mechanical and fatigue properties of cu-al-mn shape memory alloys with influence of mechanical...
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Mechanical and fatigue properties of Cu - Al - Mn shape memory alloys
with influence of mechanical cycling on amplitude dependence
of internal friction at room temperature
Agnieszka Mielczarek1,a, Werner Riehemann1,b, Sönke Vogelgesang2,c, Babette Tonn2,d
1Institute of Materials Engineering and Technology, Clausthal University of Technology,
Agricolastr. 6, D-38678 Clausthal-Zellerfeld, Germany
2Institute of Metallurgy, Clausthal University of Technology,
Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld, Germany
Keywords: Cu – Al - Mn, High Damping Materials, Shape memory alloys, mechanical and fatigue properties.
Abstract. The mechanical and fatigue properties of Cu - Al - Mn shape memory alloys with different phase fractions at room temperature were investigated. The specimens with different chemical compositions (Al: 8.9 - 12.5 wt. % and Mn: 3.3 - 9.3 wt. %) were tensile loaded with 10-3 s-1 tensile strain rate. Austenitic specimens have the highest tensile strength and fracture strain. Yield strength, tensile strength and elongation of martensitic alloys were lower compared with austenitic alloys. Fracture strain of martensitic alloys depend only little on the chemical composition. Specimens of martensitic, austenitic and three different multiple phase specimens were tested in the high cycle fatigue range at room temperature. The Woehler curves for multiple specimens depend on the phase fraction at testing temperatures. Different elements as Co, Ni, Fe and Si were alloyed to CuAl11.6Mn5. All decreased the ductility of the specimens, and their fatigue properties.
Maxima could be detected in the strain amplitude dependence of damping for multiple phase specimen. These maximum are shifted to lower damping and to higher strains with increasing number of mechanical cycles, compared to the as cast condition for not cycled specimen. The strain amplitude dependence of damping in martensitic and austenitic Cu – Al – Mn shape memory alloys does not change much during mechanical cycling.
Introduction
Damping in materials can increase strongly, when fatigue cracks are present and propagate [1 - 4]. Strain amplitude dependence of internal friction of materials with cracks is similar to damping, which is measured during stress induced martensitic transformation or during the motion of phase- and twin boundaries in shape memory alloys [4 - 7]. In both cases a maximum appears in the strain amplitude dependence of damping δ(ε) [1, 4, 5]. Therefore, it is interesting, how the fatigue affects damping (δ (ε)) and Young’s modulus of shape memory alloys. High life times are expected for most of the high damping SMA [8]. Defects, which are caused by mechanical cycling, can change the transition temperatures, and therefore the damping level, as well. Corresponding literature about the influence of mechanical cycling is rare and could not be found for Cu – Al - Mn shape memory alloys at all.
Fatigue properties of pseudo elastic Cu – Al - Mn alloys were detected for single crystals, for which the periodic cycling increases the critical strain εc amplitude (or critical stress amplitude σc) where the stress induced phase transition starts [9].
The advantages of the Cu – Al - Mn shape memory alloys (SMA), compared with common
Solid State Phenomena Vol. 137 (2008) pp 145-154Online available since 2008/Mar/07 at www.scientific.net© (2008) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/SSP.137.145
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metals, are good strength, very high damping and shape memory effects. Cu - Al - Mn are cheaper to produce comparing to widely used TiNi shape memory alloys, because there is no need to vacuum cast. The transition temperatures can be adjusted from - 180 °C until 230 °C [10 - 11] by the alloying contents, the casting conditions or subsequent heat treatment. For low aluminum contents the alloys are ductile and can be cold worked [12]. Additionally the Mn-rich Cu – Al - Mn alloys have better castability, due to their lower melting temperatures [13].
The lattice transition between martensite and austenite can be caused by temperature changes or by stress loading i.e. shape memory alloys can be fatigued by thermal and mechanical cycling. Cracks due to thermal cycling were found in all cycled specimens as is reported in another paper of this volume. Cracks have no significant effect on the amplitude dependence of damping of the martensitic samples, whereas some small influence could be observed in austenitic samples at room temperature. For this paper the mechanical and fatigue properties and the influence of mechanical cycling on the amplitude dependence of damping δ (ε) were investigated.
Experimental
The investigated alloys were obtained by melting copper (99.99 wt. %), aluminium (99.7 wt. %) and manganese (99.85 wt. %) in a mid-frequency induction furnace in normal atmosphere, followed by casting in metallic moulds preheated to 300 °C, subsequently the alloys were cooled in air. The chemical compositions of the alloys were determined by inductively coupled plasma spectroscopy (ICP) [14].
