Use of 2½ D imaging in analysis of NiTi martensite

1978 ◽  
Vol 36 (1) ◽  
pp. 610-611
Author(s):  
G. M. Michal
Keyword(s):  
Memory Effect ◽  
Monoclinic Phase ◽  
Reaction Path ◽  
Structural Characteristics ◽  
Salient Feature ◽  
Martensite Phase ◽  
Orientation Relationships ◽  
Low Symmetry ◽  
Hydride Phases ◽  
Unusual Shape

Several TEM investigations have attempted to correlate the structural characteristics to the unusual shape memory effect in NiTi, the consensus being the essence of the memory effect is ostensible manifest in the structure of NiTi transforming martensitic- ally from a B2 ordered lattice to a low temperature monoclinic phase. Commensurate with the low symmetry of the martensite phase, many variants may form from the B2 lattice explaining the very complex transformed microstructure. The microstructure may also be complicated by the enhanced formation of oxide or hydride phases and precipitation of intermetallic compounds by electron beam exposure. Variants are typically found in selfaccommodation groups with members of a group internally twinned and the twins themselves are often observed to be internally twinned. Often the most salient feature of a group of variants is their close clustering around a given orientation. Analysis of such orientation relationships may be a key to determining the nature of the reaction path that gives the transformation its apparently perfect reversibility.

Orientation Relationships and Interfaces Between Low Symmetry Phases in The Yttria-Alumina System

1994 ◽  
Vol 357 ◽  
Author(s):  
R. S. Hay
Keyword(s):  
Monoclinic Phase ◽  
Three Dimensional ◽  
Real Space ◽  
Reciprocal Space ◽  
High Symmetry ◽  
Orientation Relationships ◽  
Yttrium Aluminum ◽  
High Resolution Tem ◽  
Interphase Boundaries ◽  
Definition Of

AbstractInterphase boundaries and orientation relationships for yttria - yttrium-aluminum monoclinic and yttrium-aluminum monoclinic - yttrium-aluminum perovskite eutectics were observed by standard and high resolution TEM techniques. Three and five orientation relationships were found for each system, respectively. These eutectics all had a monoclinic phase and therefore had little potential for high symmetry overlap. In many cases low index planes with similer spacings or spacing multiples were parallel. However, presence of a monoclinic phase made definition of a three-dimensional low index near-CSL very difficult, so a combination of planes corresponding to reciprocal-space directions and zones corresponding to real-space directions were often needed for a geometric description of the orientation relationship. In general, two planes and the real-space direction corresponding to the zone for these planes described the orientation relationships. The disregistry between reciprocal-space coincidence sites was not localized by dislocations large enough to be visible.

scholarly journals Phase Transformations, Microstructure and Shape Memory Effect of NiTiAg Alloy with Different Atomic Percentages (at. % Ag) Manufactured by Casting Method

2021 ◽  
Vol 39 (4A) ◽  
pp. 543-551
Author(s):  
Saja M. Hussein ◽  
Khansaa D. Salman ◽  
Ahmed A. Hussein
Keyword(s):  
Shape Memory ◽  
Phase Transformations ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Martensite Phase ◽  
Austenite Phase ◽  
Vacuum Arc ◽  
Casting Method ◽  
Vacuum Arc Remelting ◽  
Niti Matrix

In this paper, shape memory alloys (SMAs) (NiTi-based) have been manufactured by casting with a different atomic percentage of a silver element (0, 1, 2 and 3 at. % Ag) using a Vacuum Arc Remelting (VAR) furnace. The silver element is added to the binary alloys due to its excellent properties such as (anti-corrosion, anti-bacterial and high electrical conductivity), which make these alloys using in wider applications. These alloys with different atomic percentages (Ni55Ti45Ag0, Ni55Ti44Ag1, Ni55Ti43Ag2 and Ni55Ti42Ag3) have been manufactured. The successful manufacturing process has been achieved and proved via examinations and tests. The FESEM microscopic examinations show that the silver element has been distributed uniformly and homogeneously in the NiTi matrix. Moreover, the emergence of austenite phase, martensite phase and little amount impurities. Regarding the XRD examination, showed that there is an increase in the number of peaks of Ag phase with an increase in the atomic percentage of the silver element, as well to emergence of phase (Ti2Ni) upon heating, phase (Ti 002) upon cooling, and phase (Ni4Ti3) is not desired. The starting and finishing of the phase transformations have been determined for all samples by the DSC test. The Shape Memory Effect (SME) for the alloy (Ni50Ti42Ag3) is measured to be about 89.99%.

