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OXYGEN EFFECTS ON INTERNAL FRICTION AND
MODULUS OF A TITANIUM ALLOY
B. Tittmann, L. Ahlberg, P. Beckham
To cite this version:
JOURNAL D E PHYSIQUE
Colloque C10, supplBment au n012, Tome 46, d6cembre 1985 page C10-605
OXYGEN EFFECTS ON INTERNAL FRICTION AND MODULUS OF A TITANIUM ALLOY
B.R. TITTMANN, L.A. AHLBERG AND P.M. BECKHAM
Rockwell International Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360, U.S.A.
Resume
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Les e f f e t s de 1 'oxygene sur l a f r i c t i o n i n t e r n e , l e module e t l a v i tesse du son d' un a1 1 i age a1 pha/beta de t i tane d i poni b l e commerci a1 ement ont e t e etudies dans un i n t e r v a l l e de temperature de 80 a 290 Kelvin. L ' a t t e n u a t i o n generale d e c r o i t avec l a concentration d'oxygene e t un p i c de f r i c t i o n i n t e r n e observe e n t r e 110 e t 130 degres K a presente un accroisse- ment lorque l a concentration d'oxygene augmentait. A temperature ambiante, l e s vitesses du son e t par consequent l e s modules dependent du montant d'oxygene e t peuvent c r o i t r e ou d e c r o i t r e , suivant l a d i r e c t i o n de propaga- t i o n , i n d i q u a n t que l a t e x t u r e peut a v o i r un e f f e t important. Les i n d i c a - t i o n s sont que l e p i c de f r i c t i o n i n t e r n e e s t du a une t r a n s f o r m a t i o n beta *omega dans l a phase beta de l ' a l l i a g e e t que l ' a t t e n u a t i o n generale e s t causee par l a s o l u t i o n s o l i d e d'oxygene dans l a phase alpha. Ces r e s u l t a t s sont c o n s i s t a n t s avec l e s r e s u l t a t s de l a l i t t e r a t u r e rapportes pour l e s phases i ndi v i duel les.Abstract
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The effects of oxygen on the i n t e r n a l f r i c t i o n , modulus and sound v e l o c i t y o f a commercially avai l a b l e alpha/beta ti t a n i um a1 l o y were i n v e s t i g a t e d over a temperature range o f 80 t o 290°K. The o v e r a l l back- ground damping decreases w i t h oxygen concentration and an i n t e r n a l f r i c t i o n peak observed between 110 and 130°K was found t o increase w i t h i n c r e a s i n g oxygen concentration. At room temperature, the sound v e l o c i t i e s and t h e r e - f o r e the moduli depend on t h e amount of oxygen and can e i t h e r increase o r decrease, depending upon the propagation d i r e c t i o n , i ndi c a t i ng t h a t t e x t u r e can have a strong e f f e c t . I n d i c a t i o n s are t h a t the i n t e r n a l f r i c t i o n peak i s due t o a beta S omega transformation i n the beta phase o f the a l l o y and t h a t the background damping i s caused by the s o l i d s o l u t i o n oxygen i n the alpha phase. These data are consistent w i t h l i t e r a t u r e data reported f o r the i n d i v i d u a l phases.I
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INTRODUCTIONThe e f f e c t s o f the presence o f i n t e r s t i t i a l oxygen on the mechanical p r o p e r t i e s of Ti and Ti a l l o y s have been a subject o f i n t e r e s t f o r some time. Most o f t h e pre- vious work has been done on pure beta phase a l l o y s o f Ti. Lately, t h e r e has been considerable i n t e r e s t i n Ti -6211 because o f i t s toughness and we1 dabi 1 i t y /I/. Ti -6211 i s p r i m a r i l y an a-phase m a t e r i a l w i t h the @-phase embedded i n the matrix. The purpose o f these experiments i s t o determine t h e e f f e c t s o f i n t e r s t i t i a l oxy- gen on alphalbeta phase Ti a l l o y s .
I 1
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EXPERIMENTAL PROCEDURESI n t e r n a l f r i c t i o n and modulus measurements were performed on f i v e Ti -6211 samples having from 0.075% t o 0.29% oxygen. The 0.075% sample i s t y p i c a l o f commercially avai lab1 e materi a1
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The temperature f o r the i n t e r n a l f r i c t i o n and corresponding Young's modulus measurements ranged from 80 t o 290K. Further modulus r e s u l t s were obtained a t room temperature using u l t r a s o n i c v e l o c i t y measurements.C10-606
JOURNAL
DE PHYSIQUEThe samples were c u t from pieces t h a t were r o l l e d , annealed f o r 1 h a t 925OC, then air-cooled. Reference 1 gives a d e t a i l e d d e s c r i p t i o n of t h e material. The i n t e r - nal f r i c t i o n samples were rectangular pieces 4.6 cm long, 0.5 cm wide and 0.2 cm t h i c k , which resonated i n a f r e e - f ree f l e x u r a l .mode w i t h a frequency o f about
5 KHz /2/. The sample was placed i n the i n n e r chamber o f a double Dewar system, evacuated, then 2 inn Hg o f He added as a thermal exchange gas. The sample was cooled a t a r a t e o f 0.5 K/min, w i t h data taken a t 10 min i n t e r v a l s . The room tem- perature moduli were obtained from u l t r a s o n i c v e l o c i t y measurements on cubes, 1.5 cm on a side, o r i e n t e d w i t h t h e t h r e e p r i n c i p a l d i r e c t i o n s i n t h e r o l l e d p l a t e m a t e r i a l (L,T,S).