In the Table 1 the chemical compositions, phases at room temperature and the transition temperatures of the investigated alloys are listed. After casting the specimens were cooled, so martensite start (MS) and martensite finish temperature (MF) determine the phases present at room temperature. Austenite start temperature (AS) and austenite finish temperature (AF) are relevant for the phases present at room temperature after heating from lower temperatures.
After casting the transition temperatures MF, MS, AS and AF, which are listed in table 1, were measured by differential scanning calorimetry (DSC) using a DSC 2920 (TA Instruments, New Castle) in the temperature range -100 °C to 200 °C with a cooling and heating rate of ± 3 K/min. The transition temperatures were
determined as the intersection points of the tangents in the turning points of the transition peaks and the baseline.
X-ray analyses were made with Siemens diffractometer (Co tube, λ (Co Kα1) = 1.789 Å). X-ray measurements were done at room temperature in the range 2Θ = 10° to 140°. Alloys A (see Table 1) were found to be solely austenitic with bcc phase at RT, whereas alloys M contain two types of
Table 1. Chemical composition, phases at RT and transition temperatures obtained by DSC of the investigated alloys. Relevant transition temperatures for the phases present at RT after casting are martensite finish MF and martensite start MS.
Alloy composition in wt. %
Phases at RT*
MF
in °C MS
in °C AS
in °C AF
in °C CuAl11.6Mn5 M 20 45 55 90 Cu11.3Mn6.4Fe2 M 20 43 40 90 CuAl12.5Mn3 M 80 140 120 200 CuAl11.5Mn4.8 MA1 0 42 62 100 CuAl12.7Mn3,3 MA1 6 28 26 45 CuAl11.7Mn4.6 MA2 -10 18 41 60 CuAl10.9Mn6.7 MA2 -20 20 0 136 CuAl11.9Mn4.3 MA3 < - 20 15 11 50 CuAl12.1Mn4.9 A -50 -27 -35 -8 CuAl8.2Mn10 A - - - -20 CuAl8,9Mn9,3 A - -10 - 18 CuAl9.4Mn5.7Ni4 A - - - -25
*M martensite;
MA1 multiple phase: MF <RT< AS;,
MA2 multiple phase: MS <RT< AS,
MA3 multiple phase: MS <RT< AF,
A austenitic.
146 Interaction between Defects and Anelastic Phenomena in Solids
martensite (2H and 18R) at RT. From alloys MA just the phase composition of CuAl11.7Mn4.6 alloy was obtained by XRD-analysis and peaks for bcc-phase and 2H martensite were found. The martensitic phases in the alloys MA1, MA2 and MA3 are expected to be the same after transition to martensite.
To improve the mechanical properties the following alloying elements (Co, Ni, Fe, Si) were added to the melts of alloy CuAl12.7Mn3.3 (see Table 2).
The tensile stress-strain curves were obtained with tensile testing machine INSTRON 5582. The specimens were produced as cylinder symmetric bars with a measuring length of 30 mm and diameter of 6 mm according German norm DIN50125. The tensile tests were done until rupture with 10-3 s-1 tensile strain rate at room temperature. The periodic loading curves in tensile area were performed with 10-4 s-1 tensile strain rate at room temperature.
High cycle fatigue (HCF) tests were performed on hour-glass shaped specimens with a gage diameter of 5.7 mm in rotating beam loading (R = - 1) at RT in air and at frequency of 46 Hz. The specimens were tested in electrical polished condition, after polishing with solution of 500 ml phosphor acid, 100 ml vinegar acid and 200 ml ethanol at temperature of -20 °C. Roughly 100 µm were removed from the as machined surface to make sure that no machining effects influence the
results. Internal friction versus maximum strain amplitude δ (ε) was measured at RT in vacuum (10 Pa) as the logarithmic decrement δ of free decaying bending vibrations. The bending beam specimen was single clamped with a vibrating length of 97 mm, a width of 10 mm, and a thickness of 2 mm. More details about the used damping apparatus are given in refs. [4, 15]. Controlled fatigue was realized by the bending loading of the bending beam samples in the same apparatus also used for the damping measurements controlling the
amplitude and number of vibrations.
