Phase transformations in ternary TiNix alloys

Scripta METALLURGICA

Vol. 20, pp. 733-737, 1986 Printed in the U.S.A.

Pergamon Press Ltd. All rights reserved

PHASE TRANSFORMATIONS IN TERNARYTiNiX ALLOYS K. R. Edmonds and C. M. Hwang Department of Metallurgy, Mechanics and Materials Science Michigan State University East Lansing, Michigan 48824

(Received January 27, 1986) (Revised March 4, 1986) Introduction The binary TiNi alloy displays several solid state phase transformations, undergoing thermoelastic martensitic transformation s l i g h t l y above room temperature. Immediately above the martensitic start (Ms) temperature, the TiNi exhibits a premartensitic i n s t a b i l i t y , believed to be charge density wave (COW) phenomena and associated phase transitions (1,2). In t h i s study minor additions of the t r a n s i t i o n elements Fe, Al, and Cu, to the binary TiNi a l l o y , produce a large temperature separation between the premartensitic transitions and the martensitic transformation. The charge density wave and thermoelastic martensitic transformations, in ternary TiNiX alloys, were studied using measurements of electrical resistance as a function of temperature. Thermal cycling and aging effects were investigated for four alloys. Each alloy studied contained the CsCI(B2) ordered crystal structure for the parent phase (1-4). On cooling, the alloys Ti50Ni45Fe3 and Ti59.4Ni38.7A11. 9 forms the "premartensitic" phase, with the subsequent martensitic transformation. For the Ti50Ni45Cu5 alloy the parent phase transforms to a martensitic phase on cooling. Thermal cycling apparently effects the martensitic transformation, depressing the Ms temperature with an increasing number of cycles and also exhibiting a slower austenite recovery. Multiple thermal cycles produce l a t t i c e defects and some degree of plastic deformation (dislocations) in the parent phase. The presence of dislocations presumably acts as an impediment to further martensite formation and the result is a s t a b i l i z a t i o n effect i . e . lowering of the Ms temperature. Aging apparently effects COW transitions, giving a more enhanced premartensitic hysteresis: i t can also suppress the martensitic transformation. After aging, the binary TiNi alloys have been found to decompose eutectoidally, from the high temperature B2 structure, into fcc Ti2Ni and hexagonal TiNi3. This decomposition is preceded by the formation of an intermediate precipitate as in the investigation by Koskimaki et al (5). At the beginning of precipitation, there is a stage at which the atomic arrangement of fine precipitates is coherent with the matrix. This obstructs the shape change for the martensitic transformation. Thus, i n i t i a t i o n of the transformation is more d i f f i c u l t and the Ms temperature is decreased. The Ms has been reported to be very strongly dependent on the alloy composition; decreasing the Ti content leads to a rapid lowering of Ms (6). The titanium composition of the matrix is reduced with precipitation of the fcc Ti2Ni phase. This investigation is concerned with these effects on the electrical resistance measurements. Experimental Procedure Electrical resistance samples were sectioned to be 5cm in length and Imm in diameter. The samples were annealed at go0° C for 10 minutes in evacuated quartz tubes and then quenched into ice brine. The aged specimens were annealed and quenched as above, heat treated at temperatures of 400° C and 600° C for times of lh and 4h in evacuated quartz tubes, then quenched in ice brine. Continuousmeasurement of electrical resistance as a function of temperature was performed as described e a r l i e r by Thorburg et a l . (7)

733 0036-9748/86 $3.00 + .00 Copyright (c) 1986 Pergamon Press Ltd.

