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.

TEM study of boron additions to cobalt aluminide

1988 ◽  
Vol 46 ◽  
pp. 546-547
Author(s):  
Gerald B. Feldewerth
Keyword(s):  
High Temperature ◽  
Turbine Engines ◽  
Major Drawback ◽  
University Of Missouri ◽  
Specific Strength ◽  
Aerospace Applications ◽  
Wide Range ◽  
Ordered Alloys ◽  
The University ◽  
Very High

In recent years an increasing emphasis has been placed on the study of high temperature intermetallic compounds for possible aerospace applications. One group of interest is the B2 aiuminides. This group of intermetaliics has a very high melting temperature, good high temperature, and excellent specific strength. These qualities make it a candidate for applications such as turbine engines. The B2 aiuminides exist over a wide range of compositions and also have a large solubility for third element substitutional additions, which may allow alloying additions to overcome their major drawback, their brittle nature.One B2 aluminide currently being studied is cobalt aluminide. Optical microscopy of CoAl alloys produced at the University of Missouri-Rolla showed a dramatic decrease in the grain size which affects the yield strength and flow stress of long range ordered alloys, and a change in the grain shape with the addition of 0.5 % boron.

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.

Fibrous composites with high melting-point matrices

1970 ◽  
Vol 319 (1536) ◽  
pp. 33-44 ◽  
Keyword(s):  
High Temperature ◽  
Epoxy Resins ◽  
Base Alloy ◽  
High Temperature Strength ◽  
High Melting Point ◽  
Temperature Capability ◽  
Strength And Stiffness ◽  
Nickel Base ◽  
Fibre Matrix ◽  
Selection Of

It is now well established that the strength and stiffness of materials such as epoxy resins and aluminium can be increased by the incorporation of suitable fibres. However, relatively little effort has been made to improve similarly the high temperature strength of materials intended for service above ca . 800°C. This paper is introduced with a general examination of fibre/matrix systems that offer improved high temperature capability over current materials, with reference to gas turbine blade applications. The importance of properties and characteristics that influence the selection of suitable fibre and matrix combinations, for example, density, strength, oxidation resistance and compatibility, are discussed. Experi­mental work on the strength of potentially useful fibres such as refractory metal and alumina filaments, their incorporation into nickel-base alloy matrices using vacuum-casting techniques, and the evaluation of composites are described. In terms of the measured properties and of strength predictions based on fibre and matrix data, the merits and limitations of composites relative to well-developed alloys strengthened by precipitation mechanisms are considered.

Modelling the Effect of Microstructural Randomness on the Fracture of Composite Laminates with Stochastic Cohesive Zone Elements

2009 ◽  
Vol 417-418 ◽  
pp. 13-16
Author(s):  
Zahid R. Khokhar ◽  
Ian A. Ashcroft ◽  
Vadim V. Silberschmidt
Keyword(s):  
Cohesive Zone ◽  
Composite Laminates ◽  
Composite Structures ◽  
Laminated Composite ◽  
Specific Strength ◽  
Laminated Composite Structures ◽  
Structural Applications ◽  
Fibre Reinforced Polymer ◽  
Strength And Stiffness ◽  
Cohesive Zone Elements

Fibre reinforced polymer composites (FRPCs) are being increasingly used in structural applications where high specific strength and stiffness are required. The performance of FRPCs is affected by multi-mechanism damage evolution under loading which in turn is affected by microstructural stochasticity in the material. This means that the fracture of a FRPC is a stochastic process. However, to date most analyses of these materials have treated them in a deterministic way. In this paper the effect of stochasticity in FRPCs is investigated through the application of cohesive zone elements in which random properties are introduced. These may be termed ‘stochastic cohesive zone elements’ and are used in this paper to investigate the effect of microstructural randomness on the fracture behaviour of cross-ply laminate specimens loaded in tension. It is seen from this investigation that microstructure can significantly affect the macroscopic response of FRPC’s, emphasizing the need to account for microstructural randomness in order to make accurate prediction of the performance of laminated composite structures.

The effect of thermal exposure on precipitation of Ti3Al(C,N) in Ti-48Al-IV-0.2C

1992 ◽  
Vol 50 (1) ◽  
pp. 22-23
Author(s):  
W.T. Donlon ◽  
W.E. Dowling ◽  
C.E. Cambell ◽  
J.E. Allison
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Weight Ratio ◽  
Thermal Exposure ◽  
Treatment Temperature ◽  
Field Samples ◽  
Structural Applications

Titanium aluminides are attractive candidates for high temperature structural applications because of their high strength to weight ratio at elevated temperatures. The microstructure of these alloys consists of γ-TiAl (distorted L10 structure) , plus α2-Ti3Al (ordered DO19 structure). Varying the heat treatment temperature and cooling rate of these alloys alters the volume fraction and distribution of the γ and α2 phases. This has significant effects on the room temperature ductility. In addition, precipitation of carbides has been observed during high temperature exposure. The effect of these precipitates on the mechanical properties has yet to be determined.Figure 1 shows the general microstructure that was used for this investigation. TEM foils were prepared by electropolishing using 5% perchloric, 35% 1-butanol, 60% methanol at -40°C. No precipitates were found following heat treatment in the γ+α phase field. Samples approximately 20 mm square were thermally exposed to temperatures between 625° and 1000°C for times between 1 and 2000 hours.

