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MÖSSBAUER STUDY OF METASTABLE PHASES IN Ti-3at% Mo ALLOY
Ch. Leibovitch, A. Rabinkin, M. Ron, E. Gartstein
To cite this version:
Ch. Leibovitch, A. Rabinkin, M. Ron, E. Gartstein. MÖSSBAUER STUDY OF METASTABLE PHASES IN Ti-3at% Mo ALLOY. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-604-C2-607.
�10.1051/jphyscol:19792210�. �jpa-00218590�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au n o 3, Tome 40, mars 1979, page C2-604
MOSSBAUER STUDY OF M E T A S T A B ~ E P H A S E S I N Ti-3at% M o ALLOY' Ch. Leibovitch ++ A. Rabinkin, M. Ron and E. Gartstein
Department o f Materials Engineering, Technion, I s r a e l I n s t i t u t e o f Techology, Haifa, I s r a e l
RQsum6.- Des dchantillons de Ti-3atZ Mo-0, 13atx5'~e ont Btb Btudibs par spectromBtrie Gssbauer, dif- fraction RX et microscopie dlectronique au cours de transitions de phase induite par traitements thermiques. Dans l'alliage brut de trempe, il existe deux phases martensitiques hcp-a' et orthorhom- bique a". Lorsque l'alliage brut de trempe est soumis 1 une pression de 92 kbar pendant 20 heures, il appara'it en plus 8 B 10% de phase w. Dans les bchantillons trempbs puis dBfords 1 froid, l7.effet Mgssbauer fait apparaftre le pic de la phase w, avec une aire relative de 15 % alors que les rbsul-
tats de RX et de rnicroscopie Blectronique ne sont pas significatifs. L'alliage trempB, ddformd puis recuit 1 350'~ pendant 24 heures contient une phase 0 instable en plus de la phase w. Le spectre d'un alliage trempe puis recuit sans d6formation prealable contient les spectres caractdristiques des pha- ses a', a" et 0.
Abstract.- The Mgssbauer spectroscopy X-ray diffraction and electron microscopy were applied to ana- lyse samples of a Ti-3atZ ~0-0.13at%''~e alloy in which phase transitions were induced by various treatments. In the as quenched alloy, two martensitic phases were found to be hcp-a' and orthorhombic a". An amount of about 8-10% w-phase (in addition to a' and a") appeared in a quenched sample which was soaked at 9 2 kbar for 20 h. For a quenched and cold-worked sample, the X-ray and electron micros- copy results were not conclusive whereas the Gssbauer spectrum contained an w-line with a relative spectral area A,,,lA=O. 15. In a cold-worked sample that was aged at 350'~ for 24 h a metastable phase, known as 0, appeared in addition to the wphase. The spectrum of a sample aged at 350'~ for 3.5 h (not cold-rolled) consists of a', a" and 0 lines.
1. Introduction.- The metastable phases which appear in a Ti-3atX Mo alloy when subjected to high pressu- re soaking, cold-work and heat treatments were in- vestigated in this study. The alloy was doped with 0.13at% 5 7 ~ e in order to use the Mhsbauer spectros- copy as an analytical tool.
The pressure P - under which the a + w trans- formation starts in unalloyed titanium has been de- termined in several investigations and values in the range of 70-100 kbars have been reported /1,2,3/.
It was found, as a result of a theoretical calcula- tion, that for a-Ti(Mo) alloys the a -t w equilibrium pressure, Po, decreases linearly with increasing concentration of Mo in the a-phase range /4,5/. For the Ti-3atX Mo alloy investigated in this study, the a + w transition was observed to start at 70 kbar, by means of in-situ electrical resistivity measure- ments which also showed a considerable hysteresis when the sample was unloaded.
In order to study the influence of various thermodynamical factors on the formation of stable and metastable phases, phase-transitions were also induced by plastic deformation and heat treatments.
his research is partially sponsored by Elscint Ltd., Electronic Industries and Ministry of Indus- try Comerce and Tourism of Israel.
++ In partial fulfillment of the requirements for Ph.D. degree.
The phase formation was traced by Gssbauer spectros- copy, X-ray diffraction and electron microscopy. For the purpose of ~sssbauer measurements the alloy was doped with 0.13atZ Fe, an amount of iron which is normally tolerated as an impurity in titanium alloys of technical grade purity.
The metastable phase identification and analysis by means of ~gssbauer spectroscopy was based mainly on recent investigations in the Ti-Fe system /6,7,8/.
2. Experimental Procedure.- The ~i-3at% Mo-0.13at%
Fe alloy was prepared by melting 99.9% pure sponge Ti with spectroscopical pure Mo and 5 7 ~ e iron in an arc furnace with a non-consumable electrode and con- taining argon gas as a protective atmosphere. The experimental procedures were essentially the same as described elsewhere /6,9/.
The high pressure experiments were performed in a Bridgman type apparatus with a working area of 6 mm diameter, calibrated by phase transitions of Bi.
