Effect of Nb on the Properties of Ti-Nb Random Alloys from First-Principles

2013 ◽  
Vol 747-748 ◽  
pp. 890-898 ◽  
Author(s):  
Min Jie Lai ◽  
Xiang Yi Xue ◽  
Cai Si Meng ◽  
Hong Chao Kou ◽  
Bin Tang ◽  
...  
Keyword(s):  
First Principles ◽  
Lattice Parameters ◽  
Potential Approximation ◽  
Β Phase ◽  
Ω Phase ◽  
Opposite Situation ◽  
Random Alloys ◽  
The Stability ◽  
Increasing Temperature ◽  
Nb Addition

The effect of Nb on the equilibrium lattice parameters and relative stability between β and ω phases of Ti1-xNbx (0 < x 0.4) random alloys as well as their mechanical properties in body-centered-cubic crystallographic phase was investigated using the exact muffin-tin orbitals method in combination with the coherent potential approximation. It has been found that the calculated lattice parameters of the β phase agree well with the experimental data. For ω phase, the value of a increases almost linearly with increasing Nb concentration, while the opposite situation presented for c/a. Both Nb addition and increasing temperature enhanced the stability of β phase relative to ω phase. The critical Nb concentration for the complete stabilization of β phase at 300 K, 673 K and 1273 K was 22 at.%, 17 at.% and 9 at.%, respectively. The polycrystalline bulk modulus B, Youngs modulus E and shear modulus G increased monotonously with Nb addition and reducing the Nb concentration below 30 at.% resulted in lower E compared to that of Ti-6Al-4V. The calculated G/B values demonstrate that the bcc Ti1-xNbx (0 < x 0.4) random alloys should be intrinsically ductile.

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.

Modeling of Steels and Steel Surfaces Using Quantum Mechanical First Principles Methods

2013 ◽  
Vol 762 ◽  
pp. 445-450
Author(s):  
Matti Alatalo ◽  
Heikki Pitkänen ◽  
Matti Ropo ◽  
Kalevi Kokko ◽  
Levente Vitos
Keyword(s):  
First Principles ◽  
Atomic Level ◽  
Single Atom ◽  
Quantum Mechanical ◽  
Bulk Alloy ◽  
Potential Approximation ◽  
Materials Modelling ◽  
Chemical Disorder ◽  
Steel Surfaces ◽  
Random Alloys

We describe recent progress in first principles materials modelling applied to iron alloys. First principles methods in general have proven to be an effective way of describing atomic level phenomena in solids. When applied to alloys with chemical disorder, however, the widely used supercell methods turn out to be impractical due to the vast variety of different possible configurations. This problem can be overcome using the coherent potential approximation (CPA), which enables the description of a multicomponent alloy in terms of an effective medium constructed in such a way that it represents, on the average, the scattering properties of the alloy. A bulk alloy, in the case of substitutional random alloys, can thus be described with a single atom while a slab is needed to describe surfaces. The exact muffin-tin orbitals (EMTO) method provides a first principles method that can be combined with the CPA in order to describe steels and other multicomponent alloys. We describe the EMTO-CPA method and provide examples of both bulk and surface properties that can be modelled with this method.

Electronic structure and chemical bonding of α- and β-Ta4AlC3 phases: Full-potential calculation

2008 ◽  
Vol 23 (9) ◽  
pp. 2350-2356 ◽  
Author(s):  
Wei Lu ◽  
Xiaohui Deng ◽  
Hai Wang ◽  
Haitao Huang ◽  
Lianlong He
Keyword(s):  
Electronic Structure ◽  
Chemical Bonding ◽  
First Principles ◽  
Heat Of Formation ◽  
Full Potential ◽  
Generalized Gradient ◽  
Β Phase ◽  
Α Phase ◽  
Two Phases ◽  
The Stability

First-principles total-energy and heat of formation calculations on α and β polymorphs of Ta4AlC3 have been made with a full-potential electronic structure program with the generalized gradient approximation, which shows that α phase is more stable than β phase. The charge transfer and chemical bonding of the two phases were investigated quantitatively by using Bader’s quantum theory of atoms in molecules (AIM). The results show that the bonding between Ta1-C2 is stronger in α phase than β phase, which leads to the stability of α phase.

Effect of Oxygen Content on Microstructure and Mechanical Properties of Ti-Nb-Ge Alloys for Biomedical Application

2008 ◽  
Vol 47-50 ◽  
pp. 1450-1453 ◽  
Author(s):  
Won Yong Kim ◽  
Han Sol Kim
Keyword(s):  
Mechanical Properties ◽  
Oxygen Content ◽  
Volume Fraction ◽  
Biomedical Application ◽  
Casting Process ◽  
Alloy System ◽  
Β Phase ◽  
Ω Phase ◽  
Α Phase ◽  
The Stability

The effect of Ge and oxygen content on microstructural formation and mechanical properties of Ti-Nb alloys were investigated in order to design a desirable Ti based alloy through casting process. Three phase mixtures consisting of bcc-structured β phase, orthorhombic structured α" phase and intermediate ω phase were found depending on Nb, Ge, oxygen content in the present alloy system. The volume fraction of α" phase and ω phase decreased with increasing Ge or oxygen content. This microstructural information may indicate that both Ge and oxygen act to increase the stability of β phase rather than α" phase in metastable β-Ti based alloys prepared by water quenching. Elastic modulus values were sensitive to phase stability of constituent phases.

