Ceramics and Ceramic Coatings Coursework

8/17/2019 Ceramics and Ceramic Coatings Coursework

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ENGM174 – Ceramics & CeramicCoatings

Question 1a) Describe the fracture mechanisms that occur within a ceramic

when impacte b! a spherica" pro#ecti"e$ %n answering theuestion !ou shou" escribe the e'o"ution of fracture as a

function of time as the pro#ecti"e impacts the surface$

Due to their high harness an re"ati'e"! "ow ensit! compare to meta"s(

ceramic materia"s are often use for the app"ication of ba""istic armour$ henimpacte b! a b"unt pro#ecti"e( such as a spherica" ob#ect( a ceramic wi"" formcone crac*s at the interface between pro#ecti"e an ceramic$ +igure 1 i""ustrates

an a"umina specimen after impact from a spherica" pro#ecti"e at high 'e"ocit!(c"ear"! showing the cone an raia" crac*s that ha'e forme uring the impact$

,he cone crac*s forme uner impact from a

spherica" pro#ecti"e are simi"ar to the fracturemechanism ue to uasi-static b"unt inentation$

,he cone crac*s form fo""owing the ma.imumtensi"e stress ring that occurs be"ow the contact(

as escribe b! /ert0ian contact theor!$ ,he

crac* continues to grow unti" the e"astic strainenerg! reuces be"ow the surface formation

energ! accoring to the Gith criteria$

+urthermore( uring the initia" phase of the

impact( the area of high pressure cause b! thepro#ecti"e impact reaches the rear face of the

ceramic causing crac*s to initiate a"ong with

eformation of the bac* p"ate supporting theceramic$

2s the crac*s propagate through the materia"

the! wi"" coa"esce an cause comminution( resu"ting in a cone of fracturemateria" as shown in +igure 3$ Genera""!( intergranu"ar fracture is preferab"e totransgranu"ar as the crac*s wi"" ha'e to tra'e" a"ong a further istance therefore

"engthening the time to coa"esce an comminution( a"though both mechanismsare "i*e"! to occur uring impact /a0e""( 3516)$

,he formation of the cone of fragmente materia" is a'antageous as the forceof the impactor is sprea o'er a "arge area( reucing the amage to the bac*

p"ate an ob#ects that the armour is protecting$ ,he main isa'antage is thatsince most of the materia" has been fragmente the abi"it! for the ceramic to

resist subseuent impacts is signicant"! reuce$

1

Figure 1: Cone & Radial cracks on ceramicafter projectile impact (Yamada, et al.,2010


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Figure 2: Ceramic fracture mec!anism from projectile ("adle#, 201$

b) 8tuies of the ferroe"ectric materia" 9a,i:; show that there"ati'e permitti'it! is not constant as a function of

temperature$ ith reference to the phase iagram e.p"ain thechanges in re"ati'e permitti'it! obser'e$

+erroe"ectric materia"s are capab"e of ho"ing spontaneous po"arisation( or aipo"e moment$ ,he ipo"e moment is as a resu"t of the centre of the positi'ean negati'e charges in an atomic structure being separate b! some istance$

%n orer for this to be the case the centre atom in the structure cannot beeuiistance from the surrouning atoms( otherwise the s!mmetr! wou" resu"t

in a 0ero ipo"e moment( therefore the atomic structure cannot be s!mmetric

aroun the centre point( such as a cubic structure$

,he o'era"" ipo"e moment in a piece of bu"* materia" is epenent on themoment an orientation of the omains that comprise the materia"$ ,!pica""!( a

ferroe"ectric materia" wi"" be constructe of man! i


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Figure $: *ressure 's )emperature p!ase diagram for +a)i% (a#-ard & alje, 2002

