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The energetics of interstitial oxygen (O) in β-Ti and β-Ti–X alloys (X = 3 d -, 4 d -, or 5 d -transition elements) was studied using first principles methods based on density functional theory (DFT). For small concentrations of X (=1.8 at.%), the insertion energy E ins X for interstitial oxygen along the three transition series follows a similar trend: it first decreases reaching a minimum between Groups 4 and 5 elements, then increases to reach a maximum for Group 8 elements (Fe, Ru, Os) before decreasing further. Except for the early transition elements, the interaction between X and O is repulsive. The lattice strain is found to be the dominant contribution to the insertion energy and can explain the trends along the three series. Using the calculated energetics and the lattice strain due to interstitial oxygen, a model is constructed to determine trends in maximum oxygen solubility C O, max in β-Ti–X alloys. The C O, max X decreases in the middle of each transition series.

The mixing enthalpy Δ H mix ( x ) of body-centered cubic (BCC) β-Ti with transition elements was calculated using first-principles methods based on density functional theory (DFT). The solid solution effect was treated by two different approaches, viz . special quasi-random structures (SQS) and the parametric method. The SQS- N method uses direct DFT to calculate energy of structures containing N atoms which approximate the correlation of an ideal solid solution up to some distance, whereas the parametric method employs a polynomial representation for Δ H mix ( x ) and the coefficients are calculated using DFT. Comparison of the two methods shows fair agreement for most alloys though differences as high as 40% can also be seen among some of the alloys. The trends in Δ F mix ( x ), obtained by adding entropy contribution from ideal solution model to Δ H mix ( x ) for 3d-, 4d- and 5d-transition series were analyzed in terms of e / a , the ratio of number of valence electrons to atoms. The early transition elements, between Group 4–7, was found to have very small Δ F mix ( x ) over a wide range of concentration. Stability of the alloys is analyzed by combining Δ F mix ( x ) with Hume-Rothery rules.

A technique to evaluate grain boundary fracture strength of metallic materials was developed. Coincident site lattice (CSL) boundaries were prepared by diffusion-bonding of oriented two single-crystal Ni–20Cr pieces. Microtensile specimens were fabricated across the CSL boundaries by femtosecond laser machining. Due to the highly ductile character of Ni–20Cr, notches were machined along the grain boundaries to initiate grain boundary fracture. The microtensile tests at room temperature demonstrated that Σ3(1 1 1) boundary was the strongest of all the CSL boundaries examined.

Nanostructured and ultra–fine-grained metals and alloys are becoming of engineering interest. However, little is known about the influence of grain refinement on fatigue crack behavior. In this study, fatigue crack growth behavior and the key microstructural features controlling the fatigue fracture in nanocrystalline and ultra–fine-grain nickel alloys, processed using different techniques, were investigated. White light interference microscopy as well as the combination of atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) were used to characterize the fractured surfaces of the metals. The role of grain size on the fatigue crack growth resistance and the effect of fracture surface roughness on the crack growth rate were evaluated. The combination of AFM and UFM is presented as a complementary tool to scanning electron microscopy in the fractography of metals.

Using first-principles density functional calculations, we determine effects of environmental embrittlement on Ni/Ni 3 Al interfaces. We evaluate relative stability of sites for occupation of O, H and N and estimate their effects on cleavage energies. We find that O has the most deleterious effect on interface embrittlement, followed by N and H. Changes in bonding near dopant O arising from its strong ionic character, evident in electron localization function, are responsible for the corresponding large reduction in the cleavage energy.

