The Yield Stress of the Fully-Lamellar Microstructure

1996 ◽  
Vol 460 ◽  
Author(s):  
Y. Q. Sun
Keyword(s):  
Grain Size ◽  
Yield Stress ◽  
Multilayer Structure ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Lamellar Thickness ◽  
Polycrystalline Microstructure ◽  
Fully Lamellar ◽  
The Relationship ◽  
Lamellar Interfaces

ABSTRACTThis paper is an inquiry into the relationship between the yield stress and the two length parameters in the fully-lamellar polycrystalline microstructure, the grain-size dCB and the lamellar thickness dLM. Deformation in the multilayer structure is assumed to proceed by dislocations propagating in the formation of a succession of mutually interacting pileups, blocked at the lamellar interfaces and piled-up ultimately against the grain boundary. An important case suggested is a yield stress independent of the grain size, sensitive only to the lamellar spacing.

On the Effects of Interstitial Elements on Microstructure and Properties of Ternary and Quaternary TiAl based alloys

2004 ◽  
Vol 842 ◽  
Author(s):  
Jean-Pierre Chevalier ◽  
Mélanie Lamirand ◽  
Jean-Louis Bonnentien
Keyword(s):  
Yield Stress ◽  
Fracture Strain ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Quaternary Alloys ◽  
Ultra High Purity ◽  
C And N ◽  
Fully Lamellar ◽  
Kinetics Of ◽  
Interstitial Elements

ABSTRACTTi-Al-Cr ternary and Ti-Al-Cr-Nb quaternary alloys have been studied as a function of initial purity and added interstitial content. Using strict clean processing together with either ultra high purity or commercial purity alloys, the effects of interstitial elements (essentially O, but also C and N) on microstructure and hardness, yield stress and fracture strain have been studied for both fully lamellar microstructures and duplex microstructures. The results are clear and similar trends are observed : as long as they do not precipitate, these stabilise the lamellar microstructure and affect the kinetics of the α-γ phase tranformation, leading to a higher than equilibrium value for the α2 phase for continuous cooling. Both the lamellar spacing and the α2 phase fraction correlate with increased hardness and yield stress, and also with decreasing fracture strain. The effects are significant.

Grain Refinement of Vanadium by Low Temperature Severe Plastic Deformation

2010 ◽  
Vol 638-642 ◽  
pp. 1934-1939 ◽  
Author(s):  
Y.B. Chun ◽  
S.H. Ahn ◽  
D.H. Shin ◽  
S.K. Hwang
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Low Temperature ◽  
Yield Strength ◽  
Severe Plastic Deformation ◽  
Equal Channel Angular Pressing ◽  
Tensile Elongation ◽  
Lamellar Microstructure ◽  
Lamellar Thickness ◽  
Angular Pressing

Recent advances in the severe plastic deformation technique have shown that effective refinement of the microstructure can be achieved in pure metals as well as in alloys. Among the various methods of severe plastic deformation, equal channel angular pressing has been the subject of numerous research works. Since the grain refining effect of this technique appears to reach a peak at a level of approximately 200 nm further microstructural changes are sought—deformation at a cryogenic temperature being one of the candidate routes. In the present study, we opted to combine equal channel angular pressing and low temperature plastic deformation to refine the microstructure of commercially pure V. The starting microstructure consisted of equiaxed grains with an average size of 100 micrometers. This microstructure was refined to a 200 nm thick lamellar microstructure by 8 passes of equal channel angular pressing at 350°C. The lamellar thickness was further reduced to 140 nm upon subsequent cryogenic rolling, which resulted in room temperature yield strength of 768 MPa. In the specimens, recrystallization annealed at 850°C, the grain size reached 1000 nm or larger, and the yield strength obeyed the Hall-Petch relationship with that grain size. The tensile elongation value, which was low and insensitive to the grain size in the as-deformed state, increased significantly up to 43% with the recrystallization annealing.

