lec08_menu

Metallographic Phenomena As Observ ed in Ch eeses

22.033 - Nuclear Systems Design Pro ject No v em b er 20, 2011

Cab ot Cloth b ound Cheddar (co w) - P eac ham/Greensb oro, V ermon t, USA

Har d che ese , age d 10-14 mon t hs

Cab ot Cloth b ound is a handsome natural-rinded traditional c heddar. Bandaged with m uslin and skillfully aged a minim um of 10 mon ths at the Cell ars at Jasp e r Hill. Cab ot Cloth b ound has all the c haracteristic texture of an English-st yle c heddar with the sw eet caramel and mi lky fa v ors that sets it apart from other bandaged c heddars. The fa v or profle is at once sw eet, sa v ory , n utt y , and tangy .

Willis W o o d's Pure Apple Cider J e lly - Springfeld, V ermon , USA

The W o o d family has b een making Cider Jelly since 1882. They use the same apple press they started out with to grind and press fresh apple s to mak e sw eet cider. The cider is then ev ap orated in a w o o d-fred stainless steel ev a p orator un t i l the cider is reduced t o 1/9 of its original v olume and b ecomes this sw e et and in tensely appley concen trated jelly . It couldn't b e an y simpler: just concen trated cider with nothing added, no prese r v ativ es or sw eeteners. The cider from ab out 30 to 50 apples is concen trated in ev ery p ound of Cider Jell y .

Maps removed due to copyright restrictions.

Courtesy of Formaggio Kitchen. Used with permission.

The Gran ular S t ructure of Met a ls, In tergran ular F racture

Most metals are comp osed of grains, or small r e gions of con tin uous crystallinit y . The b oundaries b et w een these grains are ca lled gr ain b oundaries . A quic k cut, p olish and etc h of most metal surfaces will rev eal the crystalline nature of the metal . An ev eryda y example can easi ly b e seen in alumin um allo y trafc p oles, where the grains can b e as large as one cen timeter in diameter.

Inter gr anular (IG) fr actur e is a failure mo de of metals, where they break along grain b oundaries i n stea d of through the metal, kno wn as tr ansgr anular (TG) f r actur e . IG fracture usually indic at e s some sort of signifcan t w eakness at the grain b oundaries of a metal. High doses of radiation, as w ell as corrosion phenomena (suc h as stress corrosion crac king, or liquid metal em brittlemen t in LF Rs) can lead metals to IG fracture.

Cheddar c heese breaks with an IG fracture pattern due to the che ddaring pr o c ess . Curds of c heddar

c heese are pressed toge t he r in large molds, draining the whey from the c u rd. These curds then p osses grain b oundaries that are m uc h w eak er than the curds themselv es.

A469 Rotor St e el from Alcator C-Mo d W-1 to ol steel, IG fracture aft e r quenc hing


Com te Le F ort (co w) - Jura, F rance
Har d che ese , age d 16-24 mon t hs
After WWI I, Marcel P etite b ough t an un used m unitions fort from the F renc h G o v ern - men t b ecause he felt that it w ould b e an ideal e n vironmen t for aging his 70lb wheels of F renc h Gruy ere kno wn as Com te. This c heese is from the high altitude Jura re - gion in southeastern F rance. The Mon tb eliard co ws graze on meado ws teami n g with pissenlit, or wild dandel ion. The crystals of lactic acid presen t inside the c heese are a b y-pro duct of the lactose fermen tation pro cess. They add a tartness and a crunc h to this c heese.	Maps removed due to copyright restrictions.
Ar isinal F renc h Bread - Cam bridge, MA, USA
Gruy ere c heeses go v ery w ell with starc hes, lik e bre ad, or pair sup erbly melted o v er p otato es. A go o d F renc h bread is an excellen t v ec t or for balancing the medium fa v ors of Com te, as w ell as cleansing the palate b et w een c h e ese tastings.
Sup ersa ura ion, F orma ion of Secondary P ar icle Precipi a es (SPPs)

Elemen ts often ha v e limited solubilities in eac h other, and as they co ol, phases of one comp osition will form with an inter dendritic liquid forming around them. This in terdendritic liquid can b ecome sup ersaturated in one elemen t as it co ols, leadi ng to precipitation of certain p ha s e s . In Com te c heese , lactic acid pro duced b y bacteria s up ersaturates and precipitates out as c ru nc h y crystals. In Zircalo ys, found as fuel cladding in L WRs, these SPPs precipitate out, leading to enhanced strength and corrosion prop erties.

