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1.
This article discusses the effects of laser welding parameters such as power, welding speed, and focus position on the weld
bead profile, microstructure, pseudo-elasticity (PE), and shape memory effect (SME) of NiTi foil with thickness of 250 μm using 100W CW fiber laser. The parameter settings to produce the NiTi welds for analysis in this article were chosen from
a fractional factorial design to ensure the welds produced were free of any apparent defect. The welds obtained were mainly
of cellular dendrites with grain sizes ranging from 2.5 to 4.8 μm at the weld centerline. A small amount of Ni3Ti was found in the welds. The onset of transformation temperatures (A
s
and M
s
) of the NiTi welds shifted to the negative side as compared to the as-received NiTi alloy. Ultimate tensile stress of the
NiTi welds was comparable to the as-received NiTi alloy, but a little reduction in the pseudo-elastic property was noted.
Full penetration welds with desirable weld bead profiles and mechanical properties were successfully obtained in this study. 相似文献
2.
Douglas E. Burkes John J. Moore Guglielmo Gottoli Hu Chun Yi 《Metallurgical and Materials Transactions A》2006,37(3):1045-1053
Combustion synthesis (CS) of nickel, titanium, and carbon (graphite) reactant particles can result in NiTi-TiC (stoichiometric)
or Ni3Ti-TiC
x
(nonstoichiometric) composites. Since NiTi exhibits both superelasticity and shape memory properties while Ni3Ti does not, it is important to understand the SHS reaction conditions under which each of these composite systems may be
synthesized. The stoichiometry of TiC
x
, for which 0.3 ≤ x ≤ 0.5, has an important controlling effect on the formation of either Ni3Ti or NiTi; i.e., formation of TiC0.7 results in a depletion of titanium and formation of Ni3Ti. This deficiency should be considered when developing the SHS reaction. This article examines the SHS conditions under
which Ni3Ti-TiC
x
composites are produced. Ignition, combustion, and microstructure characteristics of nickel, titanium, and carbon (graphite)
particles were investigated as a function of initial relative density and thermophysical properties of the reactant mixture.
Combination of the thermophysical properties and burning velocities controlled TiC
x
particle size, yielding a dependence of particle size on cooling rate. Theoretical calculations were performed and are in
good agreement with the experimental data presented. 相似文献
3.
Douglas E. Burkes Guglielmo Gottoli John J. Moore Hu Chun Yi 《Metallurgical and Materials Transactions A》2006,37(12):1045-1053
Combustion synthesis (CS) of nickel, titanium, and carbon (graphite) reactant particles can result in NiTi−TiC (stoichiometric)
or Ni3Ti−TiC
x
(nonstoichiometric) composites. Since NiTi exhibits both superelasticity and shape memory properties while Ni3Ti does not, it is important to understand the SHS reaction conditions under which each of these composite systems may be
synthesized. The stoichiometry of TiC
x
, for which 0.3≤x≤0.5, has an important controlling effect on the formation of either Ni3Ti or NiTi; i.e., formation of TiC0.7 results in a depletion of titanium and formation of Ni3Ti. This deficiency should be considered when developing the SHS reaction. This article examines the SHS conditions under
which Ni3Ti−TiC
x
composites are produced. Ignition, combustion and microstructure characteristics of nickel, titanium, and carbon (graphite)
particles were investigated as a function of initial relative density and thermophysical properties of the reactant mixture.
Combination of the thermophysical properties and burning velocities controlled TiC
x
particle size, yielding a dependence of particle size on cooling rate. Theoretical calculations were performed and are in
good agreement with the experimental data presented.
Guglielmo Gottoli, formerly Graduate Research Assistant, Metallurgical and Materials Engineering Department, Institute for
Space Resources, Colorado School of Mines 相似文献
4.
Douglas E. Burkes Guglielmo Gottoli John J. Moore Hu Chun Yi 《Metallurgical and Materials Transactions A》2006,37(13):1045-1053
Combustion synthesis (CS) of nickel, titanium, and carbon (graphite) reactant particles can result in NiTi−TiC (stoichiometric)
or Ni3Ti−TiC
x
(nonstoichiometric) composites. Since NiTi exhibits both superelasticity and shape memory properties while Ni3Ti does not, it is important to understand the SHS reaction conditions under which each of these composite systems may be
synthesized. The stoichiometry of TiC
x
, for which 0.3≤x≤0.5, has an important controlling effect on the formation of either Ni3Ti or NiTi;i.e., formation of TiC0.7 results in a depletion of titanium and formation of Ni3Ti. This deficiency should be considered when developing the SHS reaction. This article examines the SHS conditions under
which Ni3Ti−TiC
x
composites are produced. Ignition, combustion and microstructure characteristics of nickel, titanium, and carbon (graphite)
particles were investigated as a function of initial relative density and thermophysical properties of the reactant mixture.
