Influence of rare-earth metals on the high-temperature strength of Ni<Subscript>3</Subscript>Al-based alloys

The influence of the content of reaction- and surface-active alloying elements (rare-earth metals (REMs)) and the method of their introduction into cast high-temperature γ′-Ni₃Al-based intermetallic alloys, which are thermally stable natural eutectic composites, on their structure-phase state and the mechanical properties is studied. The life of low-alloy heterophase γ′ + γ cast high-temperature light Ni₃Al-based alloys is shown can be increased at temperatures exceeding 0.8T _m (T _m is the melting temperature of Ni3Al) due to additional stabilization of the single-crystal structure of these alloys with submicron and nanometer-sized particles of the phases formed by refractory and active REMs. It is also shown that stage-by-stage fractional introduction of all components into alloys during vacuum induction melting with allowance for their reaction activities (most refractory metals are introduced in the form of low-melting-point master alloys at the first stage of vacuum induction melting, and lanthanum is introduced with a master alloy in the optimal contents of 0.1–2 wt % into the charge of VKNA-1V and VKNA-25 alloys at the final stage) leads to the formation of a modified structure stabilized by nanoprecipitates of nickel and aluminum lanthanides and the phases formed by refractory metals. This method increases the life of VKNV-1V-type alloys (0.5 wt % Re) at 1000–1200°C by a factor of ∼1.7 and that of VKNA-25-type alloys (1.2 wt % Re and Co) by a factor of ∼3.     

Alloy design of FeMnSiCrNi shape-memory alloys related to stacking-fault energy

The stacking-fault energy (γ _sf ) of iron-based shape-memory alloys was calculated by the extended dislocation-node method. The results show that Ni and Mn increase the γ _sf of the alloys with an austenite structure, while Cr and Si decrease it. An expression relating the alloying elements of Ni, Cr, Mn, and Si to the γ _sf of the alloys is established. Moreover, in terms of the γ _sf values of the alloys and the Schaeffler diagram, the alloy design of iron-based shape-memory alloys is carried out. It is found that the alloy having the lowest γ _sf has the best shape-memory effect (SME), with a martensite transition temperature (M _s ) being a little lower than ambient temperature. The corresponding composition of the alloy is located in the γ-phase zone near the phase line between the γ and γ+ε phase zone and the triple point of α+γ+ε in the Schaeffler diagram.     

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

Two powder metallurgy nickel-base turbine disk alloys, RENE’95* and KM4, were studied for strength and deformation behavior at 650 °C. Two classes of microstructures were investigated: unimodal size distributions of γ′ precipitates with particle sizes ranging from 0.1 to 0.7 μm and commercially heat-treated structures with bimodal or trimodal size distributions of γ′ precipitates. The strength and deformation mechanisms were heavily influenced by the microstructure. In both alloys, deformation during compression tests consisted of a combination of a/2〈110〉 antiphase boundary (APB)-connected dislocation pairs and a/3〈112〉 partials creating superlattice intrinsic stacking faults (SISFs). In unimodal alloys, the fault density increased with decreasing particle size and decreasing strain rate. These trends, observed in compression testing, are consistent with earlier studies of similar alloys, which were tested in creep. As the γ′ size was reduced, the nature of the faults changed from being isolated within single precipitates to being extended across entire grains. Commercially heat-treated alloys, containing a bimodal distribution of γ′ particles, exhibited significantly more faulting than unimodal alloys at the same cooling γ′ size. This augmentation of the faulting in commercial alloys was apparently due to the presence of the fine, aging γ′ particles. The two typical commercial heat treatments (supersolvus and subsolvus) resulted in different deformation structures: the subsolvus behavior was similar to that of unimodal alloys with γ′ sizes between 0.2 and 0.35 μm, while the supersolvus deformation was similar to that of unimodal alloys with the 0.1 μm γ′ size. These differences were attributed to differences in the size of the fine, aging γ′ particles. Creep deformation in a commercially heat-treated material at 650 °C occurred solely by SISF-related mechanisms, resulting in a macroscopic slip vector of 〈112〉. The effects of alloy chemistry, APB energy, and microstructure on the deformation and mechanical behavior are discussed in detail, and possible effects of the faulting mechanisms on the mechanical behavior are explored. Finally, models for yield strength as a function of microstructure for bimodal alloys with large volume fractions of precipitates are found to be in need of development. RENE′95 is a trademark of General Electric Company, Fairfield, CT.     

