Surface erosion of TiC coatings under 4He+ and D+ ion irradiation

Thin Solid Films. 83 (1981) 93--106

93

METALLURGICAl. AND PROTECTIVE COATINGS

S U R F A C E E R O S I O N OF TiC C O A T I N G S U N D E R '*He + A N D D + ION IRRADIATION* A. S. RAO AND M. KAMINSKY

Argomw National Laboratory, Argonne, IL 60439 ( U.S.A .) (Received April 6. 1981 : accepted April 20, 1981)

The surface damage and erosion of chemically vapor-deposited TiC coatings irradiated by 20, 40 and 60 keV D ÷ and 4He+ were studied for as-deposited and polished surfaces. Scanning electron micrographs of irradiated TiC reveal surface damage and erosion due to blistering and surface exfoliation. The erosion yield increases with increasing ion energy for both D ~ and He ÷ irradiations, and it is generally larger for D ÷ than for He + irradiations at a given energy. The erosion yield is larger for polished than for as-deposited surfaces for both D ÷ and He ÷ irradiations. The relationship between the blister diameter and the skin thickness agrees well with a relationship derived from a gas pressure model but disagrees with a relationship derived from a model of integrated lateral stresses as a prime mechanism for blister formation.

I. INTRODUCTION

The use of materials with a low atomic number Z instead of a high atomic number in fusion devices can help to reduce plasma power losses due to radiation for identical concentrations of material released into the plasma (see, for example, refs. l-6j. TiC is one of the low to medium Z materials which are being considered for the protective coating of fusion reactor component surfaces (e.g. first walls, limiters and a r m o r plates). The aim of the present investigation was to study the surface damage and the erosion yields of TiC held at room temperature on irradiation with 4He ÷ or D ÷ ions with energies of 20, 40 and 60 keV. We expect D + ions with energies in this range to impinge on the surfaces of neutral-beam injector systems in fusion devices 7. 2. EXPERIMENTAl, PROCEDURE Chemically vapor-deposited TiC coatings with thicknesses of 10-20 lam were obtained from D. M. Mattox, Sandia National Laboratories, Albuquerque, NM. One set of samples was prepared by mechanically polishing the as-deposited TiC * Paper presented at the International Conference on Metallurgical Coatings, San Francisco. CA, U.S.A.. April6 10. 1981. 01)40-6090;81:0000-0(~0'S02.50

.~ Elsevier Sequoia:Printed in The Netherlands

94

a. S. RAO. 5t. KAM1NSKY

Fig 1. Scanning electron micrographs of as-deposited [(a)--(dll and polished [(el (h)l "I'tC surfaces: (al, le) unirradiated surfaces: {b), ~f'120 keV H e ' -irradiated surfaces: lcl. Ig140 kcV He" -irradiated surfaces: {dl. (hi 60 keV He" -irradiated surfaces. A dose of 98 -+ 3 C cm z v,as used for the irradiation of as-deposited TiC surfaces, and a dose of 45 ~ 3 C cm 2 for the polished surfaces.

SURFACE EROSION OF T i C COATINGS BY He ÷ AND D ÷ IRRADIATION

95

surfaces, while the second set was left in the as-deposited condition. Details of the preparation and characterization of the samples prior to irradiation have already been given elsewhere s. The irradiation conditions of the samples with massanalyzed D ÷ and He + beams were identical with those described elsewhere a"9. After irradiation the surface topography was examined in a scanning electron microscope.

Fig. 2. Scanning electron micrographs of as-deposited ((a)-(c)) and polished ((d)-(f)) TiC surfaces after D + irradiations: (a), (d) 20 keV D + -irradiated surfaces; (b), (e) 40 keV D+-irradiated surfaces; (c), (f) 60 keV D +-irradiated surfaces. A dose of 120 + 3 C c m - 2 was used for the irradiation of as-deposited TiC surfaces, a n d a dose of 85 + 5 C cm - 2 was used for the polished surfaces

90

3.