2bo'e 135=C( at atmospheric pressure( 9a,i:; has a cubic structure( where a""

atoms are eua""! space resu"ting in no ipo"e moment$ ,his is *nown as theCurie temperature as no spontaneous ipo"e moment is e.hibite abo'e this

temperature$ 2s the materia" coo"s it enters the tetragona" phase( where thestructure forms a rectangu"ar cuboi characterise b! a "engthening of one

imension of the cubic structure$ ,his causes a re"ati'e mo'ement of the

,itanium an :.!gen atoms( as shown in +igure 6( resu"ting in a net ipo"emoment in the 'ertica" irection$ 9e"ow appro.imate"! 6=C( the orthorhombic

phase ta*es on the structure of an irregu"ar cuboi where none of thecharacteristic "engths are eua"( as we can see in the gure this gi'es a net

ipo"e moment with a 'ertica" an hori0onta" component$ +ina""!( after further

coo"ing to be"ow ->5=C( 9a,i:; enters the rhombohera" phase whereb! one a.isis no "onger perpenicu"ar to the others( resu"ting in a further mo'ement of the

titanium atom re"ati'e to the o.!gen atoms an increasing the ipo"e moment$

Figure /: +arium )itanate spontaneous dipoles for eac! p!ase (o)*o, 200

;


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,he e


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2"uminium chromium nitrie is another coating suitab"e for the cutting of

harene stee"$ ,his ternar! coating pro'ies goo wear resistance an "owfriction at high temperatures$ ,his is "arge"! ue to the introuction of a"uminium

which( when e.pose to high temperature( forms a protecti'e o.ie "a!er he"ping

to protect the coating an too" e"in*si( 3556)$ ,he 2"CrN coating o


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coatings ha'e strong p"anar with wea* inter-p"anar boning( a""owing s"iing

between p"anes hence the "ow friction coecient$ Coatings are "imite inthic*ness ue to the fact that the coating oes not ahere we"" to itse"f$

Diamon-"i*e carbon a"so o

1>J7)$ /owe'er( the test in the stu! wereconucte using notche tensi"e specimens( a

simi"ar corre"ation between "oa rate an fracturetoughness has been shown in Ae.ura" tests of

8i"icon Carbie materia"s eerasoori!a( et a"$(

355?)$ :.ie ceramics are a"so susceptib"e to sub-critica" crac* growth( where crac*s can grow as a

resu"t en'ironmenta" attac* thereb! ecreasing thestrength an eibu"" mou"us a"though it is

un"i*e"! that this wi"" ha'e a signicant e


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"oa rate$ ,his is a resu"t of the signicant increase in strength from ; to 4 point

bening( which a"so reuces the 'ariation in resu"ts( a"ong with the reuction of surface efects from po"ishing$ +ina""!( the increase "oa rate is "i*e"! to resu"t in

a higher characteristic strength with "itt"e e


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Figure 4: 7ppro8imate speed ranges and applications for 'arious cutting and tool materials (a'is,199/

J


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,here are a few "imitations regaring use of ceramic too" materia"s$ %n particu"ar(

ceramics "ac* fracture toughness compare to meta" an carbie materia"s$ ,hisma*es ceramic too"ing more prone to crac*ing( notching an chipping which(

gi'en ceramic materia"s britt"e nature( can "ea to more freuent fai"ure of

cutting too"s$ ,hese prob"ems ha'e been a""e'iate to some e.tent through

introucing meta""ic particu"ates or whis*ers an through ege preparation of cutting eges$ :ne e.amp"e of this is the e'e"opment of 2"umina-baseceramics through aition of meta" particu"ates$ 8tuies ha'e shown that

2"umina reinforce with ,itanium Carbie 2"3:;-,iC) pro'ies an increase in

harness an toughness$ 8imi"ar"!( whis*er reinforce a"umina can pro'ie anincrease of fracture toughness b! as much as a factor of 3 as we"" as increasing

the therma" shoc* resistance 9uren( et a"$( 1>JJ)$ ,he whis*ers act to pre'entcrac* propagation through the materia" an toughness is increase through

whis*er pu"" out$

2 further "imitation of ceramic cutting too"s is their "ow therma" shoc* resistance$

,herma" shoc* can be an issue when cutting at high spees( therefore at hightemperatures( an introucing cutting Aui$ ,he "arge Auctuations in

temperature can "ea therma" crac*ing in the materia" resu"ting in fai"ure of the

too" 9rant( 1>J6)( a"though as iscusse these issues can be a""e'iate b!aing particu"ates or whis*ers$