Crack progression during compressive sustained-peak low-cycle fatigue (SPLCF) was examined in vapor phase aluminide coated single-crystal Ni-base superalloy Rene N5. Strain-controlled tests with a 120-second hold at compression were conducted at 1366 K (1093 °C) with A = –1 (R = –∞) and 0.35 pct total strain range, and were terminated at selected fractions of predicted life. Crack lengths on the surface and crack depth in longitudinal sections were examined for each specimen. All cracks appeared to have initiated at the coating surface. Failed specimens showed that cracks initially grew on (001), perpendicular to the stress axis, and then deflected to other crystallographic planes. Interrupted test specimens showed crevices initiated on the coating surface at less than 10 pct of the predicted life. The depths of crevices into the coating increased with cyclic exposure, but they did not penetrate into the substrate through the interdiffusion zone (IDZ) until about 80 pct of predicted life. Stress relaxation during compressive hold results in residual tension upon unloading. These results suggest that improving creep resistance of the substrate alloy and developing a coating system that can delay crack penetration into the substrate are keys for improved SPLCF life.

A model capable of characterizing oxidation-assisted low-cycle fatigue is described. It involves the following steps. After a few strain cycles, because of creep, a tensile stress develops during the de-straining phase of the cycle. This stress opens cracks present in the material and exposes the surfaces to the atmosphere, causing thermally grown oxide (TGO) growth. Dilatation takes place upon converting the alloy to oxide, with an associated strain rate that induces a compressive growth stress. Thereafter, during the re-straining phase of the cycle, transverse extension of the substrate induces in-plane tension in the TGO, which “pushes” the TGO into the substrate along the crack front. Finite element simulations of this process have been presented that predict crack growth per cycle, da / dN , comparable with experimental measurements. Trends in da / dN with the TGO dilatation rate and the creep strength of the superalloy have been elucidated.

The influence of severe thermomechanical treatment via multiple forging on the formation of a nanocrystalline (NC) structure in bulk samples of Alloy 718 and ATI 718Plus has been investigated. It was observed that a step-wise decrease of processing temperature from 950 down to 575°C allowed the refinement of the initial coarse grain structure to a NC state. Investigations of structural changes in the deformed samples have shown that extending the temperature interval of dynamic recrystallization to low homologous temperatures resulted in the formation of a fine-grained recrystallized structure. The temperature of NC structure formation in ATI Alloy 718Plus was 50-100°С higher than that required for alloy 718. This was due to the presence of the additional γ′-phase, which increased the recrystallization temperature. This decreased the total strain required to produce NC structure, as compared with Alloy 718. It was observed that increasing the total strain and decreasing temperatures step-wise during deformation via multiple forging resulted in a uniform structure across the cross-section of the samples. The room temperature mechanical properties of the investigated alloys with various grain sizes are also compared.

This article attempts to relate ultrasonic second harmonic generation to dislocation structures in fatigued materials. By focusing on the fact that asymmetric dislocation motion is required to generate the second harmonic, a theoretical derivation of the non-linearity parameter (ratio of the amplitude of second harmonic to square of the amplitude of the fundamental) from dislocation pile-ups is presented. In order to verify the theory, harmonic generation was measured along a failed fatigue sample of DA718, a nickel base superalloy that exhibits planar slip, and consequently dislocation pile-ups. TEM studies along the length of the failed fatigue sample revealed a banded dislocation structure, composed of pile-ups near the fracture zone and a sparse dislocation network closer to the grip region. The non-linearity parameter was found to increase by between 90% and 140% from the grip region to the fracture zone and this correlated well with the calculations based on theoretical expressions derived here. � 2007 Elsevier Ltd. All rights reserved.

This paper discusses the development of a novel processing route to produce ultra finegrain bulk alloy forgings; the microstructural response of these forgings to thermal exposure; and the comparison of mechanical properties to those from conventionally processed material. A Ni- 20Cr [wt%] alloy was processed by near-isothermal multi-axis forging to a grain size of approximately 1 μm. A heat-treatment study over the range 900 to 1200°C was conducted to determine the resultant grain size as a function of time and temperature. Tensile properties were measured at room temperature, 500°C, and 930°C. High-cycle fatigue properties were measured at room temperature. The room-temperature tensile strength was approximately 2.5 times greater than that of conventionally processed Ni-20Cr. Fatigue data showed that the room-temperature highcycle fatigue run-out stress was greater than 100% of the yield stress.