Combination of the thermophysical properties and burning velocities controlled TiC
x
particle size, yielding a dependence of particle size on cooling rate. Theoretical calculations were performed and are in
good agreement with the experimental data presented.
Guglielmo Gottoli, formerly Graduate Research Assistant, Metallurgical and Materials Engineering Department, Institute for
Space Resources, Colorado School of Mines 相似文献
5.
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
6.
H. C. Yi J. Y. Guigné T. C. Woodger J. J. Moore 《Metallurgical and Materials Transactions B》1998,29(4):867-875
Combustion synthesis (SHS) of Ni3Ti-TiB2 metal matrix composites (MMCs) was selected to investigate the effect of gravity in a reaction system that produced a light,
solid ceramic particle (TiB2) synthesized in situ in a large volume (>50 pct) of the liquid metallic matrix (Ni3Ti). The effects of composition, green density of pellets, and nickel particle size on the combustion characteristics are
presented. Combustion reaction temperature, wave velocity, and combustion behavior changed drastically with change in reaction
parameters. Two types of density effects were observed when different nickel particle sizes were used. The structures of the
combustion zones were characterized using temperature profile analysis. The combustion zone can be divided into preflame,
reaction, and after-burning zones. The combustion mechanism was studied by quenching the combustion front. It was found that
the combustion reactions proceeded in the following sequence: formation of liquid Ni-Ti eutectic at 940 °C → Ni3Ti+NiTi phases → reduction of NiTi with B→TiB2+Ni3Ti. 相似文献
7.
Fu-Cheng Yen Kuen-Shyang Hwang Shyi-Kaan Wu Shiau-Han Wu 《Metallurgical and Materials Transactions A》2011,42(8):2431-2441
This study demonstrates that a high density and a high transformation heat can be attained for PM TiNi. With the use of fine
elemental powders, a composition of Ti51Ni49, two-step heating, and persistent liquid-phase sintering at 1553 K (1280 °C), a 95.3 pct sintered density was attained for
compacts with a green density of 66 pct. A transformation heat, ΔH, of 31.9 J/g was also achieved, which is much higher than reported previously for sintered TiNi and is approaching the highest
ΔH reported to date, 35 J/g, for wrought TiNi with low C, O, and N contents. The main reason for having these properties in
powder metal TiNi with higher amounts of C, O, and N is that the extra Ti, that over the equiatomic portion in the Ti-rich
Ti51Ni49, forms Ti2Ni compound, which traps most of the C, O, and N. This results in low interstitial contents and a high Ti/Ni ratio of 50.5/49.5
in the TiNi matrix. The tensile strength, elongation, and shape recovery rate after five training cycles were 638 MPa, 14.6,
and 99.1 pct, respectively, despite the presence of Ti2Ni compounds at grain boundaries. 相似文献
8.
The phase equilibria at 1173 K have been determined in the Ni-AI-Ti system for Al contents less than 50 at. pct. The extent
of theH (Ni2AlTi) phase field has been established as well as the extent of solubility in the binary compounds γ (Ni3Al), ν(Ni3Ti), β2(NiTi), NiTi2, and ζ(AlTi3). Substantial differences were found between the phase equilibria determined in this study and previous studies, in part
due to the large solubility of Al in NiTi2. 相似文献
9.
《粉末冶金学》2013,56(1):36-41
AbstractPorous NiTi shape memory alloy was fabricated by self-propagating high temperature synthesis. Effects of solution treatment under load applied on the microstructure were investigated. The densities of the phases changed insignificantly with solution treatment but the intermetallic phases such as Ti2Ni, Ni4Ti3 and Ni3Ti2 disappeared and the density of B2(NiTi) phase increased with the load applied during solution treatment. Consequently, porous NiTi SMA with ideal pore characteristics, high chemical homogeneity and high strength for hard tissue implants was obtained. 相似文献
10.
B. Alemán Ph.D. Student I. Gutiérrez J. J. Urcola 《Metallurgical and Materials Transactions A》1995,26(2):437-446
A Ti6242 alloy has been diffusion bonded to a superalloy INCONEL 625. The microstructures of the as-processed products have
been analyzed using optical metallography, scanning electron microscope (SEM), and scanning transmission electron microscope
(STEM) techniques. The interdiffusion of the different elements through the interface has been determined using energy-dispersive
spectroscopy (EDS) microanalysis in both a SEM and a STEM. Several regions around the original interface have been observed.
Starting from the superalloy INCONEL 625, first a sigma phase (Cr4Ni3Mo2), followed by several phases like NbNi3, Ŋ/Ni3Ti, Cr(20 pct Mo), β Cr2Ti, NiTi, TiO, TiNi, and Ti2Ni intermetallics, just before the Ti6242 have been identified. Because the diffusion of Ni in Ti is faster than the diffusion
of Ti in the superalloy, a Kirkendall effect was produced. The sequence of formation of the different phases were in agreement
with the ternary Ti-Cr-Ni diagram. 相似文献
11.