&. S. RA(), M. KAMINSK'I

RliSl:I.l S

Figures l(a) and I[ej show scanning electron micrographs of unirradiated TiC coatings on Poco graphite substrates in the as-deposited condition and after mechanical polishing respectively. The as-deposited surface is rough and has an average grain size of about 9.3 I.tm. Figures l{b). llc) and l(dl show the post-irradiated sample surface of itsdeposited TiC irradiated at room temperature to a dose of 98 +- 1 C cm -' with 20 keV f i e ' , 40 keV H e ' and 60 key He + respectively. Figures l(fl, l(g) and l(h) show the topography of polished TiC samples irradiated with 20 keV H e ' , 40 keV He" and 60 keV H e ' respectively to a dose of 45-+ 3 C cm x. In addition, as-deposited and polished TiC samples were examined after irradiation at room temperature with 20 keV H e ' to doses of 60-+ 1 C cm - z and 150 +- 3 C cm - 2 respectively. The st, rfaces of as-deposited and polished TiC samples irradiated with D + are shown in Fig. 2. The scanning electron micrographs in Figs. 2[a). 2(b) and 2(cl show typical as-deposited TiC surfaces after irradiation with 20, 40 and 60 keV I)" to a dose of 120 +-3 C cm--'. In addition, an as-deposited TiC sample was irradiated with 60 keV D + to a dose of 200 + 1 C cm 2. Polished TiC samples were irradiated at room temperature with 20 keV D +, 40 keV 1) ~ and 60 kcV D + to a dose of 85 + 5 C cm - -' and the irradiated surfaces are shown in Figs. 2(d), 2(e) and 2If) respectively. In addition, a polished surface was examined after irradiation with 20 keV D" to ~l dose of 55+-2 C c m - 2 . For the ion energies and doses used in the present investigation, both asdeposited and polished TiC coatings revealed surface damage due to blistering. With the aid of a Zeiss particle size analyzer we obtained a quantitative analysis of the micrographs with respect to the blister diameter, the density of blisters and the fraction of the surface area occupied by blisters. A large number of micrographs (about 30 micrographs at a magnification of 2000 x for every irradiated spot) were examined in order to provide sufficient statistical data. The blister skin thickness and the depth of the craters left after blister exfoliation were determined from scanning electron micrographs, at a magnification of 10 000 x. The most probable diameter and the average blister diameter were determined by plotting the percentage of blisters in a given size class as a function of the blister diameter. Histograms thus obtained for as-deposited and polished TiC samples irradiated with 20, 40 and 60 keV He" or I)* are shown in Figs. 3 and 4 respectively. In Table I the data on the blister diameters, the blister skin thickness t. the density of blisters and the fraction of the area occupied by blisters arc summarized for asdeposited and polished TiC coatings irradiated at room temperature with D - and H e ' at the various energies and doses. 4. I)IS(.'I/SSI()N 4.1. Blister diameter The results presented in Table I on the most probable diameter and the average blister diameter as functions of energy indicate an increase in the diameter for increasing projectile energy for both types of projectiles. This trend is similar to that observed earlier for many metals I o and ceramic materials'" ~-'. In fact, the values for

S U R F A C E E R O S I O N OF T i C C O A T I N G S BY H e + A N D D + I R R A D I A T I O N

AS DEPOSITED SAMPLES

'°|lP°,.°

I

Dmp=O-B,u.m I

"F,o %.0.. I

I

~ 2o

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T- 'Drop

3c-

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-

Dm p = I. I5/~m OOv = I. 15p.m

co 5(] u~

[ 20keY D*on TiC I DroP=2"4/~m I

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JI

DroP= l'7"u'm

C---i. I h

z 4C

POLISHED SAMPLES

II

loi' kv'"'oT' c' I

d 40 _Z [)mp 40keYHe*on TiC 50 DroP =O.B5/~m u.J Dov : 0,95ym

AS DEmOSI'rED SAMPLES

Drop=O.S~m Oov = 0.45,u,m

20keV He*on T,C I

~-l~

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Ill

POLISHED SAMPLES

97

I

I

40keY D+on TiC Dmp'~ Dmp=2"9/~m F l D°v=2"8'u'm

40KEYD* on TiC Drop; 4.3/~ m I T "Drop Day: 4"lk~m I I

CD

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---~--

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,,

01 BLISTER DIAMETER (.u.m)

i,

2

4

6 2 4 BLISTER DIAMETER {/,~m)