The mechanical behavior and microstructure evolution of a stable β, metastable β, and β-rich titanium alloys during hot deformation in both β and α/β phase fields were studied. The effects of thermomechanical processing and alloy content on final grain size and microstructure homogeneity in the alloys are given. The processing windows in both β and α/β phase fields for the formation of homogeneous microstructures with grain sizes down to submicron values are discussed. Isothermal multiple-step forging was used to produce the billets of a β-rich alloy with homogeneous fine-grained microstructure and low ultrasonic noise.

FEM analysis was used to study the interactions between die friction, backpressure and strain rate sensitivity during equal channel angular pressing. One of the key findings is that strain rate sensitivity causes strain redistribution, resulting in higher equivalent strains and a substantial component of compression in the workpiece. This compression gives rise to effects such as lift-off of the leading end of the workpiece from the die bottom and improved die fill. Friction has different effects at room and elevated temperatures. While a moderate amount is beneficial at room temperature, friction has a detrimental interaction with strain rate sensitivity at high temperature. Backpressure, though largely beneficial, is shown to have negative effects when combined with friction and a high strain rate sensitivity.

A columnar-grain variant of single-crystal RENE N4 has been directionally solidified (DS) over a range of conditions in order to assess the possible benefits of the use of liquid metal-enhanced cooling for large cross-sectional castings. Castings were solidified at a rate of 2.5 mm/min using conventional radiation cooling and at rates between 2.5 and 8.5 mm/min using liquid-metal cooling (LMC) with tin as a cooling medium. Thermocouples inserted in the casting directly measured thermal gradients during solidification. The LMC process exhibited higher gradients at all withdrawal rates. The higher thermal gradients resulted in a refined structure measurable by the finer dendrite-arm spacing. Additionally, the conventionally cast material exhibited several freckle-type defects, while none were observed in the liquid-metal-cooled castings.

The thermal expansion behavior of three near-stoichiometric variants of ruthenium aluminide (RuAl) has been investigated. The coefficient of thermal expansion (CTE) varied between 5.5 × 10 −6 /K and 11 × 10 −6 /K in the temperature range from 400 to 1773 K. The behavior of RuAl is compared to that of other high temperature B2 intermetallics with emphasis on the use of RuAl as a bond coat material within a thermal barrier coating system.

Roll forming is a novel technique for manufacturing aircraft engine turbine disks. This paper describes an assessment of the technical and economic viability of roll forming. The capabilities of roll forming will also be compared to those of hot die forging. It was found that there is an economic pay-off for roll forming complex, low production-volume parts of nickel and titanium alloys due to a higher material yield and less expensive tooling. Roll formed disks of high temperature nickel and titanium alloys were evaluated for dimensional control, metallurgical structure, mechanical properties, and ultrasonic characteristics. The results from complex shapes indicate that disks can be produced with uniform microstructures and excellent properties. The roll formed titanium disks possessed α–β-Ti microstructures with a mean grain size of 5–10 μm. Electron back-scattering pattern analysis and inverse pole figure analyses indicated that the disks possessed essentially no crystallographic texture. Samples machined from axial, radial, and tangential sections of disks were tested in order to evaluate any anisotropy in mechanical properties of the disks.

The ultrasonic behavior of titanium alloy Ti6242 was determined as a function of ultrasonic frequency and material microstructure. The signal-to-noise ratio for synthetic flaws machined in the Ti6242 blocks was strongly influenced by microstructural condition, particularly as it was defined by electron backscatter diffraction pattern (EBDP) analysis. Ti6242 blocks with a microstructure consisting of uniform, fine, texture-free αTi particles had signal-to-noise ratios about 20 dB greater than blocks with microstructures consisting of colonies of crystallographically aligned αTi particles.