Yeon-Wook Kim Young-Soo Chung Eunsoo Choi Tae-Hyun Nam 《Metallurgical and Materials Transactions A》2012,43(8):2932-2938
Even though Ti-Ni-Cu alloys have attracted a lot of attention because of their high performance in shape memory effect and decrease in thermal and stress hysteresis compared with Ti-Ni binary alloys, their poor workability restrains the practical applications of Ti-Ni-Cu shape memory alloys. Consolidation of Ti-Ni-Cu alloy powders is useful for the fabrication of bulk near-net-shape shape memory alloy. Ti50Ni30Cu20 shape memory alloy powders were prepared by gas atomization, and the sieved powders with the specific size range of 25 to 150???m were chosen for this study. The evaluation of powder microstructures was based on a scanning electron microscope (SEM) examination of the surface and the polished and etched powder cross sections. The typical images showed cellular/dendrite morphology and high population of small shrinkage cavities at intercellular regions. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis showed that a B2-B19 one-step martensitic transformation occurred in the as-atomized powders. The martensitic transformation start temperature (Ms) of powders ranging between 25 and 50???m was 304.5?K (31.5?°C). The Ms increased with increasing powder size. However, the difference of Ms in the as-atomized powders ranging between 25 and 150???m was only 274?K (1?°C). A dense cylindrical specimen of 10?mm diameter and 15?mm length were fabricated by spark plasma sintering (SPS) at 1073?K (800?°C) and 10?MPa for 20?minutes. Then, this bulk specimen was heat treated for 60?minutes at 1123?K (850?°C) and quenched in ice water. The Ms of the SPS specimen was 310.5?K (37.5?°C) whereas the Ms of conventionally cast ingot is found to be as high as 352.7?K (79.7?°C). It is considered that the depression of the Ms in rapidly solidified powders is ascribed to the density of dislocations and the stored energy produced by rapid solidification. 相似文献
12.
Ching-Chich Leu David Vokoun Chen-Ti Hu 《Metallurgical and Materials Transactions A》2002,33(1):17-23
An investigation on the two-way shape memory effect (TWSME) induced by an electrochemical hydrogenation has been conducted
on two TiNi shape memory alloys (SMAs) (Ti49.2Ni50.8 and Ti51.1Ni48.9 denoted as materials A and B, respectively). While a bending constraint has been applied during hydrogenation, the effects
of current density, solution temperature, and charging period are studied. A two-way shape memory behavior was observed on
the bent, hydrogenated specimens. The measured ratio of TWSME of specimen A is greater than that of specimen B. The variation
of the TWSME of the specimens is relatively small during the first 50 thermal cycles. The TWSME increases first and then decreases
with increasing either current density or charging period of the electrochemical hydrogenation. The X-ray diffraction peak
corresponding to hydrides in the hydrogenated specimen still exists but becomes weaker after three months of “resting,” and
the TWSME obviously decreases with decreasing amount of hydrides. 相似文献
13.
Sangthum Srikomol Yuttanant Boonyongmaneerat Ratchatee Techapiesancharoenkij 《Metallurgical and Materials Transactions B》2013,44(1):53-62
The fabrication of nickel-titanium (Ni-Ti) alloy layers via the electrochemical codeposition and heat treatment is proposed and investigated herein. The codeposition of a Ti-dispersed Ni-matrix layer on an indium tin oxide-coated glass substrate was systematically conducted over varied current densities, Ti-particle loadings in an electrolyte and Ti particle sizes to investigate their effects on the Ti content and morphology of the layers. A moderate particle loading of approximately 2 to 6 g/dm3 led to relatively high Ti contents, whereas a decrease of particle size gave a dense and uniform layer with relatively low Ti contents. Following heat treatment, the Ni-Ti composite layers completely transformed into the Ni-Ti alloys with varying dominant phases of NiTi, Ni3Ti, and Ni solid solution depending on the alloy compositions. The assessment of the Ni-Ti phase diagram and the Ni-Ti interdiffusivity are discussed to verify the resultant phases present in the post-annealed layers. The results and analyses from this work entail the construction of the codeposition’s mechanistic views and the interaction of the hydrodynamic, gravitational, and electrophoretic forces on particles suspended in an electrolyte, which are critical to the development of the Ni-Ti component fabrication via the combined codeposition-heat treatment route. 相似文献
14.
