicDiamondCovalentSodiumMetall icSolid H2 MolecularIceHydrogen The type of bond not only determines how well a MATERIAL is held together, but alsodetermines what microscopic properties the MATERIAL possesses.

8 Properties such as theability to conduct heat or electrical current are determined by the freedom of movementof electrons. This is dependent on the type of bonding present. Knowledge of themicroscopic Structure of a MATERIAL allows us to predict how that MATERIAL will behaveunder certain conditions. Conversely, a MATERIAL may be synthetically fabricated with agiven microscopic Structure to yield properties desirable for certain 2 Rev. 0 Figure 1 Bonding TypesRev. 0 Page 3MS-01 Solids have greater interatomic attractions than liquids and gases. However, there are widevariations in the properties of solid materials used for engineering purposes. The properties ofmaterials depend on their interatomic bonds. These same bonds also dictate the space betweenthe configuration of atoms in solids.

9 All solids may be classified as either amorphous materials have no regular arrangement of their molecules. Materials like glassand paraffin are considered amorphous. Amorphous materials have the properties ofsolids. They have definite shape and volume and diffuse slowly. These materials alsolack sharply defined melting points. In many respects, they resemble liquids that flowvery slowly at room a crystalline Structure , the atoms are arranged in a three-dimensional array called alattice. The lattice has a regular repeating configuration in all directions. A group ofparticles from one part of a crystal has exactly the same geometric relationship as a groupfrom any other part of the same 4 Rev. 0 The important information in this chapter is summarized of Bonds and Their Characteristics Ionic bond - An atom with one or more electrons are wholly transferred from oneelement to another, and the elements are held together by the force of attractiondue to the opposite polarity of the charge.

10 Covalent bond - An atom that needs electrons to complete its outer shell sharesthose electrons with its neighbor. Metallic bond - The atoms do not share or exchange electrons to bond , many electrons (roughly one for each atom) are more or less free to movethroughout the metal , so that each electron can interact with many of the fixedatoms. Molecular bond - When neutral atoms undergo shifting in centers of their charge,they can weakly attract other atoms with displaced charges. This is sometimescalled the van der Waals bond. Hydrogen bond - This bond is similar to the molecular bond and occurs due to theease with which hydrogen atoms displace their in Microstructures Amorphous microstructures lack sharply defined melting points and do not havean orderly arrangement of particles.