Phase Stability of Sigma + Beta Microstructures in the Ternary Nb-Ti-Al System

1990 ◽  
Vol 194 ◽  
Author(s):  
D. T. Hoelzer ◽  
F. Ebrahimi
Keyword(s):  
Phase Stability ◽  
Orthorhombic Phase ◽  
Beta Phase ◽  
Phase Region ◽  
Nominal Composition ◽  
Two Phase ◽  
Σ Phase ◽  
Β Phase ◽  
Heat Treated ◽  
The Stability

AbstractAn alloy with the nominal composition 42Nb-28Ti-30Al (at.%) was heat treated in the sigma + beta phase region. The evolution of σ phase from the metastable β phase and the stability of the two-phase microstructure at various aging temperatures were evaluated using TEM techniques. The results indicate that the β phase in equilibrium with the σ phase at high temperatures decomposes to the orthorhombic phase at temperatures below 1200°C.

Flash Calculation Using Successive Substitution Accelerated by the General Dominant Eigenvalue Method in Reduced-Variable Space: Comparison and New Insights

SPE Journal ◽  
2020 ◽  
Vol 25 (06) ◽  
pp. 3332-3348
Author(s):  
Haining Zhao ◽  
Hongbin Jing ◽  
Zhengbao Fang ◽  
Hongwei Yu
Keyword(s):  
Stability Analysis ◽  
Phase Stability ◽  
Linear Acceleration ◽  
Phase Region ◽  
Dominant Eigenvalue ◽  
Two Phase ◽  
Eigenvalue Method ◽  
Successive Substitution ◽  
The Stability ◽  
Flash Calculation

Summary On the basis of a previously published reduced-variables method, we demonstrate that using these reduced variables can substantially accelerate the conventional successive-substitution iterations in solving two-phase flash (TPF) problems. By applying the general dominant eigenvalue method (GDEM) to the successive-substitution iterations in terms of the reduced variables, we obtained a highly efficient solution for the TPF problem. We refer to this solution as Reduced-GDEM. The Reduced-GDEM algorithm is then extensively compared with more than 10 linear-acceleration and Newton-Raphson (NR)-type algorithms. The initial equilibrium ratio for flash calculation is generated from reliable phase-stability analysis (PSA). We propose a series of indicators to interpret the PSA results. Two new insights were obtained from the speed comparison among various algorithms and the PSA. First, the speed and robustness of the Reduced-GDEM algorithm are of the same level as that of the reduced-variables NR flash algorithm, which has previously been proved to be the fastest flash algorithm. Second, two-side phase-stability-analysis results indicate that the conventional successive-substitution phase-stability algorithm is time consuming (but robust) at pressures and temperatures near the stability-test limit locus in the single-phase region and near the spinodal in the two-phase region.

scholarly journals The High-Temperature Deformation Behavior of As-Cast Ti90 Titanium Alloy

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1630
Author(s):  
Ke Wang ◽  
Yongqing Zhao ◽  
Weiju Jia ◽  
Silan Li ◽  
Chengliang Mao
Keyword(s):  
Titanium Alloy ◽  
Deformation Behavior ◽  
Processing Map ◽  
Electron Backscatter Diffraction ◽  
Phase Region ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Two Phase ◽  
Temperature Range ◽  
Β Phase

Isothermal compressions of as-cast near-α Ti90 titanium alloy were carried out on a Gleeble-3800 simulator in the temperature range of 860–1040 °C and strain rates of 0.001–10 s−1. The deformation behavior of the alloy was characterized based on the analyses of flow curves, the constructions of Arrhenius constitutive equations and the processing map. The microstructure evolution of the alloy was analyzed using the optical microscopic (OM), transmission electron microscope (TEM), and electron backscatter diffraction (EBSD) techniques. The results show that the kinking and dynamic globularization of α lamellae is the dominant mechanism of flow softening in the α + β two-phase region, while the dynamic recovery (DRV) of β phase is the main softening mechanism in the β single-phase region. The dynamic globularization of α lamellae is mainly caused by the wedging of β phase into α laths and the shearing of α laths due to imposed shear strain. The activation of prismatic and pyramidal slip is found to be easier than that of basic slip during the deformation in the α + β two-phase region. In addition, the Schmid factor of equiaxial α is different from that of lamellar α, which also varies with the angle between its geometric orientation and compression direction (CD). Based on the processing map, the low η region within the temperature range of 860–918 °C with a strain rate range of 0.318–10 s−1 should be avoided to prevent the occurrence of deformation instability.

Advances in Ambient Temperature Creep Deformation Behavior of Two-Phase Titanium Alloys

2005 ◽  
Vol 475-479 ◽  
pp. 779-784 ◽  
Author(s):  
A. Jaworski ◽  
Sreeramamurthy Ankem
Keyword(s):  
Titanium Alloys ◽  
Creep Deformation ◽  
Deformation Behavior ◽  
Creep Resistance ◽  
Volume Fraction ◽  
Beta Phase ◽  
Two Phase ◽  
Number Of Factors ◽  
Strength Difference ◽  
The Stability

In recent years, significant advances have been made in regard to the creep deformation behavior of two phase titanium alloys. It has been shown that the creep resistance depends on a number of factors, including the shape of the component phases, the strength difference between the phases, and the stability of the beta phase. For example, in two-phase materials with a similar volume fraction and morphology of phases, if the beta phase is less stable, then the creep resistance is lower. These developments will be reviewed and the reasons for such effects will be suggested.

