Ternary Alloying of Gamma Titanium-Aluminides for Hot-Workability

1990 ◽  
Vol 213 ◽  
Author(s):  
Naoya Masahashi ◽  
Y. Mizuhara ◽  
M. Matsuo ◽  
K. Hashimoto ◽  
M. Kimura ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Titanium Aluminides ◽  
Tensile Elongation ◽  
Rate Sensitivity ◽  
Dual Phase ◽  
Hot Workability ◽  
X Ray ◽  
Β Phase ◽  
Deformable Materials ◽  
Ternary Alloying

ABSTRACTA Microstructurally controlled γ(TiAl)-based alloy containing β(bcc) has shown remarkable tensile properties at high temperatures. It exhibits over 450% tensile elongation at 1473K. The strain rate sensitivity factors are calculated to be over 0.3 above 1273K. A specific texture is not observed from transmission X-ray photograph. TEM observation reveals that the precipitated β phase located at grain boundaries elongates uniformly along γ grain boundaries and causes large ductility. We propose β/γ dual phase alloys as high temperature deformable materials.

Brittle-ductile transition of titanium aluminides, alloyed by β-phase stabilization elements

2020 ◽  
Vol 2020 (01) ◽  
pp. 86-97
Author(s):  
M. V. Remez ◽  
◽  
Yu. M. Podrezov ◽  
V. I. Danylenko ◽  
M. I. Danylenko ◽  
...  
Keyword(s):  
Plastic Zone ◽  
Grain Boundaries ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Rate Sensitivity ◽  
Relaxation Processes ◽  
Main Role ◽  
Β Phase ◽  
Brittle Ductile Transition ◽  
Phase Stabilization

The temperature, structural, and rate sensitivity of the plasticity characteristics in γ-tita¬nium aluminides with different Al contents, doped with β-phase stabilization elements, are studied. Particular attention is paid to dislocation mechanisms that control the brittle-plastic transition. The main role of grain boundaries in the formation of plasticity characteristics is demonstrated. At low temperatures, the grain boundaries stop propagation of brittle transgranular cracks and confine the development of the plastic zone beyond the boundaries of an individual grain, creating the prerequisites for fracture in the microdeformation level. At elevated temperatures, the boundaries contribute to the formation of dislocations pile-up in the plastic zone with a stress concentration required to set off the Frank-Reed sources and the displacement of the plastic zone beyond the boundaries of an individual grain, changing its configuration and stress distribution and inhibiting the propagation of cracks. Acceleration of rela¬xation processes in the vicinity of the crack’s tip creates the prerequisites for the development of macrodeformation. Local relaxation processes at the crack’s tip contribute to high speed sensitivity of the plasticity characteristics. This effect has important practical consequences, since there is a temperature region near the upper working temperature of γ-TiAl alloys, where the stress value remains high (yield strength σ02 ~700 MPa and ultimate stress σul ~ 1200 MPa at bending tests) regardless of the strain rate, while deformation sharply increases at low speeds. As a result, it is possible to achieve a combination of high strength and ductility during creep tests. In samples tested by tension with low speed (10-5 s-1) the neck formation take a place. Deformation occurs by the dislocation-twinning mechanisms. At small deformations (7%) a twinning mechanism is preferable. Concentration of dislocations sharply increases at large deformations (32%) with formation of dislocation clusters. Stress relaxation on the boundary between γ-phase twins and α2-lamella, occurs by macroscopic shift on α2-lamella. Keywords: γ-titanium-aluminides, structure, strength, plasticity, brittle-ductile transition, temperature and rate sensitivity.

High-resolution x-ray analysis of dislocation networks nn tilt boundaries

1988 ◽  
Vol 46 ◽  
pp. 612-613
Author(s):  
J. R. Michael ◽  
C. H. Lin ◽  
S. L. Sass
Keyword(s):  
Grain Boundaries ◽  
Analytical Electron Microscopy ◽  
Solute Segregation ◽  
X Ray ◽  
Periodic Arrays ◽  
Analytical Electron ◽  
Primary Dislocation ◽  
Tilt Boundaries ◽  
Polycrystalline Solids ◽  
Twist Boundaries

The segregation of solute atoms to grain boundaries in polycrystalline solids can be responsible for embrittlement of the grain boundaries. Although Auger electron spectroscopy (AES) and analytical electron microscopy (AEM) have verified the occurrence of solute segregation to grain boundaries, there has been little experimental evidence concerning the distribution of the solute within the plane of the interface. Sickafus and Sass showed that Au segregation causes a change in the primary dislocation structure of small angle [001] twist boundaries in Fe. The bicrystal specimens used in their work, which contain periodic arrays of dislocations to which Au is segregated, provide an excellent opportunity to study the distribution of Au within the boundary by AEM.The thin film Fe-0.8 at% Au bicrystals (composition determined by Rutherford backscattering spectroscopy), ∼60 nm thick, containing [001] twist boundaries were prepared as described previously. The bicrystals were analyzed in a Vacuum Generators HB-501 AEM with a field emission electron source and a Link Analytical windowless x-ray detector.

Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems

1988 ◽  
Vol 133 ◽  
Author(s):  
K. S. Kumar ◽  
S. K. Mannan
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Mechanical Milling ◽  
Room Temperature ◽  
Crystalline Compound ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase

ABSTRACTThe mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.

scholarly journals Effect of High Strain Rate on Adiabatic Shearing of α+β Dual-Phase Ti Alloy

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2044
Author(s):  
Fang Hao ◽  
Yuxuan Du ◽  
Peixuan Li ◽  
Youchuan Mao ◽  
Deye Lin ◽  
...  
Keyword(s):  
Strain Rate ◽  
Split Hopkinson Pressure Bar ◽  
Damage Tolerance ◽  
Shear Bands ◽  
Dual Phase ◽  
Ti Alloy ◽  
Hopkinson Pressure Bar ◽  
Β Phase ◽  
Schmid Factor ◽  
Pressure Bar

In the present work, the localized features of adiabatic shear bands (ASBs) of our recently designed damage tolerance α+β dual-phase Ti alloy are investigated by the integration of electron backscattering diffraction and experimental and theoretical Schmid factor analysis. At the strain rate of 1.8 × 104 s−1 induced by a split Hopkinson pressure bar, the shear stress reaches a maximum of 1951 MPa with the shear strain of 1.27. It is found that the α+β dual-phase colony structures mediate the extensive plastic deformations along α/β phase boundaries, contributing to the formations of ASBs, microvoids, and cracks, and resulting in stable and unstable softening behaviors. Moreover, the dynamic recrystallization yields the dispersion of a great amount of fine α grains along the shearing paths and in the ASBs, promoting the softening and shear localization. On the contrary, low-angle grain boundaries present good resistance to the formation of cracks and the thermal softening, while the non-basal slipping dramatically contributes to the strain hardening, supporting the promising approaches to fabricate the advanced damage tolerance dual-phase Ti alloy.

scholarly journals Dynamic Softening Mechanisms and Microstructure Evolution of TB18 Titanium Alloy during Uniaxial Hot Deformation

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 789
Author(s):  
Qiang Fu ◽  
Wuhua Yuan ◽  
Wei Xiang
Keyword(s):  
Titanium Alloy ◽  
Dynamic Recovery ◽  
True Strain ◽  
Hot Workability ◽  
Compression Tests ◽  
Phase Zone ◽  
Β Phase ◽  
Stability And Instability ◽  
Dynamic Softening ◽  
Transus Temperature

In this study, isothermal compression tests of TB18 titanium alloy were conducted using a Gleeble 3800 thermomechanical simulator for temperatures ranging from 650 to 880 °C and strain rates ranging from 0.001 to 10 s−1, with a constant height reduction of 60%, to investigate the dynamic softening mechanisms and hot workability of TB18 alloy. The results showed that the flow stress significantly decreased with an increasing deformation temperature and decreasing strain rate, which was affected by the competition between work hardening and dynamic softening. The hyperbolic sine Arrhenius-type constitutive equation was established, and the deformation activation energy was calculated to be 303.91 kJ·mol−1 in the (α + β) phase zone and 212.813 kJ·mol−1 in the β phase zone. The processing map constructed at a true strain of 0.9 exhibited stability and instability regions under the tested deformation conditions. The microstructure characteristics demonstrated that in the stability region, the dominant restoration and flow-softening mechanisms were the dynamic recovery of β phase and dynamic globularization of α grains below transus temperature, as well as the dynamic recovery and continuous dynamic recrystallization of β grains above transus temperature. In the instability region, the dynamic softening mechanism was flow localization in the form of a shear band and a deformation band caused by adiabatic heating.

scholarly journals Chemical, electrochemical, thermodynamic and adsorption study of EN8 dual-phase steel with ferrite-martensite structure in 0.5 M H2SO4 using pectin as inhibitor

2021 ◽  
Author(s):  
P. R. Prabhu ◽  
Pavan Hiremath ◽  
Deepa Prabhu ◽  
M. C. Gowrishankar ◽  
B. M. Gurumurthy
Keyword(s):  
Weight Loss ◽  
Adsorption Isotherm ◽  
Surface Analysis ◽  
Potentiodynamic Polarization ◽  
Dual Phase Steel ◽  
Inhibition Efficiency ◽  
Dual Phase ◽  
X Ray ◽  
Enthalpy And Entropy ◽  
Martensite Structure

