METASTABLE θ AND ω -PHASES IN α-Ti(V), α-Ti(A) AND α-Ti(Sn) ALLOYS

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METASTABLE θ AND ω -PHASES IN α-Ti(V), α-Ti(A) AND α-Ti(Sn) ALLOYS

M. Ron, E. Ratner, G. Mengeristsky

To cite this version:

M. Ron, E. Ratner, G. Mengeristsky. METASTABLE θ AND ω -PHASES IN α-Ti(V), α- Ti(A) AND α-Ti(Sn) ALLOYS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-639-C2-643.

�10.1051/jphyscol:19792223�. �jpa-00218604�

JOURNAL DE PHYSIQUE Colloque C2, suppl6ment au n

"

3, Tome 40, mars 1979, page C2-639

METASTABLE

8

AND

w-PHASES

IN

a-Ti(~), a - T i ( ~ )

AND

a - ~ i ( ~ n ) ALLOYS' M. Ron, E. Ratner and G. ~ e n ~ e r i s t s k ~ "

Department of Materials Engineelzing, Technion, Hai fa, Israel

RQsum6.- La spectroscopie Mgssbauer a Qte appliquee 1 la mise en evidence et 1 l'analyse de phases metastables qui se foment dans des alliages a-Ti(V), a-Ti(A1) et a-Ti(Sn). Les alliages ont 6t6 dopes avec 15% en poids de 5 7 ~ e . On a observe une apparition athermale de la phase 8 dans les allia- ges trempbs en quantitC croissante par recuit jusqu'1 400°c, pour les compositions Ti-3V-0,15Fe, Ti-2A1-0.15Fe et Ti-10511-0,15Fe. Pour les compositions T-3V-0,15Fe et Ti-2AC-0,15Fe la phase w apparalt en quantitd considbrable aprPs ddformation plastique, et persiste aprGs recuit de plus de 30 heures 1 400'~. On observe que dans l'alliage Ti-0,2Fe d b f o m e 1 froid, la phase 8 disparaPt et le composb intermdtallique TiFe se forme par recuit de 22 heures 1 400'~. U n comportement analogue est observC pour les alliages Ti-2Al-Onl5Fe et Ti-IOSn-0,15Fe.

Abstract.- The Mgssbauer spectroscopy was applied to the determination and analysis of metastable thases which form in a-Ti(V), a-Ti(A1) and a-Ti(Sn) alloys. The alloys were doped with 0.15 wt% of

'Fe which is below the concentration of iron tolerated as an impurity in commercial alloys. In Ti-3V-O,15Fe, Ti-2A1-0,15Fe and Ti-1OSn-O.1SFe the 8-phase forms athermally in the quenched alloys and the relative spectral area, AelA, increases upon aging at temperatures up to 400'~. In Ti-3V- 0.15Fe and Ti-2A1-0.15Fe alloys, tne w-phase was found to form in considerable quantitites after heavy plastic deformation. For cold-worked alloys the w-phase persists upon aging at 4 0 0 ~ ~ for more than 30 h. It was found that in the cold-worked Ti-0.2Fe alloy the 8-phase disappears and the inter- metallic compound TiFe forms upon aging at 400'~ for 22 h. Similar behaviour was observed for the Ti-2A1-0.15Fe and Ti-1OSn-0.15Fe alloys.

I. 1htroduction.- The amount of alloying elements in the most important alloy Ti-6A1-4V are within the solubility limits of A1 and V in the a-phase of the binary systems Ti-A1 and Ti-V. The alloy Ti-6A1-4V

is known to age harden in two temperature ranges /I/.

At and above 550°c, where hardening is caused by the precipitation of the a2(Ti3Al)-phase within the a-phase, and at a low temperature of about 350°C.

The mechanism of the increase of hardness at this low temperature is still not fully understood. The solubility of vanadium in a-titanium increases with decreasing temperature and is -3.5 wt% at 650°C.

Vanadium decreases the martensitic temperature Ts

-

thereby stabilizing the 0-phase. A metastable w- phase is known to form when the retained 0-phase decomposes /2,3/. Aluminum is an a-stabilizer and has a wide region of solubility in a-titanium 141.

However, there is evidence for the appearance of an ordered a2 (Ti3Al)-phase within the a-region at 550'~

/5,6/. Iron is a strong 0-stabilizer in titanium alloys and has a limited solubility in a-Ti / 7 , 8 / . The Mgssbauer method has been shown, to be able to analyze phases in the Ti-Fe system in quantities

+ This research is partially sponsored by Elscint Ltd., Electronic Industries, and Ministry of In- dustry Commerce and Tourism of Israel.