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Results and Discussion The electrical resistance versus temperature for a f u l l thermal cycle between room temperature and liquid nitrogen temperature for a Ti59.4Ni38 7Fe1.9 alloy is given in Fig. 1. On cooling, the B2 parent phase transforms to the f i r s t " p r ~ a r t e n s i t i c " phase at To , indicated by the increase in electrical resistance. The second "premartensitic" t r a n s i t i o n b~gins at Td where the curve seems to show an i n f l e c t i o n point (1,2). The martensitic transformation starts at Ms, with an abrupt decrease in resistance, u n t i l the martensite f i n i s h temperature Mf is reached. On heating, the martensitic transformation exhibits a large hysteresis with the reverse transformations of the martensite phase beginning at the austenite start temperature As, with completion at the austenite f i n i s h temperature Af. A small hysteresis occurs around Td, the second premartensitic t r a n s i t i o n , while no hysteresis occurs at Tp. The transformation temperatures and thermal cycling effects of TiNiAl, TiNiFe and TiNiCu-alloys are given in Table i . In Fig. 2 a plot of electrical resistance versus temperature for the 5Oth f u l l thermal cycle for Ti59.4Ni38.7A11. 9 alloy is given. The effects of thermal cycling are more significant on the martensitic transformation. The hysteresis is depressed with Ms decreasing 17° C, with a slower austenite recovery from As to Af occurring as compared to the uncycled sample. Electrical resistance versus temperature curves for TiNiFe alloys are given in Fig. 3 and Fig. 4 for TisoNi47Fe3 and ~50Ni45Fe5 respectively. In Fig. 3 the plot contains both the premartensitic transition and the martensitic transformation, similar to Fig. I. In Fig. 4, while the premartensitic t r a n s i t i o n is evident, the martensitic transformation is believed to occur below l i q u i d nitrogen temperature. Thermal cycling of the Ti5oNi45Fe5 alloy does not effect the premartensitic t r a n s i t i o n . Fig. 5 shows the e l e c t r i c a l resistance versus temperature curve for the 50th f u l l thermal cycle for a Ti5oNi47Fe3 a l l o y . The hysteresis loop for the martensitic transformation is suppressed without changing the martensite or austenite transformation temperatures, see Table 1. The electrical resistance versus temperature curve for Ti50Ni45Cu5 is given in Fig. 6. On cooling, the B2 parent phase transforms to the martensitic phase (3,4). The electrical resistance increased abruptly at the Ms temperature on cooling and i t decreased at the As temperature on heating. These results were reversed as compared to other ternary TiNiX alloys. The electrical resistance versus temperature curve for the 20Oth complete thermal cycle for the Ti50Ni45Cu5 alloy exhibits a temperature decrease of 16° C for the Ms temperature. A comparison of t h i s alloy to the Ti59.4Ni38.7A11.g a l l o y , shows that 200 complete thermal cycles instead of only 50 complete thermal cycles, a four-fold difference, were needed to obtain a similar s h i f t in Ms. These effects are attributed to dislocations that apparently act as a barrier to the formation of martensite plates. The aging effects on TiNiAI, TiNiFe and TiNiCu alloys are given in Table 2. The aging effects of electrical resistance versus temperature for a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature for a Ti59 4Ni38 7Al1.g alloy are given in Fig. 7, Fig. 8 and Fig. 9 for aging at 400° C for l h , at 400° C for 4h'and at 600° C f o r lh respectively. A comparison of these curves to Fig. 1, the unaged specimen, reveals an enhanced hysteresis loop around Td in the premartensitic t r a n s i t i o n . Also, from these curves and data given in Table 2, i t is apparent that Ms is s l i g h t l y depressed by aging at 400° C for l h , with a s i g n i f i c a n t change when aged at 400° C for 4h. I t appears that the other transformation temperatures, Mf, As and Af, were not as greatly affected; neither was the martensitic transformation for aging at 600° C for l h . Fig. 10 and Fig. 11 show the effects of aging on the e l e c t r i c a l resistance versus temperature measurements for a TisoNi45Fe5 at 400° C for lh and at 600° C for lh, respectively. In comparision to Fig. 4, the unaged specimen, a more enhanced hysteresis loop for the premartensitic transition around Td is evident. The sample aged at 400° C for l h , was affected more than the samples aged at 600° C for lh and at 400° C for 4h, not shown. The aging effects for a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature for a TisoNi47Fe3 alloy is given in Fig. 12 for aging at 600° C for l h . For the Ti50Ni47Fe3 a l l o y , the martensite and austenite transformation temperatures are r e l a t i v e l y constant, see Table 2. The premartensitic t r a n s i t i o n is effected as in the other alloys, giving a more enhanced hysteresis. The curve for the Ti50Ni45Cu5 alloy aged at 400° C for lh is nearly identical to the unaged specimen, Fig. 6. There apparently is no effect on the TiNiCu alloy when aged for short periods of time ( l h ) , see Table 2. The curve for the sample aged at 400° C for 4h also exhibited a slower austenite (As to Af) recovery, but Ms is increased by 4° C rather than being decreased as in the other alloys. These effects are apparently caused by precipitation, which changes the matrix composition, affecting both the premartensitic and martensitic transitions.

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PHASE TRANSFORMATION IN T i N i X ALLOYS

735

References 1. 2, 3. 4. 5. 6. 7.

C, M. Hwang and C. M. Wayman, Scripta Met., I, 381 (1983). C.M. Hwang and C, M. Wayman, Scripta Met., "[7, 2345 (1983). T. Tadaki and C. M. Wayman, Metallography, 1~-,',247 (1982). K. R. Edmonds, M.S. Thesis, Michigan S t a t e ~ i v e r s i t y (1985), D, Koshimaki, M, J. Marchinkowski and A. S. Sastri, Trans. TMS-AIME, 245, 1883 (1969), K. N. Melto-~-and R. H, Bricknell, ICOMAT1979 p. 171. K. A. Thornburg, D. P. Dunne and C. M. Wayman, Met. Trans. ~, 2302 (1971). TABLE I. Thermally Cycled: Compositional (at.%) Dependence of Transfomation Temperatures (°C) in ........... TiNiCu,.TiNiFe and TiNi_AlAlloys .. Ms Mf As Af Tp

All oys Ti NiAI

.

ij-9".~--~8.7.1, 9 1St cycle 50th cycle Ti Ni Fe

.