Dendritic morphology observed in the solid-state precipitation in binary alloys

The precipitation of γ ₂ phase in Cu-Al β-phase alloys has been observed to occur in the dendritic morphology. Such morphology is rarely observed in the solid-state transformations. Earlier it was reported that the γ precipitates were formed in the dendritic shape when Cu-Zn β-phase alloys were cooled from high temperature. The characteristics of these two alloy systems have been examined to find the factors promoting the dendritic morphology in the solid-state transformations. Rapid bulk diffusion and fast interfacial reaction kinetics would promote such morphology. The kinetics of atom attachment to the growing interface is expected to be fast when crystallographic similarities exist between the parent phase and the precipitate. We have predicted the dendritic morphology in the solid-state precipitation in many binary alloy systems simply based on such crystallographic similarities. These alloys include, in addition to Cu-Al and Cu-Zn, the β-phase alloys in Ag-Li, Ag-Zn, Cu-Ga, Au-Zn, and Ni-Zn systems, γ-phase alloys in Cu-Sn and Ag-Cd systems, and δ-phase alloys in Au-Cd system. Of these, the alloys in Ag-Zn, Ni-Zn, Ag-Cd, and Cu-Sn systems were prepared and it was indeed found that the precipitates formed in the dendritic shape.     

The structure of directionally solidified two-phase Sn-Cd peritectic alloys

The structure of Sn-Cd two-phase peritectic alloys directionally solidified at various values ofG/υ (temperature gradient in the liquid divided by growth rate) is reported. The minimum value of G/υ as a function of composition required for the solidification of two-phase peritectic alloys with a planar liquid-solid interface is estimated using a simple constitutional supercooling stability criterion. At a value ofG/υ just below this minimum value, these alloys solidify with a nonplanar interface consisting of cells of α (the high temperature phase) and intercellularβ (the low temperature phase). This produces a coarse rod-like microstructure consisting of rods of α phase imbedded in aβ matrix. At a value ofG/υ above this minimum value, these alloys solidify with a planar interface which alternately deposits bands of α andβ transverse to the growth direction. No coupled growth of α andβ at a planar interface is observed in Sn-Cd two-phase peritectic alloys as was expected. To understand this, an analysis of coupled (eutectic-like) growth of two-phase peritectic alloys is presented and contrasted with the results of the Jackson-Hunt theory of lamellar eutectic growth. This calculation indicates that the coupled growth of two-phase peritectic alloys is unlikely on theoretical grounds.     

The stacking fault energy in noble metal alloys

A model for the stacking fault energy, γ, in noble metals and their alloys is developed which qualitatively explains many features of experimental observations. The model is based on bothd band and free electron contributions to the cohesion. An important prediction of the model is that γ can be decreased in noble metal alloys by the addition of a solute with an emptyd band withZ = 1 (i.e., lithium in silver). Measurements of γ were made as a function of lithium concentration in a series of Ag-Li alloys up to 25 at. pct Li using the node method. The results show that γ decreases with the addition of lithium in a manner predicted by the model.     

The influence of alloy composition on precipitates of the Al-Mg-Si system

To study how changes in solute elements affect precipitation, six Al-Mg-Si alloys aged at 175 °C were investigated by transmission electron microscopy (TEM). In alloys with 1.3 at. pct solute, when the Si/Mg ratio exceeds 5/6, a sharp hardness peak appears after 3 hours that correlates with a high density of fine Guinier-Preston (GP) zones. A second, broader peak correlates with β″ precipitates and U phases. With high Si/Mg ratios, GP zones survive for long aging times. The β″-Mg₅Si₆ phase becomes very stable in the alloy with its Si/Mg ratio closest to 6/5. Deviation from this ratio increases fractions of β′, U-phases and disordered precipitates. In Mg-rich alloys less GP zones form and the first peak is suppressed. A coarse precipitate microstructure of β″ and β′ develops, the volume fraction being much higher than in Si-rich alloys. The Mg-rich alloys overage faster. Reducing the content of solutes causes alloys with high Si/Mg ratios to have a more Mg-rich behavior.     

Microstructure and yield strength of UDIMET 720LI alloyed with Co-16.9 Wt Pct Ti

We proposed a new method for developing Ni-base turbine disc alloy for application at temperatures above 700 °C by mixing a Ni-base superalloy U720LI with a two-phase alloy Co-16.9 wt pct Ti in various contents. The microstructure and phase stability of the alloys were analyzed using an optical microscope, a scanning electron microscope, energy-dispersive spectroscopy, and an X-ray diffractometer. The yield strength was studied by compression tests at temperatures ranging from 25 °C to 1200 °C. The results show that all the alloys had a dendritic structure. Ni₃Ti (η) phase was formed in the interdendritic region in the alloys with the addition of Co-16.9 wt pct Ti, and its volume fraction increased with the increase in the addition of Co-16.9 wt pct Ti. The results of exposure at 750 °C show that the addition of Co-16.9 wt pct Ti to U720LI had a great effect on suppressing the formation of σ phase due to the reduced Cr content in the γ matrix. Compared to U720LI, the alloys with the addition of Co-16.9 wt pct Ti possessed higher yield strength. The solid-solution strengthening of γ and γ′ and higher volume fraction of γ′ were assumed to cause this strength increase.     