The high pressure chamber has been described else- where /10,11/. X-ray diffraction patterns were taken with Cu-ka radiation by means of diffractometer using a bent crystal monochromator.
3. Results.- A series of room temperature Gssbauer spectra and bar diagrams showing the position and the relative spectral area for each spectral compo- nent, for a Ti-3at% Mo-0.13 at% Fe alloy after va- rious treatments, are shown in figures la to If.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792210
Fig. 1 : Room-temperature Gssbauer spectra for a Ti-3at% Mo alloy, and bar diagrams, in which the length of the bar is proportional to AjlA (j = a', a", 0 , w, and A = total spectral area) :
a) quenched from 1 IOOOC - b) quenched, P (92 kbar) -
c) quenched, 98% rolled - d) quenched, 98 X rolled, P (90 kbar) - e) quenched, 98% rolled, aged (24 h at 350'~) - f) quenched, aged (3.5 h at 350'~).
The spectrum in figure la for a specimen in the as quenched state, consits of two a-lines. One line was attributed to the a'-phase with an hcp crystal structure and the second to the a"-phase with an orthorhombic structure. The X-ray diffrac- tion patterns in figure 2a confirm the existence of the a' and a" phases. The electron micrograph in fi- gure 3a shows a typically martensitic microstructure.
The spectrum in figure lb is for a quenched specimen after being soaked at 92 kbar for 20 h. An additio- nal broad line with an isomeric shift of -0.563 m.s-' appeared in the spectrum and was attributed to the a-phase. The appearance of the w-phase is also clearly seen in the corresponding X-ray dif- fraction pattern in figure 2b. The corresponding electron micrographs are shown in figure 3b (left
and right). The bright-field picture (left) shows changes in the microstructure which are seen in the dark-field (right) to be a colony of finely disper- sed w particles. The spectrum in figure Ic is for a quenched and cold-worked specimen. The spectral area related to the u-phase, AwlA, is 0.15. The corres- ponding X-rays diffraction lines are wider and the wlines are much less pronounced. The spectrum in figure Id is for the cold-worked specimen chat was, in addition. soaked at 90 kbar for 20 h. AwlA is seen to have been increased to 0.25.
@ Quenched . P(92 kbw)
O Quenched .98% Rolled t? Oumched .98% Rdled.
Fig.2 : X-ray diffraction patterns taken with Cu-Ka radiation using a bent crystal monochromator, for Ti-3atZ Mo.
a) quenched from 1100~~ - b) quenched, P(92 kbar) c) quenched, 98X rolled - e) quenched,989. rolled, aged (24 h at 350'~)
The spectrum seen in figure le is for a specimen
that was quenched, cold-worked and then aged at
350'~ for 24 h. This spectrum was fitted with only
one a-line, a 0-line and an w-line. The corresponding
X-ray diffraction patterns, seen in figure 2e, show
broad lines of an hcp a-structure and traces of
wlines. The specimen, the spectrum of which is
shown in figure 1f has been aged at 350'~ for 3.5 h
after the quench (not cold-worked). No w-phase line
is seen in this spectrum, which consists of the 0,
a' and a" lines. The micrograph in figure 3c shows
an area characteristic o f the microstructure of
this specimen : a fine structure within the marten-
C2-606 JOURNAL DE PHYSIQUE s i t i c p l a t e s .
F i g . 3a F i g . 3c
F i g . 3b
F i g . 3 : E l e c t r o n m i c r o g r a p h s ( ~ 6 0 . 0 0 0 ) f o r Ti-3atZ Mo a l l o y : a ) i n t h e quenched s t a t e - b ) a f t e r s o a k i n g a t 92 k b a r s f o r 20 h b r i g h t f i e l d - l e f t , d a r k f i e l d - r i g h t - c ) a f t e r a g i n g 3.5 h a t 3 5 0 ' ~ . The v a l u e s o f t h e i s o m e r i c s h i f t , l i n e w i d t h and
r e l a t i v e s p e c t r a l a r e a s f o r t h e v a r i o u s p h a s e s a r e l i s t e d i n t a b l e I .
4 . I n t e r p r e t a t i o n and d i s c u s s i o n . - The a l l o y T i - 3 a t % Mo-0.13atZ Fe a f t e r b e i n g homogenized i n t h e 6-region and quenched t o room t e m p e r a t u r e c o n s i s t s o f t w o m a r t e n s i t i c m e t a s t a b l e p h a s e s a' and a " . No a t h e r m a l 0-phase forms i n t h i s a l l o y upon q u e n c h i n g . Whereas, i n o t h e r a-Ti a l l o y s s u c h a s Ti-3wtZV, Ti-2wtZA1,Ti- IOwtZSn and even a - T i ( F e ) t h e 8-phase forms a t h e r m a l - l y upon quenching / 1 2 / . T h i s f a c t i s o f i m p o r t a n c e b e c a u s e i t shows t h a t t h e i r o n s p e c t r u m r e f l e c t s t h e p h a s e s o f t h e a l l o y r a t h e r t h a n t h o s e of Ti-Fe o n l y . F o r t h e sample s o a k e d a t 92 k b a r , A w / ~ i s 0 . 0 8 and seems t o be a p p r o x i m a t e l y e q u a l t o t h e w e i g h t f r a c - t i o n o f t h e w-phase, a s no s i g n i f i c a n t r e d i s t r i b u - t i o n o f i r o n i s e x p e c t e d upon q u e n c h i n g and p r e s s u r e s o a k i n g .
