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Confocal microscopy description of porosity defects in metallic composite alloys

K. G~wrlziriska ".*, S. Yatsuncnko b, W. Przctakicwicz a

"nstitule of Basic Technical Sciences, Maritime University of Szczecin, ul. Podgtirna 5 1/53,70-205 Szczccin. Poland "mtitutc of Physics PAN, Warsaw, Poland

Contact: e-mail: kasiag@am.szczccin.p1

Received 25.02.2008; accepted for printing 10.03.2008

Abstract

Possibilit ics of confocal microscopy applications for thc dcscripion of open porosity dcfccts in mctallic composirc alloys arc prcscntcd. This aniclc cbaractcrizcs rhc rncthnd and prcscnts its pssihle applications by describing a rcprcscntnr ivc nrcn of thc cxamined void.

Key words: AlZoy porosity; Confocal microscopy.

1. Introduction

Thc use of mtallic compsircs x m alloy rnaccrial is connected with ncw [ypcs of alloy dcrccts. eithcr unknown duc 10

a specific structure of compositcs or negligible in alloys of conventional matcrinls. Thcsc dcfcas can he divided roughly into thrcc proups:

dcfccts conncctcd with thc homogeneity of the shape and sims of rcinlorccmcnr derncnts and thcir uniform dis~rihotion.

a dcrccis conncctcd with the structure of mctntlic matrix hcing an effect of crystalli~ation in thc prcscncc ef rcinrorcemenr that may have nucleus-brming cFTcct. and campsite-specific types of porosiry.

The porosity of metallic compositcs with sakuratcd reinforcement, considering the rncchanism of its formation, belongs ta nne of the four lypes:

porosity rcsulling from insufficient saturation. porosity making up gas occIusions,

a singlc porcs or porosity due to gas emission. shrinkapc cavitics or porosirics [ 11.

Oncc porosity is assigned to one of the four typcs. it bccomcs possihlc to choose a technolagical mclhod aimed aa eliminating t hcsc dcfcas. Thc mcthod of climination can bc identified on thc basis of an nnnlysis of porosity propesties prcsenterl in Tnhle I. Thc tablc includes thc porosiry typc and the Bctors cnahling its idcntilicat ion.

Thc tablc 1 clearly shows that thc dcfccts consist of voids or various shapes and sizes and rhnt thcir distrihi~~ion throughout the cast volume may vary. Thcsc voids. affecting thc cast dcnsity, may hc generally dcfincd as prosilies. Open porosities can belong to typc 1, 2, 4 or 5, whilc closed porcs can be cIasscd as typc I . 3.4 or 5.

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Table 1. Characzcrist ics of porosity dclccts in mctnll ic compositc alloys with snruratcd scinforccmcnt [ I , 21

Porosity is cxamincd in ordcr to: 1 ) dcvdop rhc mcthod of dctcrmining the rota! porosity of

ca~ts or thcir macro-arcas by methods different from thc macroscopic ones;

2) vcriry ahc usability of microscopic mcthods o f porosity cxarninatinn which aim at thc dctcrmination of: * vssihilitics or identifying porositics. to differcotiate

pores From othcr constitucnis o f thc structure; conlcnt o f porcs in micro-arcas; distribution o f pmsitics in macro-nrcas or in rhc whole cast volumc: possibilily of porosity idcnrification.

This articlc attempts at describing open porositics in cornpsilcs hy means of confocal microscopy.

Location

S hapc

2. Characteristics of confocal microscopy

ldcntilication L~ctors

I

I I

Confocal microscopy is a vcrsion o f light microscopy Ihat features incrcawd cnnzmt as well as better sesolu~ion and possibiliry o f ohscrving objccts in thc 3D mode [3-51. I t is uscd for obtaining high qualiry irnngcs or the rcconstnlction of tbrec- dimensional imaycs. In c~nrocaI microscopy, as cornparcd to lhc

Size

--- rcsult ing from rcinforccmcnt clcmcnts dimensions

canvcnt ional widc-field fluorcsccncc microscopy. r hc nul-of- focus lighr nr flarcs that rcach thc lcns arc cliininnecd nt t l ~ c

dctcctor input. For ihis purposc an additional apcnurc (diaphragm) with a pinholc of thc propcr diamctcr 13. 1;-01 i s plnccd in front o f thc dctccror.

In a convcntional widc-ficld microscope thc wholc spccimcn is illurninatcd by a soiircc or light. Thc s ~ c i m c n either pcflccts thc light or fluorcsccs ant1 Ihc oplical signals arc collcctcd hy the tcns. This. howcvcr. collccts ihc signal From all the iltutninatcd arca o f thc spccimcn, not on1 y from rllc focal point, which makes the background against ~ b c signal From thc hcus relatively high. resulting in reduccd conIrast. The usc of apcflurc with a small pinhdc in front of thc dctcctor curs of f rhc signal corning from outside the focal planes, which significmr l y incrcascs thc conwast and quality o f the ohtaincd imagc. Thc thickness or thc focal planc, consequently ~ h c vcrtical rcsolu~ion ol' ltlc rnicroscopc usually dcpcnds on thc objcctivc lens ant! lhc opiici~l path ss wclt as on thc propties or the spccimcn 15. 8-l I].

