DEC ? 9 1 6

OAK RIDGE NATIONAL LABORATORY operated by

UNION CARBIDE CORPORATION NUCLEAR DIVISION

for the

U.S. ATOMIC ENERGY COMMISSION

'.1. 58

ORNL- TM- 1994

CREEP-RUPTURE PROPERTIES OF UNALLOYED TANTALUM, Ta-10% WAND T-111 ALLOYS

R. L. Stephenson

NOTICE This document contoins information of o preliminary nature and was prepared primori ly for internal use at the Oak Ridge Notional Laboratory. It 1s subject lo revision or correction and therelore does not represent a final report.

"

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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Abi:;tract . , .

Introduction

Materials

Experimental Details

Results and Discussion

Summary and Conclusions

iii

CONTENTS

Page

1

1

2

3

·3

16

CREEP-RUPTURE PROPERTIES OF UNALLOYED TANTALUM, . Ta-10% WAND T-111 ALLOYS

R. L. Stephenson

ABSTRACT

The long-time; high-temperature creep properties of unalloyed tantalum, Ta-10% W, and T-111 (Ta-8% W-2% Hf) were studied at 1204, 1427, and 1649°C (2200, 2600, and 3000°F). The Ta-10% W and T-111 were much stronger than unalloyed t;:mt~J,um. The properties of Ta-10% W and T-111 were almost equal for the thermomechaulL:C:t.l h'iotorii;>::; st11died. The ductilities of all three materials were excellent.

INTRODUCTION

In recent years, increasing consideration ha.s been given to tantalum­

base alloys for high-temperature structural applications. On the basis·

of short-time data, the addition of 10% W appears to improve substantially

the strength of tantalum. 1 This alloy also appears to have a low ductile­

to-brittle transition temperature, improved oxidation resistance, good

workability, and good weldabili ty. i,.2

More recently, hafnium has been added to the binary alloy. This has

resulted in' the T-111 alloy (Ta-8% W-2% Hf) which also appears to have

desirable ductility, weldability, and workabHity. 2 - 4 In view of the

potential strength offered by Ta-10% W and T-111 it was considered desir­

ablP to undertake a systematic study of their long-time (1000 hr) high~

tem:perature creep properties. The creep properties of ~Qre tantali1lll WP.re

also determined, primarily for comparative purpo::;es'.

1M. L. Torti, "90 Ta-10 W Offers High Temperature Strength Plus Ductilit.y," Space/Ae_ronautics 36, 87-93 (September 1961).

2G. G. Lessmann and D. R. Stoner, ''Welding Refractory Metal for SpacP. Power SysLern Applications," paper presented at the 9th National SAMPLE Symposium on Joining of Materials for Aerospace System::; Nov. 15~17, lgn'5, Dayton, Ohio.

3 R. G. .Donnelly and G. M. Slaughter, "Weldabili ty Evaluation of Advanced Refractory Alloys," Welding J. (N.Y.) 45, 250-s-257-s (June 1966) .

. 4R. L.· Ammon and R. T. Begley, Pilot Production and Evaluations of Tantallim Alloy Shee L, WANL-.PR-M-Uf l4 ( J\l,ne 1963).

2

MATERIALS

All materials used in this study were produced by National Research

Corporation. Their co.mpositions are shown in Tables 1, 2, and 3. All

materials were tested in the cold worked condition.

.Table 1.

Element

Tungsten Molybdenum Titanh.un Copper Aluminum Niobium Bili con Nickel Chromium Iron Nitrog~n

Uxygen Carbon Tautl::l.lum

Vendor's Analysis of Unalloyed Tantalum, Heat 2202

Weight Percent

0.004 0.001 0.0005 0.0001 0.0025

.0.0032. 0.0016 0.0005

< 0.0005 o .nmo 0.0020 o.oo~.6

0.0025 Balance

Table 2. Vendor's Analysis of Ta-10% W, Heat 1862

EleiD:ent

Tungsten Molybdenum Nickel .Chromium Iron Nickel Oxygen Carbon TantaJ..nm

Weight Percent

9.1 < 0.0010 < 0;0005 ...:::: 0.0005

0.0010 0.0023 0.0036 0.0035 Balance

3

Table 3. Analyses of T-111 Alloy, Heat 2650

Element Vendor's Analysis ORNL Analysis. (wt %) (wt %)

Tungsten 7·.4 7.5 Hafnium 2.1 1.9 Carbon 0.0049 0.0070 Oxygen 0.0057 0.0053 Hydrogen 0.0004 Nitrogen 0.0023 0.0029 Tantalum Balance Balance

EXPERIMENTAL DETAILS

The apparatus used is described in.a previou~ report. 5 The tests

were perfonned at pressures lower than 2 x 10-7 torr. Every test specimen

was analyzed for interstitial impurities. The carbon contents of most

specimens were less than 100 ppm after testing. The.after-test oxygen

content of most specimens was between 100 and 300 ppm. It was not

possible to detect any systematic dependence of the mechanical properties 0

on the posttest interstitial levels within the ranges mentioned. Sheet

specimens 0.60. in. thick with a gage section 3 x 0.2 in. were used.

