J. Mikroskopi don Mikroanalisis VoL3 No.2 2000 ISSN 1410-5594

THE EFFECTS OF IRRADIATION DOSE AND TEMPERATUREON LOOPS FORMATION IN NiJAI

SuryantoP2PN -BATAN

Kawa.~an P/I.~pip/ek .lIerpnn,i,7, Tan,i,7era11,i,7 /53/-1. Ban/en

ABSTRACT

THE EFFECTS OF IRRADIA TION DOSE AND TEMPERA TURE ON LOOPS FORMATION IN NI AL. TheJ

effects of irradiation dose and temperature on the loop formation in Ni,Al have been investigated. lhe Investigation \lIasperformed by means ora transmission electron microscope. During irradiution cxperimcnt. thc microscopc \\as opcratcd at thchighest accelerating voltage. In investigating the effect of irradiation dose. the sample was irradiated at a certain temperature forvarious dose and in investigating the effect of irradiation temperature. the sample \\'as irradiated at a certain dose for varioustemperature. The analysis was performed in the microscope operated at 200 kV to avoid additional damagc introduced by thcmicroscope. '('he loops gcncratcd by thc high cnergy clcctron irradiution \lIcrc photographcd.

ABSTRAK

PENGARUH DOSIS IRADIASI DAN TEMPERA TUR PADA FORMASllOOP DAlAM NiJAI. Pcngaruh dosis

iradiasi dan tcmpcratur pacta formasi loop dalarn Ni)AI tclah ditcliti. Pcnclitian dilakukan mcnggunakan mikroskop clcktron

transmisi. Selarna iradiasi mikroskop elektron dioperasikan dengan energi tertinggi. Dalarn mengamati pengaruh dosis iradiasi.

sampel diiradiasi pacta temperatur tertcntu untuk bcrbagai dosis dan datum rncngarnati pcngaruh tcmpcratur iradia~i. ~arnpcl

diiradiasi pacta dosis tertentu untuk berbagai tcmpcratur. Analisis dilakukan didalam mikroskop yang diopcrasikan dcngan cncrgi

rendah (200 kY) agar tidak terjadi tambahan loops. Loop yang tcrbcntuk akibat iradiasi clcktron cncrgi tinggi dif()to.

1. INTRODUCTION

In this study the effect of irradiation dose andirradiation temperature on loop formation in NiJAI gen-erated by high energy electron irradiation in an electronmicroscope were investigated.

2. EXPERIMENTS

A great advantage of the use of high voltageelectron microscope in the study related subject withelectron radiation is the insitu observation of latticedefects fonned during irradiation. The other advantageof the method is the easy control of the radiation condi-tion including a very high dose rate of electron.

Several reports showed the complication of thefonnation of point defect clusters by the irradiation attemperatures at which some kinds of point defects canmove freely. A fonnation of dislocation loops was ob-served in cooper at room temperature in an electron mi-croscope with 600 kV [I]. The loops were identified to beof interstitial type [2]. At a higher temperature as 200 "C,vacancy stacking fault tetrahedra was observed in a thinpart of a foil in addition to the interstitial type disloca-tion loops [3]. In aluminium, vacancy type dislocationloops were observed at 20°C with 1000 kV electron mi-croscope but not at 70°C [4,5]. In nickel the simultaneousfonnation of interstitial and vacancy type defects wasobserved in an intennediate temperature range aboveand below which only the interstitial type defects fonned[6]. These various observation are clearly showing thatthe formation of point defect cluster is essentiallyrelated to the irradiation temperature, migration rates ofeach kind of point defects and irradiation dose.

An ingot ofNiJAI was prcpared from pure nickeland pure aluminium rods by induction melting ina vacuum of about 1.0 x 10'" Pa. To homogenise the alloy,the ingot was annealed at 1323 oK for 48 hours in a vacuumof better than 5.0 x 10.6 Pa and then furnace cooled toroom temperature. In order to check the homogenity ofthe alloy, the ingot was subjected to x-ray diffractionanalysis and optical metallographic assessments. Inaddition, the chemical composition of the alloy \''asexamined using energy dispersive x-ray analysis.

After the ingot was cut into slices of about0.5 mm thick by spark cutting, small disc, which is 3 mmin diameter, was also made by spark cutting. The discswere polished to a thickness of 0.2 mm by hand grindingon SiC polishing papers. The foils for TEM wereelectrolytically prcpared from these discs using a Struerstwin jet electropolisher (Tenupol). The electrolytesolution for this alloy consisted of 12% of perchloric

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The Effects of Irradiation Dose and Temperature On Loops Formation in Ni.r4l) (Suryanto 5 -8)

acid (60%), 32% of2-n butoxyethanol, 56% ofmethanoland 50m I glycerine for every 1000 m I solution. The bestcondition for polishing the foils with the above solutionis as follows: Yoltage 30 volt, Flow rate 3 Unit, Tempera-ture 0 "C. After polishing, the specimens were immersedin ethanol for about 5 minutes.

