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Martensitic transformation and shape memory effect inB2 intermetallic compounds of titanium

V.N. Khachin

To cite this version:V.N. Khachin. Martensitic transformation and shape memory effect in B2 intermetal-lic compounds of titanium. Revue de Physique Appliquee, 1989, 24 (7), pp.733-739.�10.1051/rphysap:01989002407073300�. �jpa-00246097�

https://hal.archives-ouvertes.fr/jpa-00246097https://hal.archives-ouvertes.fr

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Martensitic transformation and shape memory effect in B2 intermetalliccompounds of titanium

V. N. Khachin

Siberian Physico-Technical Institute, Tomsk State University, Tomsk, U.S.S.R.

(Reçu le 16 août 1988, accepté le 28 février 1989)

Résumé. 2014 Nous avons étudié les aspects cristallographiques et cinétiques de la transformation martensitiqueet les paramètres de l’effet mémoire de forme dans les alliages Ti50Ni50-xXx (X = Fe, Co, Pd, Pt, Au, Cu) etTi50Pd50-xYx (Y = Fe, Co, Cu), 0 ~ x ~ 50. Nous avons mesuré la température, l’hystérésis, la grandeur de ladéformation et la contrainte du cisaillement martensitique pour la transformation martensitique et pour l’effetmémoire de forme. Nous avons déterminé les compositions d’alliage donnant des conditions excellentes pourl’effet mémoire de forme.

Abstract. 2014 Crystallographic and kinetic characteristics of martensitic transformations and parameters ofshape memory effect in B2 compounds of titanium Ti50Ni50-xXx (X = Fe, Co, Pd, Pt, Au, Cu) andTi50Pd50-xYx (Y = Fe, Co, Cu), where 0 ~ x ~ 50 are investigated. Temperature, hysteresis, value ofreversible deformation and stress of martensitic shear for martensitic transformations and shape memory effectare defined. Compositions of alloys with optimum conditions for shape memory effect were determined.

Revue Phys. Appl. 24 (1989) 733-739 JUILLET 1989,

Classification

Physics Abstracts81.30K

Titanium exists in BCC and HCP modifications

(T03B1~03B2 = 1115 K) and forms binary and multicom-ponent B2 compounds with Ni, Fe, Co, Pd, Pt, Au,Cu and other metals, many of them being unstableand undergoing various martensitic transformations(MT) at different temperatures [1-4]. The mostfamous among them are TiNi and alloys on its basewhere monoclinic martensitic phase B19’ is formedeither directly by B2 ~ B19’ or by rhombohedral Rstructure B2 ~ R - B19’ [5]. Shape memory effect(SME) is vividly expressed in these alloys. Atpresent new B2 compounds of titanium of the typeTi(Ni, Cu), Ti(Ni, Pd), Ti(Ni, Pt), Ti(Ni, Au),Ti(Pd, Fe) with different MT and SME character-istics are intensively investigated [2-4, 6, 7]. Some ofthe alloys have rare and SME characteristics ob-served neither in TiNi, nor in other SME alloys.However the results of the researches are not wellknown. The present paper sums the results of theauthor’s latest publications and presents new data onMT and SME in a series of triple compoundsTi50Ni50-xXx (X = Fe, Co, Pd, Pt, Au, Cu) andTisoPdso-xYx (Y = Fe, Co), where 0 x 50. Thepresent alloys cover the main compounds of titaniumwith unstable B2 lattice. The methods of making

alloys and specimens as well as methods of structureand SME -studies are described in [2-4].

Martensitic transformations.

1. SYSTEMS Ti5oNi5O-,Fe, AND Ti5oNi5O-,CO,- -MT in Ti50Ni50 - xFex (0 x 3) are studied indetail in [5, 8]. However a total (0 x 50) MTdiagram with cooling up to 4.2 K is designed only in[9]. At the same time genetically related alloyssystem Ti5oNi5o _ xCox was studied much less. Figure 1presents the resultant MT diagram which agreesqualitatively with MT diagram in Ti50Ni50 - xFex. Inthe both systems B2 -+ R -+ B19’ is the basic MT

accurately fixed against the temperature dependenceof resistivity (Fig. la). The parameters of B19’martensitic phase (a = 0.288 nm, b = 0.412 nm,c = 0.465 nm, f3 = 97.6° for TisoNi4C07) varyslightly with the change of alloy composition andthey are close to the parameters of B19’ martensitein TiNi (a = 0.289 nm, b = 0.412 nm, c = 0.464 nm,f3 = 97.3°).With the increasing of Co(Fe) content at first MT