'l'he meta.llogro.phic specimens were prepared by vibratory polishing in

a manner described by Long and Gray. 6

RESULTS AND DISCUSSION

The creep-rupture properties of unalloyed tantalum at 12U4°C (2200°F)

are given in Fig. 1. Times to 1, 2, 5, and 10% creep are plotted as a

function of stress along with the time to rupture. Similarly, the creep­

rllpture properties at 1427vC (2600"F) and 16l19°C (?OOO°F) are given in

5R. L. Stephenson, Comparative Creep-Rupture Properties of D-43 arnl B-66 Alloys, ORNL-TM-944 (November 1964).

6E. L. Long, Jr., and R. J. Gray, Metals Progr. 74(4), 145-148 (October 1958).

8

+

2

103 0.1

I•

&

+

• +

+

4

ORNL-DWG 67-8592

I I. I 111111 I I 11 " nurTunc • IO"loCREEP • 53 CREEP • 23 CREEP + t"lo CREEP

( ) RUPTURE OUCTILITY IN "lo

.... (76) (66)

'!"--. 83

• ~ (74 (44)

........... ' ' & • ~(75)

f'-,, . ' • 75) ...

+ '

10 100 IUOO 10,000

TIME (hr)

Fig. 1. Creep-Rupture Properties of Unalloyed Tantalum at J.?.04 °C (2200 °F).

Figs. 2 and 3, respectively. Figure 4 gives the secondary creep rate as

a function of strei;_;s for t-.hiaco thl"ee: tempe:r~tureR.

'I'he creep-rupture properttes ·of Ta.-10% W alloy at 1204 °C (2200 °F) am

shown in Fig .. 5 •. 'T'~.m'i6' to 1, 2, ~, and 10% creep are shown as a. functlon

of stress along with the time to rupture. Similarl:v .• thP. ~ree:p-ru.ptun:

4xto<>

f-.

. 2

- ......

4 ~

2x102

0.1

!

·-----

,__ ·-··-

• " (54)

.......

•

. r ~

o RUPTURE • 103 CREEP • 53 Cr!EEP • 2% CREEP + lo/.CAC:C:P ( ) RUPTURE OUCTILITY IN "lo

....

10

ORNL-DWG 67-8593

11 ......r--... • I'--~

J 11 (36)

.......... ['

& " . o(~-o~2)

.. _ ... ··-·· ·-·. ..

100 1000 10,000

TIME (hr)

Fig. 2. Creep-Rupture Properties of Unalloyed Tantalum at 1427°C (2600°F).

5

ORNL-DWG 67-8594

I I . • l"t:(43)

l"--1' t-

+ . . ~O) ......

B '1'..

" It • ' (72)

1'... o(42) 6

o RUPTURE • 10% CREEP • 5% CREEP • 2% CREEP + 1% CREEP ( ) RUPTURE DUCTILITY IN "lo

102 0.05 0.1 10 100 IOOO 5000

Fig. 3 . . (3000 °F).

'

-~

(/) (/) w 0:: f­(/)

B

6

4

2

B

6

4 x 102

Fig. 4.

TIME (hr)

Creep-Rupture, Properties of Unalloyed Tantalum at 1649uC

ORNL-DWG 67-8595

11 Ill I I I 11 Ill I I I

... 1204°C (2200°F) ,_

• 1427°C (2600°F)

/ IL/

• I 649°C (3000°F)

_,,,. """ _,.A' v ,,,.'•

_,.J..• v v . ~ ~

HVi -···

• .x • [/ . 1...-

,,_J.. 1...--•'

/ !/ .

- .. • - 1...- • ·/

·10 5

SECONDARY CREEP RATE (in.fin. hr)

Secondary Creep Rate vs Stress for Unalloyed Tantalum.

6

ORNL-DWG 67-8596 ..... l

-t'--. I

'~ i ~"--1;,r- -· ..... ...._ ~ ... ........... ·""'

' '· (31)

~ ...... .A.,

', ..........__ '-. ::::-- r-...... ,... (45)

I'+ ,....

