This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: VK250 Lecture 06 S TRUCTURES OF SOLUTIONS AND COMPOUNDS • Few elements used in pure state (usually alloyed) E.g. Steel (Fe & C), 2xxx Al (Al +4%Cu+Mg, Si, Mn) Titanium (Ti-6%Al-4%V) Brass (Cu = 20% Zn) Bronze (Cu + 10-30%Sn) Solid solutions • Alloy element (or ‘solute’) “dissolves” in ‘solvent’ element • Wide range of solubilities (<0.01% to 100%) Fe can only dissolve 0.007 wt% C Sn can dissolve only 0.3 wt% Pb at room temperature 2.5wt% at 183 ° C Pb can dissolve 2wt% Sn at room temperature 19wt% at 183 ° C Cu and Ni are completely soluble in each other • Two ways for atoms to dissolve: Interstitial solid solutions (if solute has small atoms such as C, B, N) E.g. , C in Fe Substitutional solid solutions E.g., Cu Sn • If there is an excess of alloying element - a precipitate is formed E.g. , sugar in water, or moisture in air) • The precipitates may be a saturated solid solution of host in alloy element E.g. Dissolve more than 2% Sn in Pb at room temperature Excess precipitates out as Sn with 0.3% Pb dissolved in it • Precipitate may be a chemical compound E.g. Fe 3 C in steels; CuAl 2 in Al/Cu systems • Region of material with uniform physical and chemical properties is called a phase E.g., Ice, water, vapor are 3 different phases of H 2 O 1 VK250 Lecture 06 At 0 ° C ice/water co-exist as a 2-phase mixture Fe 3 C is a phase that is different from Fe(0.007wt%C) Fe(0.007wt%C) is the same single phase as Fe (0.003wt%C) Analogy: 20% sugar water cannot exist in equilibrium with 10% sugar water or with pure water ⇒ all three are considered to be the same phase. When sugar precipitates from solution, a two-phase solution is formed: (i) water (fully saturated with dissolved sugar) + (ii) solid sugar (fully saturated with water) • In solids there are different types of interphase boundaries Coherent: Lattices continuous across boundary Coherent with strain: Lattices continuous across boundary but with induced strains Semi-coherent: Incoherent : Lattices continuous across boundary but with dislocations at boundary No relationship between lattices of the two phases Each of these is important in its own way for strengthening materials....
View Full Document
This note was uploaded on 09/15/2010 for the course MATSCIE 250 taught by Professor Yalisove during the Fall '08 term at University of Michigan.
- Fall '08