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GRAIN-REFINEMENT AND THE RELATED PHENOMENA IN QUATERNARY Cu-Al-Ni-Ti
SHAPE MEMORY ALLOYS
K. Sugimoto, K. Kamei, H. Matsumoto, S. Komatsu, K. Akamatsu, T.
Sugimoto
To cite this version:
K. Sugimoto, K. Kamei, H. Matsumoto, S. Komatsu, K. Akamatsu, et al.. GRAIN-REFINEMENT AND THE RELATED PHENOMENA IN QUATERNARY Cu-Al-Ni-Ti SHAPE MEMORY ALLOYS.
Journal de Physique Colloques, 1982, 43 (C4), pp.C4-761-C4-766. �10.1051/jphyscol:19824124�. �jpa-
00222107�
JOURNAL DE PHYSIQUE
CoZZoque C4, suppldment au n o 1 2 , Tome 4 3 , dkcembre 1982 page C4-761
GRAIN-REFINEMENT A N D T H E R E L A T E D PHENOMENA IN Q U A T E R N A R Y Cu-AL-Ni-Ti S H A P E MEMORY ALLOYS
* ~ e ~ m t m e n t of MetaZZurgicaZ Engineering, Famlty of Engineering, Kansai Llniversity, Japan
"~epartrnent of MechanicaZ Engineering, Faculty of Engineering, Osaka Industrial Lhliversity, Japan
(Accepted 9 August 1982)
Abstract- It was reported that the addition of a small amount of titanium (0.5
-
3.99%) to a Cu-13.93%A1-3.36%Ni ternary alloy resulted in a remarkable grain-refining. The original grain-size of about 750 microns under hot-rolled and quenched conditions of the ternary alloy was reduced to that of the order of about 100 microns by addition of tiatanium. It was suggested that several technical improvements of the mechanical properties of Cu-Al-Ni shape memory alloys, such as better formability, less cracking tendency at grain-boundaries , higher fatigue strength and hence higher reliability on application, might be expected in this way. The mechanism of the grain-refinement was explained by the presence of finely dispersed titanium-rich x-phase particles which might act as an obstacle against the grain-boundary migration. The particles on the other hand increased the thermal hysteresis of the transformation, as observed by the temperature changes in electrical resistivity and internal friction. This was again shown to be due to the obstacle effect of the x-phase particles against the movement of the interface between the beta- phase and the martensite phase.I. Introduction.- It is pointed out by several authors (1,2,3,4) that copper- base shape memory alloys, such as Cu-Zn-A1 and Cu-Al-Ni alloys, have rather poor mechanical properties when compared with TiNi which has high ductility due to small elastic anisotropy and small grain-size. The brittleness of the copper-base alloys are due to large elastic anisotropy and large grain-size
( 2 ) . The essential cause of the short fatigue life of the Cu-Al-Ni alloy is
in the low fracture toughness and in some defect formation of the alloy, which leads to crack nuclei at martensitelmatrix interfaces during transformation pseudoelasticity cycles (3). From economical point of view, however, copper- base shape memory alloys are considered to be much more suitable than TiNi, which is too much expensive and has many technical difficulties in the manufacturing processes.
Some of the present authors investigated the effect of addition of the fourth alloying elements, such as V , Co, Ti, W , Zr and 8 , on the grain-refinement of the beta-phase in the cast structure of a Cu-13.5%Al-3.O%Ni ternary alloy ingot and confirmed that Ti, Co and V were most effective for the formation of equiaxed grains and that they could also suppress the grain-coarsening of the beta-phase (5,6,7). However, the grain-coarsening process occuring in the specimens hot-rolled at about 900°C has not been systematically studied in view of inhibiting the grain-boundary migration with the precipitated particles.
The purpose of the present paper is to investigate the effect of titanium addition to a Cu-Al-Ni ternary shape memory alloy on the grain-size under hot- rolled and quenched conditions. The mechanism of the grain-refinement will be also described briefly with regard to the characteristic behaviour of the transformation and the mechanical properties of the Cu-Al-Ni-Ti quaternary shape memory alloy.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19824124
J O U R N A L L)F. I'IIYSIQTE
11. Experimenta1s.- A 7 kg-ingot of a mother alloy with the composition Cu- 13.66ZAl-3.37ZNi was melt in a graphite crucible with an induction furnace.
It was cut into small pieces (100 g) and then remelt in a graphite crucible with an electric resistance furnace under argon atmosphere. After it was melt down a certain amount of titanium supplied in a form of sponge titanium wrapped with aluminium foil was added to the melt. It was stirred and then cast into a graphite mould with a dimension oT 15 rn in diameter and 400 mm in length.
Alloys 1 to 5 were prepared in this way and the chemical composition is civen in Table 1.
Table 1 Chemical composition of alloy samples (wtZ)
Alloy Cu A l
Metallographic examinations (both micro- and macro-structures) were made by means of optical microscope on polished surfaces etched with a FeCl + HC1 + H O solution. They have been hot-rolled at 900°C to a sheet of 3 2 mm thickness and then solution-treated at various temperatures from 400 to 1000°C 2 followed by water quenching to room temperature.