,he esign on the cutting too" has a signicant e


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8ubstrate

CoatingCement

+

+

,he si0e of the insert wi"" ha'e an e


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+igure K Micrograph of fu"" scratch of DHC coating showing position of Hc1 an Hc3 Nano'ea( 351;)

test cannot be use to etermine the u"timate ahesi'e strength$ +ina""!( it is

possib"e that the epo.! ma! be permeate into coatings( egraing the ahesionbetween coating an substrate$

ii) ,he meaning of Hc1 an Hc3 in the scratch test

8cratch testing is an a"ternati'e metho to measure the ahesion of coatings$ 2scratch test is performe b! app"!ing a "oa to a conica" st!"us with a ene tipraius an cone ang"e$ 2s shown in +igure 11( a "inear motion is app"ie to the

st!"us whi"st graua""! increasing the "oa an recoring the norma" "oa(

frictiona" force an penetration$ ,he fai"ure moe of the coating epens on themechanica" an ph!sica" properties of the coating a"ong with the strength of

ahesion to the substrate$ %n thin coatings it is common for buc*"ing fai"ure tooccur whi"st thic* coatings ma! e.hibit wege

spa""ation$

,he concept of a critica" "oa was introuce to

etermine the norma" force reuire on a st!"usthat wou" resu"t in fai"ure in ahesion of the

coating to a substrate 9en#amin & ea'er(

1>6>)$ +urthering this concept( two critica" "oascan be etermine$ Hc1 can be ene as the

norma" "oa where rst crac*ing or cohesi'efai"ure of the coating occurs( usua""! /ert0ian

t!pe crac*s$ Hc3 is the norma" "oa where tota"

fai"ure of the coating through ahesi'e fai"ure or e"amination occurs$ ErrorK@eference source not foun be"ow shows the progression of a scratch test in a

iamon-"i*e carbon coating( with the "ocation of Hc1 an Hc3 inicate$ ,he gure

c"ear"! shows signs of a cohesi'e coating fai"ure past the point of H c1 fo""owe b!tota" fai"ure of the coating abo'e Hc3$

g) hat is the ma.imum short term four-point bening stress towhich a component of 'o"ume 3755mm;( mae from the same

materia"( can be sub#ecte if "ess than 3 in ;55 fai"ures can beto"erateL

,he ratio of the three point bening strength to the unia.ia" tensi"e strength;Bt) an the four point bening strength to the unia.ia" tensi"e strength 4Bt)

are respecti'e"! gi'en b!K

11

Figure 11: llustration of scratc! testsetup (C nstruments, 201


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σ 3

σ t

=[2 (m+1 )2 ]1

m

>$;O

shown in Euation ?$

ln ln( 1 P s (V 0 ) )=m lnσ −mln σ 0


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ln σ =

lnln ( 10.993 )8

+ln σ 0


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to c"ean the substrate b! sputtering( remo'ing an! surface impurities that ma!

be present b! bombarment m! ions from the p"asma g"ow ischarge$ ,he biascan a"so be use uring coating growth to impro'e the microstructure of the

coating b! increasing ensit! an surface i


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a""owing a s"ip with a "ow water content to be poure into the mou"$ ,he "iui

from the s"ip is absorbe into mou"( forming a "a!er of ceramic materia" arounthe surface$ :nce the so"i "a!er has reache the esire thic*ness the e.cess

s"ip can be remo'e for reuse whi"st the cast is "eft to r! further$ 8"ip casting is

suitab"e for creating comp"e.( thin wa""e structures howe'er( the process ta*es

a "ong time an is icu"t to automate so ma! not be suitab"e for proucing the"arge prouction 'o"umes e.pecte for the component$