R - B19’ and then MT B2 ~ R are under suppres-sion. The stabilization of initial B2 structure in its

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01989002407073300

http://www.edpsciences.orghttp://dx.doi.org/10.1051/rphysap:01989002407073300

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Fig. 1. - Diagram MT of composition TisoNiso-xCoxdependences of resistivity Ti_%Ni45Co5 (a).

transition from TiNi to TiCo (TiFe) is accompaniedby a qualitative variation of elastic properties ofcrystal lattice. It should be stressed here that data onsingle crystals TisoNiso _xFex (0 x 50 ) obtainedin [10, 11] are of particular interest. The effect ofpremartensitic softening of lattice (dC44/dT> 0,dC’/dT> 0, A = C44/C’ ~ 2) in alloys on TiNibasis gradually disappears in the process of transitionto alloys undergoing no MT therefore the tempera-ture dependence of elastic constants goes to normal(dC44/dT 0, de’ /dT 0, A 1).

2. SYSTEMS Ti50Ni50 - xXx (X = Pd, Pt, Au, Cu). -For all alloys of these systems MT evolution is thesame in quality at increasing x. Figure 2 presents thetypical MT diagram. Similar diagram was observedin Ti50Ni50 - xPdx [3], TisoNiso - xAux [4] andTi5oNi5O - xCUx [2]. The characteristic feature of thesediagrams is the change of MT B2 ~ R ~ B19’(x 7 ) into B2 -+ B19 - B19’ (7 x 14 ) andthen into B2 ~ B19 (x > 14 ) sequence, where B19 isorthorhombic phase. B19 and B19’ martensiticphases have two different space groups, where B19’is P21/m with a distortion of the angle 8 (Fig. 3,curve 1) and B19 is P2,/m2/m2/a. So the par-ameters of B19 and B19’ martensitic phases undergosignificant variations with the change of alloy compo-sition. Figure 3 presents the evolution of parametersB19 and B19’ in TisoNiso-xPtx. Similar completeevolution is observed in Ti5oNi5o-xPdx [3],Ti5oNi50 - xAux [4] and close one in TisoNiso - xCux [2].The uncommon crystallogeometric peculiarity ob-

served during MT B2 ~ B19 ~ B19’ is of greatinterest. As is seen in figure 3, crystal lattice under-goes no deformation in the direction of parameter b

Fig. 2. - Diagram MT of composition Ti50Ni50 - xPtx andtemperature dependences of resistivity Ti5oNi25Pt25 (a),Ti50Ni42.5Pt7.5 (b) and TisoNi48Pt2 (c).

at both MT. The results of Bain’s homogeneousdeformation calculations for all MT sequences in

TisoNiso - xPdx are given in table I. Analogous resultsare observed for other three systems of alloys aswell. The scheme of calculation with the applicationof tensor strain is presented in [12]. As is seen fromthe table I, the value and direction of lattice strainare change essentially after the removing of alloycomposition from TiNi and the change of MTsequence. The main peculiarity of these changes is asfollows : one of eigenvalues of tensor strain intransformed into zero (or near zero) at each out oftwo MT B2 ~ B19 - B19’, what implies an invariantplane to be present. It should be stressed in thisconnection that the above mentioned plane is theinvariant one at microscopic level, that is, it belongsto both crystal lattices simultaneously. Naturally theplane of maximum lattice correspondence is to passthe interface plane (habit plane). In fact, habit plane{334} observed experimentally in Tiso.sNi39.SCulO[13] is in good agreement with a theoreticallycalculated {19, 19, 25}, which is equivalent to{3, 3, 3.95}. The table presents orientation and the

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Table 1. - Calculation of lattice strain for martensitic transformations in the Ti50Ni50 - xPdx alloys.

angle of rotation of habit planes calculated in otheralloys which unfortunately have not been observedexperimentally as yet.One more interesting peculiarity of MT

B2 ~ B19 - B19’ should be noted here. In the caseof the second MT B19 - B19’ the maximum latticedeformation lies in a plane which was an invariantone at the first transformation. On the contrary, inthe case of the first MT B2 ~ B19 thé maximumlattice deformation is in the plane which will beinvariant one at the second transformation. That isto say, directions of the maximum and zero crystallattice deformations are interchangeable at the firstand second MT. In other words, the formation ofcomplicated monoclinic lattice at MT B2 ~ B19 ~B19’ is done through two simple « elongation-com-pression » opérations in the two interchangeabledirections with the planes undistorted in each case.One can say that marked crystallographic

peculiarities of MT 82 - B19 ~ B19’ are rare ingeneral not only for MT but also for MT in alloys

with SME they are not observed in TiNi. As it willbe said later these features will play exceptionallyimportant role in provision of optimum conditionsfor SME manifestation.