++

In partial fulfillment of the requirements for the M.Sc. degree

which were much below the detection limit of X-ray diffraction measurements. In the present study, the formation and transitions of metastable and stable phases in Ti-3V, Ti-2A1 and Ti-1OSn alloys doped with 0.15 wt% 5 7 ~ e as well as in a Ti-0.2Fe alloy are investigated by means of MEssbauer spectroscopy.

The information derived on the alloys Ti-V and Ti-A1 will be used to analyze the metastable states and phases in the Ti-6A1-4V alloy.

2. Experimental procedures.- The investigated alloys were prepared by melting titanium of purity of 99.9%

with iron (enriched with "Fe) and other constituents such as V, A1 and Sn in quantities as specified be- 104. The experimental procedures were essentially the same as those described elsewhere /10,13/.

3. Results.- The spectrum shown in figure la is for a Ti-O.2Fe alloy as quenched from 1000°~. The spec- trum consists of two lines corresponding to the a-phase and 8-phases /9,10/. Figure lb is for the same specimen after being aged at 400'~ for 22 h.

The relative area of the 8-phase AelA has increased to 0.47.

The spectrum in figure Ic is for the quenched specimen after being cold-worked, a component rela- ted to the wphase appeared in addition to the a and 0 phases. The spectrum in figure Id is for the same specimen subsequently aged at 400'~ for 20 h.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792223

JOURNAL DE PHYSIQUE

Aged 22h#Oobc

i I

1

I .

^I

I

-I -0s

o as

, i i ~

Shift Relative to

a

Fe Shii R e b t i i

to a

Fe

Fig. I : Room-temperature Miissbauer spectra for a Ti-0.2Fe alloy and bar-diagrams in which the length of the bar is proportional to AjIA with y = a, 8, w and TiFe; and A

-

the total spectral area.

a) as quenched from 1000°C

-

b) aged for 22 h at 400'~ ) c) cold-worked 80% (in the as quenched state)

-

d) aged for 20 h at 4 0 0 ~ ~ (after the cold-work).

It consists of three components related to w, a and TiFe-phases, but no 8-phase is discernable.

The spectra and bar-diagrams of figure 2a for a Ti-3V-0.15Fe alloy in the as quenched state show the presence of the a and 8 phases. Aging at 350'~

for 35 h, has the effect of increasing the relative spectral area A to almost 0.50. Further aging at

8 /A

400°C for 23 h does not practically change the rela- tive amounts AaIA and AuIA (see fig. 2b and 2c).

The spectra in figures 2d to 2h are for the same specimen, but cold-worked after being quenched.

As a result of cold-work (77%) a component related to the wphase appeared (see fig. 2e). After aging at 400'~ for 32 h the specimen (see fig. 2h) still con- sists of the three components related to the a, 8 and u-phases.

The spectrum for the quenched Ti-2A1-0.ISFe alloy in figure 3a, shows the presence of a and 8 phases. As a result of aging at 400'~ for 23 h, AeIA increases to 0.45 (see Fig. 3c). When the specimen was cold-worked a component related to the w-phase appears in the spectrum (see Fig. 3e) in addition to the a and +phases. After aging at 400'~ for 23 h the 8-phase disappeared and a new component with an isomeric shift of -0.13 appeared, while the a and u-phases persist (see Fig. 3h). The position of this new component is quite close to the position of the intermetallic Ti-Fe which is -0.'145 2 0.01 /lo/.

Typical values of isomeric shifts and line widths are given in table I. A comparison between X-ray diffraction and MEssbauer results is made in table 11.

4. Interpretation and discussion.- In the Ti-O.2Fe alloy, the metastable 8 and w-phases appear after various treatments (see fig. 1, a,b and c) in agree- ment with the results of former studies 19-121. The intermetallic compound TiFe forms upon aging at 400'~

for 22 h in a specimen that has been cold-worked.

For the cold-worked Ti-0.2Fe alloy, aged at 400°C for 22 h, it was possible to calculate from the &ss- bauer spectrum (Fig. Id) the fractional amount

%i~e' of the intermetallic compound TiFe, as well as C a and X with quite high accuracy.

a

It has been shown /12/that if the f-factors of all phases in a sample can be assumed to be equal then a simple relationship holds :

where j =

a,

8, w etc.