Internal friction and Young's modulus werc measured with a specimen of alloys 1 and 5 by means of a transverse vibration method, the size of the specimens being 2 x 10 x 100 mm. Electrical resis~ivity measurements were made by means of a d.c.-four terminal method with the same identical specimen as in the internal friction measurements.
111. Results and Discussion.- Photo 1 shows microstructures of alloys 1,2,3,4, and 5 quenched from 900°C after hot-rolling in small(1eft) and large(right) magnifications. It can be seen that the grain-size of the beta-phase is very large (about 1 mm in average) in alloy 1, where only aluminium foil without sponge titanium has been added to the mclt. In alloys 2,3,4 and 5 a remarkable grain-size refinement is observed and there arc besides a large number of small spherical particles in the grains. Martensitc plates can hardly be seen in these alloys probably due to insufficient etching or Ms-temperatures below room temperature. However, it is shown that they all undergo thermoelastic martensitc transformation at temperatures given in Tables 1 and 2. Shape memory effect was also observed in all alloy samples as will be described later.
The finc spherical particles seen in alloys 2,3,4, and 5 are called here
"x-phase", since the chemical composition and the crystal structure are still not known.
It is seen from Fig. 1 that the volume fraction of the x-phase increases linearly with increasing amount of titanium. Therefore, it is supposed that the x-phase must contain a large amount of titanium, and this was shown to be true by EPMA analysis as will be described in Fig. 5. Fig. 2 shows the effect of heating temperature on the microhardness of alloy samples. Below the betatransus temperatures, which is about 730°C, the structure of the quencheci specimens consists of the procutcctoid gamma 2 phase and alpha + gamma 2 eutectoid (pearlite-like structure) and hence the hardness numbers are rather large, i.e., 360
-
410. As the heating temperatures were increased the hardness values fell down steeply at around 730°C, where martensite phase starts to form. Above 730°C the hardness remains rather constant at about 210-
290 up to about 1000°C.It is clear from Fig.
2 that the effect of the volume fraction of x- phase on the hardness of martensite is very remarkable. The x-phase particles increase the hardness of martensite from 210 to 290 with increasing titanium content. Such a pronounced hardening effect of the x-phase particles may be a new strengthening mechanism of the Cu-Al- Ni shape memory alloys.
In order to investigate the transformation behaviour of the thermoelastic
martensite, electrical resistivity and Young's modulus were measured.
The results are given in Figs. 3 and 4. It is seen that the electrical resistivity changes in a step-wise way in the transformation temperature range between Ns and Mf (on cooling) or As and Af (on heating)
.
Photo 1 Optical
microphotographs of alloy samples. Solution- treatment at 900°C for 1 hr followed by water- quenching to room tcmperature.
-
H100pm 10pm
Table 2 .;ummary of results of measurmcnts in Cu-Al-Ni-Ti alloys
Alloy Ms As AT=As-Ms AT(50Z)
"
h ' P '-196("C) ("C) ("C) ("C) cmysec ca~/cmsecOc cal/g°C LIR cm
JOURNAL DE PHYSIQUE
The magnitude of the resistivity change is almost equal in every alloy. This means that the amount of martensite phase formed in every alloy is almost equal but the transformation temperatures are increased with increasing titanium content except for alloy 2 , where the Ms-temperature is slightly decreased.
The change of the Ms-temperatures with titanium is only an apparent effect, since titanium does not dissolve in the beta-phase but it segregates in the x-phase, as will be discussed later.
The results of measurements are summarized in Table 2, where the measured values of thermal diffusivity a
,
thermal conductivity,
specific heat C,
electrical resistivity at - 1 9 6 ° CP-,,,
!
It should be mentioned in Table 2thac the thermal hvsteresis AT(50%) eiven
0
0 1 2 3 4
T~tanium Content ( w t '1.) . . -
by the temperature difference between points
at 50% transformation on the cooling and Fig. 1 Relation between heating curves of resistivity increases with volume fraction of titanium- increasing titanium content. This may be rich x-phase particles and the also explained as a hardening effect due to titanium content in Cu-Al-Ni- the finely dispersed x-phase particles in Ti alloy samples.
the grains. It is interesting to know that there is a possibility of designing a new shape memory alloy, which has a definite hardness value and a definite amounts of thermal hysteresis, by controlling the volume fraction of the x-phase particles. The average size of the particles was about 3 microns A
450
in diameter and the maximum volume fraction 1 0
was about 2 1 per cent in alloy 5.
2
Fig. 4 shows the temperature dependence of internal friction, Young's modulus and
-
electrical resistivity in alloys 1 and 5.
6 1
350It is shown that the internal friction peaks in the transformation temperature range disappeared almost completely in alloy 5,
where the movement of interfaces between
$
g
300martensite and beta-phase is more difficult x than in alloy 1 due to the existence of the 1
E
finely dispersed x-phase particles. Although 250 the detailed composition and structure is 2 not known, very pronounced enrichment of Z titanium was observed by means of EPMA 200
analysis as shown in Fig. 5 and Photo 2. 400 500 600 700 800 900 1000
Such a close relationship between the Heating Temperature ( 'C )
thermal hysteresis AT(50%) in electrical
resistivity and the height of the internal Fig. 2 Effect of heating temperature friction peak has been already reported by 0" the micro--hardness in samples several of the present authors on Cu-Zn-ill quenched from the heating temperature shape memory alloys, where fine ~recipitates after holding for 1 hr in C U - ~ l - ~ i - T i of the proeutectoid alpha-phase particles alloy samples.
would play the same role ar in the experimental results ( 8 ) .
