共查询到20条相似文献,搜索用时 15 毫秒
1.
Yinong Liu I. Houver H. Xiang L. Bataillard S. Miyazaki 《Metallurgical and Materials Transactions A》1999,30(5):1275-1282
This work investigated the transformation-strain dependence of the stress hysteresis of pseudoelasticity associated with the
stress-induced martensitic transformation in binary NiTi alloys. The strain dependence was studied with respect to the deformation
mode during the stress-induced martensitic transformation, which was either localized or homogeneous. It was observed that
the apparent stress hysteresis of pseudoelasticity was independent of the transformation strain within the macroscopic deformation
range, for the specimens deformed in a localized manner. For specimens macroscopically deformed uniformly, the stress hysteresis
of pseudoelasticity increased continuously with increasing strain from the beginning of the stress-induced martensitic transformation.
The transformation-strain independence of the stress hysteresis for localized deformation is ascribed to be an artificial
phenomenon, whereas the transformation-strain dependence of the hysteresis for uniform deformation is believed to be intrinsic
to the process of stress-induced martensitic transformation in polycrystalline materials. This intrinsic behavior is attributed
to the polycrystallinity of the materials. 相似文献
2.
Effect of cyclic deformation on the pseudoelasticity characteristics of Ti-Ni alloys 总被引:5,自引:0,他引:5
Change in the pseudoelasticity characteristics of Ti-Ni alloys during tension cycling was investigated. The critical stress
for inducing martensites and the hysteresis of a stress-strain curve decreased with increasing number of cyclic loading, while
the permanent elongation increased. The degree of the change in these values showed a strong dependence on the maximum applied
stress during stress-induced martensitic transformation. However, no change was induced by cyclic elastic deformation even
though high stress was applied. It was also found that the stabilization of the pseudoelasticity characteristics during cyclic
loading was established using special thermomechanical treatments which are effective to raise the critical stress for slip.
Based on these results it is concluded that the cause for the effect of cyclic deformation is the generation of dislocations
in the martensitic phase. 相似文献
3.
《Acta Metallurgica》1988,36(2):291-297
The deformation and transformation behaviour associated with both the R and martensitic transformations in a near equiatomic NiTi alloy has been investigated using thermal cycling tests under constant applied load. Strain measurements exhibit separate stages of yielding associated with the R and martensitic transformations. The transformation sequence during cooling is found to depend on the applied stress, resulting from the differing stress dependencies of the R and martensitic transformation temperatures. Strain, resistivity, and DSC measurements indicate that the B2 → R transformation is characterised by a highly reversible single stage, first order reaction. Repeated thermal cycling resulted in irreversible changes to both the transformation temperatures and strains associated with the martensitic transformation. 相似文献
4.
5.
《钢铁研究学报(英文版)》2016,(1):31-36
Compositional dependences on microstructures and martensitic transformation behaviors in(Cu_(0.5)Zr_(0.5))_(100-x)Zn_x(x=1.5,2.5,4.5,7.0,10.0,and 14.0at.%)alloys were investigated.It was found that CuZr martensites were present in the present alloys.With increasing Zn content,the volume fractions of CuZr martensitic crystals and B2 CuZr phase gradually decrease and increase,respectively.With the addition of high Zn contents(i.e.,7.0,10.0,and 14.0at.%),the matrix proves to be eutectic.Thermal analysis results show that the initial martensitic transformation temperature(M_s)decreases from(412±5)K to(329±5)K as the Zn content increases from 1.5at.% to14.0at.%.The values of Msof Cu-Zr-Zn shape memory alloys are inversely proportional to the number and concentrations of valence electrons(i.e.,e_v/a and c_v),respectively,implying that the martensitic transformation in CuZrZn alloys could be of electronic nature. 相似文献
6.
Shape memory properties of Ni-Ti based melt-spun ribbons 总被引:1,自引:0,他引:1
R. Santamarta E. Cesari J. Pons T. Goryczka 《Metallurgical and Materials Transactions A》2004,35(3):761-770
Shape-memory properties of equiatomic NiTi, Ni45Ti50Cu5, and Ni25Ti50Cu25 ribbons made by melt spinning have been studied by temperature inducing the martensitic transformation under constant tensile
loads. Recoverable strains above 4 pct can be obtained under ∼100 MPa loads for the NiTi and Ni45Ti50Cu5 ribbons, transforming to B19’ martensite. The B19 martensite is formed in the Ni25Ti50Cu25 ribbon after crystallization, and according to the lowering in transformation strain as Cu content increases, the recoverable
strain is close to 2.5 pct for ∼150 MPa load. The transformation temperatures exhibit a linear dependence on the applied stress,
which can be quantitatively described by means of a Clausius-Clapeyron type equation. The NiTi and Ni45Ti50Cu5 ribbons exhibited some degree of two-way shape-memory effect (TWSME) after thermomechanical cycling. Texture analyses performed
on the different ribbons allow us to better understand the transformation strains obtained in each ribbon. The amounts of
shape-memory effect (SME) and nonrecoverable strain shown by the studied ribbons are of the same order as those already observed
in bulk materials, which makes melt spinning an ideal substitute to complicated manufacturing processes if really thin samples
are needed. However, applicable stresses in melt-spun ribbons are limited by a relatively “premature” brittle fracture caused
by irregularities in ribbon thickness. 相似文献
7.