The concentration of iron in the intermetallic compound TiFe was assumed to be stoichiometric,

cTiFe

= 58.3 wtX. Then, from (I) with %iFelA = 0.75 (taken from the spectrum of figure Id) the weight fraction is X = 0.00257. Now, C can be estimated

TiFe a

with quite high accuracy.

I l

m - ..-.,

D S - Aged 32h#0Ooc

10.40

-

-i

^{-05 0 0 5 mrAh} b

Aged 32M00.c

12.30 -

, -I -05 0 a5

mb/s

Shift Rdotive to a Fe Shift Relative to

u

Fe

Fig. 2 : Room temperature Mgssbauer spectra for a Ti-3V-0.15Fe alloy and bar-diagrams in which the length of the bar is proportional to Aj/* with y = a, 8, w and TiFe; and A the total spectral area.

a) as quenched from 1050°C

-

b) 'aged for 35 h at 350'~ (after quench)

-

c) aged for 23 h at 400°C (after quench)

-

d) as quenched from 1 0 5 0 ~ ~ (same as in a)

-

e) cold-worked 77% (in the as quenched state)

-

f) aged for 10 h at 160°C (after cold-work)

-

g) aged for 38 h at 350'~ (after cold-work)

-

h) aged for 32 h at 4 0 0 ~ ~ (after cold-work).

The weight fraction X was estimated from the depen- Xu = 0.004, is obtained from ( 1 ) . On the other hand,

W

dence of the isomeric shift-IS on the iron concen- the presence of the w-phase was not discernable in

W

tration-C as given in previous studies / 1 1 , 1 2 / and the X-ray patterns. The lowest fraction discernable

W

compared with an estimate from X-ray diffraction by X-ray can be estimated as say Xu

-

^{0.03 and}

measurements. From equation (2) in reference /]I/ correspondingly a concentration C _W

-

0.5 is obtained the concentration corresponding to IS = -0.513 is As is seen from (2) a change in by almost an or-

W

about CW = 4.5 wt%. Thus the weight fraction, der of magntiude changes the value of Ca insignifi-

c2-642 JOURNAL DE PHYSIQUE cantly, namely from 0.0302 wt% to 0.0313 wt%

a

n .'

21 62 - 21.62

-

⁶⁸

' .

& \,j'

21.12- 21.12

- t

' 77% Rolled

9.67

-

4 f 4I

6-

2

J

0

E

0 ^5.3,

^-

0 0

5.17 -

11.47 -

5.9 5 Aged 8 5h/3500c

584

9.72

-

9.20

-

^10.23

-

n b

-I -0.5

o

a5 mm/sx -I -QJ

o as

mm/s

S h i Relative to a Fe Shift Relative to a Fe

Fig. 3 : Room temperature MGssbauer spectra for a Ti2A1-0.15Fe alloy and bar-diagrams in which the length of the bar is proportional to A j / * with y = a, 8, w and TiFe; A

-

the total spectral area.

a) as quenched from 1 0 5 0 ~ ~

-

b) aged for 33 h at 350'~

-

c) aged for 23 h at 400'~

-

d) as quenched from 1050°c (same as in a)

-

e) cold-worked 77% (in the as quenched state)

-

f) aged for 23 h at 160'C (after cold-work)

-

g) aged for 8.5 h at 350'~ (after cold-work)

-

h) aged for 23 h at 400'C (after cold-work)

In the alloy containing 3wt%V the +phase forms upon quenching and persists upon aging at up to 4 0 0 " ~ for 23 h. The w-phase appears upon cold- working and persist up to aging at 400'~ for 32 h.

However, the presence of an intermetallic compound, such as Ti(Fel-xVx), could not be discerned. In the alloy containing 2wt%Al the metastable phases form in a similar way. But aging a cold-worked alloy at 400'~ for 22 h results in a line at -0.13 mm.s-'. An

(-0.145 mrn.s-I). The small difference can be attri- buted to the presence of some A1 in the intermetallic compound Ti(Fel-xAlx). The alloys containing Sn (the spectra for which are not shown) show larger relative areas of the 8-phase than any other of the three alloys in the as quenched state.

5. Conclusions.- The phase analysis by means of a s s - bauer spectroscopy in Ti-Fe alloys was extended to alloys of technological importance. The amount of isomeric shift quite close to that of TiFe " ~ e used as a dopent is below the concentration of

iron tolerated in commercial alloys.

