Structural analysis of ω-like diffuse scattering from quenched Cr-Ti alloys

1992 ◽  
Vol 50 (1) ◽  
pp. 28-29
Author(s):  
W. Sinkler ◽  
D. E. Luzzi
Keyword(s):  
Diffuse Scattering ◽  
Reciprocal Lattice ◽  
Equilibrium Phase ◽  
Pure Titanium ◽  
Peak Shift ◽  
Cubic Phase ◽  
Solute Content ◽  
Β Phase ◽  
Ti Alloys ◽  
Cr System

Incommensurate diffuse scattering is seen in electron diffraction from the quenched-in body centered cubic phase (β phase) of alloys composed of titanium or zirconium with other early transition metals. Such diffuse scattering is related to the commensurate ω phase, a high pressure equilibrium phase of pure titanium, which also forms in dilute quenched alloys after annealing. The present study concerns ω-like diffuse scattering in the quenched (β phase of the Ti-Cr system. It is shown that the diffuse scattering in concentrated alloys consists of ω diffraction maxima which have undergone ordered displacements from commensurate ω reciprocal lattice positions. The displacement magnitude increases with solute content (see figure 1). A general expression in reciprocal space for the dependence of the diffuse peak shift on (hkl)ω was found. A model based on this expression correctly predicts the location of all diffuse peaks.

Development of the Snoek Anelastic Relaxation Correlated with Oxygen in β-Ti Alloys

2019 ◽  
Vol 298 ◽  
pp. 59-63 ◽  
Author(s):  
Zheng Cun Zhou ◽  
J. Du ◽  
S.Y. Gu ◽  
Y.J. Yan
Keyword(s):  
Internal Friction ◽  
Physical And Mechanical Properties ◽  
Peak Height ◽  
Relaxation Peak ◽  
Interstitial Oxygen ◽  
Internal Friction Peak ◽  
Β Phase ◽  
Ti Alloys ◽  
Interstitial Atoms ◽  
The Stability

The β-Ti alloys exhibit excellent shape memory effect and superelastic properties. The interstitial atoms in the alloys have important effect on their physical and mechanical properties. For the interstitial atoms, the internal friction technique can be used to detect their distributions and status in the alloys. The anelastic relaxation in β-Ti alloys is discussed in this paper. β-Ti alloys possesses bcc (body center body) structure. The oxygen (O) atoms in in the alloys is difficult to be removed. The O atoms located at the octahedral sites in the alloys will produce relaxation under cycle stress. In addition, the interaction between the interstitial atoms and substitute atoms, e.g., Nb-O,Ti-O can also produce relaxation. Therefore, the observed relaxational internal friction peak during the measuring of internal friction is widened. The widened multiple relaxation peak can be revolved into Debye,s elemental peaks in Ti-based alloys. The relaxation peak is associated with oxygen movements in lattices under the application of cycle stress and the interactions of oxygen-substitute atoms in metastable β phase (βM) phase for the water-cooled specimens and in the stable β (βS) phase for the as-sintered specimens. The damping peak height is not only associated with the interstitial oxygen, but also the stability and number of βM in the alloys.

scholarly journals First principles computation of composition dependent elastic constants of omega in titanium alloys: implications on mechanical behavior

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
R. Salloom ◽  
S. A. Mantri ◽  
R. Banerjee ◽  
S. G. Srinivasan
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
First Principles ◽  
Young's Modulus ◽  
Group Vi ◽  
Group V ◽  
Β Phase ◽  
Ti Alloys ◽  
Ω Phase ◽  
Stabilizer Concentration