Results and discussions
In Fig. 1 the results of tensile tests at room temperature are shown. The tensile tests were done until failure with the austenitic specimen CuAl8.2Mn10/A with low aluminium content, and with the homogenized martensitic specimen CuAl11.3Mn6.4Fe.2/M. The austenitic specimen with higher Al-contents shows a yield strength of about 300MPa and a tensile strength of about 600 MPa. In case of Cu – Al - Mn SMA with higher aluminium content (∼ 12 wt. %) the plastic elongation balanced at 7 %. Varying the contents of Al from 8 to 12 w. % and the content of Mn from 5 to 10 wt. % different fracture strains in these alloys can be found. This can be explained with the increase of the ductility with decreasing aluminium content [12, 16]. In a future paper it will be shown that aluminium content strongly influences the possible degree of cold working. The Cu-Al-Mn alloys with 8 wt. % of Al could be cold rolled after casting with by 80 %, whereas Cu – Al - Mn alloys with 12 wt. % of Al could be cold rolled after casting only by 12 % deformation degree [4]. It was found that all tensile mechanical properties, yield strength, tensile strength and plastic elongation of martensitic alloy CuAl11.3Mn6.4Fe2 were lower compared with austenitic alloys. Commonly the yield strength, tensile strength, and Young’s modulus of martensitic alloys have lower level compared to austenitic alloys.
Table 2. Chemical composition and transition tempera-tures of investigated alloys obtained by DSC.
Alloy composition in wt. %
Grain size in µm
AF
in °C MS
in °C AS
in °C MF
in °C
CuAl11.4Mn5.1 250 125 71 45 20 CuAl11.4Mn5.1Co0.2 160 80 38 40 3 CuAl11.6Mn5.1Co1.1 160 80 38 44 0
CuAl11.5Mn5.1 260 120 40 46 0 CuAl11.3Mn4.9Ni1 240 113 20 65 -20 CuAl11.2Mn4.9Ni2 320 65 38 42 18 CuAl11.5Mn4.9/ 240 90 45 55 20
CuAl11.7Mn5Fe1.1 520 120 75 65 25 CuAl11.7Mn5Fe2.2 880 140 95 85 35 CuAl12.3MN5.3 312 65 38 42 18
CuAl11.9Mn5.1Si0.5 120 50 20 22 -20 CuAl11.8Mn5.1Si1.4 70 35 10 0 -40
Solid State Phenomena Vol. 137 147
Elongation in case of martensitic Cu – Al - Mn shape memory alloys in this composition range (see table 2) depends less on the chemical composition and was found for many alloys to be between 9 and 11 %. It is well known that the Young’s modulus in SMA is higher in austenite than in martensite, and is minimum, when stress induced phase transformations can occure within the temperature range MF < T < MD (above MD no stress-induced transformation can take place) [17].
For comparison of elastic properties some tensile load and relief of the stress tests in some stress stages were done up to maximum stress 300 MPa without fracture. The austenitic specimen CuAl9.4 - Mn5.7 - Ni3.9 achieved the maximum stress of 300 MPa for the elongation of 0.25 %, whereas the multiple phase specimen CuAl11.9Mn7/MA2 was elongated by 2 % for 300 MPa stress. From figures 1a and 1b can be concluded that the phases in the samples present at testing temperature are responsible for the mechanical properties of Cu – Al - Mn shape memory alloys. In Fig. 1c cyclic stress-strain curves are shown for CuAl11.5Mn4.8/MA1, CuAl11.7-Mn4.6/MA2 and CuAl11.9-Mn4.3/MA3. The stress-strain curves are strongly affected by testing temperature, especially critical tensile stress σc (see Fig. 1 c) and slope of the strain-stress curve dσP/dε (see Fig. 1 c). Both quantities increase with testing temperature in the region of higher martensitic transition temperatures. The martensitic, austenitic and three different multiple phase specimens were tested in the high cycle fatigue range. The results are shown in Fig. 2. The martensitic alloy CuAl11.6Mn5 reaches the 107 fatigue strength at 125 MPa, and the austenitic alloy CuAl12.1Mn5.1 reaches 107 fatigue strength at 165 MPa. The corresponding Woehler curves cross each other at 165 MPa
for NF = 106. For NF < 10
6 the austenitic specimens break at lower cycle numbers than martensitic ones. The Woehler curve of MA1 (CuAl11.6Mn4.6, with MF < RT < MS) has the highest fatigue limit (145 MPa) of all multiple phase specimens.