Effect of hot-forging on beta phase transformation of a high niobium containing titanium aluminide alloy

2015 ◽  
Vol 29 (10n11) ◽  
pp. 1540009
Author(s):  
Liang Cheng ◽  
Xiangyi Xue ◽  
Bin Tang ◽  
Hongchao Kou ◽  
Jinshan Li
Keyword(s):  
Titanium Aluminide ◽  
Volume Fraction ◽  
Hot Forging ◽  
Beta Phase ◽  
Phase Region ◽  
Practical Significance ◽  
Hot Workability ◽  
Present Alloy ◽  
Β Phase ◽  
B2 Phase

In this paper, ingot breakdown process of a high Nb containing TiAl alloy with a chemical composition of Ti –42.63 Al –8.11 Nb –0.21 W –0.09 Y (at.%) has been investigated under conventional forging conditions. It was found that the present alloy possesses superior hot-workability that can be successfully forged by conventional upsetting route due to the appearance of large amount of β/B2 phase, though shear band was observed in the forged-pancake. Further studies revealed that hot-working performed in (α + β) phase region which can effectively impede the β → α transformation and thus significantly increase the volume fraction of β/B2 phase. In contrast, the amount of β/B2 phase was notably reduced by heat treatment at the same conditions. This stress-induced effect is considered to be responsible to the superior hot-workability of the present alloy and the mechanism has been discussed and reasonably clarified. It was also suggested that the stress-induced effect has practical significance that it allows the implementation of conventional multi-step forging process which can develop fine and uniform microstructures suitable for secondary processing.

Tensile Property Improvements of Spinodal Cu-15Ni-8Sn by Two-Phase Heat Treatment

1982 ◽  
Vol 104 (3) ◽  
pp. 234-240 ◽  
Author(s):  
T. J. Louzon
Keyword(s):  
Heat Treatment ◽  
Single Phase ◽  
Phase Region ◽  
Two Phase ◽  
Heat Treated ◽  
Slow Kinetics ◽  
Increased Strength ◽  
Kinetics Of ◽  
Phase Solution ◽  
Strength And Ductility

A heat treatment has been developed which produces significant improvements in the tensile properties of Cu-15Ni-8Sn spinodal alloy. The treatment involves solution heat treatment in the two-phase region rather than the single-phase region normally used. After quenching and aging, increased strength and ductility of the alloy over single phase solution heat-treated and aged values were found. The mechanical properties obtained were superior to any previously observed for material of the compositions studied in the solution treated, quenched, and aged condition. Also, the alloys’ transformation kinetics were greatly slowed by the two phase heat-treatment. It is suggested that the increase in strength and slow kinetics of transformation observed are caused by grain size effects and by grain boundary modifications. Resistivity data and etching response corroborate these arguments.

Microstructure Control and Mechanical Property Correlation in Titanium Alloy Ti-6Al-4V Fasteners for Space Applications

2015 ◽  
Vol 830-831 ◽  
pp. 354-357
Author(s):  
S.V.S. Narayana Murty ◽  
Sushant Manwatkar ◽  
P. Ramesh Narayanan
Keyword(s):  
Mechanical Property ◽  
Titanium Alloy ◽  
High Strength ◽  
Beta Phase ◽  
Strength Properties ◽  
Head Region ◽  
Two Phase ◽  
Space Applications ◽  
Β Phase ◽  
Torque Values

High strength fasteners of Titanium alloy Ti-6Al-4V are widely used in both launch vehicle and satellite structures. Ti-6Al-4V fasteners having three different types of microstructures were analysed for mechanical properties to understand the role of two phase α+β or transformed β phase in the head region. Based on the microstructure-mechanical property correlations, it was concluded that the presence of transformed beta phase will not affect the strength properties, but will produce scatter in percentage elongation, percentage reduction in area and failure torque values. Therefore, it is recommended that the microstructure of aerospace titanium alloy Ti-6Al-4V fasteners should contain homogeneous two phase α+β throughout.

Phase Stability of β-Ti Phase in the TiAl Alloys with the Combined Addition of M Elements

2015 ◽  
Vol 1760 ◽  
Author(s):  
Hirotoyo Nakashima ◽  
Masao Takeyama
Keyword(s):  
Phase Stability ◽  
Strong Interaction ◽  
Relative Phase ◽  
Composition Dependence ◽  
Phase Region ◽  
Negative Interaction ◽  
Tial Alloys ◽  
Quaternary Systems ◽  
The Third ◽  
Β Phase

ABSTRACTPhase equilibria among the β-Ti, α-Ti and γ-TiAl phases were examined at 1473 K, in order to reveal the M/Nb ratio dependence of the relative phase stability of β phase in the Ti-Al-Nb-M (M: V, Cr, Mo) quaternary systems. In all of the quaternary systems, the expansion of β phase region toward the lower (Nb+M) content side is observed due to the existence of negative interaction to stabilize the β phase between the third and fourth elements (i.e. Nb-V, Nb-Cr and Nb-Mo). Composition dependence of the interaction is quantified as a function of the M/(Nb+M) ratio at 42 at.% Al. The strong interaction energy existing between the different group elements should be taken into account to design the multi-component TiAl alloys.