Pay your attention to MT B2 ~ B19 realization athigh temperatures with small hysteresis that providesreal conditions for high-temperature SME display.

3. SYSTEM Ti50Pd50 - xYx (Y = Fe, Co, Cu). - Thecompound Ti5oPdso undergoes one MT B2 ~ B19 at783 K [3, 14]. The substitution of palladium for ironor cobalt makes B2 structure stabilized : the tem-

perature of MT B2 ~ B19 falls down (Fig. 4), theeffect of premartensitic softening is decreased [15],the lattice strain is suppressed significantly (Fig. 5,curve 1). The present system is suitable for studyingdistabilization process of B2 compounds (TiFe andTiCo) with respect to one simple MT B2 ~ B19.

First in the case of alloying TiPd with copper( 5 at % Cu) the temperature of MT B2 ~ B19falls down and then with (> 10 at % Cu) the

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Fig. 3. - The effect of composition of Ti(Ni, Pt) onparameters initial (ao ) and martensitic B19 (a, b, c), B19’(a’, b’, c’, 03B2) phases and hysteresis MT.

Fig. 4. - Diagram MT of composition TisoPdso _ xCox (left)and TisoPdso-xFex (right) and temperature dependences ofresistivity TisoPd4sCos (a) and TisoPd40FelO (b), TisoPd3sFels(c).

intensive B2 structure desintegration into two tetra-gonal phases with the ratio c/a 1 and c/a > 1occurs. The results of investigations of these alloyswill be published separately [16], therefore they arenot considered here in detail. In connection withthese investigations, work [17] should be noted.Thus spectrum of MT B2 ~ B19, B2 ~ R, 82 -

R ~ B19’ and B2 ~ B19 ~ B19’ are realized in B2

compounds on the basis of titanium. The most

Fig. 5. - The effect of composition of Ti(Pd, Fe) onparameters initial (ao ) and martensitic B19 (a, b, c) phasesand value deformation of lattice (1).

interesting cyrstallographic peculiarities are observedat MT B2 -. B19 - B19’.

Shape Memory Ef fect. - Shape memory effect isobserved in all alloys during MT with particulartemperature, magnitude and hysteresis of reversiblestrain which are connected with each transformation

(Figs. 6, 7).It should be pointed out that the essential feature

of SME at MT B2 ~ B19 is its realization at hightemperatures up to 800 K (Fig. 6, curve 1). How-ever, the magnitude of macroscopic reversible defor-mation (as a lattice strain - see Tab. I) is relativelynot high - 7-8 %, but QM is rather high 2013 150-200MPa even within the interval Ms-Mf. That is,conditions for realizing anelastic (reversible) defor-mation at MT 82 - R are far from optimum ones.Narrow hysteresis (3-5 K) and small value (- 1 %)

of reversible strain due to closeness of given transfor-mations to transitions of the second order (Fig. 6,curve 2) is the peculiarity of SME at MT 82 - R.This SME type has been studied well enough earlier,see for example [18].Undoubtedly, the first and the most evident SME

peculiarity at B2 ~ R ~ B19’ and B2 ~ B19 ~ B19’is its two-stage character of accumulation and recov-ery of deformation (Fig. 7), with the resultant revers-

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Fig. 6. - SME at B2 ~ B19 MT in Ti50Pt36Ni14 (1), andreversible SME at B2 ~ R MT in Ti50Ni45Fe5 (2) afterprior plastic deformation 7.3 % at 353 K. Stress 200 MPafor (1) suppressed during the heating.

Fig. 7. - Reversible SME at B2 ~ R ~ B19’ MT inTi49Ni5j (1) and at B2 ~ B19 ~ B19’ in TisoNï39Auu (2)after prior plastic deformatious 6.0 % at 453 K (1) and0.3 % at 323 K (2).

ible strain reaching significant value 2013 11-12 % [12].The stress of martensite shear drops sharply. Es-pecially anomalously low values (20-40 MPA) areobserved at MT B2 ~ B19 ~ B19’ within the interval

Fig. 8. - Temperature dependence of 03C3M and diagram of03C3(03B5) in TisoNi40PdlO (1) and TisoNi40AulO (2).

Fig. 9. - The effect of composition of Ti(Ni, Pd) (1) andTi(Ni, Cu) (2) on reversible deformation accumulated atcooling alloy with stress 100 MPa.