A model that combines the phenomenological theory of martensite with a generalized Schmid’s law has been used to predict the
principal stress combinations required to induce the martensitic transformation in unconstrained NiTi shape memory alloy (SMA)
single crystals. The transformation surfaces prescribed by the model are anisotropic and asymmetric, reflecting the unidirectional
character of shear on individual martensite habit planes. Model predictions of the transformation strain as a function of
stress axis orientation for a uniaxial applied stress further demonstrate the anisotropy of the stress-induced transformation
in NiTi single crystals. Model results for the uniaxial stress case compare favorably with previously published experimental
observations for aged NiTi single crystals. 相似文献
8.
It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few systematic works on the SM effect in Co and Co-based alloys. In this study, the fcc/hcp martensitic transformation and the SM effect were investigated in Co-Al binary alloys(mole fraction of Al=0~16%).The γ/ε martensitic transformation temperatures were found from the DSC measurements to decrease with increasing Al content, while the transformation temperature hystereses were observed to increase from 60 ℃ at x(Al)=0 to 150 ℃at x(Al)= 16%. The SM effect evaluated by a conventional bending test was enhanced by the addition of Al over 4%(mole fraction) and Co-Al alloys containing over 10%(mole fraction) exhibit a good SM effect associated with the hcp →fcc reverse transformation above 200 ℃. The SM effect was significantly improved by precipitation ofβ (B2) phase and the maximal shape recovery strain of 2. 2% was obtained, which can be explained by precipitation hardening. The crystallographic orientations between theβ, ε and γ phases were also determined. Finally, the magnetic properties were investigated and it was found that the Curie temperature and saturation magnetization of Co-14% Al(mole fraction) are 690 ℃and 120 emu/g, respectively. It is concluded that the Co-Al alloys hold promise as new high-temperature and ferromagnetic SM alloys. 相似文献
9.
During the last decade, the use of press-hardened components in the automotive industry has grown considerably. The so-called tailored tempering, also known as partial press hardening, employs locally heated tools seeking to obtain bainitic transformations. This leads to (seamless) zones within the formed parts with higher ductility. Due to the intrinsic nature of this process, phase transformations happen under the influence of high loads and in pre-deformed austenite. The austenite pre-strain state and applied stresses affect the kinetics of the bainitic transformation. Moreover, stresses have an additional relevant effect in this process, the so-called transformation plasticity. Linear transformation plasticity models have been successfully used to predict the behavior in the presence of low stresses. Nonetheless, because of the process’s severe conditions, these tend to fail. A strong nonlinearity of the transformation plasticity strain is observed for applied stresses above the austenite yield strength. Using thermomechanical tests on sheet specimens of a manganese-boron steel (22MnB5), widely utilized in the industry, the effect on the bainitic transformation of various degrees of deformation in the range of 0 to 18 pct, applied stresses in the range of 0 to 250 MPa and the transformation plasticity effect are investigated in this work. 相似文献
10.
Nickel-rich β-NiAl alloys, which are potential materials for high-temperature shape-memory alloys, show a thermoelastic martensitic transformation,
which produces their shape memory effect. However, the transformation to Ni5Al3 phase during heating of NiAl martensite can interrupt the reversible martensitic transformation; consequently, the shape
memory effect in NiAl martensite might not appear after heating. The phase transformation process in binary Ni-(34 to 37)Al
martensite was investigated by differential thermal analysis (DTA) method, and we found that the condition of reversible martensitic
transformation was not the β → Ni5Al3 transformation, but rather the M → Ni5Al3 transformation occurring at 250 °C to 300 °C. Therefore, the transformation temperature of M → Ni5Al3 determined the highest operating temperature for the shape memory effect. For verifying the critical temperature, the phase
transformation process was investigated for eight ternary Ni-33Al-X alloys (X=Cu, Co, Fe, Mn, Cr, Ti, Si, and Nb). Only Ti,
Si, and Nb additions were found to be effective in dropping the M
s temperature, and they facilitated the shape memory effect in Ni-33Al-X alloys. In particular, the addition of Si and Nb raised
the transformation temperature of M → Ni5Al3, a potentially beneficial effect for shape memory at higher temperatures.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
11.
12.