.

.

.

Td

.

-68 -85

-160 -170

-40 -42

-11 -18

26 25

18 18

-96 -97

-196 -196

-90 -90

-60 -61

-2 -2

-13 -13

<-196 <-196

<-196 <-196

<-196 <-196

<-196 <-196

-52 -52

-70 -70

61 45

48 30

65 50

79 61

l~p . . . .

Td

Bo--~-3

Ist cycle 50th cycle 50-45-5 1St cycle 50th cycle Ti Ni Cu

5o--~-5

1st cycle 200th cycle

TABLE I f . Aging Effects: Compositional (at.%) Dependence of Transformation Temperatures (°C) in TiNiAl, TiNiFe and TiNiCu Alloys. Alloys

................ Ms . . . .

TiNiAl ~.7-1.9 400°C (lh) 600°C (lh) 40O°C (4h) TiNiFe ~'OT2F~'~-5 400°C (lh) 600°C (lh) 400°C (4h) 50-47-3 400°C (lh) 600°C (lh) TiNiCu ~ 5 400°C (lh) 500°C (lh) 400°C (4h)

.

.

Mr.

.

...... As . . . . . .

Af

. . -40 -41 -40 -40

-11 -10 -12 -12

25 25 25 25

18 18 18 18

-52 -52 -52 -52 -2 -3 -6

-70 -70 -70 -70 -I 3 -14 -I 7

-68 -70 -68 -83

. -160 -160 -160 -160

<-196 <-196 <-196 <-196 -96 -97 -97

<-196 <-196 <-196 <-196 -196 -196 -196

<-196 <-196 <-196 <-196 -90 -90 -90

<-196 <-196 <-196 <-196 -60 -63 -63

61 61 60 65

48 48 49 46

65 65 65 65

79 78 79 85

736

Vol. 20, No. S

PHASE TRANSFORMATION' IN TiNiX ALLOYS

Mf ~f

.,-

.,-

.~

.,~,

,

.,~

.;

,

Trc)

FIG, 2. Electrical resistance vs. temperature for a full thermal cycle between room temperature and liquid nitrogen temperature, 50th full thermal cycl e, Ti 59.4Ni 38.7AI l.g alloy.

FIG. 1. Electrical resistance vs. temperature for a full thermal cycle between room temperature and liquid nitrogen temperature, Tisg.4Ni38.7A11. 9 alloy.

,n _e Tp

y

Tp

L " .,.'

.,"

T ('el

.,'

,'-

o

Ni4y Fe 3

"

o'

i,i.c ~

FIG, 4. Electrical resistance vs. temperature for ful I thermal cycle between room temperature and liquid nitrogen temperature, TisoNi45Fe5 alloy.

FIG. 3. Electrical resistance vs. temperature for full thermal cycle between room temperature and liquid nitrogen temperature, Ti50Ni47Fe3 alloy.

"/1

,"

Ms

iZ A. _a ' - l

g$

,~

,-

•

'~

,

.

,

,

.

T re)

FIG. 5. Electrical resistance vs, temperature for full thermal cycle between room temperature and liquid nitrogen temperature, 50th full thermal cycle, Ti50Ni47Fe3 alloy,

FIG. 6. Electrical resistance vs. temperature for full thermal cycle between 100° C and liquid nitrogen temperature, Ti 50Ni45Cu5.

Vol

20, No. S

pHASE TRANSFORMATION

IN TiNiX ALLOYS

737

s~

ur

,~.

.,-

"

o'

-tso

-~oo

.

T{'C)

FIG. 7. Electrical resistance vs. temperature for a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature, Aged @400° C for 1 hr., Ti59.4Ni38.TA11.9 a l l o y .

TI~jI,4NI34.TAII .t

FIG, 8. Electrical resistance vs. temperature for a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature, Aged @400° C for 4 hrs., Ti59.4Ni38.TA11. 9 alloy.

TIsoNI4sFe t

~s

Tp

~ t

MT

' .1~.o

,Lo

.... ~

~o

T('C)

FIG. 9. Electrical resistance vs. temperature for a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature, Aged @600° C for 1 h r . , Ti59.4Ni38.7A11.9 a l l o y .

FIG. 10. Electrical resistance vs. temperature for a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature, aged @400° C for 1 h r . , Ti50Ni45Fe5 a l l o y .

TIsoNt4sFes

Mj

T~ r..

r T CC~

FIG. I I . Electrical resistance vs. temperature for a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature, aged @ 600° C for 1 h r . , TisoNi45Fe5 a l l o y .

To

T('C)

FIG. 12. E l e c t r i c a l resistance vs. temperature f o r a f u l l thermal cycle between room temperature and l i q u i d nitrogen temperature, aged @ 600° C f o r i h r , , Ti50Ni47Fe3.