Below MF and above MD the SMA-material shows a similar fatigue behavior like non shape memory metals. In between plastic stress-induced and pseudo-elastic transition can take place. Moreover, mechanical and fatigue properties depend on the testing temperature. Martensite start
0.0 0.5 1.0 1.5 2.0 2.50
100
200
300
400
500
600
0 5 10 15 200
100
200
300
400
500
600
CuAl9.4Mn5.7Ni3.9 / A
CuAl11.9Mn7 / MA2
σ in MPa
ε in %b)
CuAl8.2Mn10 / A
CuAl11.3Mn6.4Fe2 / M
σ in MPa
ε in %a)
Fig. 1. Tensile tests at room temperature: a) Typical tensile curves for austenitic specimen with low aluminium content and for homogenized martensitic specimen, tensile strain velocity of 10-3 s-1; b) Cycling tests for austenitic and multiple phase alloys tensile strain velocity of 10-4s-1.
0 2 40
200
400
600
σ in MPa
ε in %
CuAl11.5Mn4.8/MA1
CuAl11.7Mn4.6/MA2
CuAl11.9Mn4.3/MA3
σC
dσP/dε
Fig. 1 c. Cyclic stress-strain curves for three multiple phase
Cu – Al – Mn alloys at RT.
148 Interaction between Defects and Anelastic Phenomena in Solids
temperature MS depends on the stress of cyclic loading and the dependencies of stress-induced transformation have to be considered [8]:
MS (σ) = MS+∆T = MS + εβγσβγ Sβγ-1 (1)
where β and γ are austenite and martensite phase, εβγ and σβγ are strain and stress connected with martensitic β-γ transformation and Sβγ is the entropy in Jm
-3K-1. Obviously, Woehler curves depend
besides surface parameters on the phases, which are present at testing temperature. Hornbogen [8] and Eggeler et al. [18] measured Woehler curves for CuZnAl- and NiTi-SMA and found out, that the pseudo elastic alloys have better fatigue properties compared to pure martensitic or austenitic alloys, whereas the fatigue strength of martensitic alloys was higher than of austenitic alloys. This fact can be confirmed by this study, where the best fatigue strength shows austenitic specimen.
Different alloying elements as Co, Ni, Fe and Si were added to the melt with average composition CuAl11.6-Mn5. The corresponding as cast alloy is martensitic at RT. By increasing the Co- and Si-contents the grain size can
be reduced (see table 1). Ni and Fe support the shape memory effects and much higher peaks for endo- and exo-reactions can be found in DSC-measurements during martensitic transition compared to the DSC investigations of the alloy CuAl11.6Mn5.
Moreover, additions of these elements decreased the ductility of the specimens (Fig. 3 a). In case of addition of 0.2 wt. % Cobalt to the melt the fracture strain increased slightly, but the new composition moved the transition temperatures to MA1-multiple phase range. Yield strength and tensile strength were not improved by the addition of 1.1 wt. % Cobalt. The alloy CuAl11.6Mn5.1Co1.1/MA2 shows a higher strain hardening compared to alloys with lower Co-contents. The addition of Ni decreases all mechanical properties. The addition of 2.2 wt. % Fe does not change the transition temperatures comparing to initial alloy. The elongation and tensile strength become lower, whereas the yield strength becomes greater, especially in the case of CuAl11.7Mn5Fe2.2. The addition of 1.5 wt. % Si improves the yield strength and decreases fracture strain. The improvement of the yield strength can be well explained with decreasing grain sizes (see Table 2) by the Hall-Petch-relation. Sutou et al. [19] grain refined CuAl7.6Mn9.7 with Cr and V. The alloys were martensitic. All mechanical properties i.e. elongation, yield strength, tensile strength could be increased by this grain refinement. This could not be achieved with V and Cr in the present investigation. Chemical analysis did not confirm the content of Cr and V added to the melt, because some amounts were combusted during the melting and casting process.
The martensitic temperatures can be decreased by addition of Co, Ni, Fe and Si (see table 2). The same was found after addition of Cr and V I [19].
The specimens with additional alloying contents were additionally mechanically loaded with 165 MPa by investigation of rotating beam loading (R = - 1) at room temperature (RT) in air and at 46 Hz. Relevant results are shown in Fig. 3b. All additional alloying contents of Co (max.: 1.2 wt. %), Ni (max.: 2 wt. %), Fe (max.: 2.2 wt. %) and Si (max.: 1.4 wt. %) reduce the number of
105
106
107
100
150
200
250
105
106
107
100
150
200
250
σ
Nf
A
M
MA1
σ
Nf
MA1
MA2
MA3
Fig. 2. Woehler curves for different states of Cu – Al - Mn SMA obtained at RT after electrochemical polishing, f = 46 Hz.