6

B

Fig. 3. Histograms of the distributions of blister diameter for as-deposited and polished TiC surfaces irradiated under normal incidence and at room temperature with 20, 40 and 60 keV He + ions (for asdeposited surfaces the dose was 98 + 1 C cm - 2: for polished surfaces the dose was 45 + 3 C cm 2). Fig. 4. Histograms of the distributions of blister diameter for as-deposited and polished TiC surfaces irradiated under normal incidence and at room temperature with 20, 40 and 60 keV D ~ ions (for asdeposited surfaces the dose was 12(1+ 3 C cm - 2. for polished surfaces the dose was 85 -+ 5 C cm - 2}. the average blister diameters D~v observed for He ÷-irradiated polished TiC surfaces (Table I) fit very well into the range of blister diameters reported earlier for other He+-irradiated materials (see ref. 10, Fig. 5). Power curve fits were applied to Day v e r s u s t plots in order to determine the parameters B and /3 in the relationship D,~ = B t p. The values obtained for both He ~- and D +-irradiated TiC coatings (for polished and as-deposited surfaces) are shown in Table II. The values obtained for polished TiB 2 and niobium surfaces are included for comparison. The niobium data have been reported previously t 3. An examination of Table II indicates that the value of/3 depends on the target material, the surface finish and the type of ion. These results are contrary to predictions m a d e on the basis of lateral stress models t4'~5. According to these models,/3 is independent of the target material and the type of ion and has a value of 1.5, as shown in the last two c o l u m n s of Table II. Table II reveals, however, a g o o d agreement between the experimentally determined values of/3 and those calculated according to an expression based on a gas pressure m o d e l ~6-t8. In connection with this m o d e l it has been shown that the gas pressure p needed to deform the blister skin can be written as TM ,7 p = 16ayt2/3D

z

(1)

98

A . S . RA(), M. KAMINSKY

L.,

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SURFACE EROSION OF T i C COATINGS BY H e + A N D D + I R R A D I A T I O N

V. ._o 0~ 0 II

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where cry is the yield strehgth, t is the blister skin thickness and D is the blister diameter. Assuming that the helium atoms which arc located in bubbles within a thin slab of ARp [the range straggling in the implanted ion distributiont give rise to the required gas pressure p. from the ideal gas law wc can write p =

tl c

ARp

k7

121

where n~. is the critical dose for blister formation. Equating eqns. (I} and 121 and assuming that t = Rp, we obtain (.16o-, / ~2

D = 13n.kT ]

RpI~Rp) I -

{3l

Since ARp varies with the projected range Rp, the relationship between D and Rp (or t) cannot be linear. Power curve fits of calculated values ~'~'z~' of Rp and ARp for the energy range 20-500 keV were used to determine the relationship ARp = aRpL t.'or the energy range where Rp is found to be equal to t, eqn. (3} can bc written as

[16aa, l ' 2

=

B R p I~ =

B I I~

(4)

Table I1 reveals that the exponents fi calculated according to cqn. 14l compare well with those obtained from experimental results.

4.2. Fracture characteristics if/blister skin,s Figures 1 and 2 reveal that many blister skins fracture in characteristic patterns. Within a given grain, blister skins often fracture into two halves or four quadrants. The fourfold fracture appears to be predominant. The fracture lines of one blister skin arc often closely aligned with those of another skin within a given grain {scc white arrows in Figs. 1 and 2). In several cases it can be sccn that the fracture along the diameter of the skin has been completed while the fracture perpendicular to this fracture line is incomplete. This results, for example, in a blister skin fracture into one half-section and two equal quadrant sections. Finally, it should be noted in Figs. 1 and 2 that the fracture lines of blister skins in one grain are aligned along two preferential directions (which are perpendicular to each other) but differ in direction from the fracture lines of blister skins on other grains. The observed predominance of the fourfold fractures is thought to be related to the prcferred cleavage of transition metal monocarbides on 1100} planes. For these carbides the easy growth direction is along ~100] when they arc drawn from the melt: ~. If this is also true for chemically vapor-deposited metal monocarbides, the grains will show a strong tendency to have a ~,100] direction close to the surface n o r m a 1 2 2 , 23

4.3. The density olblisters The density of blisters was calculated by counting the total number of blisters m many electron micrographs. The blister density per unit area was determined from the area of the sample examined and the number of blisters present in the area. The