Table I : Typical values of isomeric shift' and line width ++ for a. 0 , w, and TiFe phase

Alloys

:

^{Treatment i 1 ; 1 1 ; I I 1 I 1}

1

I

i re :

I . s . ~

: ^r

^:I.s.

t I r W I TiFe

{

r ~ i ~ e

t 1

I ^I I 1 I ^{1 I 1 1}

Ti-0.2Fe :Quenched 1000°C

:

^-0.019

:

^0.348

:

^-0.314

:

^0.361

:

^-0.611

:

^0.396

: -

¹

-

:

80% Cold Rolled

:

^{1 1 I I I I I I I I 1 I 1 I}

I I I 1 1 1 I I 1

I

Ti-3V-

:

^{Quenched 1 OOO'C}

0.15Fe

:

- - -

¹

- - -

I

Ti-2A1- :Quenched I 0 0 0 " ~ 0.15Fe :+77% Cold Rolled

:+Aged 23 h/160°c

- - -

I

Ti-IOSn- :Quenched 1000°~

0.15Fe :+71% Cold Rolled :+Aged 3h/450°C

++

+ Relative to a-Fe

-

not corrected for final sample thickness

Table I1 _: Comparison of X-rays and Mijssbauer results

I t

Alloys

:

Treatments I ¹ Phases identified by

I

I X-ray

'

I _I

:

diffraction

: ,

^{~Essbauer spectrum}

I I I

Ti-0.2Fe

:

Quenched 1000°C, Rolled 80%

:

^CL

:

^{a, w and TiFe}

:

Aged 400°C/22 h t I

:

(Fig. Id)

t 1 I

1 1 1

Ti-3V-0.15Fe

: _:

^{Quenched 1000~}

c

^I I a

:

^{a, @}

Aged 400°c/32 h I I

:

^{(Fig. 2c)}

1 1 I

1 1 1

Ti-2A1-0.15Fe: Quenched 100O0~, Rolled 78%

:

^a

:

a, w, Ti(Fe,-,Al,)

:

Aged 400DC/23 h I I

:

^{(Fig. 3h)}

I 1 I

I 1 1

Ti-1OSn-0.15Fe1 Quenched IOOO'C, Rolled 71% a

:

^{a, TiFe}

:

Aged 462'~/3h t I

:

(not shown)

1 t I

The same metastable phases 0 and w as well as stable 131 Hickman, B.S., J. Mat. Sci.

4

(1969) 554.

a-phase and intermetallic compounds were present in 141 Ref. 121, page 137.

all these alloys. In most cases X-ray diffraction 151 Crossley,F.A., Met. Soc. TSM-AIME

236

(1966) 1174.

was unable to discern any other phase but a-phase. / 6 / Shablen, C.E., Met. Trans.? (1971) 277.

In the cold worked Ti-0.2Fe alloy aged at 400'~ the /7/ Ref. 121, page 82.

concentration of iron in the a-phase was found to be Ca = 0.03 wt%. After cold-work and aging at 400°C for 20 h an intermetallic compound forms in Ti-O.2Fe Ti-2Al-O.I5Fe, Ti-lC-Sn-O.15Fe alloys while the +phase disappeared. However, in the Ti-3V-0.15Fe alloy, no intermetallic compound forms and the

@-phase persists for the same treatments.

References

/8/ Blasius, A., Gonser, U . , J. Physique (1976) 66-397.

/9/ Stupel, M., Ron, M. and Weiss, B.Z., J. Physique Colloq.

35

(1974) C6-483.

/lo/ Stupel, M., Ron, M. and Weiss, B.Z., J. ~ppl.

Phys.

47

^{(1976) 6.}

/II/ Stupel, M., Weiss, B.Z. and Ron, M., Acta Met.

25 (1977) 667.

-

1121 Ron, M., Stupel, M. and Weiss, B.Z., Acta Met.

25 (1977) 1355.

-

1131 Biran, A . , Shoskani, A. and Montano, P.A., Nucl /I/ Welsch, G., Lutjering, G., Gazioglu, K. and

Bunk, W., Met. Trans A g (1977) 69. Instrum. Methods

2

(1970) 21.

/2/ Molchanova, E.K., "Phase Diagrams of Titanium Alloys" "Israel Program for Scientific Transla- tions" 1965, p. 13. Translated from "Atlas Dia- gram Sostoyaniya Titanouykh Splavov" Publisher (Mashinostroenie, Moskwa) 1964.