Solid State Phenomena Vol. 137 149
cycles to fatigue at 165 MPa.
The influences of a cyclic loading on the amplitude dependence of damping for multiple phase (MA1), austenitic and martensitic specimen are shown in Figs. 4 a and b, 5 a and b. Controlled fati-gue can be realized by bending loading of the bending beam samples in the same apparatus, which was used for the damping measurements controlling the amplitude and number of vibrations. The fatigue in damping apparatus was strain controlled with strain amplitude 10-3. Young’s modulus for martensitic specimens was measured to be 105 GPa, as an average value for all martensitic alloys at RT [4, 20], the measurements were performed by two different methods, by stress-strain tensile tests and by resonant frequency method [21]. The average Young’s modulus of all austenitic specimens at RT was found to be 120 GPa. The Young’s modulus of multiple phase specimens is lower compared to austenitic and martensitic specimens and depends on the volume fraction of the present phases. In Fig. 4 a and b the influence of cycling loading on δ (ε) are shown for CuAl12.7Mn3.3/MA1. Both the damping measurements and mechanical loading were done with resonant frequency at RT.
0 3 6 90
100
200
300
400
500
600
700
800
0 3 6 90
100
200
300
400
500
600
700
800
0 3 6 90
100
200
300
400
500
600
700
800
σ in MPa
ε in %
CuAl11.4Mn5.1 /M
CuAl11.4Mn5.1Co0.2 /MA1
CuAl11.6Mn5.1Co1.1/MA1
σ in MPa
ε in %
CuAl11.5Mn5.1 /M
CuAl11.3Mn4.9Ni1 / MA1
CuAl11.2Mn4.9Ni2 / M
σ in MPa
ε in %
CuAl11.5Mn4.9/M
CuAl11.7Mn5Fe1.1 / M
CuAl11.7Mn5Fe2.2 /M
0 3 6 90
100
200
300
400
500
600
700
800
σ in MPa
ε in %
CuAl12.3MN5.3 / M
CuAl11.9Mn5.1Si0.5 / MA1
CuAl11.8Mn5.1Si1.4 / MA1
Fig. 3 a. Engineering strain-stress dependence obtained by uniaxial tensile strain at room temperature.
Average composition CuAl11.6Mn at room temperature with additional alloying components: Co, Ni, Fe and Si.
150 Interaction between Defects and Anelastic Phenomena in Solids
10-5
10-4
10-3
0,00
0,02
0,04
0,06
0,08
0,10
δ
ε
1.0 x 102
3.7 x 103
1.5 x 104
7.0 x 104
1.4 x 105
1.1 x 106
a)
0,01
10-5
10-4
10-3
0,00
0,01
0,02
0,03
0,04
0,05δ
ε
6.0 x 106
8.0 x 107
1.0 x 108
2.0 x 108
2.5 x 108
4.0 x 108
b)
Fig. 4. Strain amplitude dependence of damping for alloy CuAl12.7Mn3.3/MA1 as cast for different
number of cycles: a) N = 0 to 1.1 x 106 and b) 6 x 106 to 4 x 108.
101
102
103
104
105
106
107
108
109
3600
3800
4000
4200
4400
f N2
N
Fig. 4 c. Square of the resonant frequency for different numbers of cycles for CuAl12.7Mn3.3/MA1; εmax = 10
-3 for which the Young’s modulus was obtained and at which fatigue test was performed.
- Co0.5 Co1.2 Ni1 Ni2 Fe1.1 Fe2.2 Si0.5 Si1.40,0
2,0x105
4,0x105
6,0x105
8,0x105
1,0x106
1,2x106
1,4x106
NF
CuAl11.6Mn5 +
σ = 165MPa
Fig. 3 b. Influence of different alloying elements on numbers of cycles until failure at 165 MPa, f =
46 Hz of average composition CuAl11.6Mn5 at room temperature, obtained at RT after electrochemical polishing.
Solid State Phenomena Vol. 137 151
10-6
10-5
10-4
10-3
0,000
0,002
0,004
0,006
0,008
0,010
δ
ε
1.0 x 102
4.2 x 103
1.7 x 104
8.1 x 104
1.7 x 105
3.0 x 106
a)
10-5
10-4
10-3
0,00
0,01
0,02
0,03
0,04
δ
ε
1.0 x 102
2.4 x 103
4.6 x 104
9.4 x 104
1.9 x 105
3.0 x 106
b)
Fig. 5. Strain amplitude dependence of damping for: a) as cast austenitic alloy CuAl8.9Mn9.3/A for different number of cycles; b) as cast martensitic alloy CuAl12.5Mn3/M for different numbers of cycles.
