me_350_-_lect_5_-_ch_6___8.20090907.4aa5954256b304.66426990

me_350_-_lect_5_-_ch_6___8.20090907.4aa5954256b304.66426990...

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Unformatted text preview: ME 350 Lecture 5 Ch 6 & 8 Ch 6 Metals: Alloys Binary Phase Diagrams Metal Types Ch 8 Polymers: Fundamentals of Polymer Technology Thermoplastic Polymers Thermosetting Polymers Elastomers Guide to the Processing of Polymers Alloys Any homogeneous mass of material, in which the grains all have the same crystal lattice structure: A mixture or compound of two or more elements, at least one of which is metallic: alloy Two main categories: 1. Solid solutions - An alloy in which one element is in another to form a 2. Intermediate phases - When the amount of the dissolving element in the alloy exceeds the limit of the base metal, a forms in the alloy Two Forms of Solid Solutions 1. solid solution - atoms of solvent element are replaced in its unit cell by dissolved element 2. solid solution - atoms of dissolving element fit into vacant spaces between base metal atoms in the lattice structure In both forms, the alloy structure is generally than either of the component elements Two Forms of Solid Solutions Types of Intermediate Phases 1. Metallic compounds consist of a metal and nonmetal, such as Fe 3 C ( ) 2. Intermetallic compounds two metals that form a compound, such as Mg 2 Pb In some alloy compositions, the intermediate phase is mixed with the primary solid solution to form a twophase structure Some twophase alloys are important because they can be heat treated for much higher strength than Phase Diagrams A graphical means of representing the phases of a metal alloy system as a function of composition and temperature A phase diagram for two elements (at atmospheric pressure) is called a Inverse Lever Rule - Example 0 10 20 30 40 50 60 70 80 90 200 150 100 % A Temperature C Liquid Nickel-Copper Binary Phase Diagram : A melt is formed with 35% Ni and 65% Cu, it is slowly cooled from 1300C to ~1270C: initial solid is Ni, initial liquid is Ni middle solid is Ni middle liquid is Ni Inverse Lever Rule Example 2 0 10 20 30 40 50 60 70 80 90 200 150 100 % A Temperature C Iron-Carbon Phase Diagram = = Fe 3 C = Austenite can dissolve carbon up to about Ferrite phase can dissolve carbon up to about The difference in solubility between alpha and gamma provides opportunities for strengthening by heat treatment Steel and Cast Iron Defined Ironcarbon alloy containing from 0.02% to 2.1% carbon: Ironcarbon alloy containing from 2.1% to about 4.3% carbon: Both contain other alloying elements besides carbon (Ni, Eutectic and Eutectoid Compositions Composition of Fe-C system @ 4.3% C: Phase changes from solid (...
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me_350_-_lect_5_-_ch_6___8.20090907.4aa5954256b304.66426990...

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