AbstractFor decades the poor mechanical properties of Ti alloys were attributed to the intrinsic brittleness of the hexagonal ω-phase that has fewer than 5-independent slip systems. We contradict this conventional wisdom by coupling first-principles and cluster expansion calculations with experiments. We show that the elastic properties of the ω-phase can be systematically varied as a function of its composition to enhance both the ductility and strength of the Ti-alloy. Studies with five prototypical β-stabilizer solutes (Nb, Ta, V, Mo, and W) show that increasing β-stabilizer concentration destabilizes the ω-phase, in agreement with experiments. The Young’s modulus of ω-phase also decreased at larger concentration of β-stabilizers. Within the region of ω-phase stability, addition of Nb, Ta, and V (Group-V elements) decreased Young’s modulus more steeply compared to Mo and W (Group-VI elements) additions. The higher values of Young’s modulus of Ti–W and Ti–Mo binaries is related to the stronger stabilization of ω-phase due to the higher number of valence electrons. Density of states (DOS) calculations also revealed a stronger covalent bonding in the ω-phase compared to a metallic bonding in β-phase, and indicate that alloying is a promising route to enhance the ω-phase’s ductility. Overall, the mechanical properties of ω-phase predicted by our calculations agree well with the available experiments. Importantly, our study reveals that ω precipitates are not intrinsically embrittling and detrimental, and that we can create Ti-alloys with both good ductility and strength by tailoring ω precipitates' composition instead of completely eliminating them.

Stacking Faults in a High Nitrogen Face-Centered-Cubic Phase Formed on Nitrogen-Modified Austenitic Stainless Steel

2008 ◽  
Vol 373-374 ◽  
pp. 318-321
Author(s):  
J. Liang ◽  
M.K. Lei
Keyword(s):  
Stainless Steel ◽  
Plasma Source ◽  
Peak Shift ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
X Ray Diffraction ◽  
High Nitrogen ◽  
X Ray ◽  
Peak Asymmetry ◽  
Face Centered

Effects of stacking faults in a high nitrogen face-centered-cubic phase (γΝ) formed on plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel on peak shift and peak asymmetry of x-ray diffraction were investigated based on Warren’s theory and Wagner’s method, respectively. The peak shift from peak position of the γΝ phase is ascribed to the deformation faults density α, while the peak asymmetry of the γΝ phase is characterized by deviation of the center of gravity of a peak from the peak maximum (Δ C.G.) due to the twin faults density β. The calculated peak positions of x-ray diffraction patterns are consistent with that measured for plasma source ion nitrided 1Cr18Ni9Ti stainless steel.

scholarly journals Capabilities of X-ray diffuse scattering method for study of microdefects in semiconductor crystals

2018 ◽  
Vol 4 (4) ◽  
pp. 125-134
Author(s):  
Vladimir T. Bublik ◽  
Marina I. Voronova ◽  
Kirill D. Shcherbachev
Keyword(s):  
Diffuse Scattering ◽  
Reciprocal Lattice ◽  
Lattice Parameter ◽  
Formation Mechanisms ◽  
Scattering Method ◽  
X Ray ◽  
Semiconductor Crystals ◽  
The Matrix ◽  
Decomposition Stages ◽  
Defects Analysis

The capabilities of X-ray diffuse scattering (XRDS) method for the study of microdefects in semiconductor crystals have been overviewed. Analysis of the results has shown that the XRDS method is a highly sensitive and information valuable tool for studying early stages of solid solution decomposition in semiconductors. A review of the results relating to the methodological aspect has shown that the most consistent approach is a combination of XRDS with precision lattice parameter measurements. It allows one to detect decomposition stages that cannot be visualized using transmission electron microscopy (TEM) and moreover to draw conclusions as to microdefect formation mechanisms. TEM-invisible defects that are coherent with the matrix and have smeared boundaries with low displacement field gradients may form due to transmutation doping as a result of neutron irradiation and relaxation of disordered regions accompanied by redistribution of point defects and annihilation of interstitial defects and vacancies. For GaP and InP examples, a structural microdefect formation mechanism has been revealed associated with the interaction of defects forming during the decomposition and residual intrinsic defects. Analysis of XRDS intensity distribution around the reciprocal lattice site and the related evolution of lattice constant allows detecting different decomposition stages: first, the formation of a solution of Frenkel pairs in which concentration fluctuations develop, then the formation of matrix-coherent microdefects and finally coherency violation and the formation of defects with sharp boundaries. Fundamentally, the latter defects can be precipitating particles. Study of the evolution of diffuse scattering iso-intensity curves in GaP, GaAs(Si) and Si(O) has allowed tracing the evolution of microdefects from matrix-coherent ones to microdefects with smeared coherency resulting from microdefect growth during the decomposition of non-stoichiometric solid solutions heavily supersaturated with intrinsic (or impurity) components.