The maximum damping decreases strongly with increasing number of cycles N. This decrease in damping due to cycling loading occurs during the first 106 cycles. The specimen CuAl12.7-Mn3.3/MA1 resisted 4×10
8 mechanical cycles without failure. Adoptively, CuAl12.7Mn3.3/MA1 at 90 MPa exhibits fatigue strength. The position of the maximum in δ (ε) changed the position with increasing numbers of cycles i.e. it moves to lower levels and higher strains. Dissipation of the energy by motion of phase- and twin- boundaries can cause a more permanent or irreversible transformation between martensite and austenite. This could as well bear out the fact, that the decrease of the damping in accompanied by increase of the resonant frequency, i.e. Young’s modulus (see Fig. 4 c). This behaviour could be explained by aging of the specimen [4] or anelastic phenomena, too. However, less martensite in the microstructure was found for N = 4×108 compared to as cast state in the micrographs of the specimen CuAl12.7Mn3.3/MA1. This effect supports the statement that martensitic phases transit to austenite during cycling loading, which could also be due to aging. Moreover, all alloys containing the mixture of phases, will slightly change their phase composition simply due to the heating of the specimen due to cycling. Therefore, after fatigue its state correspond to some partial transformation cycle with higher austenite content.
For comparison two Cu – Al - Mn shape memory alloys were cyclically loaded with maximum strain εmax = 10
-3. Alloy CuAl8.0Mn9.3 (see Fig. 5 a) was austenitic and CuAl12.5Mn3 martensitic (see Fig. 5 b) at room temperature. Only small c hanges in δ (ε) with increasing cycling numbers were observed until N=3x106 in both cases. The damping curves of austenitic Cu – Al – Mn SMA has a similar regime as the stain amplitude dependence δ (ε) = δ0 + δH (ε) (δ0 damping background and δH (ε) amplitude dependent damping due to hysteretic effects) forecast by the Granato and Lücke theory [22], but can not be explained by this model [23].
Conclusions
The austenitic specimens of Cu – Al - Mn shape memory alloys with aluminium contents from 8.9 to 12.5 wt. % and Mn contents 3.3 - 9.3 wt. % have high yield strength and tensile strength compared to martensitic and multiple phase alloys. For lower aluminium contents the fracture strain can achieve 18 %. With increasing aluminium contents Cu – Al - Mn-alloys become brittle.
All tensile mechanical properties like yield strength, tensile strength and elongation of martensitic alloys were lower compared with austenitic alloys. Fracture strain in case of martensitic alloys depends less on the chemical composition and was found for many alloys to be in the range 9 - 11 %.
152 Interaction between Defects and Anelastic Phenomena in Solids
The highest fatigue properties were obtained for austenitic Cu – Al – Mn alloys. The level of Woehler- curves for multiple specimens depends on the phases at testing temperatures (RT) and show the highest level for multiple phase specimen with more martensite. Additions of Co (max.: 1.2 wt. %), Ni (max.: 2 wt. %), Fe (max.: 2.2 wt. %) and Si (max.: 1.4 wt. %) decline the ductility of the specimens, and their fatigue properties at 165MPa in rotating beam loading (R = - 1) at RT in air.
The strain amplitude dependence of damping of multiple phase specimen decreased due to mechanical cycling whereas the resonant frequency increased. This can be explained with the fact that the specimen becomes more austenitic with increasing time of cycling loading but also with usually found internal friction effects. The damping curves of martensitic and austenitic Cu - Al - Mn SMA do not change much with number of cycling with 0.001 maximum strain amplitude until 3 × 106 cycles.
Acknowledgements
This work was supported by Deutsche Forschungsgemeinschaft (DFG).
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154 Interaction between Defects and Anelastic Phenomena in Solids
Interaction between Defects and Anelastic Phenomena in Solids 10.4028/www.scientific.net/SSP.137 Mechanical and Fatigue Properties of Cu-Al-Mn Shape Memory Alloys with Influence of Mechanical
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