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: https://www.wileyplus.com/WileyCDA/Section/Fundamentals-of-

Materials-Science-and-Engineering-An-Integrated-Approach-4th-Edition.id-810680.html

• FE free Reference Handbook: http://cbt.ncees.org/fe-reference-handbook/ • FE review manual: http://ppi2pass.com/shop/fe-eit-exam/fe-eit-exam-review-

materials/fe-review-manual-ferm3.html • Practice problems: http://ppi2pass.com/shop/fe-eit-exam/fe-eit-exam-review-

materials/fe-practice-problem-package.html

Thermal ProcessingCooling 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 550oC, 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.

C3S

C2S

C3A

C4AF

gypsum

K2SO4

lime and/or calcite

silica

periclase (with Mg)C=CaO, S=SiO2, A=Al2O3, F=Fe2O3 all hydrated