Effects of Cooling Rate and Sn Addition on the Microstructure of Ti-Nb-Sn Alloys

2011 ◽  
Vol 172-174 ◽  
pp. 190-195 ◽  
Author(s):  
Giorgia T. Aleixo ◽  
Eder S.N. Lopes ◽  
Rodrigo Contieri ◽  
Alessandra Cremasco ◽  
Conrado Ramos Moreira Afonso ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cooling Rate ◽  
Melting Furnace ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Β Phase ◽  
Arc Melting ◽  
Ti Alloys ◽  
Ω Phase

Ti-based alloys present unique properties and hence, are employed in several industrial segments. Among Ti alloys, β type alloys form one of the most versatile classes of materials in relation to processing, microstructure and mechanical properties. It is well known that heat treatment of Ti alloys plays an important role in determining their microstructure and mechanical behavior. The aim of this work is to analyze microstructure and phases formed during cooling of β Ti-Nb-Sn alloy through different cooling rates. Initially, samples of Ti-Nb-Sn system were prepared through arc melting furnace. After, they were subjected to continuous cooling experiments to evaluate conditions for obtaining metastable phases. Microstructure analysis, differential scanning calorimetry and X-ray diffraction were performed in order to evaluate phase transformations. Depending on the cooling rate and composition, α” martensite, ω phase and β phase were obtained. Elastic modulus has been found to decrease as the amount of Sn was increased.

Diffuse scattering anisotropy and theP21/a↔A2/aphase transition in titanite, CaTiOSiO4

2001 ◽  
Vol 34 (2) ◽  
pp. 108-113 ◽  
Author(s):  
Thomas Malcherek ◽  
Carsten Paulmann ◽  
M. Chiara Domeneghetti ◽  
Ulrich Bismayer
Keyword(s):  
Diffuse Scattering ◽  
Paraelectric Phase ◽  
Reciprocal Lattice ◽  
Group Setting ◽  
Paraelectric Phase Transition ◽  
Charge Coupled Device ◽  
Intensity Measurements ◽  
Lattice Position ◽  
Boundary Position ◽  
Scattering Anisotropy

Diffuse scattering in titanite has been measured at three temperatures, 0.951Tc, 1.053Tcand 1.177Tc, using synchrotron radiation.Tc= 487 K is the temperature of the antiferroelectric paraelectric phase transition. Charge-coupled device (CCD) intensity measurements were centred about the \bar{4}01 reciprocal-lattice position (space-group settingP21/a) and extended beyond the neighbouring \bar{4}11 and \bar{4}\bar{1}1 fundamental positions. Planar diffuse scattering intensity is observed normal to [100] with a lens-shaped maximum centred at \bar{4}01. On approachingTcfrom above, the intensity of the maximum at \bar{4}01 increases, while intensity scattered into the planes decreases at large distances to the critical zone-boundary position. The intensity distribution is interpreted in terms of a two-dimensional spin-1/2 Ising model, in which individual spin states represent the collective displacement of octahedrally coordinated Ti atoms parallel to [100].

scholarly journals Phase Stability of Nanocrystalline Grains of Rare-Earth Oxides (Sm2O3 and Eu2O3) Confined in Magnesia (MgO) Matrix

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2201
Author(s):  
Chen Barad ◽  
Giora Kimmel ◽  
Hagay Hayun ◽  
Dror Shamir ◽  
Kachal Hirshberg ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Rare Earth ◽  
Mixed Oxides ◽  
Sol Gel ◽  
Equilibrium Phase ◽  
Cubic Phase ◽  
Direct Heating ◽  
Pure Oxide ◽  
Heat Treated ◽  
Heating Treatment