Ms-Mf (Fig. 8). Such MT sequence is characterizedby more narrow hysteresis (Fig. 3, curve 2). That isMT B2 ~ B19’ is more optimal for SME manifes-tation what is graphically seen in figure 9, where thereversible deformation value accumulated under thesame stress at the cooling of alloy is at its maximum.

Discussion.

The MT spectrum is realized in B2 compounds oftitanium. Nevertheless only two basic martensiticreactions B2 ~ B19 and B2 ~ R should be chosen

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from the variety of structural transformations and allthe rest chains of transformations B2 ~ R ~ B19’and B2 ~ B19 ~ B19’ should be regarded as theresult of successive realization of these two MT. Thisis really the case.

As was shown, the formation of MT chains andmonoclinic structure of B19’ occurs gradually at thechange of composition of alloy from TiPd (Ti Pt,TiAu) to TiNi and further to TiFe (TiCo). So MTB2 ~ B19 are complicated gradually in B2 ~ B19 ~B19’ and through B2 ~ B19’ in B2 -+ R - B19’.Such MT B2 --+ B19 evolution testihes to gradualdestabilization of initial B2 structure to a new MT

forming R phase. The destabilization of B2 structureoccurs gradually and initially TR (B2 ~ R)Ms (B2 ~ B19 ). In this case the formation « R-martensite » in B19 phase gives the results in mono-clinic distortion of the latter, that is B19 ~ B19’. It iseasy to demonstrate it because the direction of

[III]B2 is equivalent to [101]B19 and rhombohedraldeformation of B2 lattice is equivalent to monoclinicB19 distortion relatively. And so, the value ofmonoclinic distortion depends on intensity of thesecond (R) MT canal development. Originally,when TR «,Ms and « R-canal » starts formation,monoclinic angle is small (Fig. 3, curve 1). As far asthe second « R-canal » is developing the temperatureof its realization rises and approaches (TR = MS ) oreven exceeds (TR > MS) temperature of the first MT(Ms ). The monoclinic angle of B19 structure reachcsit maximum and R-phase is formed evidently. Itshould be pointed out that the monoclinic distortionof B19 phase and the scheme of Bain’s deformationare changed simultaneously with the development ofthe second MT canal. Tension is changed by com-pression along b axis. Such change is the result ofcrystallography of MT B19 ~ B19’. The tension oforthohombic lattice along [101] direction, whichprovides monoclinic distortion should be ac-companied by compression of lattice in perpendicu-lar [010] direction which is b axis. In short, both themonoclinic distortion and the compression along baxis are the consequence of only one reason :realization of the second « R-canal » MT.

Thus, the main peculiarities of the MT developingin B2 compounds of titanium can be given as thefollowing scheme

The concrete MT sequence is defined by compositionof alloy.The most striking peculiarity of anelastic behavior

of B2 compounds of titanium are anomalously lowvalues of om and narrow hysteresis at MT B2 ~B19 ~ B19’. Such conditions of developing anelasticdeformation are associated first of all with crystal-logeometry of MT sequence. A total (or near total)lack of the displacements of atoms and intemalstress in habit planes {334} B2 (for B2 -+ B19) and

{100} (for B19 ~ B19’), that is practically idealcoherence of the interfaces provides a low resistanceof material against their motion (low UM and narrowhystérésis).Low values of elastic modules at the moment MT

[10, 11] and stage by stage deformation of latticepromotes lowering accomodational strains too andeffective development of anelastic deformation.That is to say, the optimum for SME manifestationat MT B2 ~ B19 ~ B19’ is connected with combi-nation of several favourable factors with the presenceof total coherence of the interface being determinantamong them.

One more peculiarity of anelastic behavior of B2compounds of titanium is the SME realization athigh temperatures in the process of MT B2 ~ B19. Itwas for the first time that by direct nickel titaniumalloying the temperature MT and mechanical proper-ties could be increased simultaneously, this enabledone to preserve thermoelastic property of MT andpractically the total SME up to 800 K. It should benoted that SME is not higher than 400-420 K inalloys on TiNi basis. Naturally, alloy productionwith high temperature SME broadens the region ofits technical application. The scientific value of thisresult is obvious for the principal possibility ofrealization of thermoelastic MT SME at highertemperatures than it was believed before. Thusdifferent MT and total SME are realized in B2

compounds of titanium. In this connection B2 com-pounds of titanium occupy chief position amongother alloys with SME and will be a perspective basefor the subsequent working out of new alloys of thisclass.

References

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