G. I. Nosova 《Russian Metallurgy (Metally)》2017,2017(3):216-220
The fcc → fct martensitic transformation in Mn–Cu alloys, which contain two isomorphous fcc phases with different manganese contents, is considered. The influence of the ratio of contents of these phases, the phase dispersity, and the state of interphase boundaries on the development of the martensitic transformation in the volume of the alloys is described. As a result of these factors, the martensitic transformation can cover the entire volume of an alloy, including particles with the manganese content that is lower than the critical content required for the martensitic transformation to occur in single-phase solid solutions, and can take place only in manganese-rich particles. In the first case, a general tetragonal structure modulated with respect to lattice parameter c forms in the volume of a two-phase alloy. 相似文献
13.
I. Karaman H. Ersin Karaca Z. P. Luo H. J. Maier 《Metallurgical and Materials Transactions A》2003,34(11):2527-2539
A Ti-49.8 at. pct Ni alloy was severely deformed at three different temperatures using equal-channel angular extrusion (ECAE).
Three deformation temperatures—room temperature (below the martensite finish temperature), 50 °C (below the austenite start
temperature), and 150 °C (above the austenite finish temperature)—were selected such that the initial deforming phase (B2
austenite or B19’ martensite) and the initial governing deformation mechanism (martensite reorientation, stress-induced martensitic
transformation, or dislocation slip in martensite) would be different. The X-ray analysis results revealed that all processed
samples mostly contained a deformed martensitic phase, regardless of the initial deforming phase and the deformation mechanism.
Although the martensite start temperature did not change, the austenite start temperature decreased significantly in all deformation
conditions, probably because of the effect of the internal stress field caused by the deformed microstructure. All deformation
conditions led to an increase in the strength levels and some deterioration of shape-memory characteristics. However, a subsequent
low-temperature annealing treatment significantly improved pseudoelastic strain levels while preserving the ultrahigh strength
levels. The sample deformed at room temperature followed by the low-temperature annealing resulted in the most promising strength
and shape-memory characteristics under compression, such that a 5.3 pct shape-memory strain at a 2200 MPa strength level and
a 3.3 pct pseudoelastic strain at a 1900 MPa strength level were achieved. The differences between the strength levels and
the shape-memory characteristics after severe deformation at different temperatures were attributed to the different amounts
of plastic deformation and the resulting deformation textures, since at each deformation temperature the deformation mechanism
was different. It is concluded that the severe marforming using ECAE could easily improve strength levels of NiTi alloys while
preserving the shape-memory and pseudoelasticity (PE) characteristics and, thus, improve the thermomechanical fatigue behavior.
However, lower deformation temperatures are necessary to hinder formation of macroshear bands, and ECAE angles larger than
90 deg should be used to reduce the amount of strain applied in one pass. 相似文献
14.
The wear behavior of shape memory alloys is linked to the thermoelastic martensitic transformation. Due to this transformation,
these alloys have the ability to absorb a high amount of energy before undergoing plastic deformation and subsequent fractures
caused by wear. In this study, the effect of sliding velocity and load on the dry wear behavior of CuZnAl alloys has been
characterized. Weight loss as a function of the Ms transformation temperature at different sliding velocities and loads was studied for the different alloys. The weight loss
and friction coefficient of the alloys as a function of load showed linear and exponential relationships, respectively; however,
when considered versus applied sliding velocity, independently of which phase was present, they showed an exponential relation
and no direct relation, respectively. 相似文献
15.
Bing-Yun Li Li-Jian Rong Xing-Hong Luo Yi-Yi Li 《Metallurgical and Materials Transactions A》1999,30(11):2753-2756
TiH2 powder is added as a reactant and pore-forming agent to produce porous NiTi shape-memory alloys (SMAs). The transformation
behavior of porous NiTi alloys is investigated because it is relevant to the engineering and medical applications of SMAs.
It is found that the transformation behavior of porous NiTi alloys is different from that of cast NiTi alloys. It is demonstrated
for the first time, by in situ X-ray diffraction (XRD), that there is no R-phase transformation in porous NiTi alloys, and a broadened, two-peak phenomenon observed with a differential scanning calorimeter
(DSC) is not associated with R-phase transformation. The characteristic transformation temperatures of porous NiTi alloys are independent of sintering temperature,
sintering time, TiH2 content, and the heating/cooling rate during thermal cycling between +123 and +423 K. Further, the latent heats of transformation
are associated with the TiH2 content and the sintering conditions. 相似文献
16.
The effects of small amount additions of Sm on the martensitic transition and magnetic phase transition of polycrystalline Ni-Mn-Ga alloys were investigated. The experimental results show that the Sm doped alloys also undergo a thermal-elastic martensitic transformation and reverse transformation during cooling and heating process and the addition of Sm decreases the martensitic transformation temperature and Curie temperature in different degree respectively. Ni-Mn-Ga alloys of adding Sm still possess Heusler structure, but their crystal lattice parameters are modified slightly. The addition of a proper amount of Sm does not basically decrease Tc of the alloy when avoiding the appearance of second phase. In addition, the doped alloys have favorable toughness because of grain refinement of Sm. 相似文献
17.