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EXPERIMENTAL RESULTSThe i n t e r n a l f r i c t i o n i n Ti-6211 as a f u n c t i o n of temperature and oxygen content i s shown i n Fig. 1. The data e x h i b i t a s u b s t a n t i a l peak centered a t about 120K w i t h a h a l f - w i d t h o f about 40K. A s i m i l a r peak has been seen and s t u d i e d i n o t h e r Ti a1 l o y s by Sommer e t a1 /3/ and Buck e t a1 /4/. The peak i s thought t o a r i s e as a r e s u l t o f a t h e r m a l l y a c t i v a t e d re1 a x a t i on process i n v o l v i n g p S't w phase t r a n s - formation having an a c t i v a t i o n energy o f 0.22 eV and a r e l a x a t i o n time o f zo =
2 10-l4 s. Fig. 1 I n t e r n a l f r i c t i o n i n Ti -6211 as a f u n c t i o n o f temperature and oxygen content. DEGREES KELVIN
The width o f the peak i s about a f a c t o r o f two, t o o broad f o r a s i n g l e r e l a x a t i o n process. This i s probably due t o t h e presence o f nuclei metastable +phase i n t h e $-phase. Reference 3 shows t h a t t h e h e i g h t o f the i n t e r n a l f r i c t i o n peak i s a f u n c t i o n o f a1 1 oy content and f i r s t increases w i t h a1 1 oy addition, goes through a maximum, and then decreases w i t h f u r t h e r additions. The data o f Fig. 1 show t h a t the a d d i t i o n o f oxygen increases t h e peak height. This i s c o n s i s t e n t w i t h t h e e f f e c t o f a l l o y composition on peak height, i.e., when oxygen i s added, the
p-
phase m a t e r i a l r e a c t s as i f t h e a l l o y i n g i s increased /4/. Thus, i t appears t h a t t h e $-phase i s a low concentration a l l o y . V e r i f i c a t i o n o f t h i s using STEM micro- a n a l y s i s of t h e p-phase has been started.F i g . 2 Young's modulus i n T i -6211 as a f u n c t i o n o f temperature and oxygen content.
The r e s u l t s o f t h e c o r r e s p o n d i n g Young's modulus d a t a f r o m t h e i n t e r n a l f r i c t i o n measurements a r e shown i n Fig. 2. The d a t a show l i t t l e small o r no modulus d e f e c t , which i s c o n s i s t e n t w i t h p r e v i o u s o b s e r v a t i o n s /4/ i n o t h e r Ti a l l o y s . The modulus i s seen t o i n c r e a s e w i t h oxygen c o n t e n t , as expected, because t h e a s s o c i a t e d i n c r e a s e o f t h e volume f r a c t i o n o f a-phase m a t e r i a l which has a h i g h e r modulus t h a n t h e @-phase /I/.
To determine t h e d i r e c t i o n a l dependence o f t h e e f f e c t s o f oxygen on t h e modul us, shear and 1 ongi t u d i n a l measurements were made a t u l t r a s o n i c f r e q u e n c i e s i n t h e p r i n c i p a l p r o p a g a t i o n and p o l a r i z a t i o n d i r e c t i o n s on a cube f r o m each sample. The r e s u l t s o f t h e shear data a r e shown i n Fig. 3, and demonstrate t h a t t e x t u r e i s p l a y i n g an i m p o r t a n t r o l e and may overshadow t h e e f f e c t o f oxygen on t h e modulus.
PROP POL 0 0.1 0.2 0.3 % OXYGEN PROP POL 0 0 4.6 0 .-
g
4.4 % OXYGEN PROP POLX o .
% OXYGEN Fig. 3 Shear modulus i n T i -6211 as a f u n c t i o n o f oxygen c o n t e n t . I V-
CONCLUSIONC10-608 JOURNAL D E PHYSIQUE
The u l t r a s o n i c v e l o c i t y measurements reveal t h a t both t e x t u r e and oxygen a f f e c t the modulus.
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ACKNOWLEDGEMENTSThe authors are deeply indebted t o Prof. Otto Buck, Iowa S t a t e U n i v e r s i t y f o r h i s help i n t h e i n t e r p r e t a t i o n o f these data. We a l s o thank Bob Housley f o r t h e use o f h i s i n t e r n a l f r i c t i o n apparatus, and H. Chaskelis, NRL, who provided t h e samples.
REFERENCES
/1/ Buxbaum, S. R. and Green, R.E. Jr.
,
Non D e s t r u c t i v e Methods f o r M a t e r i a l Property Determi nation. Plenum Press, (1984), Eds. Rudd and Green 271. /2/ Nowick, A. S. and Berry, B. S., A n e l a s t i c Relaxation i n C r y s t a l l i n e Solids,Academic Press, New York, (1972) 627
/3/ Sommer, A. W., Motokura, S.