The Effect of the Treatment of Localised Friction in Two-Phase Mixtures on the Stability of Parallel Channels

2002 ◽  
Author(s):  
H. N. Abdou ◽  
V. B. Garea ◽  
A. E. Larreteguy
Keyword(s):  
Homogeneous Model ◽  
Stability Boundary ◽  
Density Wave ◽  
Phase Region ◽  
Experimental Results ◽  
Exact Equation ◽  
Two Phase ◽  
Heated Channel ◽  
Phase Mixture ◽  
The Stability

A one-dimensional analytical model has been developed to be used for the linear analysis of density-wave oscillations in a parallel heated channel. The heated channel is divided into a single-phase and a two-phase region. The two-phase region is represented by the homogeneous model. The localised friction at the channel exit is treated considering the two-phase mixture. The exact equation for the total channel pressure drop is perturbed around the steady state. The stability characteristics of the heated channel are investigated using the Nyquist criterion. The marginal stability boundary (MSB) is determined in the two-dimensional thermodynamic equilibrium space parameters, the subcooled boiling number and the phase change number. The predictions of the model are compared with experimental results published in open literature. The results indicate a more stable system with (1) low system pressure, (2) high inlet restriction, (3) low outlet restriction, and (4) high inlet velocity. The results show that the model agrees well with the available experimental data. In particular, the results show the significance of correcting the localised friction due to the presence of the two-phase mixture in the two-phase region: explicit inclusion of the two-phase localised friction improves the agreement with experimental results. This effect is more important for high heating power and high inlet subcooling.

scholarly journals An improved reduction method for phase stability testing in the single-phase region

2020 ◽  
Vol 18 (1) ◽  
pp. 1316-1322
Author(s):  
Dan Vladimir Nichita ◽  
Catinca Secuianu
Keyword(s):  
Phase Stability ◽  
Reduction Method ◽  
Phase Region ◽  
Binary Interaction ◽  
Stability Testing ◽  
Number Of Components ◽  
Mixture Phase ◽  
Residual Functions ◽  
Binary Interaction Parameters ◽  
The Stability

AbstractA new reduction method for mixture phase stability testing is proposed, consisting in Newton iterations with a particular set of independent variables and residual functions. The dimension of the problem does not depend on the number of components but on the number of components with nonzero binary interaction parameters in the equation of state. Numerical experiments show an improved convergence behavior, mainly for the domain located outside the stability test limit locus in the pressure–temperature plane, recommending the proposed method for any applications in which the problematic domain is crossed a very large number of times during simulations.

Influence of elemental B addition on the heat-treated cast structures of Ti–47Al–2Cr–(2–4)Nb alloys

1997 ◽  
Vol 12 (3) ◽  
pp. 665-680 ◽  
Author(s):  
J. Y. Jung ◽  
J. K. Park
Keyword(s):  
Equilibrium Composition ◽  
Nucleation Site ◽  
Phase Region ◽  
Chemical Diffusivity ◽  
Two Phase ◽  
Cast Structure ◽  
Size Refinement ◽  
Formation Kinetics ◽  
Phase Sequence ◽  
Heat Treated

The influence of elemental B addition on the heat-treated cast structure of Ti–47Al–2Cr–(2–4)Nb alloys has been investigated using x-ray diffractometry, optical microscopy, scanning and transmission electron microscopy, and tensile testing. The phase sequence is β → β + α → α → α + γ → α + β + γ → β + γ. The addition of (0–2 at. %) B does not change the phase sequence. It, however, tends to stabilize α phase by shifting the (α + β + γ) three-phase region toward a higher (Cr + Nb) content. The B addition does not significantly alter the equilibrium composition within (α + γ) two-phase field. The B addition markedly accelerates the lamellar formation kinetics and enhances the thickening rate of γ plates, despite the fact that it increases both the misfit between α and γ plates and the α/γ interfacial energy. The acceleration of lamellar formation kinetics is thus believed to be primarily due to the enhancement of chemical diffusivity as a result of B addition. The B addition induces a significant refinement of heat-treated cast structure. This is primarily due to the role of boride to disperse the interdendritic γ regions to a fine network and to refine the dendrite cell size. Further refinement arises from the boride's role to act as the nucleation site for γ grains and from the intrinsic B effect to enhance the chemical diffusivity and the γ thickening rate. The addition of a small amount of B enhances both the strength and tensile ductility of near gamma structure. The strengthening arises from grain size refinement and from the boride dispersion. The calculation of fracture strain suggests that an enhancement of ductility for small B addition (up to ∼0.2 at. %) is mostly due to its effect to refine the γ grains.

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