Low-Temperature XRD Study of Phase Transformations in NiTi and TiNiCo Shape Memory Alloys Used for the Preparation of the Prototypes of Medical Implants

2013 ◽  
Vol 203-204 ◽  
pp. 125-128 ◽  
Author(s):  
Zdzisław Lekston ◽  
Maciej Zubko
Keyword(s):  
Low Temperature ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Phase Transformations ◽  
Powder Diffraction ◽  
Diffraction Method ◽  
Martensite Phase ◽  
Scanning Calorimetry ◽  
Two Phase ◽  
X Ray

The NiTi shape memory alloys with ternary additions of Co are being considered for future applications in the construction of medical products. In this study the commercially available Ni50.8Ti49.2 medical alloy and Ti50Ni48.7Co1.3 alloy obtained by the conventional VIM technique, were used to prepare shape memory and superelastic staples. The phase transformations in the wires of those alloys after various thermo-mechanical and thermal treatments have been defined by the differential scanning calorimetry (DSC) method and three-point bending and free recovery ASTM F2082-06 tests. In this work the courses of phase transformations in the studied alloys were investigated by means of the low-temperature X-ray powder diffraction method. In both alloys after cold working and annealing during cooling two phase transformations occur: from parent B2-phase to rhombohedral R-phase and monoclinic B19’ martensite phase. Such phase transformations are fully reversible during heating and the obtained characteristic temperatures from DSC and X-ray powder diffraction measurements are in good agreement.

Characterization of the Phase Transformations in the Shape Memory Alloy Ni-36 at.% Al

1991 ◽  
Vol 246 ◽  
Author(s):  
J.A. Horton ◽  
E.P. George ◽  
C.J. Sparks ◽  
M.Y. Kao ◽  
O.B. Cavin ◽  
...  
Keyword(s):  
High Temperature ◽  
Shape Memory ◽  
Phase Transformations ◽  
Hot Extrusion ◽  
Exothermic Peak ◽  
Nickel Aluminum ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Transmission Electron

AbstractA survey by differential scanning calorimetry (DSC) and recovery during heating of indentations on a series of nickel-aluminum alloys showed that the Ni-36 at.% Al composition has the best potential for a recoverable shape memory effect at temperatures above 100°C. The phase transformations were studied by high temperature transmission electron microscopy (TEM) and by high temperature x-ray diffraction (HTXRD). Quenching from 1200°C resulted in a single phase, fully martensitic structure. The initial quenched-in martensites were found by both TEM and X-ray diffraction to consist of primarily a body centered tetragonal (bct) phase with some body centered orthorhombic (bco) phase present. On the first heating cycle, DSC showed an endothermic peak at 121°C and an exothermic peak at 289°C, and upon cooling a martensite exothermic peak at 115° C. Upon subsequent cycles the 289°C peak disappeared. High temperature X-ray diffraction, with a heating rate of 2°C/min, showed the expected transformation of bct phase to B2 between 100 and 200°C, however the bco phase remained intact. At 400 to 450°C the B2 phase transformed to Ni2Al and Ni5Al3. During TEM heating experiments a dislocation-free martensite transformed reversibly to B2 at temperatures less than 150°C. At higher temperatures (nearly 600°C) 1/3, 1/3, 1/3 reflections from an ω-like phase formed. Upon cooling, the 1/3, 1/3, 1/3 reflections disappeared and a more complicated martensite resulted. Boron additions suppressed intergranular fracture and, as expected, resulted in no ductility improvements. Boron additions and/or hot extrusion encouraged the formation of a superordered bct structure with 1/2, 1/2, 0 reflections.

Heusler Type CoNiGa Alloys with High Martensitic Transformation Temperature

2007 ◽  
Vol 546-549 ◽  
pp. 2241-2244 ◽  
Author(s):  
Yun Qing Ma ◽  
Cheng Bao Jiang ◽  
Yan Li ◽  
Cui Ping Wang ◽  
Xing Jun Liu
Keyword(s):  
High Temperature ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensite Phase ◽  
Optical Observations ◽  
Martensitic Transformation Temperature ◽  
Transformation Behavior ◽  
X Ray ◽  
Austenitic Transformation

A strong need exists to develop new kinds of high-temperature shape-memory alloys. In this study, two series of CoNiGa alloys with different compositions have been studied to investigate their potentials as high-temperature shape-memory alloys, with regard to their microstructure, crystal structure, and martensitic transformation behavior. Optical observations and X-ray diffractions confirmed that single martensite phase was present for low cobalt samples, and dual phases containing martensite and γ phase were present for high cobalt samples. It was also found that CoNiGa alloys in this study exhibit austenitic transformation temperatures higher than 340°C, showing their great potentials for developing as high-temperature shape-memory alloys.