~ .....

..... ~ • ~' I' ' I""--, "r-.

' I" ;-..., !'--

I'-. I'

2

+

" I'-. r-.. " -"' RUPTURE "' " - . 10% CREEP +

• 5% CREEP ~ - -·-• 2% CREEP

""' >--+ 1 % CREEP

'f"-, () RUPTURE .DUCTILITY IN % + 4

·--···· 2><1a • D.I 10 100 1000 10.000

TIME (hrl

Fig. 5. Creep-Rupture Properties of Ta-10% W Alloy at 1204°C (2200 °F) .

properties at 1427°C (2600°F) and 1649°C (JOOO°F) are given in Figs. 6

and' 7 .• respectively. The se.condC1r~1,r cr~~P r::i.to io given as a fun(;tion uf

stress for these three temperatures in Fig. 8.

"F'i gi1rP. 9 givP.s th~ o;reep ·rupture properties uf T-111 at 1204 "C

(2200°F). Similar curves are given for T-111 at 1427°C (2600°F) and

(/) (/) ct-'+

ORNL-OW~ 67-8597

(51)

~ 4 - 0 RUPTURE ~ I\ \ "' • W"lo CREEP [ \

- .A. 5 "In C:RE F, P -t--1--H-ttiTt--t--t-i--tt--+i-t--j-~\-f-1 tttttt--k', "i-+-t-H-1-

• 2% CRF.:FP + 1% CREEP

2 ,___ () .RUPTURE DUc;:T!l,,ITY IN % --t--t-r-H-rH>t--t--r-r-iri-t;rrr--r-r-ror-·-"l"M'11

1J L---L..-1-..L...J...J...J..JCJ.J__'--'L.......l...-L...WLI..LI.--'--'-'-'-'~LI--;-'-'--'->..L.-'..LI..L.--'--i......i.-'-'-'--LI-' . 0.1 10 100 1000 W,000

TIME (hr)

Fig. 6. Creep-Rupture PropP.rties of Ta-10% W J\.lloy at 1427°0 (2600 °F).

8

~ 6 Cf) Cf)

w ~ 4 Cf)

0 - •

~

• 2 -+

403 0.1

()

+. ...................

......... ' (55) - .... -....

.......... r-... r--.. +'- r-

', " l'--:-..1

ft

RUPTURE iO"lo CREEP 5% CREEP 2% CREEP 1% CREEP RUPTURE DUCTILITY IN "lo

I

7

ORNL-OWG 67-8598

........... ......... f'-... (43) .... f-.....1 ....

' .......... 1 ........ .........

......... , '" '• ........... ~8) ............._ 1-... "

...,.._ r-., "'I , ....

I', I" r-.,

..........

'-....

" '", '!-

' '

100 1000 W,000 TIME (hr)

Fig. 7. ( 3000 °F) .

Creep-Rupture Properties of Ta-10% W Alloy at 1649°C

4x10 4

2

- 104 ·u; 0. 8

~ 6 w a:: f­(f)

4

2

I-' A

/ v

ORNL-DWG 67-8599

, .....

l>' /

,,,.,.. I;'~ WI - v ~ .--_....., _...i.- .,; vii'

~/ / ...... .....

... ./' /

./' "" / ./

/ I;" 0 I(

..... !;" ....

A 1.204°C (2200°F) / v. 0 1427°C (2900°F) ·o 1649° C (3000° F)

~

/ vi.-

v 10-5 10-4 10-3 10-2

SECONDARY CREEP RATE (in.fin. hr)

Fig. 8. Secondary' Creep Rate vs Stress for ~a-10% W Alloy .

. '•

8

ORNL -DWG 67-8600

i'i" r-.... - ., (31) I I Ill ."- .. ['--...._

(34) -............ -~ ;. -....... "-.. Ill

(J2) • + . ........ ' ... ll ~ ... ~- .. l' ... r-. ., ,..._

(24) ........ ........ i-. (56) ....

f"-. •,

"'-+, r--- r-.r, 1-i.~ I'-.. r---[I

I'-.. r---,.... r ..... ,...

I"- f'. "' RUPTURE r......

2

• 10% CREEP ' • 5% 'CREEP ........

6

• 2% CREEP + r-..... ]'...• + 1% CREEP ",.... ..... ( ) RUPTURE DUCTILITY IN "lo

I"-... ..... 4

,

'

2x10~ . 0.1 10 100 1000 .