% dcscrihc porosities in metallic composic alloys thc aultlors uscd an OLYMPUS-madc confocal Inscr scanning rn i cmsco~ OCS 3100 (Ficures I and 2). Thc rcscarch has hccn donc n1 OLYMPUS prcmiscs thanks to the ceurtcsy of thc company.

Frcqucncy of occwrrcncc

mcurs rcpcatcd!y -

t

2

3

I

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rcinrorccmcnt spaccs not filled

cnt rappcd gas buhhlcs

prccipitntcd giis hubblcs

varicd. dcpcnding on solidification prcssurc in isolatcd arcas inclitding rcinfnrccmcnt clernents

5

cnst gcornttry. 1 tcnding to appcar near isolatcd arcas in isolatcd areas

OECLI~S ill random in rhc wtlolc volumc of lhc cnsl

shrinkngc cavi~ics and porosif ics

rcgardlcss of alloy gcomctry

random

in isolarcd: arcas

4 rcgardlcss or

random

comparahlc with thc dimensions of rcinfosccmcnt clcrncnts

comparnblc with thc dimctlsions OF rcinrorccmcnt clcmcnt s. somciirncs milch srnnllcr

I varicd. dcpcndcnt on tbc mnnncr o f crystallizntion. incrcasinp rownrds hc cenrrc sf isolarcd arca

gas prosiry

------- irrcgolar, dcpcndent on thc manncr of crysinlliza!ion

in places o f smallcsz distances bctwccn rcinforccmcnt elements

random

in places lnvourahlc to nuclcation, on rhc rcin forccment

occi~rs rcpcatcdly in isolatcd arms

occurs at random I i n isola~cd arcas

incrcnsing townrds thc ccntrc of isolatcd nrca.

rcsul t ing from rcinrorccmcnt stnrctiirc

sptlcrical

spherical

random spherical

KT-

Fig. l . Confocal lascr scanning m i c r o s c o ~ O D 3 100 hy OLYM13US 181

Thc OLS 3 101) conrocnl rnicmscopc madc by OLYMPUS consisrs of two indcpcnrlcnt pans (Fig. 1) - an optical micmscnpc (_crc.cn Sralnc in thc diaynrn) and confocal microscopc (rcd framc in the diagram). Thc rnicroscopc has two dncctors (CCD and photomulriplicr). A whirc light LED i~ 11sctI m a sourcc or light. Scanning is plcrforrncd with thc usc of il hluc lascr diodc with a wave kngt h of 408 nm.

Thanks to an XY scanncr in which MEMS technology (MicmEclcctmMcchanical S Y ~ C ~ ) i s c t n ~ l o ~ c d (Fig. 3) t i c Fig. 2. Diagram of;m OLYMPUS-rn:rlc cnnrclcat I,lscr scanning confocal lascr scanning rnicroscopc 013 3100 has a resolution micrnscopc 01,s 3 1 I)O [ X I 120xt2Onm inrhcXYpIanc.and 10nm along thcZaxis. with thc maximum magnification 120x - 14400~.

.I ) 17 J

Fig. 3. a) XY scanncr of an 01-YMPUS-n~adc confocnl lascr $canning microscopc Om 3 100. b) image with maximum rcsolution [HI

Thc examination and ohscrvations OF the spccimcn are performed in rcnt tirnc. 3'hc mcnsiirc~ncnt consisls in scanning sclcctcd area of rhc spccimcri, planc hy planc. rnoving along the Z axis fm~n thc lowcst to thc hiyhcst marksd plarlc. 'l'hus a thrce- dirncnsional rccanstnlclion or lhc scaiincrl Iinapc i s ohlaincd. Thc conrocnl lascr scanning lnicroscopc OCS 3 1110 cnahlcs viewin? thc cxnminctl objccr in 2 0 or 3D motlc. 'Thc ac~ual capi~hilitics of thc rncihnd and dcvicc arc shown hy zE~c cxaminn~inn of such dciccts as pornsilica that occur in mcznllic composircs.

3. Examplc of porosity analysis Thc cxamincd spccimcn ~vit h pnnlsi~icf w;tc a ~nc~nll ic cnmpositc formcd by satura'linn. t \ I t r~ i i tn~t~rn-s iEic 'o~i rutt~fr)rccmcn~ prcl'r>r~n\ wcrc ~nscncd i a l t r l il IIICI;II ~lloir lil ( r~i1irr1r~~enc111 matcrial w a q

hcarcd in a fvrnacc at a FClilpCr;lt~~r~ r ~ l ' 71~0'C for 3{){1I)O seconds). inf i l~ntcd by liquid alun~inium il[loy ( AISi 1 3 ) ; ~ t ~ d ~atttr~31cd unrlcr pressure of I5 MPa in ihc pcriotl or' 3000 rccotids. A11 lhc technological rcquircmcnts I'or ;~lloys ~>rnrlucctl by saturillinrl using thc l iq i~ id prcssiny mcthotl \rcrc s,t~i<licrl 1 I ] . Thc arca rvhcrc a void was idcn~iticd (1:1g. 3 ) \K\$ choccn ;it r.rnrlcrlt~.

