Solution and Precipitation Hardening in Carbon-Doped Two-Phase γ-Titanium Aluminides

1996 ◽  
Vol 460 ◽  
Author(s):  
F. Appel ◽  
U. Christoph ◽  
R. Wagner
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Precipitation Hardening ◽  
Titanium Aluminides ◽  
Activation Parameters ◽  
High Temperature Strength ◽  
Thermal Treatments ◽  
Two Phase ◽  
Carbon Doped ◽  
Titanium Aluminide Alloy

ABSTRACTA two-phase titanium aluminide alloy was systematically doped with carbon to improve its high temperature strength. Solid solutions and precipitates of carbon were formed by different thermal treatments. A fine dispersion of perovskite precipitates was found to be very effective for improving the high temperature strength and creep resistance of the material. The strengthening mechanisms were characterized by flow stresses and activation parameters. The investigations were accompanied by electron microscope observation of the defect structure which was generated during deformation. Special attention was paid on the interaction mechanisms of perfect and twinning dislocations with the carbide precipitates.

High Temperature Strength of Ir/Ir2Y Two Phase Alloys in the Ir-Pt-Y System

2010 ◽  
Vol 654-656 ◽  
pp. 424-427
Author(s):  
Nobuaki Sekido ◽  
Yoko Yamabe-Mitarai
Keyword(s):  
High Temperature ◽  
Binary System ◽  
Precipitation Hardening ◽  
Solid Solution Phase ◽  
High Temperature Strength ◽  
Strengthening Mechanisms ◽  
Solution Hardening ◽  
Two Phase ◽  
Fcc Phase ◽  
High Temperature Compressive Strength

Possibilities of heat resistant alloys based on a C15 Laves phase and an FCC phase have been examined in the Ir-Pt-Y ternary system. Although the Ir solid solution phase (A1) and the Ir2Y phase (C15) are not in equilibrium in the Ir-Y binary system, this equilibrium is attained by small Pt additions to the binary system. High temperature compressive strength of an A1/C15 monovariant eutectic alloy was found to be much lower than that of Ir-15Nb, an Ir based γ/γ' alloy. Low strength of the present alloys is attributed to the absence of effective strengthening mechanisms that operate in the A1 phase; for Y is hardly dissolved within the A1 phase, by which solution hardening and precipitation hardening are not available.

Influence of Si and W Additions on High Temperature Oxidation of γ-α2 Ti-Al Alloys

1996 ◽  
Vol 460 ◽  
Author(s):  
A. Tomasi ◽  
C. Noseda ◽  
M. Nazmy ◽  
S. Gialanella
Keyword(s):  
High Temperature ◽  
Titanium Aluminides ◽  
Isothermal Oxidation ◽  
High Temperature Strength ◽  
Thermal Treatments ◽  
X Ray Diffraction ◽  
Temperature Oxidation ◽  
Oxidation Rates ◽  
Arc Melting ◽  
Bulk Alloys

ABSTRACTTitanium aluminides have potential interest for high temperature applications because of their low density and high temperature strength. In this study the isothermal oxidation behavior in air and in the temperature range 700–850°C of γ-α2Ti-Al bulk alloys with different additions of W (0–9.5 wt.%) and Si (0–5.0 wt.%) was investigated. The samples were prepared by arc-melting starting from pure element powders (99.99%). After thermal treatments, for homogenisation and phase stabilisation, the samples were tested using a thermal analysis apparatus in order to evaluate their oxidation resistance. The oxidation rates show the beneficial effect of the W and Si additions. The growth and adherence of the protective scale on alloys have been investigated in conjunction with detailed oxide scale characterisation using the techniques of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results of the study are used for critical assessment of the oxidation mechanisms leading to the formation of surface layers of different compositions.