《Acta Metallurgica Materialia》1993,41(1):253-263
The martensitic transformation on subambient cooling has been monitored in defect-free nanocrystalline f.c.c. FeCo particles that have been coherently precipitated in a Cu matrix; such a CuFeCo system was chosen for study because the f.c.c. → b.c.c. transformational driving force in FeCo alloys is exceptionally large. Transformation is found to occur at a driving force of ∼ 10kJ/mol, a factor of 7 higher than the known critical driving forces for heterogeneous nucleation in bulk alloys. The observed transformation characteristics are entirely consistent with classical homogeneous coherent nucleation, whereas heterogeneous nucleation and homogeneous semicoherent nucleation can be ruled out in this case. An observed variation in transformation temperatures is explained by the experimentally-determined differences in Co content (and, hence, in transformational driving force) among the FeCo precipitates in relation to their distribution of particle sizes. The role of thermal activation in the homogeneous nucleation process is demonstrated by applying a high magnetic field to impose an increment of driving force at low temperatures. 相似文献
18.
The compressive response of martensitic NiTi shape memory alloy (SMA) rods has been investigated using a modified Kolsky compression bar at various strain rates (400, 800, and 1200 s?1) and temperatures [room temperature and 373 K (100 °C)], i.e., in the martensitic state and in the austenitic state. SEM, DSC, and XRD were performed on NiTi SMA rod samples after high strain rate compression in order to reveal the influence of strain rate and temperature on the microstructural evolution, phase transformation, and crystal structure. It is found that at room temperature, the critical stress increases slightly as strain rate increases, whereas the strain-hardening rate decreases. However, the critical stress under high strain rate compression at 373 K (100 °C) increase first and then decrease due to competing strain hardening and thermal softening effects. After high rate compression, the microstructure of both martensitic and austenitic NiTi SMAs changes as a function of increasing strain rate, while the phase transformation after deformation is independent of the strain rate at room temperature and 373 K (100 °C). The preferred crystal plane of the martensitic NiTi SMA changes from (\( 1\bar{1}1 \))M before compression to (111)M after compression, while the preferred plane remains the same for austenitic NiTi SMA before and after compression. Additionally, dynamic recovery and recrystallization are also observed to occur after deformation of the austenitic NiTi SMA at 373 K (100 °C). The findings presented here extend the basic understanding of the deformation behavior of NiTi SMAs and its relation to microstructure, phase transformation, and crystal structure, especially at high strain rates. 相似文献
19.
The transformation behavior of Ni-Mn alloys in the vicinity of the stoichiometric composition has been studied using transmission
electron microscopy, X-ray diffraction, optical microscopy, and electrical resistivity measurements. The transformation behavior
was found to be markedly different in Mn-rich alloys and Ni-rich alloys. In Mn-rich alloys a martensitic transformation between
L20 (B2) and L10 structures takes place, which possesses many features common to alloys exhibiting a thermoelastic martensitic transformation.
On the other hand, in Ni-rich alloys an order-disorder transformation between A2 and L10 structures occurs. The martensitic transformation features {111} transformation twins as the transformation substructure
while the ordering reaction involves {101} order twins. In the Mn-rich alloys, the martensitic phase, if either slowly cooled
or annealed at intermediate temperatures, becomes “tempered”, resulting in a noncrystallographic, essentially featureless
microstructure apart from the presence of occasional {111} twins.
Formerly with University of Illinois. 相似文献
20.
《Acta Metallurgica》1987,35(11):2779-2789
The subject of this study is the behaviour of single and polycrystals undergoing a thermoelastic martensitic transformation which leads to creation of different variants of martensite. The overall behaviour is the superposition of contributions from the phase transformation and from other mechanisms of deformation—for example plasticity. Two classes of behaviour can then be distinguished: pure transformation plasticity exclusively due to phase transformation (the martensitic transformation); and coupled transformation plasticity in which plastic flow couples with the intrinsic (martensitic) contribution. For the first, a thermomechanical analysis based on the Gibbs-free energy gives the transformation criterion and the associated flow rule. The analysis, for the case of a single crystal, introduces the interaction matrix between the variants of the created martensite. This matrix determines the different classes of interaction between the variants. A phenomenological constitutive relation (transformation threshold for the rule of strain hardening) has been proposed for a polycrystal. It is similar to that proposed by Drücker and Prager. The results of theoretical analyses have been compared with the experimental data, for both single and polycrystals, obtained for pseudoelastic alloys of the Cu-Zn-Al type. 相似文献