Microstructures and Creep Properties of Powder Metallurgy Ti-48Al-2Cr-2Nb + W

2007 ◽  
Author(s):  
H. Saari ◽  
S. Bulmer ◽  
D. Y. Seo ◽  
P. Au
Keyword(s):  
Heat Treatment ◽  
Powder Metallurgy ◽  
Lamellar Microstructure ◽  
Controlled Cooling ◽  
Tial Alloys ◽  
Creep Properties ◽  
Rupture Ductility ◽  
Heat Treated ◽  
Fully Lamellar ◽  
Lamellar Interfaces

The microstructures and creep properties at 760 °C and 276 MPa of three powder metallurgy TiAl alloys (Ti-48Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb+0.5W, and Ti-48Al-2Cr-2Nb+1W (atomic percent)) are presented. The results indicate that the addition of W to the base composition, the use of a solution heat treatment combined with controlled cooling (to generate a fully lamellar microstructure), and the use of an aging heat treatment (to generate precipitate particles at the lamellar interfaces) improve creep properties dramatically. The solution heat treated and aged Ti-48Al-2Cr-2Nb+1W alloy has a time to 0.5% strain of 8.3 hours, a time to 1% strain of 46.4 hours, and a creep life of 412 hours with a rupture ductility of 16.9%.

Processing and Alloy Development to Optimise the Properties and Cost-Effectiveness of Components Manufactured from TiAl-Based Alloys

2004 ◽  
Vol 449-452 ◽  
pp. 25-30 ◽  
Author(s):  
Xin Hua Wu ◽  
D. Hu ◽  
M.H. Loretto
Keyword(s):  
Grain Size ◽  
Powder Processing ◽  
Thermomechanical Processing ◽  
Plastic Anisotropy ◽  
Lamellar Microstructure ◽  
Size Control ◽  
Research Programme ◽  
Alloy Development ◽  
Grain Size Control ◽  
Fully Lamellar

The IRC has carried out a major research programme over the last ten or so years aimed at developing the processing and optimisation of TiAl-based alloys. This work has covered melting, the production of shaped castings, powder processing and a range of thermomechanical processing routes in parallel with alloy development. In this paper the work aimed at understanding the factors that influence the properties of thermo-mechanically processed and cast samples of TiAl-based alloys will be reviewed. It is shown that the use of boron to control the grain size of castings leads to limited ductility in the stronger and more highly alloyed TiAl alloys because ribbon-like borides up to 200µm in length can be formed. It is also shown that although a fully lamellar microstructure offers a good balance of properties their plastic anisotropy leads to pre-yield fracture and to reduced fatigue life. It is clear that grain size control is essential if an acceptable balance of properties is to be obtained but that if casting is to be used grain refinement via boron addition is not totally satisfactory. A simple heat treatment can be used to refine the microstructure of cast boron-free alloys, which leads to ductility comparable with that in wrought samples and the associated convoluted microstructure should also eliminate pre-yield cracking.

Microstructural Effect on Environmental Embrittlement of Isothermally Forged TiAl-Based Intermetallic Alloys

2002 ◽  
Vol 753 ◽  
Author(s):  
T. Takasugi ◽  
T. Tsuyumu ◽  
Y. Kaneno ◽  
H. Inoue
Keyword(s):  
Tensile Strength ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Testing Temperature ◽  
Intermetallic Alloy ◽  
Dual Phase ◽  
Intermetallic Alloys ◽  
Environmental Embrittlement ◽  
Fully Lamellar ◽  
Microstructural Effect

ABSTRACTThe TiAl-based (Ti-46Al-7Nb-1.5Cr (at%)) intermetallic alloy was tensile tested in vacuum and air as a function of temperature to investigate microstructural effect on the moisture-induced embrittlement. The reduction in tensile strength (or elongation) due to testing in air diminishes as testing temperature increases. From the fracture strength (or elongation)-temperature curves, it was found that the near gamma grain microstructure was most resistant, and the dual-phase microstructure most susceptible to moisture-induced embrittlement. Also, the moisture-induced embrittlement of the TiAl-based intermetallic alloy with fully lamellar microstructure depends on the lamellar spacing, and reduced with decreasing lamellar spacing.