%n#ection mou"ing is a p"astic forming metho that uses a mi.ture of a ceramic

power an biner that( when heate form a 'iscous Aui that can be formeinto the esire shape$ ,he biner use is norma""! a thermop"astic po"!mer

materia"$ ,he granu"ate ceramic mi.ture is heate an pressurise in thein#ection mou"ing machine( "iuef!ing the mi.ture so that it is ab"e to Aow into

the mou" of esire shape$ 2fter coo"ing( the component is remo'e from the

mou" an unergoes the ebining process$ %nitia""!( an! so"ub"e biner can beremo'e through soa*ing in a so"ution an subseuent"! the remaining biner is

remo'e through a heating$ ,he in#ection mou"ing process can be hea'i"!automate ma*ing it suitab"e for the sca"e of prouction that is reuire for the

turbocharger rotors( a"though the biner remo'a" process ta*es a substantia"

amount of time$

8hown in ,ab"e 3 be"ow are the mechanica" properties for 8i"icon Nitrie an

irconia$ 2s iscusse ear"ier( it is important for a turbocharger rotor to ha'e a"ow mass in orer to increase performance$ 8i"icon Nitrie e.hibits a substantia""!

"ower ensit! of the two materia"s$ 2"though irconia has reuce sti>5)$

)a3le 2: aterial and mec!anical properties for ilicon >itride and ?irconia (Ceratec, 201

Ceramic SiliconNitride (Si3N4)

Zirconia(ZrO2) TZP

SiliconCarbide

(SiC)

Material

Properties

Units

Densit! gBcm; ;$3? ?$56 ;$1Mou"us ofE"asticit!

Ga 376 355 415

+"e.ura" 8trength(

4pt

Ma 765 1555 415

Compressi'e8trength

Ma 3655 3555 3355

+racture

,oughness

Ma

m1B37 15 ;$3

eibu"" Mou"us - 16 16 15

16


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Ceramic ower

,he unia.ia" pressing proceure fees ceramic power into a ie which is then

compresse into the esire shape$ +igure 13 shows a schematic i""ustrating the

proceure$ Inia.ia" pressing is suitab"e for manufacture of simp"e( "ow aspectratio shapes such as mechanica" sea"s an the process can be easi"! automate

for rapi prouction of components$ 2 signicant rawbac* from the process isthat the ensit! of the compresse ceramic is not uniform throughout the

component( resu"ting from the friction between partic"es an the ie wa""s$

+urthermore( it is possib"e that crac*s ma! form in the component when pressureis re"ease an uring e#ection$

,he mechanica" properties shown in ,ab"e 3 show that whi"st 8i"icon Carbiee.hibits high sti


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"ength( meaning that an! energ! is uic*"! transferre across partic"es$

rouction of bu"* Diamon materia" can on"! be achie'e at 'er! hightemperatures an pressures( 1455= an 6Ga Capper( 3556)$

Figure 1%: sp% !#3ridised 3onding (left cr#stal structure (rig!t (*es!cel, 2011

Diamon-Hi*e carbon is the name gi'en to carbon a""otropes with an amorphous

structure( which can ta*e se'era" i


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on"! suitab"e for use on non-ferrous components$ Diamon coatings are

e.treme"! usefu" for optica" app"ications( gi'en that the! o


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@eferences9aumgarten( 9$ 2$( ,oronato( D$ 8$ & Rep"er( $ +$( 3511$ n'estigation ofol#3denum isulAde and )ungsten isulAde as 7dditi'es to Coatings for Foul

Release #stems , Den'erK Materia"s Engineering an @esearch Haboroator!( ,echnica" 8er'ice Center$

9en#amin( $ & ea'er( C$( 1>6>$ easurement of ad!esion of t!in Alms. Honon(@o!a" 8ociet!( pp$ 1?;-17?$

9one""i( M$ et a"$( 3555$ 8tructura" an Mechanica" roperties of Diamon-Hi*e

Carbon +i"ms repare 9! u"se Haser Deposition ith Far!ing Haser %ntensit!$

aterials Researc! ociet#, Fo"ume 6>;$

9rant( G$( 1>J6$ ,herma" 8hoc* @esistance of Ceramic Cutting ,oo"s$ urface

JJ$ C:M2@%8:N :+ /:,-

%8:8,2,%C2HHT-@E88ED 2ND IN%2U%2HHT /:,-@E88ED 2HIM%N2-,%,2N%IM-C2@9%DE CI,,%NG ,::H8$$ 7merican Cermaic ociet# +ulletin, ?7?)( pp$ 155;-