Microstructural characterization of plasma-processed Ti-Al metal matrix composites

1989 ◽  
Vol 47 ◽  
pp. 552-553
Author(s):  
M. G. Burke ◽  
M. N. Gungor ◽  
M. A. Burke
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Plasma Processing ◽  
Microstructural Characterization ◽  
High Temperature Strength ◽  
Matrix Composites ◽  
Intermetallic Matrix ◽  
Long Time ◽  
Strength And Stiffness ◽  
Intermetallic Matrix Composites

Intermetallic matrix composites are candidates for ultrahigh temperature service when light weight and high temperature strength and stiffness are required. Recent efforts to produce intermetallic matrix composites have focused on the titanium aluminide (TiAl) system with various ceramic reinforcements. In order to optimize the composition and processing of these composites it is necessary to evaluate the range of structures that can be produced in these materials and to identify the characteristics of the optimum structures. Normally, TiAl materials are difficult to process and, thus, examination of a suitable range of structures would not be feasible. However, plasma processing offers a novel method for producing composites from difficult to process component materials. By melting one or more of the component materials in a plasma and controlling deposition onto a cooled substrate, a range of structures can be produced and the method is highly suited to examining experimental composite systems. Moreover, because plasma processing involves rapid melting and very rapid cooling can be induced in the deposited composite, it is expected that processing method can avoid some of the problems, such as interfacial degradation, that are associated with the relatively long time, high temperature exposures that are induced by conventional processing methods.

Recent Advances in Development and Processing of Titanium Aluminide Alloys

2000 ◽  
Vol 646 ◽  
Author(s):  
Fritz Appel ◽  
Helmut Clemens ◽  
Michael Oehring
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Environmental Stability ◽  
Physical Metallurgy ◽  
Specific Strength ◽  
Wide Range ◽  
Structural Applications ◽  
Strength And Stiffness ◽  
Nickel Base

ABSTRACTIntermetallic titanium aluminides are one of the few classes of emerging materials that have the potential to be used in demanding high-temperature structural applications whenever specific strength and stiffness are of major concern. However, in order to effectively replace the heavier nickel-base superalloys currently in use, titanium aluminides must combine a wide range of mechanical property capabilities. Advanced alloy designs are tailored for strength, toughness, creep resistance, and environmental stability. Some of these concerns are addressed in the present paper through specific comments on the physical metallurgy and technology of gamma TiAl-base alloys. Particular emphasis is placed on recent developments of TiAl alloys with enhanced high-temperature capability.

Localized Oxidation Near Cracks and Lamellar Boundaries in a Gamma Titanium Aluminide Alloy

1994 ◽  
Vol 364 ◽  
Author(s):  
J. Kameda ◽  
C. R. Gold ◽  
E. S. Lee ◽  
T. E. Bloomer ◽  
M. Yamaguchi
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Lamellar Structure ◽  
Oxidation Behavior ◽  
Stress Axis ◽  
Surface Cracks ◽  
Gamma Titanium Aluminide ◽  
Titanium Aluminide Alloy ◽  
Scanning Auger Microprobe ◽  
Local Oxidation

AbstractSmall punch (SP) tests on single grained titanium aluminide (Ti-48 at.%Al) specimens with 12° and 80° lamellar orientations with respect to the tensile stress axis were conducted at 1123 K in air. Brittle cracks readily extended through the thickness in the 80° lamellar structure. In a SP specimen with the 12° lamellar structure load-interrupted at the strain of 0.43%, surface cracks with the depth of 15–25 μm were formed along lamellar boundaries. Local oxidation behavior on partly sputtered surfaces in the load-interrupted 12° lamellar specimen was examined using scanning Auger microprobe (SAM). Oxygen enriched regions were observed near cracks and some lamellar layers. The mechanisms of high temperature oxygen-induced cracking are discussed in terms of the local oxidation near cracks and lamellar boundaries.