Rare-earth (RE) oxides are important in myriad fields, including metallurgy, catalysis, and ceramics. However, the phase diagram of RE oxides in the nanoscale might differ from the phase diagrams for bulk, thus attracting attention nowadays. We suggest that grain size in the nanoscale also determines the obtained crystallographic phase along with temperature and pressure. For this purpose, nanoparticles of Sm2O3 and Eu2O3 were mixed in an inert MgO matrix via the sol-gel method. This preparation method allowed better isolation of the oxide particles, thus hindering the grain growth process associated with increasing the temperature. The mixed oxides were compared to pure oxides, which were heat-treated using two methods: gradual heating versus direct heating to the phase transition temperature. The cubic phase in pure oxides was preserved to a higher extent in the gradual heating treatment compared to the direct heating treatment. Additionally, in MgO, even a higher extent of the cubic phase was preserved at higher temperatures compared to the pure oxide, which transformed into the monoclinic phase at the same temperature in accordance with the phase diagram for bulk. This indicates that the cubic phase is the equilibrium phase for nanosized particles and is determined also by size.

scholarly journals Influence of hydrogen on mechanical properties of pure titanium T40 (grade 2) and TA6V ELI (grade 23): a local approach of fracture

2020 ◽  
Vol 321 ◽  
pp. 09004
Author(s):  
Alexandre POLONI ◽  
Abdelali OUDRISS ◽  
Juan CREUS ◽  
Stéphane COHENDOZ ◽  
Jamaa Bouhattate ◽  
...  
Keyword(s):  
Cathodic Polarization ◽  
Hydrostatic Stress ◽  
Equivalent Plastic Strain ◽  
Pure Titanium ◽  
Tensile Tests ◽  
Solubility Limit ◽  
Local Approach ◽  
Hydrogen Charging ◽  
Β Phase ◽  
The Impact

The effect of hydrogen charging by cathodic polarization on T40 (grade 2) and TA6V ELI (grade 23) in artificial seawater appeared to be dependent on the metallurgical structure of the alloys. Mechanical tensile tests were performed on smooth samples and with different notches without and with hydrogen charging. Evolution of the fracture mode has been studied and the impact of hydrides was questioned. FEM calculation offers the opportunity to associate the local hydrostatic stress σm and equivalent plastic strain εpeq leading to the fracture and to illustrate the evolution of these conditions with hydrogen absorption and hydrides formation. Hydrogen charged by cathodic polarization appeared to have a small impact on grade 2 reducing its A%, whereas it leads to a strong embrittlement of grade 23 when the solubility limit of β-phase is exceeded and hydrides formed.

Microstructure and Mechanical Properties of Sintered Ti-Cu Alloys

2010 ◽  
Vol 93-94 ◽  
pp. 99-104 ◽  
Author(s):  
P. Pripanapong ◽  
Luangvaranunt Tachai
Keyword(s):  
Mechanical Properties ◽  
Cast Alloy ◽  
Exothermic Reaction ◽  
Equilibrium Phase ◽  
Pure Titanium ◽  
Equilibrium Phase Diagram ◽  
Cu Alloys ◽  
Effect Of Copper ◽  
Sintered Alloys ◽  
Dental Applications

The use of titanium for medical and dental applications is on the rise because of their excellent biocompatibility. However, some properties of pure titanium are not sufficient. Alloying with copper can improve mechanical properties needed for dental use. A recent research on Ti-Cu cast alloy indicated that ductility decreased with increasing copper concentration, but addition of copper improved grindability and wear resistance, with lower corrosion resistance. The objective of this research is to study sintering of Ti-Cu alloys; their microstructure and hardness, and the effect of copper content to their sintered density. Ti-Cu alloys were produced via powder metallurgy. Titanium powder was mixed with copper powder with chemical composition of 2, 4, 7 and 10 wt%. Lubricant was added in alloy powder with 0.5% of total weight, followed by cold compaction under 254 MPa pressure. Debinding and sintering was carried out at 400oC for 0.5 hr and 1000oC for 1 hr respectively in argon atmosphere. Condition with highest density was found in 10wt%Cu composition; having highest hardness of 317 Hv. Differential thermal analysis of Ti-15Cu under N2 atmosphere showed exothermic reaction at 1078oC. Phase formation of the sintered alloys followed the Ti-Cu equilibrium phase diagram.

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