FE-3: Review of materials science for the FE exam Last revised February 22, 2014 by W.R.Wilcox at Clarkson University. Part 2: Thermal processing, Concrete, Composite materials Based on the following: ES 260 text: Materials-Science-and-Engineering-An-Integrated-Approach-4th-Edition.id htmlhttps:// Materials-Science-and-Engineering-An-Integrated-Approach-4th-Edition.id html FE free Reference Handbook: FE review manual: materials/fe-review-manual-ferm3.htmlhttp://ppi2pass.com/shop/fe-eit-exam/fe-eit-exam-review- materials/fe-review-manual-ferm3.html Practice problems: materials/fe-practice-problem-package.htmlhttp://ppi2pass.com/shop/fe-eit-exam/fe-eit-exam-review- materials/fe-practice-problem-package.html

Thermal Processing Cooling through a phase transition If cool very slowly, get equilibrium phases. –Must be slow enough that a large amount of diffusion has time to occur in both old and new phases. –Final product is that given by the phase diagram, with the new phase(s) being of uniform composition. If cool more rapidly, so that diffusion is small in either the new phase(s), the old phase, or all of these. –Still get equilibrium phases, but may take time for transformation to be complete. –Get composition variation in new phase(s). Cool very rapidly by quenching in oil or water to room temperature –Diffusion doesn't occur. –Can get high-temperature phase. –Can get non-equilibrium phase that doesn’t show on phase diagram Can then heat back up for some time to allow changes to occur (annealing) Examples: transformations starting with austenite containing some interstitial carbon.

Rapidly cool austenite of eutectoid composition to a given temperature. Hold at that temperature and track the amount converted to pearlite versus time. Pearlite bainite Below about 550 o C, get a different arrangement of cementite and ferrite, a very fine structure called "bainite".

Very rapid cooling by quenching in a liquid produces a non-equilibrium phase, martensite, which is in the form of platelets with a body-centered tetragonal structure containing excess interstitial carbon. The transformation from austenite to martensite occurs close to the speed of sound without diffusion. Many crystal defects with internal stresses. Very hard and brittle. Influence of cooling rate on structure obtained Martensite In tempering, a martensitic steel is heated back up to convert some of the martensite to ferrite and cementite, thereby relieving the residual stress and making the steel tougher. The time and temperature determine the amount of conversion and the final properties.

But the cooling rate inside an object is less than at the surface. Conduction of heat is not instantaneous, even in metals. Copied from FE Manual

Because cooling rate is highest at the surface, the final hardness is highest at the surface. Jominy hardenability test: A cylindrical steel bar is quenched at one end with room temperature water. Hardness is measured versus distance.

Composite materials Typically strong particles or rods dispersed in a ductile matrix. Get combinations of properties that cannot be obtained with a single-phase material. Many ways to make, e.g.: –Precipitation during or after solidification. –Mixed in the melt prior to solidification. –Wind fibers on a mold, add a liquid polymer or a monomer that is polymerized by a chemical reaction. Examples: tires, fiberglass, concrete, thoria dispersed nickel. Properties

Concrete Made by mixing Portland cement with fine aggregate (sand), coarse aggregate (gravel) and water. Hardens over time by formation of crystal hydrates Can add reinforcing fibers or rods.

Phases present in cured Portland cement Detection of x-rays emitted in a scanning electron microscope enables analysis of composition (acronyms EDS, EDX, XEDS). Image is 256 µm x 200µm. C 3 S C 2 S C 3 A C 4 AF gypsum K 2 SO 4 lime and/or calcite silica periclase (with Mg) C=CaO, S=SiO 2, A=Al 2 O 3, F=Fe 2 O 3 all hydrated