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Fig. 4. The object chosen for a 2D description. Composite AlSi 1 1 reinforced with aluminium-silicon dibrcs

After scanning the chosen area we have a representative a three-dimensional reconstrtrction we obtain an irnagc of two-dimensional area of the examined object (void) so that ahc examined object (Fig. 5 ) with nurncrical valucs in thc we can estimate the parameters of this discontinuity. After X, Y, Z system range.

Thc mcrhotl rnakcs i t possiblc to accurately and unequivocally ~ h c volume and arca (Fig. 9 ) or ~ h c cxatnincd nhjccr - in this cusc specify t hc nurncrical valucs in any of thc XY, XZ and YZ planes. x porosity in an alloy. as sbow~l in Figures I 10 K and in TabIc 2 as wcll as to mcastirc

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Otr]e~:l.re LWS I,'PLFLN lCx Clyrnps Patska z m . : IrnegePlxds 102: x:68 k ~ ; l ! m Epbarc8

Fig. 6. Thc cxamincd void - tncasurcd parameters of the objca (void dcpths at its vario~~s points)

Fig. 7. Profile o f the exalnincd objcct along thc XZ axis and rhc mcasurcd pamrnctcrs

Tahlc 2. Mcasurcd paratnctcr vnl ucs OF the cxamincd points

Width Ifcigh~ 1 1 U P P ~ ~ Lower

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.. . , -- --. -- I . . l... ,...I..,., .,...-. ...a. I P..

Fig. 8. Thc cxamined void - mcnsurcd paramctcrs of thc objcc~ (cstirnntcd distnnccs bclwccn clcmcnts within ~ h c void)

v m . ~ I ~ _ A W S o r r n w 1 9 ~ 9 2 0 0 ~ 1 1 rn

Rys. 'I. Thc cxalnincd void - mcnsurcd parameters OF rhe objcct (esrimatcd votumc and arm)

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The measurement by rncans oi an OLYMPUS-made confocal laser scanning microscope OZS 3100 took less than a minute. As a result. the choscn void in a composite alIoy was cxamincd in order to estimate its geometric parameters such as the shapc (3D), depth, width. volume and arcas. Thc obtained reports will be used for further analysis. The method allows for an accuratc descrip~ion of thc cxamincd dcfcct and its classification into one of the porosity types as givcn in Table 1. I t will bc borne in mind that thc rrcqucncy of occutrencc should bc tcstcd with this method by examining a larger area of the sample, which goes beyond the scope of this article.

Literature

[ I I K. Galvdzi Aska K., Struczure Defects Classification of Casts from Saturated Metal Composites, Doctoral Dissertation, Technical University of Szczccin, 2003 (in Polish).

121 J. Jackowski, Gas occlusions in salurated cast composites, Ko~npozyv (Composites) 2 (2002) 4, s. 1 80- I X4. (in Polish).

[3] R.H. Wcbb, Confocal optical microscopy, Rcp. Prog. Phys. 59 (1996), 42747 1.

[4] D. Shotton (ed), Electronic Light Microscopy - Tcchaiqucs in Modcrn Biomedical Microscopy, (Wilcy-Liss), 1993,35 1.

[5 ] T. Wilson, Scanning optical microscopy, Scanning, 1985, 7, 79-87.

[6] R.H. Webb, Confocal microscops Opt. Photon, News 2. 1991,8-13.

[7] J.K. Stevens, L.R. Mills, J. Trogadis (eds), Three- Dimensional Confocal Microscopy. CA: Acadcmic. San Diego 1993.

[8] http://www.ntrndt.ml. [9] T. Wilson (cd), Confocal Microscopy, London: Acadcmic

1990. [lo] T. Wilson, C.3.R. Sheppard, Theory and Pract icc of Scanning

Optical Microscopy, London: Acadcmic 19M. [ I I ] E.M. SIater. H.S. Slater, Light and Electron Microscopy.

(Cambridge: Cambridge Un ivcrsity Press), 1 993.

Zastosowanie mikroskopii konfokalnej do opisu wady typu porowatoid w odlewach z metalowych materiaI6w kompozytowych

Streszczenie

W pracy przedstawiono motliwoici zastosowania mikroskepii konfokalnej do opisu wady porowatoit5 lypu otrrartego w odlewach z rnetalowych malerialbw kompozytowych. W niniejszym artykute scharak~eryzowano metode i zaprezentowano je j rnotliwoSci na przyktadzie reprczentatywnego obszaru badanego obiektu (pustki).

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ARCHIVES o l FOUNDRY ENGINEERING Vo lume 8 , S p e c i a l Essue 112008. 95-101