.. 10,000.

TIME!(llr)

Fig. 9. Creep-Rupture Properties of T-111 Alloy at 1204°C (2200°F).

1649°C (JOOO°F). in Figs. 10 and 11, respectively. Figure 12 gives the

secondary creep rate as a function of stress at these temperatures.

The rupture' elongation in percent is given in parentheses beside

each point on the stress-rupture curves. In all three materials the

ductilities are excellent.

4x10 4

'

2

·;;; E: 104 en en 8 lJ.J a:: I-en 6

• ... IQ ( 48) • i'-r-- f=::::::t--. ...... "---' +r--i-- ~-

.. ,, (59)

r--0 19·t ;. r-- ~ ..... l'-(62)(27)

1"' r--;. ~ ~..... . ;. ~ .. ..._ ;. ....._(54) I -- ;. r--... ........... - -¢ RUPTURE r--. "• ''"--- ~. ~ ... , • 10% CRE.EP

-~

4

• 5% CREEP r--. ' 1-1-

" i'r, • ?.% C:RFFP r ... - 1 "In CREEP +

I-

2x10 3

0.1

(1 )11 i~llUR.i 11rm1r 1i n

'f\

10 100 TIME (hr)

ORNL-OWG 67-8601

I'( (62)

,. ...

" ~

1000 10,000

Fig. 10. Creep-Rupture Properties of T-111 Alloy at 1427°C (2600°F).

§ Cf) Cf) w a:: tr;

' ~~ ~ 104

8

6

4

2

1a3 0.1

k I'

1'1' [',,_ 1'r-

!'.... K

I'-

Ill (61)

~ !',..(51) -, '

" " ,, -......

)'.._ "' "-,... "~ .. !'-."

9

ORNL -DWG 67-8602

o RUPTURE • 10% CREEP • 5% CREEP • 2% CREEP + 1% CREEP ( ) RUPTURE DUCTILITY IN "lo

!'-.._

f-...._ ~65

t--..._ ....... !'.....

K" "' " .. ~ ~)

~ ~ ;....

"' 1"-r-, ( )

"" f-...._

"' 10 100 1000 10,000

TIME (hr)

Fig. 11. Creep-Rupture Properties of T-111 Alloy at 1649°C (JOOO°F).

4x104 ORNL-UWG 67-8603

I I 1111111 I v 6 1204°C (2200°F)

~ O 1427°C (2600°F) ....-'"" o 1649°C ( 3000°F)

~ .4

........ t>"'"i,.. _.. ""'"-<

v k' i..,..0-.... ~ _........ _..

_...... ........ .....

2

104

--JJ

/ ....-'"" ,,,/7

·v; 8 .?;-

Cf)

"' w 6 a:: f-Cf)

~ v ,,

4 I/

l/ I

2

s ccmm11RY CREEP R/\TF I.in / in hr)

FiE• 1?.. Secondary Creep Rate vs Stress for T-111 Alloy.

10

Figure 13 shows a photomicrograph of an unalloyed tantalum specimen

with a rupture lii'e of 27. 5 hr at 1204 °C (2200 °F). It is clear that the

material has recrystallized and attained a substantial grain size under

these conditions. Specimens tested for longer times at correspondingly

lower stresses frequently develop a pronounced substructure rather than

a larger grain size. Figure 14 shows a microstructure typical of these

specimens.

At 1427°C (2600°F), only a short time is required for the develop­

ment of quite large grains in unalloyed tantalum. This is illustrated

by the photomicrograph of a specimen with a rupture life of 7.0 hr at thls

temperature, shown in Fig. 15. Figure 16 shows the microstructure of a

specimen tested at a stress which produced failure in 466.0 hr at 1427°C

(2600°F). The microstructure is similar in appearance to the subgrains

in Fig. 14, except th1'l.t. these small areas gi vc the appearance or llf~i ng

Fig. 13. Photomicrograph of Unalloyed Tantalum Specimen Which Failed After 27.5 hr at 6000 psi and 1204°C (2200°F). Etchant: NH4-H2o-EF. l OOx.

11

~-, ,,.

Fig. 14. Photomicrograph of Unalloyed Tantalum Specimen Which Failed After 693.6 hr at 2750 psi and 1204°C (2200°F). lOOx. Reduced 6%.

Fig. 15. H1nt.nmi r.rograph of Unalloyed Tantalrnn Specimen Which Failed After 7.0 hr at 3500 psi and 1427°C (2600°F). lOOX.