Relationship between Strength and Grain Size of Friction Stir Processed and Annealed High Purity Aluminum

2014 ◽  
Vol 922 ◽  
pp. 372-375
Author(s):  
Sho Kobayashi ◽  
Tomo Kawakatsu ◽  
Yorinobu Takigawa ◽  
Tokuteru Uesugi ◽  
Kenji Higashi
Keyword(s):  
Grain Size ◽  
Chemical Composition ◽  
Yield Stress ◽  
Coarse Grain ◽  
Petch Relation ◽  
Friction Stir ◽  
Grain Sizes ◽  
Fine Grain ◽  
High Purity Aluminum ◽  
The Relationship

A relationship between yield stress and grain size was examined in FSP-ed and annealed 5N-Al (99.9996% purity) in order to reveal the relationship on materials with equal chemical composition, because the large positive deviations of yield stress from the Hall–Petch relation obtained by plots with coarse grain size were reported in the fine grain sizes with SPD processed and we focused on amount of impurities during SPD processing about this phenomenon. The purity of FSP-ed samples on this study were 99.9988% Al (Fe +8at.ppm). Annealing this sample at various temperatures, the relationship between yield stress and grain sizes was obtained on materials with equal chemical composition. However, the yield stress of sample as FSP-ed is higher than that following Hall-Petch relation obtained by subsequently annealed samples plots. As a result, the positive deviation is occurred by factors other than the impurities.

scholarly journals Quantifying the High-Temperature Separation Behavior of Lamellar Interfaces in γ-Titanium Aluminide Under Tensile Loading by Molecular Dynamics

2021 ◽  
Vol 7 ◽  
Author(s):  
Hariprasath Ganesan ◽  
Ingo Scheider ◽  
Christian J. Cyron
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Lamellar Microstructure ◽  
Atomistic Simulations ◽  
Temperature Separation ◽  
Fully Lamellar ◽  
Separation Behavior ◽  
Lamellar Interfaces

γ-titanium aluminide (TiAl) alloys with fully lamellar microstructure possess excellent properties for high-temperature applications. Such fully lamellar microstructure has interfaces at different length scales. The separation behavior of the lamellae at these interfaces is crucial for the mechanical properties of the whole material. Unfortunately, quantifying it by experiments is difficult. Therefore, we use molecular dynamics (MD) simulations to this end. Specifically, we study the high-temperature separation behavior under tensile loading of the four different kinds of lamellar interfaces appearing in TiAl, namely, the γ/α2, γ/γPT, γ/γTT, and γ/γRB interfaces. In our simulations, we use two different atomistic interface models, a defect-free (Type-1) model and a model with preexisting voids (Type-2). Clearly, the latter is more physical but studying the former also helps to understand the role of defects. Our simulation results show that among the four interfaces studied, the γ/α2 interface possesses the highest yield strength, followed by the γ/γPT, γ/γTT, and γ/γRB interfaces. For Type-1 models, our simulations reveal failure at the interface for all γ/γ interfaces but not for the γ/α2 interface. By contrast, for Type-2 models, we observe for all the four interfaces failure at the interface. Our atomistic simulations provide important data to define the parameters of traction–separation laws and cohesive zone models, which can be used in the framework of continuum mechanical modeling of TiAl. Temperature-dependent model parameters were identified, and the complete traction–separation behavior was established, in which interface elasticity, interface plasticity, and interface damage could be distinguished. By carefully eliminating the contribution of bulk deformation from the interface behavior, we were able to quantify the contribution of interface plasticity and interface damage, which can also be related to the dislocation evolution and void nucleation in the atomistic simulations.

THE INVESTIGATION ON LAMELLAR MICROSTRUCTURE TRANSFORMATION AND STABILITY IN TIAL BASED INTERMATELLICS

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2279-2284
Author(s):  
WEI ZHANG ◽  
YUE MA ◽  
SHENGKAI GONG
Keyword(s):  
Lamellar Structure ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Microstructure Transformation ◽  
Β Phase ◽  
Microstructure Stability ◽  
The Stability ◽  
Fully Lamellar

Microstructure stability in fully lamellar (FL) structure TiAl based intermatellics have been studied. The experiment results have shown that the smaller the lamellar spacing is, the more instable the lamellar structure is. The distinct lamellar spheroidization occurs at 1150°C holding for 24h. This phenomena may be caused by lamellar coarsening and decomposition. The linear residual β phase distributed in the Ti -47 A 1-2 Cr -2 Nb alloy may prevent lamellar spheroidization and improves the stability of lamellar structure significantly.

Sign in / Sign up

Export Citation Format

Share Document