lec08

Metals and Cheeses: Unconventional Pairings

Lecture 8

22.033 /22.33 – Nuclear Engineering Design Project No v . 21, 201 1

What's the Deal?

Many of you are using metals in your designs

– S ome are at very high temperatures

– S ome are at very high stresses

Understanding the structure and failure of metals is key to a successful design

Many concepts are hard to grasp, at first

– H opefully this class will help you to remember them with cheese pairings

Metallic Crystal Structures

Cabot Clothbound Cheddar (Gr eensbor o, V T , USA)

Alloy Fe-12C r -2Si

Grain Boundaries

Grains

Grains: More Examples

Cabot Clothbound Cheddar (Gr eensbor o, V T , USA)

Alloy A469

Grains: More Examples

Cabot Clothbound Cheddar (Gr eensbor o, V T , USA)

Chedda r , cut surface

Intergranular (IG) Fracture

Cabot Clothbound Cheddar (Gr eensbor o, V T , USA)

W1 tool steel, after quenching and br eaking in a vise

IG Fracture Side by Side

Cabot Clothbound Cheddar (Gr eensbor o, V T , USA)

Courtesy of Christensen Materials Engineering. Used with permission.

IG fractur e of sensitized 304 stainless steel IG fractur e of Cabot cheddar cheese,

http://site.christensenmateria ls.com/Services.htm l showing matching fractur e surfaces

Supersaturation, Precipitation

Comté Le Fort (Jura, France)

Especially relevant for Zircaloy fuel cladding

– Z ircaloy is Zr with minor additions

• S n, Sb, Fe

– T hese form secondary particle precipitates

(SPPs)

• SPPs can guard against corrosion

– Dissolved elements increase strength

Comté cheese has lactic acid SPPs

Precipitation of SPPs

Comté Le Fort (Jura, France)

TEM image of tin oxide SPP i n Zir caloy after oxidation

R. Adam son, F . Garzarolli, B. Cox, A. St rasser , P . Rudling. “Corrosion Mechanism s

in Zirconium Alloys.” IZNA7, Special T opic Re port, ANT International, Skultuna, Sweden, 2007.

Phase Precipitation Side by Side

Comté Le Fort (Jura, France)

Lactic acid SPPs on the cut surface of

Source: H. C. Furtado, I. L. May . “ High tem p erature degradation in power plants and refineries .” Materials

Resear ch 7, no. 1.1 (2004): 103-1 10. License CC B Y -NC Comté cheese

Phase Precipitation in Steel

Comté Le Fort (Jura, France)

Courtesy of Dimitri Kopeliovich. Source: Kopeliovich, D. “ Iron-carbon phase diagram .” SubsTech.

Phase Precipitation in Steel

Comté Le Fort (Jura, France)

Pearlite forms when dissolved carbon in austenite precipitates out

T wo phases: ferrite (mostly Fe, light) and cementite (Fe 3 C, dark)

Note how grains of pearlite are still aligned

http://hsc.csu.edu.au/engineering_studies /application/civil/1-1/answers.htm l

SPPs and Fracture Surfaces

Comté Le Fort (Jura, France)

MnS particles on the fractur e surface Lactic acid SPPs on the fractur e of alloy A469 fr om Alcator C-Mod surface of Comté cheese

Creep Lifetime and Failure

Br ebis Abbaye de Belloc (Aquitaine, France)

Metals can deform under a static (constant) load well below their rated failure strengths

– This is called creep

– P roceeds via a number of mechanisms

• M ost involve vacancy or dislocation mvmt.

– Generally speeds up with temperature

Creep lifetime can limit reactor performance

Creep Lifetime and Failure

Br ebis Abbaye de Belloc (Aquitaine, France)

T91 r equires a delicate balance between creep lifetime (harder is better) and toughness (softer is better)

The precise heat treatment is key to dialing in T91's properties

Deviations can be disastrous!

G. Guntz, M. Julien, G. Kottm ann, F . Pellicani, A. Pouilly , and J. C. V a illant. The T91 B ook. V a llourec Industries, France, 1990.

Creep Lifetime and Failure

Br ebis Abbaye de Belloc (Aquitaine, France)

Creative Commons license. For more information, see http://ocw.mit.edu/fairuse .

Cr eep failur e in T91 pipe due to pr olonged heat tr eatment and oversoftening

R. Swanekam p. Handling Nine-Chrom e Steel in HRSGs. Power Engineering, V o l 100:2, 2006.

Creep Lifetime Can Limit LFRs

Br ebis Abbaye de Belloc (Aquitaine, France)

Courtesy of Elsevier, Inc., http://www.sciencedirect.com . Used with permission.

Cr eep ruptur e lifetimes of HT9 and T91 s teels at 650 Celsius

R.L. Klueh a nd A. T . N elson. Ferritic/martensitic steels for next -generation reactors. Journal of Nuclear Materials, 371(1-3): 3752, Septem ber 2007.

Creep Lifetime and Failure

Br ebis Abbaye de Belloc (Aquitaine, France)

Cr eep deformation of Abbaye de Belloc under static gravity load at r oom temperatur e

Defects and Stress Concentration

Sottocener e al T artufo (Lombar d y , Italy)

Defects (voids, inclusions, cracks, scratches) locally increase stresses in materials

– D ependent on the geometry , NOT the total size

– P roportional to the ratio of the major & minor flaw axes, or the radius of curvature of a flaw tip

The sharper the flaw, the worse it is!

Crack Stress Concentration Map

Sottocener e al T artufo (Lombar d y , Italy)

© National Institute of Advanced Industrial Science and Technology (AIST), Japan. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse .

Str e ss concentration map near a crack tip using elasto-luminescent coating

AIS T . Diagnosing dam a ges in structures and their dange r level at the sam e tim e using elastico-lum inescent m a terials. Accessed at http://www .aist.go. jp/aist_e/latest_res earch/2009/20090107/20090107.ht m l .

Uniaxial Tensile Cheese Specimen

Sottocener e al T artufo (Lombar d y , Italy)

Rounded corners to avoid other stress concentrators

V oid (gas bubble)

Inclusion (truf f le)

Uniaxial tensile specimen fabricated fr om Sottocener e al T artufo

Cheese Fracture Surface

Sottocener e al T artufo (Lombar d y , Italy)

Fractur e occurr ed in plane with the void F urther testing fractur ed on the inclusi on

Fracture Surfaces Side by Side

Sottocener e al T artufo (Lombar d y , Italy)

Cleavage planes

Vo i d

V oid-induced fractur e in A469 V oid-induced fractur e in Sottocener e

Sensitization, IG Corrosion