Microstructures and High-temperature Strength of Silicide-reinforced Nb Alloys

2000 ◽  
Vol 646 ◽  
Author(s):  
C.L. Ma ◽  
Y. Tan ◽  
H. Tanaka ◽  
A. Kasama ◽  
R. Tanaka ◽  
...  
Keyword(s):  
High Temperature ◽  
Quaternary System ◽  
Eutectic Reaction ◽  
High Temperature Strength ◽  
Quaternary Alloys ◽  
Two Phase ◽  
Practical Applications ◽  
Arc Melting ◽  
Heat Treated ◽  
Very High

ABSTRACTThis article describes the phase stability, microstructures and mechanical properties of silicide-reinforced Nb alloys in Nb-Mo-W-Si quaternary system prepared by arc melting and heat treatment. There exists an equilibrium two-phase field of Nb solid solution (Nbss) and α(Nb,Mo,W)5Si3 in a Nb-rich region of this quaternary system. Alloys in this region have a eutectic reaction of L → Nbss+β(Nb,Mo,W)5Si3 during solidification. The β(Nb,Mo,W)5Si3 transforms to the stable α(Nb,Mo,W)5Si3 at very high temperature. The cast and heat treated hypoeutectic alloys consist of dendritic Nbss, network-shaped Nbss matrix and α(Nb,Mo,W)5Si3. These quaternary alloys exhibit excellent high-temperature strength, although the fracture toughness is still unacceptable for practical applications.

Stress Driven Phase Transformations and Recrystallization Processes in Two-Phase Titanium Aluminide Alloys

2000 ◽  
Vol 652 ◽  
Author(s):  
Fritz Appel ◽  
Michael Oehring
Keyword(s):  
Phase Transformation ◽  
Titanium Aluminide ◽  
Electron Microscope Study ◽  
Phase Boundaries ◽  
Two Phase ◽  
Titanium Aluminide Alloy ◽  
Lower Solubility ◽  
Term Creep ◽  
Titanium Aluminide Alloys

ABSTRACTThe paper presents an electron microscope study of phase transformation and recrystallization in an intermetallic α2(Ti3Al) + γ(TiAl) titanium aluminide alloy, after long-term creep. The mechanisms are closely related to the atomic structure of the α2/γ phase boundaries and are probably driven by a non-equilibrium of the phase composition leading to the dissolution of the α2 phase. The α2 /γ transformation is accompanied by the formation of precipitates, because the γ(TiAl)phase has a significantly lower solubility for interstitial impurities than the α2(Ti3Al) phase.

Evolution of hot rolling texture in β (B2)-phase of a two-phase (O+B2) titanium–aluminide alloy

2008 ◽  
Vol 483-484 ◽  
pp. 551-554 ◽  
Author(s):  
S.R. Dey ◽  
Satyam Suwas ◽  
J.-J. Fundenberger ◽  
J.X. Zou ◽  
T. Grosdidier ◽  
...  
Keyword(s):  
Hot Rolling ◽  
Titanium Aluminide ◽  
Rolling Texture ◽  
Two Phase ◽  
Titanium Aluminide Alloy ◽  
B2 Phase

The Effect of Ni on the High-Temperature Strength of Al-Si Cast Alloys

2011 ◽  
Vol 690 ◽  
pp. 274-277 ◽  
Author(s):  
Florian Stadler ◽  
Helmut Antrekowitsch ◽  
Werner Fragner ◽  
Helmut Kaufmann ◽  
Peter J. Uggowitzer
Keyword(s):  
High Temperature ◽  
Load Transfer ◽  
Elevated Temperatures ◽  
Close Contact ◽  
Sem Analysis ◽  
High Temperature Strength ◽  
Phase System ◽  
Two Phase ◽  
Eutectic Si ◽  
Cast Alloys

In order to investigate the effect of Ni on the high-temperature strength of Al-Si cast alloys, tensile properties of hypoeutectic and eutectic alloys were determined at 250 °C after long-term annealing at test temperature. LOM- and SEM-analysis revealed the existence of Al3Ni-phases in close contact to eutectic Si. It was shown that the strength can be increased by the addition of Ni, though just to a certain level, depending on the fraction of eutectic phase in the alloy. The alloys were considered as a coarse two-phase system where a hardening effect is caused by load transfer to the harder phase, which requires a certain connectivity/contiguity of the latter. The paper describes the extent of contiguity of the eutectic as well as the hard silicon and Al3Ni-phases within the eutectic, and discusses their contribution to an enhanced strength of Al-Si alloys at elevated temperatures.

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