A rough e s t i m a t e o f t h e r e l a t i v e i n t e g r a l i n t e n s i t y o f t h e X-ray l i n e s g i v e s a s i m i l a r v a l u e f o r t h e w-phase w e i g h t f r a c t i o n . F u r t h e r c o l d - w o r k i n g and p r e s s u r e s o a k i n g i n c r e a s e t h e amount o f t h e w-phase which i s r e p r e s e n t e d by t h e r e l a t i v e a r e a AwlA. It i s s e e n t h a t a g i n g a t 3 5 0 ' ~ c a u s e s t h e a p p e a r a n c e o f a new component - t h e 0-phase l i n e .
5. Conclusions.- The T i - 3 a t % Mo a l l o y i n t h e a s quen- ched s t a t e c o n s i s t s o f two m a r t e n s i t i c m e t a s t a b l e p h a s e s , a' and a". No m e t a s t a b l e w o r 8 p h a s e s were d i s c e r n e d .
The a + w t r a n s f o r m a t i o n s t a r t s a t 70 k b a r .
Soaking a t 92 k b a r f o r 20 h p r o d u c e s a f r a c t i o n o f
o n l y 8-10 p c t o f t h e w-phase. T h i s i m p l i e s t h a t t h e
t r a n s f o r m a t i o n i n t h i s a l l o y i s q u i t e s l u g g i s h . A
w e i g h t f r a c t i o n o f a b o u t 15 p c t of t h e u-phase i s
formed by heavy p l a s t i c d e f o r m a t i o n and i s i n c r e a s e d
t o 25 p c t by s u b s e q u e n t s o a k i n g a t 90 k b a r f o r 20 h .
Table I : Room temperature Mgssbauer parameters for the a', a", a, 8 and w phases
homer Shifts are given relative to Q Fe 0
d
e
The metastable 8-phase was not observed in the References as quenched, cold-worked or pressure soaked alloys.
/ I / Zylbershteyn, V.A., Nosova, G.I. and Estrin,E.I.,
However, lines related to the @-phase, with conside- Fiz. Metal. Metaloved. 2 (1973) 584.
rable spectral area, are seen to appear in the G s s - /2/ Jayarman, A., Klement .Jr., K., and Kennedy,G.C., Phys. Rev. 131 (1963) 644.
bauer spectra for the aged alloys.
/3/ Bundy, F.W., "New Materials and Methods of Stu- dying Metals and Alloys", (Moscow, Metalurgya) Acknowledgements.- The authors acknowledge with deep 1966, p. 230.
appreciation the help of Mr. E. Ratner and Mrs. G. /4/ Leibovitch, Ch., Rabinkin, A. and Ron, M. (to be published).
Mengeritsky. Also the help of Ms. Abigail Solomon is
/5/ Kaufman, L. and Bernstein, K . "Computer Calcula- greatly appreciated.
tion of Phase diagrams". Ac. Press, N.Y. and London) 1970.
/6/ Stupel, M., Ron, M. and Weiss, B.Z., J. Appl.
Phys. 2 (1976) 6.
171 Stupel, M., Wess, B.Z. and Ron, M., Acta Met.
25 (1977) 667.
-
181 Ron, M., Stupel, M. and Weiss, B.Z., Acta Met.
25 (1977) 1356.
-
/9/ Biran, A., Shoshani, A. and Montano, P.A., Nucl.
Instrum. Methods 2 (1970) 21.
Treatment
Quenched IlOOOc
Quenched ,
P(92 Kbarl Quenched, 98% Rolled
Quenched ,
98% Rolled, P ( 90 k bar)
Quenched, 98% Rolled, Aged ( 2 4 h / 3 5 0 ° c )
Quenched, Aged ( 3 . 5 h / W c )
/lo/ Berman, I.V. and Brandt, N.B., Pis'me Zh. Eksp.
Teor. Fiz. 1 (1968) 412.
/11/ Homan, C.G., J. Phys. Chem. Solids 2 (1975) 1249.
/I21 Ron, M., Ratner, E. and Mengeritsky, G. (this conference).
1.~3
(mmA)
-0.282
-0.265
re
:mm/s)
0.465
0.334
I.s'Z
( m W
-0.363
-0.623
-0.557
-0.651
1 1.s.a' I'aY
(mm/s) 0.308
0.365
0.391
0.342
0.272
r w
( m q
0868
0.564
0.981
0.476
A