A more familiar example of sup ersaturation and p re cipitation of a s e condary phase can b e found in ca r b on steel. Steel with more carb on than is soluble i n ferrite a lone will precipitate out as p e arlite , a lamell ar mixture of ferrite (with little carb on) and c ementite (F e 3 C) . The line at t he lo w e r left of the F e-C phase diagram sho ws just ho w little c arb on i s soluble in ferrite alone.

The lactic acid crystals in this c heese are a result of sup ersaturation in the in terdendritic liquid as the c heese formed.

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

Iron-Carb on Phase Diagram [1] Microstructure of p earlite, sho wing ligh t bands

of ferrite a nd dark bands of ceme n tite [2]

Brebis Abba y e de Bello c (sheep) - A quitaine, F rance

Har d che ese , age d 6 months

Abba y e de Bello c is made from sheep's milk b y the Benedictine monks at the monastery of Notre Dame. Dev e lop ed in 1960, the recip e i s based on that of Ossau- Irat y . The milk co mes exclusiv ely from the Manec h breed of sheep, courtesy of surrounding farms. The resulting c h e ese is mild, ric h, and smo oth. The texture is somewhat frm, with fa v ors o f bro wn butter, n uts, caramel.

Courtesy of Formaggio Kitchen. Used with permission.

Maps removed due to

Cerise Noire, Conf ure de l'Ardec he - S . Sylv es re, F rance

These are organic small-batc h handmade pr e s e rv es made b y Sylvie and P ascal R a u - nic her at La F erme de Mazairas in the small to wn of St. Sylv estre in the region of Ardec he. Their tin y farm sp ecializes in organic fruit, using un usual v arieties with tons of fresh fa v o r . Handpic k ed organic blac k c herries are lo vingly co ok ed, on a lo w heat un til this ric h preserv e has a striking dark purple color and fa v or that has a w arm sw eetness and a mello w tartness. Best w he n paired with sheep's milk c heeses.

copyright restrictions.

Courtesy of Formaggio Kitchen. Used with permission.

Creep: Deformation Under Constan t Load

Metals, esp ecially those at high temp erature, can undergo cr e ep failur e ev en at loads far b elo w their rated strength. This is b ecause constan t loads, suc h as pressure or gra vit y , do cause dislo cations presen t in the metal to mo v e. These efe cts increase in sp eed with highe r temp e r a t ure. Creep lifetimes for metals in fast reactor en vironmen ts range from mon ths to y ears, and can b e the limiting factor i n high temp erature materials p erformance or fuel cycle le ngth.

This c hee s e undergo es a creep-lik e phenomenon due to gra vit y , whe r e it will deform irrev ersibly under the constan t load of gra vit y . T91, a creep resistan t steel, still p ossesses a fnite creep lifetime. A high pressur e gradien t across a pip e w all can cause the diameter of the pip e to gradually thin, ev en tually re s ulti ng in a cr e ep ruptur e once the w all thi c kness is reduced enough. Creep lifetime can b e greatly reduced with an improp er heat treatmen t (see b elo w), suc h as o v ertemp ering T91 to mak e it to o soft.

more information, see http://ocw.mit.edu/fairuse .

Creep rupture lifetimes for HT-9 and T91 [ 3] Creep rupture fail ure of T91 pip e [4]

Sotto cenere al T art u fo (co w) - Lom bard y , Italy

Blende d / Flavor e d Che ese (black trufes), age d 3 months

This un usual c heese is coasted with a fne, pressed la y er of ash. Made from whole co w's milk, it has a ric h, crea m y texture and is laced with blac k trufes. The tru f e aroma delicately fa v ors eac h bite.

Courtesy of Formaggio Kitchen. Used with permission.

Solmiela o Miele de Mela a (spruce honeydew) - Sicili a, I aly

Miele di Melata, or 'honeydew h o n e y ,' is honey from uncultiv ated and forested zones. It is distinctiv e from other honeys for the fact that it comes not from fo w ers, but from the sugary secretions of the le a v es of some arb o r e al essence and shrubs, in this case, spruce trees. These secretions are caused b y sp ecifc t yp es of aphids (metcalfa pruinosa, or plan thopp ers) biting the lea v es, allo wing the sap to leak out and b e collected b y b ees.

Maps removed due to copyright restrictions.

Stress Concen trators and Reduction in T ensile Strength

Defects in metals can pr o duce regions of str ess c onc entr ation . These defects c an

include foreign b o dies ( inclusions) , secondary precipitated phases, v oids (due to casting or due to irradiation), crac ks, and mec hanical defects suc h as scratc hes or w elding errors.

