In situ synchrotron radiation measurements of orthorhombic phase formation in an advanced TiAl alloy with modulated microstructure

2015 ◽  
Vol 1760 ◽  
Author(s):  
M. Rackel ◽  
A. Stark ◽  
H. Gabrisch ◽  
F.-P. Schimansky ◽  
N. Schell ◽  
...  
Keyword(s):  
Orthorhombic Phase ◽  
High Energy ◽  
X Ray Diffraction ◽  
Tial Alloys ◽  
Temperature Range ◽  
Atomic Displacements ◽  
Two Phases ◽  
O Phase ◽  
Thermal Stability Of

ABSTRACTNew low aluminium high niobium TiAl alloys exhibit a nano scale modulated microstructure consisting of lamellae with a tweed substructure. These tweed like appearing lamellae are a modulated arrangement of at least two phases. One constituent of the crystallographic modulation in the lamellae is an orthorhombic phase, which is closely related to both the hexagonal α2-Ti3Al phase and the cubic B2 ordered βo-TiAl phase.In this study the nature and formation of this orthorhombic phase has been investigated by high-energy X-ray diffraction.Measurements have shown that the newly formed orthorhombic phase is structurally comparable to the O phase (Ti2AlNb). It forms in the temperature range of 550 °C to 670 °C from the α2 phase by small atomic displacements and chemical reordering. The in situ experiments yielded information about the thermal stability of the orthorhombic phase. After dissolving at temperatures above 700 °C the phase can be re-precipitated by annealing within the temperature range of formation.

scholarly journals Thermal stability of wurtzite Zr1−xAlxN coatings studied by in situ high-energy x-ray diffraction during annealing

2015 ◽  
Vol 118 (3) ◽  
pp. 035309 ◽  
Author(s):  
L. Rogström ◽  
N. Ghafoor ◽  
J. Schroeder ◽  
N. Schell ◽  
J. Birch ◽  
...  
Keyword(s):  
Thermal Stability ◽  
High Energy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermal Stability Of

An in-situ, high-energy X-ray diffraction study of the thermal stability of delithiated LiVPO4F

2015 ◽  
Vol 273 ◽  
pp. 1250-1255 ◽  
Author(s):  
Ying Piao ◽  
Chi-kai Lin ◽  
Yan Qin ◽  
Dehua Zhou ◽  
Yang Ren ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Diffraction Study ◽  
High Energy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermal Stability Of

Thermal stability of Nb thin films on sapphire

1996 ◽  
Vol 11 (5) ◽  
pp. 1255-1264 ◽  
Author(s):  
Thomas Wagner ◽  
Marko Lorenz ◽  
Manfred Rühle
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Orientation Relationship ◽  
High Energy ◽  
X Ray Diffraction ◽  
Model Study ◽  
Transmission Electron ◽  
The Stability ◽  
Thermal Stability Of

The Nb/α−Al2O3 system has been used as a model study for investigating the stability of different MBE grown epitaxial Nb films on α−Al2O3 substrates. The films were grown at 800 °C in ultrahigh vacuum. The growth process was monitored in situ by reflection high energy electron diffraction (RHEED). After deposition the structure of the film was investigated by x-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) which encompasses also selected area diffraction (SAD). Both techniques revealed the following orientation relationship between the Nb film and the α–Al2O3 substrate: (0001)α–Al2O3‖ (111)Nb; [2110]α–Al2O3‖ [110]Nb. The stability of the niobium films was investigated by annealing the Nb-film/α–Al2O3 system to temperatures up to 1500 °C for different periods of time. Surprisingly, the orientation relationship between the Nb film and the substrate changed to (0001)α–Al2O3‖ (110)Nb; [0110]α–Al2O3‖ [001]Nb. A model will be developed which shows that above a critical film thickness the growth orientation is metastable with respect to its crystallographic orientation. Furthermore, high resolution transmission electron microscopy (HREM) was performed to investigate the defect structure of the annealed Nb/α–Al2O3 interface.

Ferroelectric and proton conducting behavior of a new elpasolite-related vanadium oxyfluoride (NH4,K)3VO2F4

2010 ◽  
Vol 25 (7) ◽  
pp. 1251-1263 ◽  
Author(s):  
Sadequa J. Patwe ◽  
S. Nagabhusan Achary ◽  
Kalpathy Ganapathy Girija ◽  
C.G. Sivan Pillai ◽  
Avesh K. Tyagi
Keyword(s):  
Orthorhombic Phase ◽  
Impedance Analysis ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
First Order ◽  
Two Phases ◽  
Ferroelectric Hysteresis

A new elpasolite-type (NH4,K)3VO2F4 compound was prepared and characterized by x-ray diffraction, differential scanning calorimeter (DSC), impedance analysis, and electrical polarization measurements. It crystallizes in an orthorhombic lattice with unit-cell parameters: a = 8.9584(4), b = 18.6910(14), c = 6.2174(4) Å, V = 1041.04(11) Å3, Z = 6. NH4+, and K+ ions are distributed statistically over crystallographically four equivalent sites. There are two distinguishable vanadium atoms forming cis- and trans-VO2F4 octahedra present in the unit cell. High-temperature studies by DSC and in situ x-ray diffraction revealed a first-order structural transformation from orthorhombic to cubic lattice around 343 K. Impedance measurements show two different kinds of conductivity behaviors for the two phases. In orthorhombic phase a significant conductivity resulting from involvement of protonic species is observed. In the orthorhombic phase, a clear ferroelectric hysteresis loop is observed.

scholarly journals In-Situ High-Energy X-ray Diffraction Study of Austenite Decomposition During Rapid Cooling and Isothermal Holding in Two HSLA Steels

2021 ◽  
Vol 52 (5) ◽  
pp. 1812-1825
Author(s):  
Sen Lin ◽  
Ulrika Borggren ◽  
Andreas Stark ◽  
Annika Borgenstam ◽  
Wangzhong Mu ◽  
...  
Keyword(s):  
Isothermal Holding ◽  
Weight Percent ◽  
High Energy ◽  
Decomposition Kinetics ◽  
Bainitic Transformation ◽  
Austenite Decomposition ◽  
X Ray Diffraction ◽  
Rapid Cooling ◽  
X Ray

AbstractIn-situ high-energy X-ray diffraction experiments with high temporal resolution during rapid cooling (280 °C s−1) and isothermal heat treatments (at 450 °C, 500 °C, and 550 °C for 30 minutes) were performed to study austenite decomposition in two commercial high-strength low-alloy steels. The rapid phase transformations occurring in these types of steels are investigated for the first time in-situ, aiding a detailed analysis of the austenite decomposition kinetics. For the low hardenability steel with main composition Fe-0.08C-1.7Mn-0.403Si-0.303Cr in weight percent, austenite decomposition to polygonal ferrite and bainite occurs already during the initial cooling. However, for the high hardenability steel with main composition Fe-0.08C-1.79Mn-0.182Si-0.757Cr-0.094Mo in weight percent, the austenite decomposition kinetics is retarded, chiefly by the Mo addition, and therefore mainly bainitic transformation occurs during isothermal holding; the bainitic transformation rate at the isothermal holding is clearly enhanced by lowered temperature from 550 °C to 500 °C and 450 °C. During prolonged isothermal holding, carbide formation leads to decreased austenite carbon content and promotes continued bainitic ferrite formation. Moreover, at prolonged isothermal holding at higher temperatures some degenerate pearlite form.

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