S U R F A C E EROSION OF

TiC

C O A T I N G S BY

He + A N D D ÷ I R R A D I A T I O N

101

values for as-deposited and polished TiC irradiated with 20, 40 and 60 keV He + or D ÷ are given in Table I. The density of small blisters (of average diameter less than 2 pm) falls in the ranges (3-13)x 107 cm -2 and (1-2)× 1 0 6 c m - 2 for He + and D ~ irradiations respectively. The corresponding values for larger blisters (of average diameter greater than 2 ~tm) were found to be (1-2) × 107 cm - 2 and (3-7) x 106 cm - 2 respectively. Furthermore, the blister density decreased with increasing projectile energy (Fig. 2). For a given ion energy an increase in total dose resulted in a decrease in the total number of blisters, with one exception: for as-deposited TiC samples irradiated with 20 keV He + an increase in ion dose from 60 + 1 to 9 8 + 1 C cm -2 caused an increase in the total blister density from 3 x 107 to 4.8 x 1 0 7 blisters c m - 2. An increase in the blister density with increase in dose has also been observed in other materials (e.g. palladium24). An increase in the blister density with an increasc in dose was observed in metals 1° only when numerous small blisters were present over the entire irradiated area. However, when large blisters are present, a decrease in blister density is expected because of the increase in blister skin exfoliation and blister coalescence zS. These trends are in good agreement with the present observations. A direct comparison of the blister density in TiC with this quantity for other materials is not possible since, to our knowledge, no data are available for the high doses used in the experiments reported here. For this reason, only a brief discussion will be given of the blister densities observed in metals and ceramic materials irradiated at room temperature with He + and D + to doses up to 2 C c m - 2.

Blister densities in the range (6-10)× 106 cm -z were observed in niobium during He + irradiation and in the range (I-2t x l0 s cm -2 for D ÷ irradiation of niobiumZ6, zv. For certain types of ceramic coatings, blister densities in the ranges (1-2) x 106 cm - z and (2-3) x 105 cm - 2 were observed 28' 29 for 100 keV He" and D + irradiations respectively to a dose of 0.5 C c m - 2.

4.4. Area occupied by blisters The fractional area occupied by blisters was determined for each irradiated sample from the blister diameters and the blister densities. Table I lists the fractions so determined, and it can be seen that an increase in ion energy increases the area fraction occupied by blisters for both the as-deposited and the polished samples irradiated with He + or D +. For a given energy an increase in dose resulted in an increase in the area fraction of blisters. This suggests that in TiC an "'equilibrium" surface for blistering was not reached even for irradiations to doses of about 200 C cm - 2. It is not possible to compare the values for the area occupied by blisters in TiC at very high doses with values typical of other materials because of the lack of data in this dose range. ~t significantly lower doses, 0.5 MeV He + ions produced blisters in niobium and vanadium which occupied about 87°/;, and 52~0 respectively of the irradiated area for a dose of I C cm - 2 (refs. 29 and 30). For 100 keV He + irradiation the corresponding values for the area occupied by blisters were 35~i, and 30~,, respectively31.

4.5. Erosion yields due to surface exfoliation The erosion yield due to surface exfoliation is determined from the measured values of the average blister diameter, the average blister skin thickness and the area

102

a . S . RA(). M. KAMINSK5

lost due to blister exfoliation (Table I). The erosion yield gives the ratio of the number of molecules lost from thc lattice through surface exfoliation per unit arca to the number of ions striking this area. The total surface erosion yield is the sputtering yield s determined from Rutherford backscattering plus the erosion yield due to surface exfoliation. These values for both as-deposited and polished TiC samples irradiated with D + and He' are shown in Table III together with the ion flux. T A B L E 111 NPI'TTFR

"~ll [ D S .