B. Geetha Priyadarshini S. Aich M. Chakraborty 《Metallurgical and Materials Transactions A》2011,42(11):3284-3290
Ni-rich Ni-Ti alloy thin films were fabricated by radio frequency (RF)-direct-current (DC) magnetron sputtering using elemental
Ni and Ti as sputter targets. Si (100) was chosen as a substrate that was either held at room temperature or at 573 K (300 °C)
during the depositions. The 380-nm-thick films were characterized by field emission scanning electron microscopy, energy dispersive
spectroscopy, grazing incidence X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy,
and Vickers microhardness tester. The results suggests that because of the lack of surface mobility of the adatoms at the
room temperature, the deposited films were smooth and amorphous, with a crystallite size of 15 nm accompanied with a porous
morphology. At higher substrate temperatures, an increase in the surface diffusion leads to the formation of partially crystalline,
rougher films with a denser, compact, fibrous grain microstructure. The formation of Ni-rich precipitates such as Ni4Ti3, Ni2Ti, and Ni3Ti along with small amount of the NiTi phase were attributed to the localized heating and cooling within the grains. Few grains
exhibited band structures that are believed to be a result of <110> type II twins. 相似文献
15.
Gopinath Thirunavukarasu Sukumar Kundu Brajendra Mishra Subrata Chatterjee 《Metallurgical and Materials Transactions A》2014,45(4):2078-2090
In the current study, solid-state diffusion bonding between Ti-6Al-4V (TiA) and 304 stainless steel (SS) using pure nickel (Ni) of 200-μm thickness as an intermediate material was carried out in vacuum. Uniaxial compressive pressure and temperature were kept at 4 MPa and 1023 K (750 °C), respectively, and the bonding time was varied from 30 to 120 minutes in steps of 15 minutes. Scanning electron microscopy images, in backscattered electron mode, revealed the layerwise Ti-Ni-based intermetallics like either Ni3Ti or both Ni3Ti and NiTi at titanium alloy-nickel (TiA/Ni) interface, whereas nickel-stainless steel (Ni/SS) interface was free from intermetallic phases for all the joints. Chemical composition of the reaction layers was determined by energy dispersive spectroscopy (SEM–EDS) and confirmed by X-ray diffraction study. Maximum tensile strength of ~382 MPa along with ~3.7 pct ductility was observed for the joints processed for 60 minutes. It was found that the extent of diffusion zone at Ni/SS interface was greater than that of TiA/Ni interface. From the microhardness profile, fractured surfaces, and fracture path, it was demonstrated that the failure of the joints was initiated and propagated apparently at TiA/Ni interface near Ni3Ti intermetallic for bonding time less than 90 minutes, and through Ni for bonding time 90 minutes and greater. 相似文献
16.
Takahiro Sawaguchi Morio Sato Akira Ishida 《Metallurgical and Materials Transactions A》2004,35(1):111-119
The grain-size effect on shape-memory behavior of fine-grained Ti35.0Ni49.7Zr15.4 thin films was investigated by transmission electron microscopy. The films, with various grain sizes ranging from about 150
to about 400 nm, were prepared by heat treatment of amorphous films at the three different annealing temperatures of 773,
873, and 973 K, for three different annealing times of 5 minutes, 1 hour, and 10 hours. The film annealed at 773 K for 5 minutes
showed a nearly single phase of (Ti,Zr)Ni, while the films annealed at high annealing temperatures and/or long annealing times
showed λ
1 precipitates. For a high annealing temperature of 973 K, the critical yield stress (σ
c) was dominantly dependent on the grain size of the matrix, obeying the Hall-Petch equation. On the other hand, for a low
annealing temperature of 773 K, σ
c was dominantly dependent on the amount of λ
1 precipitates. The M
S temperature decreases almost linearly with increasing σ
c. The films showed sufficient fracture toughness, probably due to the nanometer scale of the grain size and the agglomerated
shape of λ
1 particles. 相似文献
17.
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
18.
NiTi wires of 0.5 mm diameter were laser welded using a CW 100-W fiber laser in an argon shielding environment with or without
postweld heat-treatment (PWHT). The microstructure and the phases present were studied by scanning-electron microscopy (SEM),
transmission-electron microscopy (TEM), and X-ray diffractometry (XRD). The phase transformation behavior and the cyclic stress–strain
behavior of the NiTi weldments were studied using differential scanning calorimetry (DSC) and cyclic tensile testing. TEM
and XRD analyses reveal the presence of Ni4Ti3 particles after PWHT at or above 623 K (350 °C). In the cyclic tensile test, PWHT at 623 K (350 °C) improves the cyclic deformation
behavior of the weldment by reducing the accumulated residual strain, whereas PWHT at 723 K (450 °C) provides no benefit to
the cyclic deformation behavior. Welding also reduces the tensile strength and fracture elongation of NiTi wires, but the
deterioration could be alleviated by PWHT. 相似文献
19.
Bikas C. Maji Madangopal Krishnan Gouthama R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(8):2153-2165
The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The
microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition
does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct
Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced
α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and
results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si. 相似文献