Composition-Dependent Collapse of β {111} Planes Leading to ω Precipitation in Ti-Nb Alloys: A First-Principles Study

2014 ◽  
Vol 788 ◽  
pp. 164-170
Author(s):  
Wen Chao Ou ◽  
Hong Chao Kou ◽  
Cai Si Meng ◽  
Bin Tang ◽  
Jin Shan Li
Keyword(s):  
Electronic Structure ◽  
Density Of States ◽  
First Principles ◽  
Energy Barrier ◽  
Phase Precipitation ◽  
Potential Approximation ◽  
Ω Phase ◽  
Nb Content ◽  
Total Energies ◽  
Omega Transformation

The effects of Nb content on the collapse of β {111} planes leading to ω phase precipitation were investigated in binary Ti-Nb alloys by first-principles exact muffin-tin orbitals-coherent potential approximation (EMTO-CPA) method. In accordance with the accepted mechanism of the beta to omega transformation occurring due to the collapse of the bcc {111} planes, the total energies of β Ti-Nb binary alloys containing multiple states corresponding to different Nb concentration ranging from 20at.% to 30at.% were calculated. The results indicated that the total energies for the same Nb content are not monotonically decreasing with the z (z denotes the degree of collapse of β {111} planes) value increasing, but keeping an energy barrier to cross. The energy barrier increases gradually along with increasing Nb content. The density of states (DOS) was given to elucidate the changes of electronic structure during the collapse of β {111} planes.

scholarly journals Discovery of New Ti-Based Alloys Aimed at Avoiding/Minimizing Formation of α” and ω-Phase Using CALPHAD and Artificial Intelligence

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 15
Author(s):  
Rajesh Jha ◽  
George S. Dulikravich
Keyword(s):  
Artificial Intelligence ◽  
Toxic Elements ◽  
Alloy Composition ◽  
Calphad Approach ◽  
Self Organizing Maps ◽  
Β Phase ◽  
Ω Phase ◽  
Complete Dataset ◽  
The Stability ◽  
Python Programming

In this work, we studied a Ti-Nb-Zr-Sn system for exploring novel composition and temperatures that will be helpful in maximizing the stability of β phase while minimizing the formation of α” and ω-phase. The Ti-Nb-Zr-Sn system is free of toxic elements. This system was studied under the framework of CALculation of PHAse Diagram (CALPHAD) approach for determining the stability of various phases. These data were analyzed through artificial intelligence (AI) algorithms. Deep learning artificial neural network (DLANN) models were developed for various phases as a function of alloy composition and temperature. Software was written in Python programming language and DLANN models were developed utilizing TensorFlow/Keras libraries. DLANN models were used to predict various phases for new compositions and temperatures and provided a more complete dataset. This dataset was further analyzed through the concept of self-organizing maps (SOM) for determining correlations between phase stability of various phases, chemical composition, and temperature. Through this study, we determined candidate alloy compositions and temperatures that will be helpful in avoiding/minimizing formation of α” and ω-phase in a Ti-Zr-Nb-Sn system. This approach can be utilized in other systems such as ω-free shape memory alloys. DLANN models can even be used on a common Android mobile phone.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

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.

Site preference and atomic ordering in the ternary Rh5Ga2As: first-principles calculations

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Nilanjan Roy ◽  
Sucharita Giri ◽  
Harshit ◽  
Partha P. Jana
Keyword(s):  
Total Energy ◽  
First Principles ◽  
Density Functional ◽  
Structure Type ◽  
Site Preference ◽  
X Ray Diffraction ◽  
Atomic Ordering ◽  
Functional Theory ◽  
The Stability ◽  
Bonding Characteristics

Abstract The site preference and atomic ordering of the ternary Rh5Ga2As have been investigated using first-principles density functional theory (DFT). An interesting atomic ordering of two neighboring elements Ga and As reported in the structure of Rh5Ga2As by X-ray diffraction data only is confirmed by first-principles total-energy calculations. The previously reported experimental model with Ga/As ordering is indeed the most stable in the structure of Rh5Ga2As. The calculation detected that there is an obvious trend concerning the influence of the heteroatomic Rh–Ga/As contacts on the calculated total energy. Interestingly, the orderly distribution of As and Ga that is found in the binary GaAs (Zinc-blende structure type), retained to ternary Rh5Ga2As. The density of states (DOS) and Crystal Orbital Hamiltonian Population (COHP) are calculated to enlighten the stability and bonding characteristics in the structure of Rh5Ga2As. The bonding analysis also confirms that Rh–Ga/As short contacts are the major driving force towards the overall stability of the compound.

scholarly journals Anion ordering and vacancy defects in niobium perovskite oxynitrides

2021 ◽  
Vol 2 (7) ◽  
pp. 2398-2407
Author(s):  
Joshua J. Brown ◽  
Youxiang Shao ◽  
Zhuofeng Ke ◽  
Alister J. Page
Keyword(s):  
First Principles ◽  
First Principles Calculations ◽  
Defect Engineering ◽  
Vacancy Defects ◽  
The Stability

First-principles calculations predict the stability and mobility of vacancy defects in niobium perovskite oxynitrides, aiding defect engineering for enhanced photocatalysis.

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