I R()NI()N

~II [()S

ANI) HIISTFR FX|:()I IAllO\ Samph' state

As d e p o s i t e d As d e p o s i t e d As deposited Polished Polished Polished As d e p o s i t e d As d e p o s i t e d As d e p o s i t e d Polished Polished Polished

Implanted ions

"q'le"

I)"

FOR

Dill

I()

BI I S I I ' R

I XI()l

l~.[l()N

~,%D l ( ) l

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He ~ \NI) J)" IRR,'~I)IAIlO%o! "]"i(." Ion em'rg)" (keY)

20 40 60 20 40 60 20 41) 60 20 40 60

Ion.flu\" ( × l0 t s ions c m 2 s '1

12 2.0 2.3 1.2 2.(} 2.3 1. I 2. I 3.0 1.0 1.7 2.8

Sputterint,, yield" I × 10 2 I.IIOIYIS ion

4.56 3.06 1.70 4.05 2.61 1.70 0.81 0.43 0.40 0.65 ().32 I).21

i)

Erosion din" to hlister e.x'lidiati,m h I × I0 2 atoms ion ~ I

"lotal yield due to ~putteritt.~atul erosion caused hy hli~,ter c vloliat ion (*1(} " atOlllS ioi1 i )

0.13 4--0.(X~ 0.25 4- 0.05 0.50 " 0.10 0.13 + 0.07 0.72 .) (}.15 2.63 t 0 . 1 5 (/.30 _+0.03 0.37 ~ 0,06 0.86 _* 0.05 0.83 + 0.07 1.55 t 0.05 2.45-0.15

4.68 .t. 0.06 3.31 -+ 0 0 5 2.20+_0.10 4.18 + 0.07 3.33±0.15 4.33 ' 0.15 1. I I 4- I).1.13 0.80 ± 0.06 1.26 _- 0.05 1.48 - 0.07 1.87 _' 0.05 2.66 1"0.15

"' See ref. 3 I. h In the estimate of the erosion yield for I)" irradiation the surlace area lost because of grain boundars fracture is also included.

The results in Table 1II indicate that for H e - irradiations the sputtering yields are higher than the erosion yields due to surface cxfoliation. This trend is reversed for D - irradiations of polished TiC surfaces. Furthermore, the sputtering yields for both He ~ and D + irradiations are higher for as-deposited than for polished samples, a trend that we have reported previously 32 for TiB 2. This trend is thought to be due in part to the enlarged surface area for the as-deposited surface and to the fact that a larger fraction of the incoming beam strikes the rough as-deposited surface at oblique angles. The erosion yield due to surface exfoliation is smaller for the asdeposited surface than for the polished surface, a trend reported previously I~ for asdeposited and polished TiB 2 surfaces. F'or rough surfaces the coalescence of gas bubbles is reduced, a process which is essential for blister growth, For H e ' irradiated TiC surfaces the sputter yields arc considerably larger than the erosion yields due to surface cxfoliation (Table lilt. Therefore an estimate of the surface recession rate due to sputtering was made to determine whether the rate was large enough to influence the surface damage due to blistering. From the ion fluxes and the sputter yields (Table 1II) for the polished -IiC surfaces, the recession rates for the

SURFACE EROSION OF

TiC

COATINGS BY

He +

AND

D+

IRRADIATION

103

20, 40 and 60 keV He + irradiations were 2,4 x 10 - 9 , 1.6 x 10 - 9 and 1.0 x 10 -9 cm S-1. These recession rates are too small to influence the surfaces damage due to blistering significantly 33. A plot of the erosion yield (due to surface exfoliation) against, the projectile energy E is shown in Fig. 5. The following trends appear. (1) The yields increase with increasing projectile energy for both types of surface and both types of ion. (2) At a given energy the yields for as-deposited TiC are larger for D ÷ than for He* irradiations. (3) The yields for the as-deposited surfaces are lower than those for polished surfaces.

2oI E

i: "6

q

I.C

uJ

i

20 40 60 PROJECTILE ENERGY (WeV)

Fig. 5. The erosion yield due to surface exfoliation caused by He ÷ and D ÷ irradiations of as-deposited and polished TiC surfaces for different ion energies: O, He ÷ on as-deposited T i C ; O , He ÷ on polished TiC; U], D ÷ on as-deposited TiC; I , D ÷ on polished TiC.