12

Fig. 16. Photomicrograph of Unalloyed Tantalum Specimen Which Failed After 466. 0 hr at l '500 J:lRi ::ind 1427 °C ( 2600 °F) . lOO>C .

separated by high angle boundaries. At 1649°C (3000°F), very large grains

are deveJ,.ol)ed .• as shown in fi'i e;. 17 . Tt. is noteworthy that in no ease

are voids observed.

The microstructure of a Ta-10% W specimen which failed after 737.3 hr

at l204°C (2200°F) is shown in Fig. 18. Specimens tested at 1427°r,

(2600°F) and 164-9°C (3000°F) arc shown in Figs. J9 and 20, respectively.

A slight tendency toward the formation of grain-boundary voids can be

seen in Fig. 19 , whi.le very large grain-boumlary voids are prominent in

Fig. 20.

The microstructures of ~-111 specimens tested at 1204, 1427, and

1649°C (2200, 2600, and 3000°F) are shown in Figs. 21, 22, and 23,

respectively. The same increasing tendency for grain-b?undary separation

with increasing temperature is evident.

Upon comparison of cree.IJ-rupLure data presented here, it is apparent

that the addition of 10% W has a pronounced effect on the strength. The

further addition of 2% Hf, however, has had little effect for the material

histories examined here. Since precipitates too large to contribute to

dispersion strengthening are observed (Fig. 23), it ts :possible that a heat

treatment which places these in solution and reprecipitates them in a morP.

finely dispersed state may produce an improvement of T-111 over Ta-JO% W.

13

Fig. 17. Photomicrograph of Unalloyed Tantalum Specimen Which Failed After 374.9 hr at 650 psi and 1649°C (3000°F). lOOx.

Fig. 18. Photomicrograph of Ta-10% W Specimen Which Failed After 737.3 hr at 17,000 pci and 120~°C (2200°F). Etchant: 25 HF-25 HN03-5 glycerin. lOOx.

14

Fig. 19 . Photomicrograph of Ta-10%W Specimen Which Failed After 441.8 hr at 9000 psi and 1427°C (2600°F). l OOX.

Fig. 20. Photomicrograph of 'I'a-10% W Specimen Which Failed After 270.6 hr at 4500 psi and 1649°C (JOOO°F). lOOX.

Fig. 21. Photomicrograph of 975.1 hr at 17,500 psi and 1204°C lOOx.

15

T-111 Alloy Specimen Which Failed Af'ter (2200°F). Etchant: H20--HF-NH03-H2 S04.

Fig. 22. Photomicrograph of T-111 Alloy Specimen Which Failed Af'ter 575 .4 hr at 7500 psi and 1427°C (2600°F). lOOx .

16

. ..• Jj.: . •/

Fig. 23. Photomicrograph of 'l'-111 Alloy Specimen 'Which l<'ailed After 493.2 hr at 3500 psi and 1649°C (3000"F). 100>< .

Tne rpicrostructures of the unalloyed tantalum appear very clean; those of

the 'l'a-lU'fo alloy show only a slight indication o:t' a :preci:pi tate while

:precipitates are distinctly visible in the T-111 alloy microstructures.

Grain growth is much faster in tantalum than in Ta-10% W or T-111. Grain

growth appears to be slightly greater in Ta-10% W than in T-111 at

1427 and 1649°C . (2600 and 3000°F). The :precipitates in T-111 are probably

HfC and Hf02 and may be responsible for the additional grain-growth

inhibition.

SUMMARY AND C:ONC:HTRTONR

The creep-rupture properties of cold worked tantalum) Ta-10% WJ

and T-111 (Ta--8% W-2% Hf) at 1204) 1427) and 1649°C (2200) 2600) and

3000°F) are presented. It is apparent from these data that substantial

solution strengthening is derived from the addition of tungsten to

tantalum. No further strengthening was observed upon the addition of

17

hafnium to this binar~ alloy for the material conditions investigated.

However, some additional grain-size stabilization was noted in the T-111,

possibly due to hafnium-base precipitates in the microstructure.

Good rupture ductilities were observed in all cases.

ACKNOWLEDGMENTS

The author wishes to express his appreciation for the contribution

made to this work by others. Those who m~rit specific mention

~. R. Weir, ·Jr. for guidance and. suggestions during the course of the

~ork, H. R. Gaddis and C. W. Houck for the preparation of the photomicro­

graphs, C. K. Thomas for performance of the experimental de.tails,

H. Inouye and H. E. McCoy, Jr. for review of the manuscript, and the

Metals and Cera.mies Division Reports Office for the preparation of this

rP.port.

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