Irradiation was carried out on grains of NiJAIspecimen in a lEal 4000-FX which can be operated upto 400 kY. The specimen was mounted into a hot stagespecimen holder and heated to a required temperature.The accelerating voltage was set to low voltage to find asuitable area for experiment and then, the irradiation con-ditions such as accelerating voltage were set up. Then,the electron beam was condensed and directed to thechosen area without concern for the crystal orientation.The specimen was irradiated for a required dose. Thetemperature range of this experiment was set up from400 "C to 550 'C. The experiments were repeated forirradiation temperature of 500 "C and a range ofirradiation dose.

Displacement rates were measured using the beamcurrent. If the value of the beam current was 5.1 I x 10-7Afor an area approximately 5 ~m in diameter and the dis-placement cross section is 25 barns, therefore the dis-placement rate is 4 x 10-4 dpa sol. At this displacementrate, the time for a nominal dose of 0.12 dpa is 5 minutes.

TEM assessment was carried out on a JEOL4000-FX, which is equipped with double tilt specimenholders, which can be used to select the desired beamdirection. The accelerating voltage used for irradiationwas 400 kY while for analysis the results were set to200 kY. The loops generated by the electron irradiationwere recorded by taken their photographs.

3. RESULTS

Experiments investigating the effects of irradia-tion temperature on microstructure were carried out for anominal temperature range of400 to 500 "C for the same

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dose. The experiments were performed on an area withapproximately the same thickness and the microscopeconditions ( i.e. energy of electron, spot size) were keptthe same. The results of these experiments are shown inFigure 1-4. This figure shows that the centre of the

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l'igurc 2. Loops in Ni,AI Gencratcd by Elcctron irradia-tion at 450 "C for a dose of 0 12 dpa

Figure I. Loops in Ni,AI Gcncratcd by Electron irradia-tion at 400 "C for a dose of 0.12 dpa

J. Mikroskopi dun Mikroanalisis VoL3 No.2 2000 ISSN 1410-.~594

irradiated area was damaged severely and loops wereobserved as large as 100 nm in diameter. A way from thecentre of the loops were smaller. The largest loops wereobserved after irradiation at 500 °C for a dose of 0.12dpa. The smallest loops were observed after the irradia-tion at 400 °C. Therefore, as the irradiation temperatureincreases, the loop diameter increases. Figure 9 showsthe loop diameter as a £tinction of temperature.

It is not only the diameter of the loops, whichchanges with irradiation temperature, but also thedensity of the loops. Figure I -4 shows the changes ofthe loop density as a function of temperature. It wasobserved that the highest loop density was found afterthe specimens were irradiated at 400 °C. Therefore. theloop density decreases as the irradiation temperatureincreases.

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C'. \ ,'.'.I'igure 7, Loops in NiJAI Generated by 1,Icctron irradia-

tion at 500 "C for a dose of ()36 dpa

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Figure 5. Loops in Ni,AI Generated by Electron irradia-tion at 500 "C for a dose of 0.072 dpa. Figure 8 I.oops in Ni,Al (iencratcd hy 1;lccmln irradia.

tion at 500 "C for a dose of 0.72 dpa

Figure 9. The average diameter of loop~ in Ni,AI gcncr-ated by electron irradiation for a dosc of 0.12 dpa at

various temperatures

Figure 6. Loops in Ni,AI Generated by Electron irradia-tion at 500 "C for a dose of 0,12 dpa.

diation dose, the loop population is low. This popula-tion increases as the dose of irradiation increased. Thesmallest loops were observed for high irradiation dosewhile the largest loops were obtained from the experi-ment at low dose. The average diameter of loops as afunction of irradiation dose was illustrated in figure 10.

Figure 5 -8 are the micrograph of irradiated areaas results of experiments investigating the effect of irra-diation dose on the loop formation. The experiments wereperformed on the same thickness area and on the samecondition ofmicroscope. This figure shows for low irra-

The Effects of Irradiation Dose and Temperature On Loops Formation in Ni.,Al) (Suryanto 5 -8)

5. REFERENCE

[IJ. M.J.MAKIN,Phi/.Mag.,1968,18,637.[2J. M. lPOHORSKI and M.S. SPRING, Phi/. Mag., 1969,

20,937.[3J. M. IPOHORSKI and M.S. SPRING, Phi/. Mag., 197O,

22,1279.[4J. K. SHIRAISHI, A. HISHINUMA. Y. KA T ANO and

T. T AOHA, J. Phys. .S'oc. Japan. 1971. 30.295.

[5]. K. SHIRAISHI, A. HISHINUMA. Y. KA T ANO and

T. TAOHA,J. Phys. Soc. Japan, 1972,32,964.[6]. K.URBAN,Phys.Stat.So/id.1971, A4,761.Figure 10. The average diameter of loops in Ni,AI gene-

rated by electron irradiation at 500"C for various doses

4. CONCLUSION

The effect of temperature on the loop formationgenerated by electron irradiation in a transmissionelectron microscope is significant. For low irradiationtemperature the loop density is high while for high irra-diation temperature it is low. The largest loop formationis obtained for high temperature while the smallest loopformation is obtained for low temperature of electronirradiation.

The loop formation generated by electron irradia-tion in a transmission electron microscope is affected bythe irradiation dose. The lowest loop density is obtainedfor low irradiation dose and the highest loop density isfound for high dose. The largest loop formation isobtained for low irradiation dose and the smallest loopformation is observed for high irradiation dose.

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