scholarly journals NiMn-Based Metamagnetic Shape Memory Alloys

2009 ◽  
Vol 635 ◽  
pp. 23-31 ◽  
Author(s):  
Ryosuke Kainuma ◽  
K. Ito ◽  
W. Ito ◽  
R.Y. Umetsu ◽  
T. Kanomata ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Powder Metallurgy ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Parent Phase ◽  
Martensite Phase ◽  
Ternary Alloys ◽  
Plasma Sintering ◽  
Spark Plasma

The magnetic properties of the parent and martensite phases of the Ni2Mn1+xSn1-x and Ni2Mn1+xIn1-x ternary alloys and the magnetic field-induced shape memory effect obtained in NiCoMnIn alloys are reviewed, and our recent work on powder metallurgy performed for NiCoMnSn alloys is also introduced. The concentration dependence of the total magnetic moment for the parent phase in the NiMnSn alloys is very different from that in the NiMnIn alloys, and the magnetic properties of the martensite phase with low magnetization in both NiMnSn and NiMnIn alloys has been confirmed by Mössbauer examination as being paramagnetic, but not antiferromagnetic. The ductility of NiCoMnSn alloys is drastically improved by powder metallurgy using the spark plasma sintering technique, and a certain degree of metamagnetic shape memory effect has been confirmed.

Formation and Dissolution of Hydride Precipitates in Zirconium Alloys: Crystallographic Orientation Relationships and Stability after Temperature Cycling

2016 ◽  
Vol 879 ◽  
pp. 2330-2335 ◽  
Author(s):  
Egle Conforto ◽  
Stephane Cohendoz ◽  
Cyril Berziou ◽  
Patrick Girault ◽  
Xavier Feaugas
Keyword(s):  
Hydrogen Content ◽  
Hydrogen Diffusion ◽  
Zirconium Alloys ◽  
Temperature Cycling ◽  
Nuclear Industry ◽  
X Rays ◽  
Orientation Relationships ◽  
Hydrogen Distribution ◽  
Cycle Number ◽  
Hydride Phases

Hydride precipitation due to the spontaneous and fast hydrogen diffusion is often pointed as causing embrittlement and rupture in zirconium alloys used in the nuclear industry. Transmission Electron Microscopy (TEM) and X-Rays Diffraction (XRD) have been used to study the precipitation of hydride phases in zirconium alloys as a function of the hydrogen content. The orientation relationships observed between the hydride phase and the substrate were similar to those previously observed in Titanium hydrides grown on Titanium. Dislocation emission from the hydride precipitates has been directly related to the relaxation of the misfit stresses appearing during the transformation. The stability of the hydride phases after several dissolution-reprecipitation cycles have been studied by DSC, TEM and XRD for different total hydrogen content in several alloys. The energy of precipitation observed is lower than that of the dissolution in each case studied. The temperature associated with these two processes slightly increase as a function of the cycle number, as a result of the homogenizing hydrogen distribution in the alloy bulk. The same hydrides phases present before cycling were also observed after 20 cycles. However, transition phases poorer in hydrogen than the dominant one may precipitate at the interface with the substrate. The evolution of these transitions phases with the temperature increase will be investigated by TEM in-situ heating in the next future.

Kinetics and Mechanism of the C49 to C54 Titanium Disilicide Polymorphic Transformation

1993 ◽  
Vol 320 ◽  
Author(s):  
Z. Ma ◽  
G. Ramanath ◽  
L.H. Allen
Keyword(s):  
Polymorphic Transformation ◽  
Structural Transition ◽  
Structural Characteristics ◽  
Kinetics And Mechanism ◽  
Orientation Relationships ◽  
Titanium Disilicide ◽  
Transmission Electron ◽  
Interphase Boundaries ◽  
Two Phases

ABSTRACTThe kinetics and mechanism of the C49 to C54 TiSi2 polymorphic transformation have been investigated in a temperature range from 660 to 720°C using in situ sheet resistance measurement and transmission electron microscopy. The kinetics results were correlated with the microstructural changes during the phase transformation. The main structural characteristics demonstrating the mechanism of the transformation were established by examining the nucleation and growth of the C54-TiSi2 in the polycrystalline C49-TiSi2 thin films. It was found that the C54 nuclei predominantly formed at grain edges (three-grain junctions) of the C49 phase and grew very fast by moving its incoherent interphase boundaries. Preliminary results have not revealed rigorous orientation relationships between the two phases. It is suggested that the C49 to C54 structural transition is massive in nature.

scholarly journals Solute hydrogen and hydride phase implications on the plasticity of zirconium and titanium alloys: a review and some recent advances

2017 ◽  
Vol 375 (2098) ◽  
pp. 20160417 ◽  
Author(s):  
E. Conforto ◽  
I. Guillot ◽  
X. Feaugas
Keyword(s):  
Prismatic Slip ◽  
Misfit Dislocations ◽  
Orientation Relationships ◽  
Compact Structure ◽  
Hardening Process ◽  
Pyramidal Slip ◽  
Recent Advances ◽  
The Impact ◽  
Thermal Stability Of ◽  
Hydride Phases

In this contribution, we propose a review of the possible implications of hydrogen on mechanical behaviour of Zr and Ti alloys with emphasis on the mechanisms of plasticity and strain hardening. Recent advances on the impact of oxygen and hydrogen on the activation volume show that oxygen content hinders creep but hydrogen partially screens this effect. Both aspects are discussed in terms of a locking–unlocking model of the screw dislocation mobility in prismatic slip. Additionally, possible extension of this behaviour is suggested for the pyramidal slip. The low hydrogen solubility in both Zr and Ti leads in many cases to hydride precipitation. The nature of these phases depends on the hydrogen content and can show crystallographic orientation relationships with the hexagonal compact structure of the alloys. Some advances on the thermal stability of these phases are illustrated and discussed in relation with the deepening of the misfit dislocations. Under tensile loading, we showed that hydrides enhance the hardening process in relation with internal stress due to strain incompatibilities between the Zr and Ti matrix and hydride phases. Different plastic yielding processes of hydrides were identified, which progressively reduce these strain incompatibilities. This article is part of the themed issue ‘The challenges of hydrogen and metals’.

scholarly journals A Review of Hydride Precipitates in Titanium and Zirconium Alloys: Precipitation, Dissolution and Crystallographic Orientation Relationships

2020 ◽  
Vol 321 ◽  
pp. 11042
Author(s):  
Egle CONFORTO ◽  
Xavier FEAUGAS
Keyword(s):  
Zirconium Alloys ◽  
Zirconium Hydride ◽  
Misfit Dislocations ◽  
Orientation Relationships ◽  
Ti Alloys ◽  
Local Plastic Strain ◽  
Bulk Scale ◽  
Hydride Phases ◽  
Zr Alloys

This work proposes a review of recent results on the formation and dissolution of hydrides in HCP alloys (Ti and Zr alloys) correlated to the nature of crystallographic hydride phases and their ORs. The crystallographic coherence observed between the surface hydride layer and the substrate is very important for many applications as for biomaterials devices. Five particular orientation relationships (OR) were identified between titanium/zirconium hydride precipitates and the oc-Ti and a-Zr substrates. In addition, the nature of hydrides have a large implication on the ductility, the strain hardening, and the local plastic strain accommodation in the Ti alloys. Our studies using XDR, TEM and SEM-EBSD have been demonstrating that the nature of the hydride phase precipitates depends on the hydrogen content. DSC has been used to obtain the hydride dissolution and precipitation energy values at the bulk scale, whose difference can be associated to misfit dislocations. Local in-situ TEM dissolution observations show the depinning of part of misfit dislocations during dissolution process. Hydride reprecipitation is thus possible only if hydrogen is not driven away during heating by misfit dislocations depinning.

Highly dense and compositionally inhomogeneous nano-agglomerates in an epitaxial La0.8Sr0.2MnO3 thin film grown on (100)SrTiO3

2005 ◽  
Vol 20 (3) ◽  
pp. 571-579 ◽  
Author(s):  
Y.L. Zhu ◽  
X.L. Ma ◽  
D.X. Li ◽  
H.B. Lu ◽  
Z.H. Chen ◽  
...  
Keyword(s):  
Thin Film ◽  
Colossal Magnetoresistance ◽  
Molecular Beam ◽  
Compositional Analysis ◽  
Salient Feature ◽  
Dark Field ◽  
Orientation Relationships ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Field Imaging

Microstructures in the thin film of La0.8Sr0.2MnO3 grown on (100) SrTiO3 by laser molecular beam epitaxy were characterized by transmission electron microscopy. Highly dense and dimensionally uniform nano-agglomerates were found embedded in thin film of La0.8Sr0.2MnO3. High-angle angular dark-field imaging, elemental mapping, and compositional analysis revealed that the nano-agglomerates are rich in manganese and poor in lanthanum. The ratio of Mn/La in the nano-agglomerates fluctuates. A salient feature of this compositional fluctuation within the nanoscale isthe formation of cubic MnO phase, which appears as the core of the nano-agglomerates.The La0.8Sr0.2MnO3 film is domain-oriented and two domains were identified on the basis of orthorhombic lattice. The orientation relationships between La0.8Sr0.2MnO3 domains and MnO were determined as [010]LSMO,1//[001]MnO and (100)LSMO,1//(110)MnO; [101]LSMO,2//[001]MnO and (010)LSMO,2//(100)MnO. The domain structuresand compositional inhomogeneities within nanoscale result in a textured microstructure, which is one of the most important parameters for tuning electronic properties in colossal magnetoresistance oxides.

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