Orientation and morphology variants of the α2 phase in B2 parent matrix in a super α2 titanium aluminide alloy

1990 ◽  
Vol 48 (4) ◽  
pp. 980-981
Author(s):  
Lawrence H. Edelson
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Continuous Phase ◽  
High Temperature Phase ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Crystal Lattices ◽  
B2 Phase

Titanium aluminides are potential low density, high stiffness, high-temperature materials that use ordered crystal lattices to retain strength at elevated temperatures. The super α2 system is based on the hexagonal DO19 α2 phase (Ti3Al), but has sufficient β (BCC, high temperature phase) stabilizing elements (Nb, V and Mo) so that a continuous B2 ordered cubic phase is retained to room temperature. Transmission electron microscopy (TEM) images and selected area electron diffraction (SAD) patterns were used to analyze the crystallography and morphology of the α2 phase that forms when 100% B2 phase is aged at 1000°C for one hour. TEM is the only technique that provides both precise crystallographic and morphological analysis of the phase transformation.The microstructure produced from 100% B2 material, formed by ice brine quenching the super-α2 alloy from 1250°C, by aging at 1000°C for 1 hr is shown in the scanning electron micrograph in Figure 1. The dark discontinuous phase is acicular α2, while the light continuous phase is the ordered cubic B2 phase.

Static and Dynamic Strain Ageing in Two-Phase Gamma Titanium Aluminides

2000 ◽  
Vol 646 ◽  
Author(s):  
U. Christoph ◽  
F. Appel
Keyword(s):  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Deformation Behaviour ◽  
Dynamic Strain ◽  
Dynamic Strain Ageing ◽  
Two Phase ◽  
Fast Kinetics ◽  
Strain Ageing ◽  
Wide Range ◽  
Dislocation Pinning

ABSTRACTThe deformation behaviour of two-phase titanium aluminides was investigated in the intermediate temperature interval 450–750 K where the Portevin-LeChatelier effect occurs. The effect has been studied by static strain ageing experiments. A wide range of alloy compositions was investigated to identify the relevant defect species. Accordingly, dislocation pinning occurs with fast kinetics and is characterized by a relatively small activation energy of 0.7 eV, which is not consistent with a conventional diffusion process. Furthermore, the strain ageing phenomena are most pronounced in Ti-rich alloys. This gives rise to the speculation that antisite defects are involved in the pinning process. The implications of the ageing processes on the deformation behaviour of two-phase titanium aluminide alloys will be discussed.

Composition and microstructure of a nickel-base superalloy, UDIMET 720

1989 ◽  
Vol 47 ◽  
pp. 280-281
Author(s):  
k.L. More ◽  
M.K. Miller
Keyword(s):  
High Temperature ◽  
Grain Boundaries ◽  
Analytical Electron Microscopy ◽  
Grain Boundary Sliding ◽  
Nickel Base Superalloy ◽  
High Temperature Strength ◽  
Phase Form ◽  
Wide Range ◽  
Nickel Base ◽  
Udimet 720

A wide range of nickel-base superalloys are currently used for land- and marine-based turbines. Small amounts of carbon and boron are added to improve the high temperature mechanical properties of these alloys. During a standard heat treatment, large carbides evolve at the grain and twin boundaries and small, intragranular precipitates of the γ′phase form. It has been proposed that the carbides improve the high temperature strength by inhibiting grain boundary sliding. The role of boron is, however, not fully understood. Decker suggests that boron stabilizes the γ′ precipitates and prevents the formation of denuded zones at the grain boundaries thus inhibiting microcrack formation at transverse grain boundaries. The purpose of this study was twofold; to characterize the microstructure of Udimet 720 using atom probe field-ion microscopy (APFIM), analytical electron microscopy (AEM), and secondary ion mass spectroscopy (SIMS) and to determine if boron and carbon segregate to boundaries and γ/γ′interfaces. This is a continuation of work started by Burke et al.

Dislocation structures in titanium aluminides deformed at 815°C

1990 ◽  
Vol 48 (4) ◽  
pp. 984-985
Author(s):  
W.T. Donlon ◽  
W.E. Dowling ◽  
J.E. Allison
Keyword(s):  
High Temperature ◽  
Automobile Industry ◽  
Titanium Aluminides ◽  
Thermomechanical Processing ◽  
High Strength ◽  
Fatigue Properties ◽  
Major Drawback ◽  
Cast Material ◽  
Heat Treated ◽  
Structural Applications

Ordered (L10) intermetallic γ-TiAl alloys are candidates for high temperature structural applications in the automobile industry because of their low density and high strength at elevated temperature. The major drawback of these materials is their low ductility at ambient temperature. Improvements in low temperature ductility may be achieved without sacrificing the desired high temperature performance by optimizing the microstructure through thermomechanical processing. This investigation measured the tensile and fatigue properties of an “as-cast” and cast plus heat treated Ti-48A1-1V-0.2C (at%) alloy at 25 and 815°C.The microstructure of both samples consisted of primary γ grains with an average intercept size of 100 μm, and regions of a γ matrix with α2 lathes. The vol% of the primary γgrains was 40% and 85% in the “as-cast” and cast plus heat treated samples, respectively. Figure 1 shows the microstructure of the “as-cast” material.

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