The high cost of aerospace alloys and their components makes them prime candidates for net-shape manufacturing techniques. Conventional processes for manufacturing disk components include hammer, hot die, and isothermal forging. This paper will examine the potential of a revolutionary approach for the manufacture of aircraft engine disks, superplastic roll forming. The process of superplastic roll forming, developed at the Institute for Metals Superplasticity Problems, Ufa, employs pairs of small opposed rollers to shape a cylindrical workpiece into a complex axisymmetric shape by simultaneously adjusting the roll gap and by moving the rolls radially outward on the workpiece while it is rotated about its axis of symmetry. Both the workpiece and the rolls are maintained at temperatures close to the beta transus. This paper will describe metallurgical evaluations of superplastically roll formed disks of alloy VT25. The evaluations of the disks included microstructure, crystallographic texture, heat treatment response, tensile strength, stress rupture resistance, and ultrasonic characteristics. The disk microstructures were found to be uniform and without any strongly textured colonies. Mechanical properties of the roll formed VT 25 were compared with those of Ti-6242S, IMI834, and conventionally forged VT25. The RF VT25 disk was found to possess low ultrasonic noise and high inspectability, which provided an increase in signal to noise for synthetic flaws.

Nitrogen-rich inclusions can lead to a reduction in fatigue life of highly stressed titanium-alloy components (found in the compressor sections of power generation gas turbines, turbine sections of power generation steam turbines, wing sections of aircraft air frames, and compressor and fan sections of aircraft jet engines, for example). It is the ”crack starting” nature of the nitrogen-rich inclusions that is the problem, not the presence of nitrogen in the system, per se. This paper covers the theory and laboratory experiments used to evaluate ESR (electro-slag refining) as an alternative technique for rapid dissolution of nitrogen-rich inclusions in titanium and titanium alloys. Five variations of melt rate, slag temperature and inclusion type were evaluated. One variant showed complete dissolution of the inclusions. Several of the other variants showed partial dissolution of the inclusions. The kinetics were observed to occur at a rate 100 to 1000 times faster than the rate of dissolution of nitrogen-rich inclusions by immersion in liquid titanium.

This paper describes measurements of the dissolution rate of nitrided Ti sponge and monolithic TiN rod in molten Ti-6242. The dissolution rate is described in terms of an interface recession rate that was 2.2 μm/s for a Ti-6242 temperature of 1725°C and dissolution times between 1 and 100 min. Similar dissolution rates were measured for nitrided sponge and monolithic rod. This report also describes the microstructural and chemical interdiffusion phenomena that occur during dissolution of solid δTiN in molten Ti-6242. There is a N-containing solid αTi layer and a N-solidified βTi layer between the solid δTiN and liquid Ti-6242 during dissolution. Microprobe measurements indicate that diffusion of Al, Zr, Sn and Mo into δTiN did not occur. Steep N concentration profiles were observed in the αTi layer. Al, Zr, Sn and Mo were observed in the N-solidified βTi layer, but their concentrations were depleted with respect to Ti-6242. The N-solidified βTi layer contained

Motivated by the vital role played by grain boundaries and interfaces in Ni-based superalloys in influencing mechanical properties such as creep rupture strength, fatigue crack growth rates and resistance towards environmental embrittlement, we use first-principles simulations to estimate fracture strengths of Ni Σ3(111) grain boundary, Ni Σ5(012) grain boundary, Ni/Ni 3Al interfaces and Ni/boride interfaces through determination of their work of separation. We find that Ni/boride interfaces have higher fracture strengths than the other commonly occurring interfaces in Ni-alloys, such as NiΣ5 & NiΣ3 grain boundaries and coherent Ni/Ni 3Al interfaces, and are less susceptible to oxygen-induced embrittlement. Our calculations show how the presence of Mo at Ni/M 5B3 (M = Cr, Mo) interfaces leads to additional reduction in oxygen-induced embrittlement. Through Electron-LocalizationFunction based analyses, we identify the electronic origins of effects of alloying elements on fracture strengths of these interfaces and observe that chemical interactions stemming from electronegativity differences between different atomic species are responsible for the trends in calculated strengths. Our findings should be useful towards designing Ni-based alloys with higher interfacial strengths and reduced oxygen-induced embrittlement.

The ultrasonic properties of titanium-nitrogen-oxygen inclusions within Ti-6A1-4V (Ti64) blocks were measured and related to inclusion chemistry. Sound velocities were measured on Ti-N-O alloy samples that had been prepared by powder metallurgy and ingot-melting techniques. The contributions to sound velocity from oxygen and nitrogen contents were determined. Then, Ti64 blocks were hot isostatic pressing (HIP) bonded to contain inclusions of the Ti-N-O alloys. The signal-to-noise ratios of reflections from uncracked inclusions were found to be an increasing function of inclusion interstitial content and were related to changes in sound velocity with inclusion chemistry. Measurements were made of the reflectance of titanium-nitrogen inclusions in titanium and Ti64.

Low cycle fatigue tests were conducted at 482 °C (900 °F) on forgings and extrusions of a rapidly solidified powder metallurgy titanium base alloy with and without rare earth additions. The variables studied were process temperature and heat treatment. Rare earth dispersions reduced fatigue life, and fracture surfaces indicated internal fatigue crack initiation at rare earth particles.

The paper considers the scientific basis of a new methodological approach for processing bulk and sheet nanostructured semi-finished products from nickel base alloys 718 and 718Plus. This approach involves carrying out severe thermo-mechanical processing (STMP) using primarily schemes of multiple isothermal forging (or forging followed by rolling) at temperatures decreasing gradually from (0.9-0.8)Tm to (0.6-0.5)T m. Such processing results in a step-by-step structure refinement: a coarse-grained macroduplex type structure transforms to a microduplex one (d=1-3μm) and then to a nanoduplex structure (d=0.5–0.05μm). The paper considers examples of production of complex profile turbine engines components from materials with a microduplex type structure and shows the possibility for applying semi-finished products with a nanoduplex type structure in advanced manufacturing procedures of pneumatic forming and pressure welding under low temperature superplasticity (LT SP) conditions.

The requirements for greater aircraft-engine performance, greater thrust-to-weight ratios, and greater fuel efficiency have resulted in significant increases in turbine gas-path temperatures. Present-day aircraft engines have combustion-gas temperatures well in excess of the melting temperatures of the airfoil alloys, and therefore rely on sophisticated cooling methods to keep the alloys solid. Both materials and airfoil blade designs have evolved to sustain these increasing demands (Bewlay et al., 1999a; Subramanian et al. 1996). Advances in high-temperature materials have had a major impact on the efficiency of gas-turbine engines, so that currently superalloys provide a maximum surface temperature capability of*1150 8C. The evolution in HPTB (high pressure turbine blade) cooling technology is illustrated schematically in Figure 1. In the 1960s, equiaxed-grain Ni-based superalloys were cooled with radial cooling passages and with film cooling holes at the leading and trailing edges to reduce the interaction with the combustion gases. This advance over uncooled hardware improved blade durability, and allowed an increase in turbine inlet temperatures to greater than 1100 8C (2000 8F). Once cooling of hardware became routine, and the ability was developed to cast airfoils with more complex cooling schemes, these gains in cooling effectiveness were coupled with improved investment casting technology, and with the introduction of directional solidification for the production of HPTBs with either columnar or single-crystal microstructures. In the past decade, the potential of new alloys strengthened with intermetallic compounds with low densities, high elastic moduli, and high melting ranges (Dimiduk et al., 1993; Subramanian et al., 1997) has been explored. Intermetallic-based compound materials, such as Nb or Mo silicides, have been combined with metallic second phases in order to generate composites with a combination of attractive hightemperature properties and acceptable low-temperature properties. Nb-silicide based in-situ composites with Nb3Si and/or Nb5Si3 silicides have been shown to have great potential because of their attractive balance of highand low-temperature mechanical properties (Mendiratta et al., 1993; Bewlay et al., 1996, 1997). These materials have the potential to surpass the performance of Ni-based superalloys. This chapter will describe directional solidification and single-crystal technologies, with particular consideration to their role in present and future aircraftengine applications. Areas that will be covered include Ni-based superalloys strengthened by Ni3Al, DS eutectics of Ni-based superalloys, and DS Nb-silicide-based in-situ composites. This chapter will compare the role that Ni-based superalloys and Nbsilicide composites play in improving the performance of gas-turbine engines. Microstructures, phase compositions, and mechanical behavior will be reviewed.

The mechanical behavior of RuAl-base intermetallic alloys with alloying additions of boron, niobium and platinum has been investigated. Compression tests have been performed at room temperature and 973 K. While the addition of alloying elements results in solid solution strengthening, the strain-rate sensitivity and the activation volumes do not show a significant variation, thereby suggesting that the macroscopic flow mechanisms are not strongly affected. Deformation substructure analysis of the niobium-containing alloy shows the presence of and dislocations, while the platinum-containing alloy additionally contains a significant density of dislocations.

This paper will describe the refinement of a coarse-grained alloy 718 microstructure to microcrystalline (MC), submicrocrystalline (SMC), and nanocrystalline (NC) structures by high-strain plastic deformation. Dynamic recrystallization occurs during high-strain hot plastic deformation leading to the formation of an MC structure with a grain size of 1-4 pm. The 6 phase precipitated as plates, and during deformation, these plates were broken up into smaller particles. These particles take the form of ellipsoids located mainly at the triple junctions of the recrystallized grains. A SMC structure was formed in alloy 7 18 during severe plastic deformation in the temperature range 0.67-0.60 T,. During dynamic and static recrystallization, the MC structure transformed to the SMC structure, and 6-phase plates precipitated uniformly throughout the matrix. The size of these precipitates was similar to the matrix grain size (0.2-0.5 pm). Further reduction in the processing temperature to 0.5 T, provided additional refinement of the microstructure to a grain size of less than 0.1 pm. The formation of NC structures in alloy 718 by cold severe plastic deformation (0.18 T,) was also studied. The microstructure evolution during combined torsion and compression was examined. With increasing strain, a cellular structure was formed, which was then refined to a granular structure with a grain size of 30-40 nm, with high angle grain boundaries and a high level of residual stress within the grains. The influence of the initial grain size on deformation mechanisms during superplastic deformation of alloy 718 was also studied. For grain sizes of 0.1-0.08 pm, superplasticity (6=350%, m=0.37) was observed at a temperature of 600°C and a strain rate of 1.5~ ~O-~s-l.

This paper will describe the generation of micro- and sub-microcrystalline structures in two Ni-based alloys that are typically strengthened by phases, such as γ′ and γ″+δ. The relationship between the superplastic behavior and microstructure will be discussed. High strain deformation processing in the temperature range of 0.9 Tm to 0. 6Tm results in reduction of the initial coarse-grained structure (>100 µm) to a range of structures including microcrystalline (MC) (grain size

During the diffusion bond process, parts are heated to about one half the absolute melting point, pressed together at a stress below the macroscopic yield stress, and conditions maintained for a specified time. Bonding proceeds through three steps: local yielding of contact points upon initial application of stress; creep deformation on the bonding plane to yield discontinuous voids; and closure of voids by vacancy diffusion. Presently, nondestructive evaluation emphasizes detection of residual unbonds and voids, from incomplete void isolation or closure.

In the work described subsequently, synthetic “hard alpha” inclusions have been fabricated within Ti-6A1-4V (Ti64) forgings. Several compositions of synthetic hard alpha were made by arc melting Ti sponge and TiN powder. Small solid cylinders of the titanium-nitrogen alloys were made by electro-discharge machining (e. d. m.) the arc-melted ingots to diameters of 0.031, 0.047, 0.062, and 0.078 inches, respectively, with heights equal to the respective diameter. Sets of eight or sixteen each identical cylinders were hot isostatic press (HIP) bonded within forged Ti64 blocks to yield uncracked inclusions with sharp interfaces with the Ti64 matrix. Detectability of the uncracked hard alpha was estimated as a function of flaw size, orientation, and nitrogen content from ultrasonic signal to noise ratios determined from C-Scan images of the blocks. Relationships of detectability to physical properties of hard alpha, and methodologies of signal to noise determinations are discussed.

First-principles density functional theory (DFT) calculations were used to determine decohesion properties of Σ5(012) grain boundary of Ni with dopants B, C, S, Cr, and Hf. The relative stability of sites was evaluated and cleavage energies were calculated. Electronic structure was used to understand these properties in terms of changes in bonding with addition of dopants. It was found that strengthening of the Ni grain boundary results from Hf, B, and Cr doping. In contrast, the grain boundary weakens with S and C doping. These results should be useful in the design of next-generation nanostructured Ni-based alloys with improved mechanical behavior.

Control of furnace atmosphere is a key factor in the use of silica-bonded alumina shell molds for the directional solidification of eutectic superalloys reinforced with tantalum monocarbide whiskers. The use of a furnace atmosphere which is simultaneously oxidizing to aluminum in the eutectic alloy and reducing to silica phases in the mold results in the formation of an alumina barrier layerin situ at the metal/mold interface and an absence of silica phases in the mold region adjacent to this barrier layer. The presence of this microstructure permits castings of eutectics at metal temperatures up to 1750°C.

Superalloy eutectics strengthened with monocarbide whiskers are highly anisotropic in strength. Mechanical behavior transverse to the growth axis is governed largely by the fracture resistance of the matrix grain boundaries. While the matrices of these eutectics are essentially columnar grained superalloys, there are significant differences between d.s. superalloys and superalloy-monocarbide eutectics. These differences arise, in part from different solidification processes and from the alloying limitations in eutectic systems.

In the aligned Ni-MC eutectic alloys being developed for jet engine blade applications, the fibers are considered to be Tac, Tic, etc. In fact, these fibers will contain Cr, Mo, W and possibly other elements as substitutions for the “M” constituent, and often will not be stoichiometric. Quantitative chemical analysis of fibers is difficult because of their size. However, lattice parameter measurements can be used to learn much a out the carbide chemistry and stoichiometry. Results will be described in detail for fibers extracted from simple Ni-TaC, Ni,Cr-TaC and Ni,Cr,AI-Tac systems. In addition, experiments on mixed (Ta,V)C and (Ta,Ti)C carbides will be discussed. Carbide lattice parameters can be understood in terms of the free energies of formation of the various carbides.

Melt spinning has been carried out on binary TiAl alloys at three Ti/Al ratios. Antiphase domains were observed in one ribbon specimen, but no significant disordering was induced by the rapid solidification as indicated by X-ray and electron diffraction analyses. Bending tests of both the ribbons and the consolidated counterparts showed a decrease in ductility with increasing Al concentration. This compositional effect can be correlated with the TiAl tetragonality (the c/a ratio) as well as the grain structure.

Titanium alloys containing alpha matrices with various rare earth compound dispersions were prepared by melt extraction. The melt extracted material was HIPped, extruded, and thermally exposed to yield various microstructures including transformed beta and equiaxed alpha. Tensile and creep tests were conducted on material in the different microstructural conditions. Trends in mechanical behavior as a function of alloy chemistry and process history are discussed. The alloys with a transformed beta microstructure had superior creep resistance. Alloys containing dispersoids had better tensile ductilities compared with those which did not contain a dispersoid.Portions of this work were carried out under Air Force Contract F33615-83-C-5034.