In a comparison of the yields in Fig. 5, it should be kept in mind that different sets of yields were obtained for different doses (Table I). However, the dependence of the yields on the dose is small for the dose range studied (Tables I and III). Therefore a comparison of the yields appears justified. The increase in the erosion yields with increasing projectile energy E can be related to the increase in the projected range (and thereby in the thickness of the exfoliated skin) with E. The trend that the erosion yields for D ÷ irradiations are larger than those for He* irradiations can, in part, be related to the difference in the penetration depths of these ions at a given E and, in part, to the difference in the permeabilities of these gases in ceramic materials such as TiC. In general, D ÷ is less permeable than He* in ceramic materials tt An estimate of the total number of lattice atoms removed per unit area from a TiC-coated armor plate during the operation of neutral-beam injectors in Princeton's tokamak fusion test reactor can be made. The D O fluxes striking the armor plate per second reach values of about 1.7 × 1015 particles cm-2 at 40 keV, 2.9 x 1015 particles cm - 2 at 60 keV and 12 x l0 t 5 particles cm- 2 at 120 keV ~. These values were estimated on the assumption that 10~o of the neutral beam would not be absorbed by the plasma. On the basis of the total yields shown in Table III and if we

104

.,X. S. RA(). M. KAMINSK~

assume that a n estimated number of 10"* pulses )'ear ~of D" strike the armor plates with a pulse duration of 1.5 s, the as-deposited TiC loses about 1.7 x 1() iv TiC molecules cm 2 year- ~ and 2.9 × 10 ~7 TiC molecules cm -2 year ~ for the 40 kcV and 60 k e y I) ~ irradiations respectively. The polished TiC loses about 4.8 × 10 ~TiC molecules cm- 2 year- ~ and 8.1 × 1017 TiC molecules cm- 2 year ~ for the 40 keV and 60 keV I ) ' irradiations respectively. The values correspond to equivalent thickness losses o f a b o u t 100 and 171 A for the as-deposited surface and 282 and 476 A for the polished surface. Thesc thickness losses are small in comparison with the proposed coating thickness of about 10 s A. 5. ( ' ( ) N ( ' I . I ' S I ( ) N S

The present studies of the damage and erosion of polished and as-deposited TiC surfaces under 20, 40 and 60 keV D ' and He ~ irradiations at high doses {about 60-2(X) C cm 2) reveal the following major restllts. I1) The polished and as-deposited TiC surfaces show damage and surface erosion due to blistering and surface exfoliation for the 20, 40 and 60 kcV irradiations performed. 12) Many blister skins fracture into four equal quadrants, and w.ithm a given grain the fracture lines of blisters appear to be aligned along preferred directions. We speculate that the fractures occur preferentially on the I100) planes, the preferred cleavage planes for many transition metal monocarbides. 13) The relationship between the experimentally determined average blister diaineter and the mean blister skin thickness agrees well with a relationship derived on the basis of a gas presstire model but disagrees with a relationship derived on the basis of integral lateral stresses. 14) For the erosion yield due to surface exfoliation the following trends were observed. (a) The yields increase with increasing ion energy tor both 1)' and He" irradiations. (hi The yields due to D - irradiations are larger than those due to H e irradiations for as-deposited TiC surfaces. (el The yields for as-deposited surfaces are smaller than those for polished surfaces for both D + and He + irradiations. (d) The effect of dose on the yields is small for the dose range studied. The trends (al (d)tire identical with those that we have reported previously for TiB 2 coatings ~ 15) The erosion yields typical for He ~ irradiations of polished and as-deposited TiC surfaces are smaller than experimentally determined physical sputtering yields for these systems s. However, R~r the D - irradiation of polished TiC surfaces the erosion yields are larger than the physical sputtering yields. (6) An estimate of the total number of lattice atoms removed per unit area from a TiC-coated armor plate during the operation of neutral-beam injectors in Princeton's tokamak fusion test reactor for a period of a year reveals that the corresponding thickness loss of tile coatings is small in comparison with the thickness that we propose to use.