The str ess c onc entr ation factor is a function of the ge ometry of the fa w, or the ratio of the ma jor and

minor axes of the fa w and its radius of curv ature, NOT its o v erall size. The stress at the ma jor axes of an elliptical fa w (suc h as a crac k, v oid, or sc r a t c h) is giv en b y:

σ max

= σ appl ied

� 1 + 2 � a �

(1)

r

where a is the length of the crac k or fa w and r is its radius of curv atu re at the tip. As r approac hes zero, the stress approac hes infnit y . This σ max is therefore the streess ac t ual ly applied to a section of materia l near a crac k, whic h explains wh y materials with fa ws can fail w ell b elo w th e ir rated strength for in tact material. Materials therefore tend to fracture at the si t e s of these fa ws. In this c heese, inclusions are si m ulated b y the trufe fak es. Pulling on t he tensile sp ecimen (made out of the c heese) will in v ariably result in failure at one of the trufe fak es, if they are presen t in the narro w section of the sample. SEM microgr aphs of metals

with crac ks and inclusions will rev e al their fa ws on the fracture surfaces.

MnS inclusions on the fracture surface of A469 rotor steel fr o m Alcator C-Mo d

© 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 .

Stress concen trations of a crac k as visualized

Queso Azul de V aldeon (co w & goat ) - V aldeon, S pain

Blue che e s e , age d 3 months, wr app e d in s yc amor e le aves

This not to o spicy blue is a blend of co w and goat's milk. Before aging, it is wrapp ed in sycamore le a v es, g iving it an earth y fa v or with ofsets the tangy blue ma k i n g a fan tastically w ell-balanced taste. The exp e r i ence when eating V a ldeon o ccurs in almost three separate stages. It sends a s ho c k to the senses at frst, surprising and un usual, but b y mid-palate, it subsides and the spicy fruit in this c hee se is presen t. The fnish l ea v es an electricit y on the tip of y our tongue.

Maps removed due to copyright restrictions.

Solmiela o Miele de Bergamo o (Bergamo blossom) - Sicilia, I aly

Bergamot, b est kno wn for lending its distinctiv e fragrance to Earl Grey tea, pro vides the p ollen for this exceedingly rare hone y . Tin y amoun ts are pro duced at a time, o wing to the fnic kiness of the b ergamot blossom. It do es not gro w on Sicily , but rather in nearb y Calabria . The Solmielato honey pro ducers m ust therefore transp ort their b eehiv es b y ferry to the b ergamot gro v es in Calab ri a b y ferry , whe r e they release their b ees to gather this rare p ollen.

Grain Boundary Sensitization, Seg regation, and IG A ttac k

Under certain conditions, metals can undergo sensitization , where they b ecome more susceptible to failure b y corrosion or stress than b efore. This can o ccur in a n um b er of scenarios. One, sho wn in the fgure b elo w, sho ws what happ ens when 304 stainle ss steel is heated b et w een 400-850 Celsius for a prolonged p erio d of time. The carb on in the s te el com bines with c hromium on the grain b oundaries, forming c hromium carbides. This lo cally depletes the s urrounding metal, resulting in easier IG attac k of the steel.

Blue c he ese is quite similar to the after efects of a sensitized steel. Up on ino culation with the mold required to mak e blue c heese and exp osu re to o xygen, the mold attac ks the w eak er curd b oundaries of the c heese faster than the curd itself. This results in the v eined structure of blue c heese.

[6]

Cheese descriptions adapted from h ttp://www.formaggiokitc hen. com / , h ttp://ohioauthorit y .com/articles/fo o d -

and-drink/the-cultur ed -palate-strong-attractions , h ttp://fr.wikip edia.org/wiki/Abba y e de Bello c , and h ttp://www.solmielato.it/ Maps pro vided b y Go ogle Maps ( h ttp://maps.go ogle.com/ )

[1] Ima ge source: h ttp://www.substec h.com/

[2] Ima ge source: h ttp://hsc.csu.edu.au/engineering studies/transp ort/2522/heat treat answ ers.h tml

[3] R. L. Klueh and A.T. Nelson. F erritic/martensitic steels for n ext-generation reactors. Journal of Nuclear Materials, 371(1-3):37�52, Septem b er 2007.

[4] R. Sw anek amp. "Handling Nine-Chrome S teel in HRSGs." P o w er Engineering, V ol 100:2, 2006.

[5] AIST. "Diagnosing damages in structures and t heir danger lev el at the same time using elastico-luminescen t materials." A ccessed at h t tp://www.ndt.net/searc h/do cs.php3?id=7506&con ten t =1 , T su kuba, Japan, 2008.

[6] Im age source: h ttp://www.solidmetals.net/2011/05/02/sensitization-of-stainless-steel/

MIT OpenCourseWare http://ocw.mit.edu

22.033 / 22.33 Nuclear Systems Design Project

Fall 201 1

For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .