scholarly journals Electronic Origin of α″ to β Phase Transformation in Ti-Nb-Based Thin Films upon Hf Microalloying

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1288
Author(s):  
José Julio Gutiérrez Moreno ◽  
Nikolaos T. Panagiotopoulos ◽  
Georgios A. Evangelakis ◽  
Christina E. Lekka
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Phase Transformation ◽  
Formation Mechanisms ◽  
Electronic Density ◽  
Electronic Band ◽  
Lattice Constants ◽  
Β Phase ◽  
Α Phase ◽  
Low Energies

We present results on thin Ti-Nb-based films containing Hf at various concentrations grown by magnetron sputtering. The films exhibit α” patterns at Hf concentrations up to 11 at.%, while at 16 at.% Hf, the β-phase emerges as a stable structure. These findings were consolidated by ab initio calculations, according to which the α”–β transformation is manifested in the calculation of the electronic band energies for Hf contents between 11 and 18 at.%. It turns out that the β-phase transition originates from the Hf 5d contributions at the Fermi level and the Hf 6s hybridizations at low energies in the electronic density of states. Bonding–anti-bonding first neighbor features existing in the shifted plane destabilize the α″-phase, especially at high Hf concentrations, while the covalent-like features in the first neighborhood stabilize the corresponding plane of the β-phase. Thin films measurements and bulk total energy calculations agree that the lattice constants of both α″ and β phases increase upon Hf substitution. These results are important for the understanding of β-Ti-based alloys formation mechanisms and can be used for the design of suitable biocompatible materials.

scholarly journals Investigation of phase transformation in Fe microalloyed Ti6Al4V alloy during continuous heating process

2020 ◽  
Vol 321 ◽  
pp. 12010
Author(s):  
Changliang Wang ◽  
Feng Li ◽  
Can Ding ◽  
Hui Chang ◽  
Lian Zhou
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
Expansion Method ◽  
Ti6al4v Alloy ◽  
Continuous Heating ◽  
Heating Process ◽  
Β Phase ◽  
Α Phase ◽  
Phase Transition Temperatures ◽  
Evolution Of Microstructure

The phase transformation and dilatometric curves in Fe microalloyed Ti6Al4V alloy (Ti6Al4V-Fe) during continuous heating at 1 ℃ /min heating rate had been studied by dilatometer and metallographic methods, and β phase transition temperatures of alloy were obtained. In order to validate the accuracy of these β phase transition temperature and microstructure evolution, the relative phase concentration and the evolution of microstructure which were acquired by cooling after tempering were analyzed by metallographic microscope. The results illuminated that the expansion method was able to accurately measure the β transformation temperature of Ti6Al4V-Fe alloy. The lathy-shaped α phase decreased significantly disappeared in the range of 838℃ to 988℃, and the α→β phase transformation occurred.

Study of the phase transition properties and electronic band structures of VO2 thin films grown on different substrates

2018 ◽  
Vol 6 (2) ◽  
pp. 026409
Author(s):  
Yunfeng Guo ◽  
Yuzhi Zhang ◽  
Liangmiao Zhang ◽  
Xinrui Lv ◽  
Lingnan Wu ◽  
...  
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Band Structures ◽  
Electronic Band ◽  
Vo2 Thin Films ◽  
Electronic Band Structures

scholarly journals Kondo scenario of the γ–α phase transition in single crystalline cerium thin films

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Xie-Gang Zhu ◽  
Yu Liu ◽  
Ya-Wen Zhao ◽  
Yue-Chao Wang ◽  
Yun Zhang ◽  
...  
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Single Crystalline ◽  
Α Phase

Effect of Deposition Conditions on Intrinsic Stress, Phase Transformation and Stress Relaxation in Tantalum Thin Films

1991 ◽  
Vol 239 ◽  
Author(s):  
A. Mutscheller ◽  
L. A. Clevenger ◽  
J.M.E. Harper ◽  
C. Cabrai ◽  
K. Barmakt
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Phase Transformation ◽  
Stress Relaxation ◽  
Compressive Stress ◽  
Stress Relief ◽  
Beta Phase ◽  
Alpha Phase ◽  
Intrinsic Stress

AbstractWe demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes complete stress relaxation and a large decrease in the resistance of tantalum thin films. 100 nm beta tantalum thin films were deposited onto thermally oxidized <100> silicon wafers by dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured during temperature-ramped annealing in purified He. Upon heating, films that were initially compressively stressed showed increasing compressive stress due to thermo-elastic deformation from 25 to 550°C, slight stress relief due to plastic deformation from 550 to 700°C and complete stress relief due to the beta to alpha phase transformation at approximately 700–800°C. Incomplete compressive stress relaxation was observed at high temperatures if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800°C. This incomplete beta to alpha phase transition was most commonly observed on samples that had radio frequency substrate bias greater than -100 V. We conclude that the main stress relief mechanism for tantalum thin films is the beta to alpha phase transformation that occurs at 700 to 800°C.

Phase Transformations of the Ti-40% Nb Alloy Under External Influence

2016 ◽  
Vol 683 ◽  
pp. 174-180 ◽  
Author(s):  
Yuri P. Sharkeev ◽  
Zhanna G. Kovalevskaya ◽  
Margarita A. Khimich ◽  
Vladimir A. Bataev ◽  
Qi Fang Zhu ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Phase Transformation ◽  
Severe Plastic Deformation ◽  
Phase Transformations ◽  
Optical Metallography ◽  
External Influence ◽  
Β Phase ◽  
Α Phase ◽  
Pressing Operation ◽  
Loading Axis

The phase transformations of the alloy Ti-40 mas % Nb after tempering and severe plastic deformation are studied. The phase transformations of the alloy according to the type and conditions of external influences are analyzed using methods of XRD, SEM and optical metallography. It is determined that inverse phase transformation of the metastable α''-phase to equilibrium β-phase is carried out after severe plastic deformation. Complete phase transformation α'' → β is typical for the mode, which consists of three pressing operation with the change of the loading axis in cramped conditions, followed by a multi-pass rolling in grooved rolls.

scholarly journals Process Oxygen Flow Influence on the Structural Properties of Thin Films Obtained by Co-Sputtering of (TeO2)x-ZnO and Au onto Si Substrates

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1863
Author(s):  
Leonardo Bontempo ◽  
Sebastião G. dos Santos Filho ◽  
Luciana R. P. Kassab
Keyword(s):  
Thin Films ◽  
Structural Properties ◽  
Single Phase ◽  
Oxygen Flow ◽  
Oxidizing Agent ◽  
Tellurium Oxide ◽  
Si Substrates ◽  
Β Phase ◽  
Α Phase ◽  
Electrochemical Mechanism

In this study, we investigated the structural properties of TeO2-ZnO (TZ) and TeO2-ZnO-Au (TZA) thin films sputtered under different oxygen concentrations and either annealed or not annealed at 325 °C in air for 10 or 20 h. The lattice changes of the tellurium oxide were shown to be inherent in the polymorph properties of the α and β phases. The β phase was formed for null oxygen flow and the α phase was formed for different oxygen flows (0.5–7.0 sccm) during TZ and TZA sputtering. Au was encountered in its single phase or as AuTe2. The annealing had very little influence on the α and β phases for both TZ and TZA. It is worth noting that SiO2 and orthotellurate anions are both formed for not-null oxygen flow. An electrochemical mechanism was proposed to explain the SiO2 growth at the TZ/Si or TZA/Si interface, taking the orthotellurate anion as oxidizing agent into account.

Phase Transformation Cycle β→ α′ + α + α"→ β in Ti6Al4V Alloy

2015 ◽  
Vol 828-829 ◽  
pp. 232-238 ◽  
Author(s):  
Kalenda Mutombo ◽  
Siyasiya Charles ◽  
Waldo Stumpf
Keyword(s):  
Thermal Expansion ◽  
Phase Transformation ◽  
Phase Field ◽  
Xrd Analysis ◽  
External Stress ◽  
Ti6al4v Alloy ◽  
Β Phase ◽  
Α Phase ◽  
Sequential Transformation ◽  
Dsc Thermograms

The β-phase transforms to α′, α and α" within a range of temperature from the β-transus (Tβ) to about 600°C, considering no external stress is applied. Two types of microstructure were obtained: acicular martensite when rapidly cooled and lamellar α/β when slowly cooled from the β phase field. The sequential transformation of β into α′, α-phase, α2, and α" was revealed as peaks on the coefficient thermal expansion (CTE) curves, however, reversed transformations: α"→β, and α→β, were revealed by the DSC thermograms. The presence of β, α′, α, α2 and α" was identified by means of XRD analysis and HRTEM.

Pressure-Induced Phase Transition of the Alkali Metal Amalgam KHg2

1993 ◽  
Vol 48 (1) ◽  
pp. 11-14 ◽  
Author(s):  
Heinz-Jürgen Beister ◽  
Karl Syassen ◽  
Hans-Jörg Deiseroth ◽  
Dirk Toelstede
Keyword(s):  
Phase Transition ◽  
Major Change ◽  
Normal Pressure ◽  
Structure Type ◽  
Type Structure ◽  
Lattice Constants ◽  
First Order ◽  
Β Phase ◽  
First Order Phase Transition ◽  
First Order Phase

Potassium amalgam , KHg2, is a shiny black-purple air-sensitive alloy crystallizing, like RbHg2 and CsHg2, in the CeCu2 structure type, which is an open variant of the AlB2 type. We have investigated the phase stability of KHg2 under pressure by powder X -ray diffraction. At 25 kbar KHg2 undergoes a reversible first order phase transition into the AlB2-type structure. Lattice constants and interatomic distances of the high pressure β-phase phase near the phase transition are close to the values for normal pressure NaHg2 which also crystallizes in the AlB2-type structure. The extremely short K - K distances in the β-phase (dK-K = 3.23 Å) indicate that a major change in charge transfer between K atoms and Hg sublattice is associated with the first-order structural transition, driving the potassium atoms towards a positively charged K+ state.

X-ray study of the twinning and phase transformation of phosphocristobalite (AlPO4)

1977 ◽  
Vol 55 (7-8) ◽  
pp. 677-683 ◽  
Author(s):  
H. N. Ng ◽  
C. Calvo
Keyword(s):  
Phase Transformation ◽  
Transition Temperature ◽  
Short Range ◽  
X Ray ◽  
First Order ◽  
Β Phase ◽  
Α Phase ◽  
Short Range Correlations

Crystals of the cristobalite polymorph of AlPO4 (phosphocristobalite) up to 3 mm in breadth were grown from a V2O5 flux. In the α phase (C2221), the presence of twin domains prevents an accurate resolution of the structure as a function of temperature. The six twin components of this phase readily lead to a disordered β phase [Formula: see text] with short range correlations as suggested previously. The α–β transformation is first order with a substantial hysteresis in the transition temperature.

Effect of Quenching and Reheating on Isothermal Phase Transformation in Ti-15Nb-10Zr Alloy

2010 ◽  
Vol 638-642 ◽  
pp. 582-587 ◽  
Author(s):  
Sengo Kobayashi ◽  
Ryoichi Ohshima ◽  
Kiyomichi Nakai ◽  
Tatsuaki Sakamoto
Keyword(s):  
Phase Transformation ◽  
Solution Treatment ◽  
The Other ◽  
Matrix Microstructure ◽  
Iced Brine ◽  
Β Phase ◽  
Solution Treated ◽  
Α Phase ◽  
Other Hand ◽  
Means Of Transmission

Isothermal phase transformation in Ti-15Nb-10Zr (at%) alloys has been examined by mainly means of transmission electron microscopy. Specimens solution-treated at 1000°C in  phase field were directly held at temperatures between 350 and 450°C for 1.8-86.4ks, which are called "DH (direct holding)-specimen". On the other hand, some specimens solution-treated at 1000°C were quenched into iced brine and then aged at temperatures between 350 and 450°C, which are called "QA(quench and aging)-specimen". In the DH-specimen held at 400°C α phase formed in β matrix. Microstructure evolution of QA-specimen aged at 400°C, on the other hand, is as follows.  phase formed in β matrix after aging for 1.8ks and further aging led to growth of  phase. After prolonged aging, α phase started to form in β matrix. These experimental results indicate that process of the quenching and reheating promotes the formation of  phase. Specimen quenched into iced brine after solution treatment exhibited α'' phase formation. The α'' phase in the quenched specimen would transform into β phase during reheating to the aging temperature. Reversion process of α''  β phase could promote the formation of  phase in β. Microstructure formation in the DH- and QA-specimens at 350 and 450°C will also be explained.

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