SURFACE EROSION OF T i C COATINGS BY H e + AND D + IRRADIATION

105

ACKNOWLEDGME,'NTS

It is with pleasure that we would like to thank R. W. Nielsen and R. W. Chamberlin, Jr., for the operation of the radiation facilities and P. R. Zschack for sample preparation. We are grateful to Dr. A. Turner, Argonne National Laboratory, for a discussion of the fracture characteristics of refractory metal monocarbides and to Drs. V. E. Krohn and R. Ringo, Argonne National Laboratory, for carefully reading this manuscript. This work was supported by the U.S. Department of Energy under Contract W-31-109-ENG-38. REFERENCES 1 W.M. Stacey, J r., et al., Proc. 2nd Top. Meet. on the Technology of Controlled Nut'lear Fusion, Vol. I, in U.S. ERDA Cor!L Publ. 769035-P1, 1976, p. 21 (U.S. Energy and Research Development Administration) (available from National Technical Information Service, Springfield, VA). 2 M. Kaminsky, Proc. 2nd Top. Meet. on the Technology oJControlled Nueh,ar Fusion, Vol. 1, in U.S. ERDA Con/] Puhl. 769035-PI, 1976, p. 149 (U.S. Energy and Research Development Administration) (available from National Technical Information Service, Springfield. VA). 3 T. Rossing, S. K. Das and M. Kaminsky, J. Vac. Sei. Teehnol., 14 (1977) 550. 4 D. M. Mattox. Coord., 1st Wall Coating Workshop Rep., 1978 (Sandia National Laboratories, Albuquerque, NM). 5 D.M. Mattox, A. W. Mullendore, H. O. Pierson and D. J. Sharp, Low-Z coatings for fusion reactor applications, 8th Syrnp. on Engineering Problems o/Fusion Research, Vol. 3, 1979, p. 1605 (Conf. 79CHI441-5NPS). 6 S.K. Das, M. Kaminsky and P. Dusza. ,1. Vae. Sci. Technol., 17(1977) 710. 7 M. Kaminsky, S. K. Das and J. Cecchi, Fusion TeehnohJgy, Vol. 2, Commission of the European Communities, Pergamon, Oxford, 1978, p. 789. 8 M. Kaminsky and R. Nielsen, Proc. bit. ConL on Metallurgical Coatings, San k)'ancisco. CA, April 6 10, 1981, in ThinSolidFilms, 83(1981) 107. 9 M. Kaminsky, S. K. Das and R. Ekern, Nuel. Technol., 29 (1976) 303. 10 S.K. Das and M. Kaminsky, Adv. Chem. Ser., (I 58) (1976). I 1 S.K. Das and M. Kaminsky, Thhl Solid Fihns, 63 (1979) 269. 12 M. Kaminsky and S. K. Das, J. Nucl. Mater., 85~6 (1979) 1095. 13 S.K. Das, M. Kaminsky and G. Fenske, J. Appl. Phys., 50 (5) (1979) 330,~. 14 M. Risch, J. Roth and B. M. V. Scherzer, Plasma Wall Interactions, Pergamon, New York, 1977. p. 391. 15 E.P. Eernisse and S. T. Picraux, J. Appl. Phys., 48 (1977) 9. 16 M. Kaminsky. Adv. Muss Spectrom., 3 (1964) 69. 17 S. K. Das and M. Kaminsky, J. Appl. Phys., 44 (1973 ) 25. 18 J.H. Evans, J. Nucl. Mater., 61 (1976) 1. 19 D.K. Brice, SAND Rep. 75-0622, 1977 (Sandia National Laboratories, Albuquerque, NM). 20 H.H. Anderson and J. F. Ziegler, ttydrogen Stopping Po~ers and Ranges in All Elements. Vol. 3, Pergamon, Oxford, 1977. J. F. Ziegler, Helium Stopping Powers and Ranges in All Elements, Vol. 4, Pergamon, Oxford. 1977. 21 D.J. Rowcliffe and G. E. Hollox, Res. Rep. KLR-71-14, May 1971 (Brown Boveri). 22 A. Mullendore, personal communication, Sandia National Laboratories, Albuquerque, NM, 1981. 23 A.P.L. Turner, personal communication, Argonne National Laboratory, 1981. 24 G.J. Thomas and W. Bauer, Radiat. Eft., 17 (1973) 221. 25 M. Kaminsky and S. K. Das, Faculty blstitute Course on Materials Technology fi~r Controlled Therrnonuclear Fusion. Argonne National Laboratory, August 9, 1976. 26 S.K. Das and M. Kaminsky, in S. P. Picraux, L. P. Eernisse and F. L. Vook (eds.), Applications ~1 Ion Beams to Metals, Plenum, New York, 1974, p. 543.

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