IV. Summary.- The effect
of addition of titanium by 16 0.5
-
3.99 wt% to a ternaryalloy with a chemical
2
150
composition Cu-13.93%A1-
5 - 1 4 3.36ZNi has been investigated on the grain-size refinement by means of optical microscopy, .- l 3 measurements of electrical * resistivity, internal friction
8
1 2and Young' s modulus,
-
.: 11
respectively. It was found
1
that (1) the formation of 8 large and long columnar iii 10 grains in the ternary cast
alloy ingots was completely 9
suppressed in the quaternary -50 0 50 100
alloy ingots, resulting in Temperature ( * C )
equiaxed grains which Fig. 3 Changes in electrical resistivity with made them much more
martensite and reverse martensite transforma- for the subsequent hot-working.
( 2 ) The grain growth in beta- tions in quenched samples of Cu-Al-Ni-Ti alLoys
Solution-treated at 800°C for 1 hr followed by phase range during hot-working
quenching to room temperature.
and solution-treatment was completely suppressed in the quaternary alloy specimens, average grain-diameter after hot-working and quenching being about 30 microns in comparison with that of about
1 mm in the ternary alloy specimens. This enhanced grain refining effect was confirmed metallographically to be due to the presence of finely dispersed Ti-rich x-phase particIes which had been formed by a peritectic reaction on solidification of the alloy ingots and then broken into small particles during the hot-working and annealing processes. (3) The hot-working ability of
the quaternary alloy ingots on forging and rolling was consequently improved to a great extent and hence a higher performance on use of the new alloy material might be expected in the future. (4) The Ms-temperature was not directly influenced by titanium but was simply dependent on the soluble
-50 0 50 100 150
Temperature ( * C )
Fig. 4 Temperature dependence of inter- nal friction, Young's modulus and elect- rical resistivity in Cu-Al-Ni (alloy 1) and Cu-Al-Ni-Ti (alloy 5) samples.
JOURNAL DE PHYSIQUE
Fig. 5 Distribution profiles of titanium Photo 2 An EBS image (Ti-Ka) of and aluminium in a Cu-13.5%A1-3.0%8i the same sample as in Fig. 5, show- ternary alloy sample added with 1.0% ing the distribution of the Ti- Ti. Sample was solution-treated at rich x-phase. The arrows A and 3
950°C for 10 min and then rapidly cooled correspond to those in Fig. 5.
to room temperature by water-quenching.
amount of aluminium and nickel in beta-phase. ( 5 ) According to the results of measurements of electrical resistivity, internal friction and Young's modulus a systematic change in the transforniation behaviour with the titanium content was observed; i.e., i t changed from a soft thermoelastic martensite type with a small thermal hysteresis ( d T = 6 " C in alloy 1) to a hard thermoelastic martensite type with a large thermal hysteresis (AT=27OC in alloy 5). The terms
"soft" and "hard" arise from "soft and hard-magnetic materials". Although the physical meaning is quite different, it may be convenient to classify shape memory alloys in such a way. The effect of size and volume fraction of the x- phase particles on the mobility of interfaces between martensite phase and beta- phase was discussed in connection with the previous data.
Acknowledgement
The authors would like to express their hearty thanks to Prof. T. Okamoto, Osaka University, for his help in EPPlA analysis, and also to Dr. H. Kusamichi, Kobe Steel, Ltd., for his cooperation in alloy preparations.
References
K. Shimizu and 11. Sakamoto: Science and Technology,
5
(1981) 358 & 394 ( in Japanese).S. Isliyazaki, K. Otsuka, 11. Sakamoto and K. Shimizu: Hetal Physics Seminar, 4 (1980) 1 1 1 ( in Japanese ) .
- H. Sakamoto, K. Shimizu and K. Otsuka: Trans. J L M ,
22
(1981) 579.S. Hiyazaki, K. Otsuka, H . Sakamoto and K. Shimizu: Trans. JIM,
2
(1981) 244.H. Matsumoto, T. Tanaka, T. lrizawa, T. Sugimoto, K. Sugimoto and K. Kamei:
Journal of Japan Copper Kescnrch Association, 17 (1978) 92 (in Japanese).
K. Kamei, H. Hatsumoto, K. Sugimoto, T. ~ugimoto and T. lrizawa: ibid.
2
(1980) 201 (in Japanese).
K. Kamei, K. Sugimoto, H. Matsumoto, T. Sugimoto and 'T. tri~awa: ibid.
20
(1981) 25 (in Japanese).
K. Sugimoto: "Internal Friction and Ultrasonic Attenuation in Solids", Supplement au J. de Physique, F.A.S.C. 10, C5-1981, Part 11, C5-971.