1556$

Capper( $( 3556$ +ulk Cr#stal Bro-t! of anostructured Coatings for ig! *erformance )ools, s$"$Ke*0eug ,echni*$

C8M %nstruments( 351?$ cratc! )est. V:n"ineW2'ai"ab"e atK httpKBBwww$csm-instruments$comB8cratch

V2ccesse 5? 2pri" 351?W$

Da'is( P$ @$( 1>>6$ 7 pecialit# and3ook: )ool aterials. 1st e$ s$"$K28M

%nternationa"$

Do%,oM8( 355?$ Ferroelctric aterials. V:n"ineW2'ai"ab"e atK httpKBBwww$oitpoms$ac$u*Bt"p"ibBferroe"ectricsBine.$php

V2ccesse 15 2pri" 351?W$

DuJ7$ 7 et!od For #namic Fracture

nitiation )esting f Ceramics, ro'ienceK 9rown Ini'erist!( Di'ision of

Engineering $

/a!war( 8$ 2$ & 8a"#e( E$ /$( 3553$ ,he pressure-temperature phase iagram of9a,i:;K a macroscopic escription of the "ow-temperature beha'iour$ ournal of

*!#sics: Condensed atter, 14;?)( pp$ 6>>-?54$

1>


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/a0e""( $ P$( 3516$ 7rmour: aterials, )!eor# and esign. s$"$KC@C ress$

/oriba( 355J$ )( pp$ 17J>-17>?$

8an'i* Coromant( 351?$ nsert !ape. V:n"ineW2'ai"ab"e atK

httpKBBwww3$coromant$san'i*$comBcoromantBpfBMeta"wor*ingXrouctsX5?1BtechXaX6$pf

V2ccesse 5J 54 351?W$8himi0u( ,$( ,a*ama( R$( Eno*ishima( /$ & Mi*ame( R$( 1>>5$ 8i"icon Nitrie

,urbocharger @otor for /igh erformance 2utomoti'e Engines$ 7< nternational.

8tern( R$ /$( 1>>?$ etallurgical and Cermaic *rotecti'e Coatings. 1st e$

s$"$K8pringer Nether"ans$

8u"0er( 3551$ *rotecting *umps against 73rasi'e "ear , s$"$K 8u"0er ,echnica"@e'iew$

a"e!( /$( 3514$ +allistic mpact ec!anisms f aterials. V:n"ineW2'ai"ab"e atK httpKBBwww$'irginia$euBmsBresearchBwa"e!Bba""istic-impact$htm"


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ang( H$( 8u( P$ +$ & Nie( U$( 3515$ Corrosion an tribo"ogica" properties an

impact fatigue beha'iors of ,iN- an DHC-coate stain"ess stee"s in a simu"atebo! Aui en'ironment$ urface and Coatings )ec!nolog#, 3566)( pp$ 16>>-

1?56$

eerasoori!a( ,$( Mo!( $ & Casem( D$( 355?$ 2 +our-oint 9en ,echniue to

Determine D!namic +racture ,oughness of Ceramics$ ournal of t!e 7mericnCeramic ociet#, J>;)( pp$ >>5->>6$

Tamaa( M$( 8e*ine( R$( Ruma0awa( ,$ & ,anabe( T$( 3515$ @e"ationship betweenthe cone crac* an fracture moe in ceramics uner high-'e"ocit!-pro#ecti"e

impact$ ournal of t!e Ceramic ociet# of apan, pp$ >5;->5J$

e"in*si( $( 3556$ )!e Case For 7 C!romium6+ased Coating. V:n"ineW

2'ai"ab"e atK httpKBBwww$mmson"ine$comBartic"esBthe-case-for-a-chromium-base-coating


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Ceramics and Ceramic Coatings Coursework