3Substitutional Solid Solubilty How much one element will dissolve in another is determined by the Hume Rothery rulesAtomic radii should be within 15% of each otherCrystal structure should be the same for each element for good solubilityElectronegativities should be similar.The valences of the atoms should be similar.Good solubility Cu –Ni, Cu-Au; Cu r=0.128A, Ni r=0.125, Au r=0.144Crystal structure Ti- HCP, Al - FCCPoor soluility Na-Cl Na electronegativity 0.9, Cl 3.0Valences – Zn 2+, Cu 1+Only indicate solubility from these rules.DOES NOT APPLY TO THE ELEMENTS H,C,O,N,B THESE FORM INTERSTITIALSOLID SOLUTIONS.
4Iron Carbon Phase Diagram Liquid1538C3367 SUBLIMESFe - a then g then d912C 1394Cg +LSteelsEutectoidS1 -> S2 + S3-> a + F e3CPeritecticS1+L -> S2d + L -> gFe3C- cementiteA compoundg + Fe3Ca + Fe3C
5Stainless Steel Phase Diagram Ternary phase diagram for stainless steels. In this case an isothermal section at a constanttemperature is used.
6Lever Arm RuleDetermine the AMOUNTS of each phase use the Inverse Lever Arm Rule.Amount of solid = wa-wl/ws-wlAmount of liquid = ws-wa/ws-wlAmount of solid at 1300C is therefore / = 8/13 = 0.615= 61.5%Amount of liquid at 1300C is therefore / = 5/13 = = 38.5%
7Change Average Composition 50% Determine the AMOUNTS of each phase use the Inverse Lever Arm Rule.Amount of solid = wa-wl/ws-wlAmount of liquid = ws-wa/ws-wlAmount of solid at 1300C is therefore / = 5/13 = 0.385= 38.5%Amount of liquid at 1300C is therefore / = 8/13 = = 61.5%
8Microstructures and Composition Pro-eutectic phase is formed before the eutectic reaction, eg a in the a+L region of phase diagram.
10Lead Tin Microstructures 15%Pb 85%SnEquiaxed Single Phase Grain Structure
11Homeworks.From the PbSn phase diagram, for a 70% Pb, 30%Sn alloy, at what temperature does solid first form. At the eutectic temperature, how much proeutectic phase is present and how much eutectic phase? What are the compositions at 100oC?For a steel containing 0.4% C:-a) At what temperature does austenite start to transform on cooling from 950oC? b) How much proeutectoid phase is present at the eutectoid temperature c) What is its composition?d) Upon quenching the steel from 950oC to 50oC what phases will be present and what will be the composition?