Aging Effects of Cu-Zn-Al Shape Memory Alloys Studied by the Alchemi Measurements

1991 ◽  
Vol 246 ◽  
Author(s):  
K. Shimizu ◽  
Y. Nakata ◽  
O. Yamamoto
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Parent Phase ◽  
Stacking Faults ◽  
Martensite Phase ◽  
Reverse Transformation ◽  
Aging Effects ◽  
Scanning Calorimetry ◽  
Martensite Stabilization ◽  
Cu And Zn

AbstractThe aging effects of two kinds of Cu-Zn-Al shape memory alloys (Cu-ll.4 Zn-18.7A1 (A) and Cu-ll.2Zn-17.lAl (B) in at%) have been examined by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and atom location by channeling enhanced microanalysis (ALCHEMI). In the directly quenched (D.Q.) state, alloy A was the parent phase, Ms being 253 K, and alloy B was the martensite phase. The alloy B was subjected another quenching treatment as follows: It was once quenched into an oil bath at 423 K and held for 300 s, followed by quenching into iced water (step quench (S.Q.) ). The D.Q. alloy B did not exhibit the reverse transformation because of a stabilization of the martensbite phase, but the S.Q. alloy B did and its As temperature of the reverse transformation was raised with the progress of aging at the martensitic state. Fraction of Zn atoms at the Cu(2) site examined by the ALCHEMI measurements was almost the same in the parent phase of D.Q. alloy A and its aged one, indicating no change in Cu and Zn atom sites, while it was gradually decreased in S.Q. alloy B with the progress of aging. The fraction of Zn atoms in D.Q. alloy B was much lower than those in the S.Q. alloy B and its aged one. TEM observation of the S.Q. alloy B revealed that stacking faults as the lattice invariant shear in the M18R martensites decreased in the density with the progress of aging. The decrease in the fraction of Zn atoms and in the density of stacking faults well corresponds to the increase in As temperature, and thus the martensite stabilization was attributed to a disordering between Cu and Zn atoms and to an annihilation of stacking faults.

New trends in differential scanning calorimetry

1989 ◽  
Vol 67 (6) ◽  
pp. 983-990 ◽  
Author(s):  
H. Tachoire ◽  
V. Torra
Keyword(s):  
Differential Scanning Calorimetry ◽  
Acoustic Emission ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Phase Transformations ◽  
Entropy Production ◽  
Thermomechanical Treatment ◽  
Scanning Calorimetry

Recent applications of differential scanning calorimetry in the study of solid–solid transformations are presented. The importance of the deconvolution of the thermograms and of the modelling of the calorimetric equipment is stressed.Investigations of the phase transformations of the martensitic type in shape-memory alloys have made clear the influence of thermomechanical treatment of the material and have evaluated the influence of defects on the dynamics of transformation. A combination of calorimetric and acoustical observations has demonstrated irreversibilities, even in the so-called thermoelastic transitions. Keywords: martensitic transformation, differential scanning calorimetry, entropy production, thermomechanical treatments, acoustic emission.

Magnetic Phase Diagram of the Ferromagnetic Shape Memory Alloys Ni2MnGa1-xCux

2011 ◽  
Vol 684 ◽  
pp. 165-176 ◽  
Author(s):  
K. Endo ◽  
T. Kanomata ◽  
A. Kimura ◽  
M. Kataoka ◽  
H. Nishihara ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Magnetic Phase Diagram ◽  
Alloy System ◽  
Martensite Phase ◽  
Austenite Phase ◽  
Magnetic Shape Memory ◽  
Ferromagnetic Shape Memory Alloys ◽  
Scanning Calorimetry

X-ray powder diffraction, permeability, magnetization and differential scanning calorimetry measurements were carried out on the magnetic shape memory alloys Ni2MnGa1−xCux (0 ≤ x ≤ 0.25). On the basis of the experimental results, the phase diagram in the temperature– concentration plane was determined for this alloy system. The determined phase diagram is spanned by the paramagnetic austenite phase (Para-A), paramagnetic martensite phase (Para-M), ferromagnetic austenite phase (Ferro-A), ferromagnetic martensite phase (Ferro-M) and the premartensite phase. It was found that the magnetostructural transition between the phases Para-A and Ferro-M can occur in the concentration region 0.12 < x ≤ 0.14 and that Ni2MnGa1−xCux has the characteristics of the phase diagram similar to those of the phase diagrams of Ni2+xMn1−xGa and Ni2Mn1−xCuxGa. In order to understand the phase diagram, the phenomenological free energy as a function of the martensitic distortion and magnetization was constructed and analyzed.

Martensitic Transformation of TiAu Shape Memory Alloys

2007 ◽  
Vol 561-565 ◽  
pp. 1541-1544 ◽  
Author(s):  
Hideki Hosoda ◽  
Ryosuke Tachi ◽  
Tomonari Inamura ◽  
Kenji Wakashima ◽  
Shuichi Miyazaki
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory ◽  
Parent Phase ◽  
Stoichiometric Composition ◽  
Transformation Strain ◽  
Martensite Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Rich Side

Martensitic transformation temperatures were measured and transformation strains were evaluated in a promising high temperature shape memory alloy TiAu with a compositional range from 46 to 53mol%Au. It was found by differential scanning calorimetry that martensitic transformation start temperature (Ms) is kept almost constant value of 880K in the Au-rich side of the stoichiometric composition. On the other hand, Ms decreases monotonically with decreasing Au content in the Au-poor side. X-ray diffraction analysis revealed that apparent phase of all the alloys at room temperature is B19 martensite phase. Under an assumption that the atomic volume is constant during martensitic transformation, the lattice parameters of B2 parent phase and maximum transformation strain were calculated. It was found that the maximum transformation strain depends on chemical composition and that it reaches 10.75% for Ti-53mol%Au alloy. The value is comparable to that of Ti-Ni.

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