AbstractThis paper presents the corrosion and inhibition behavior of heat-treated EN8 dual-phase steel with ferrite-martensite structure with pectin in 0.5 M sulphuric acid. The corrosion studies were performed using the weight loss method, electrochemical techniques such as potentiodynamic polarization measurements, and impedance spectroscopy. The study was done at different concentrations of pectin in the temperature range of 40 to 70 °C and immersion time of 1, 3, 5, and 7 h. The results showed that the inhibition performance of pectin has enhanced with an increase in pectin concentration and decreased with the temperature and time of exposure. From the weight loss study, highest inhibition efficiency of 76.43% was achieved at 5.0 g/L at 1 h of exposure at 40 °C. The maximum inhibition efficiency of 62% was obtained with 5.0 g/L of pectin at 40 °C by potentiodynamic polarization method. The energy, enthalpy, and entropy of activation and also thermodynamic parameters like free energy, enthalpy, and entropy of adsorption were assessed and discussed. Appropriate adsorption isotherm was fit to the obtained experimental outcomes and achieved Langmuir adsorption isotherm to be the best fit and obeyed physical adsorption. Surface analysis: scanning electron microscopy, X-ray diffraction techniques, atomic force microscopy, and energy dispersive X-ray were done with and without the addition of pectin. The metal surface appears to be uniform and smooth in the presence of pectin and adsorption was confirmed by surface analysis.

scholarly journals X-Ray Investigations of the Low-Temperature Phases of the Organic Metals α- and β-(BEDT-TTF)2I3

1986 ◽  
Vol 41 (11) ◽  
pp. 1319-1324 ◽  
Author(s):  
H. Endres ◽  
H. J. Keller ◽  
R. Swietlik ◽  
D. Schweitzer ◽  
K. Angermund ◽  
...  
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Slight Variation ◽  
X Ray ◽  
Organic Metals ◽  
Β Phase ◽  
Α Phase

The structure of single crystals of the organic metals α- and β-(BEDT-TTF)2I3* was determined at 100 K, well below the phase transitions indicated by resistivity and thermopower measurements as well as by differential thermal analysis. In the α-phase no unusual change of the room temperature unit cell but a slight variation in the triiodide network and especially a more pronounced dimerization in one of the two donor stacks have been found. The β-phase develops a superstructure with a unit cell volume three times as large as that at room temperature and with pronounced distortions of the I3--ions.

Microstructural Analysis and Wear Behavior of Cryogenically Treated Ti-6Al-4V Alloy

2014 ◽  
Vol 592-594 ◽  
pp. 1331-1335 ◽  
Author(s):  
Haider Nasreen ◽  
S. Beer Mohamed ◽  
S. Rasool Mohideen
Keyword(s):  
Grain Boundaries ◽  
Wear Behavior ◽  
Cryogenic Treatment ◽  
Microstructural Analysis ◽  
Wear Loss ◽  
Β Phase ◽  
Α Phase ◽  
Treated Sample

This paper helps in understanding the effects of cryogenic treatment on microstructural variation, hardness and wear behavior of Ti-6Al-4V alloy. The microstructure indicates white β-phase dispersed on the grain boundaries of dark α-phase. Cryogenic treatment at-186 °C for 10 h led to the transformation from β-phase to α-phase, resulting in coarsening of α. Hardness of the cryogenically treated sample was observed to decrease and wear loss was observed to increase; this can be attributed to the coarsening of α-phase.

scholarly journals Effect of Zr Addition on the Mechanical Properties and Superplasticity of a Forged SP700 Titanium Alloy

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 906
Author(s):  
Dong Han ◽  
Yongqing Zhao ◽  
Weidong Zeng
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Titanium Alloy ◽  
Tensile Properties ◽  
Superplastic Deformation ◽  
Volume Fraction ◽  
Tensile Elongation ◽  
Β Phase ◽  
Zr Addition ◽  
Fine Microstructure

The present study focuses on the effect of 1% Zr addition on the microstructure, tensile properties and superplasticity of a forged SP700 alloy. The results demonstrated that Zr has a significant effect on inhibiting the microstructural segregation and increasing the volume fraction of β-phase in the forged SP700 alloy. After annealing at 820 °C for 1 h and aging at 500 °C for 6 h, the SP700 alloy with 1% Zr showed a completely globular and fine microstructure. The yield strength, ultimate tensile strength and tensile elongation of the alloy with optimized microstructure were 1185 MPa, 1296 MPa and 10%, respectively. The superplastic deformation was performed at 750 °C with an elongation of 1248%. The improvement of tensile properties and superplasticity of the forged SP700 alloy by Zr addition was mainly attributed to the uniform and fine globular microstructures.

Sign in / Sign up

Export Citation Format

Share Document