The influence of cobalt,tantalum, and tungsten on the microstructure of single crystal nickel-base superalloys

The influence of composition on the microstructure of single crystal nickel-base superalloys was investigated. Co was replaced by Ni, and Ta was replaced by either Ni or W, according to a matrix of compositions based on MAR-M247. Substitution of Ni for Co caused an increase inγ′ solvus temperature, an increase inγ-γ′ lattice mismatch, and the precipitation of W-rich phases in the alloys with high refractory metal levels. Substitution of Ni for Ta caused large decreases inγ′ solvus temperature,γ′ volume fraction, andγ-γ′ lattice mismatch, whereas substitution of W for Ta resulted in smaller decreases in these features. For the alloys withγ′ particles that remained coherent, substitution of Ni for Co caused an increase inγ′ coarsening rate. The two alloys with the largest magnitude of lattice mismatch possessedγ′ particles which lost coherency during unstressed aging and exhibited anomalously low coarsening rates. Creep exposure at 1000 °C resulted in the formation ofγ′ lamellae oriented perpendicular to the applied stress axis in all alloys.     

Development of ultrafine lamellar structures in two-phase γ-TiAl alloys

Processing of two-phase γ-TiAl alloys (Ti-47Al-2Cr-2Nb, or minor modifications thereof) above the α-transus temperature (T _α ) produced unique refined-colony/ultrafine lamellar structures in both powder-and ingot-metallurgy (PM and IM, respectively) alloys. These ultrafine lamellar structures consist of fine laths of the γ and α ₂ phases, with average interlamellar spacings (λ _L ) of 100 to 200 nm and α ₂-α ₂ spacings (λ _α ) of 200 to 500 nm, and are dominated by γ/α ₂ interfaces. This characteristic microstructure forms by extruding PM Ti-47Al-2Cr-2Nb alloys at 1400 °C and also forms with finer colony size but slightly coarser, fully lamellar structures by hot-extruding similar IM alloys. Alloying additions of B and W refine λ _L and λ _α in both IM Ti-47Al (cast and heat treated at 1400 °C) and IM Ti-47Al-2Cr-2Nb alloys (extruded at 1400 °C). The ultrafine lamellar structure in the PM alloy remains stable during heat treatment at 900 °C for 2 hours but becomes unstable after 4 hours at 982 °C; the ultrafine lamellar structure remains relatively stable after aging for >5000 hours at 800 °C. Additions of B+W dramatically improve the coarsening resistance of λ _L and λ _α in the IM Ti-47Al alloys aged for 168 hours at 1000 °C. In both the PM and IM Ti-47Al-2Cr-2Nb alloys, these refined-colony/ultrafine lamellar structures correlate with high strength and good ductility at room temperature, and very good strength at high temperatures. While refining the colony size improves the room-temperature ductility, alloys with finer λ _L are stronger at both room and high temperatures. Additions of B + W produce finer as-processed λ _L and λ _α in IM TiAl alloys and stabilize such structures during heat treatment or aging. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

Solidification of Nb-bearing superalloys: Part I. Reaction sequences

The solidification reaction sequences of experimental superalloys containing systematic variations in Fe, Nb, Si, and C were studied using differential thermal analysis (DTA) and microstructural characterization techniques. The reaction sequences responsible for microstructural development were found to be similar to those expected in the Ni-Nb-C ternary system and commercial superalloys of comparable composition. The solute-rich interdendritic liquid generally exhibited two eutectic-type reactions at the terminal stages of solidification: L → (γ+NbC) and L → (γ+Laves). The Ni-base alloys with a high C/Nb ratio represented the only exception to this general solidification sequence. This group of alloys terminated solidification with the L → (γ + NbC) reaction and did not exhibit the γ/Laves constituent. At similar levels of solute elements (Nb, Si, and C), the Fe-base alloys always formed more of the γ/Laves eutectic-type constituent than the corresponding Ni-base alloys. Silicon additions also increased the amount of the γ/Laves constituent that formed in the assolidified microstructure, while C additions promoted formation of γ/NbC. The influence of Nb was dependent on the C content of the alloy. When the C content was low, Nb additions generally promoted formation of γ/Laves, while Nb additions to alloys with high C led to formation of the γ/NbC constituent. The results of this work are combined with quantitative analyses for developing γ-Nb-C pseudoternary solidification diagrams in a companion article.     

Low cycle fatigue behavior of Ti-Mn alloys: Cyclic stress-strain response

The cyclic stress-strain response at constant total strain has been determined for a series of binary Ti-Mn alloys which have been heat treated at a constant temperature of 700 °C to produceα,α-β, and β phase microstructures where the chemical composition ofα andβ phase has been kept constant. The α phase hardens during cyclic straining and the amount of hardening increases with strain. Theβ phase initially softens but hardens with increasing number of cycles. Theα -β alloys show a mixture of these behaviors with softening at low strains and hardening at higher strains. Softening in theα -β alloys is not expected, particularly in the higherα alloys, because plastic strains are much higher inα than inβ at low strains. Transmission electron microscopy has indicated that this behavior is due to dislocation rearrangement inα phase. It has not been possible to ascertain the reason for softening ofβ phase, which may be due either to an increased mobile dislocation density or metallurgical instability of the alloy or both.     

Enthalpy of formation and heat capacity of Fe-Mn alloys

The partial and integral enthalpies of mixing of liquid Fe-Mn alloys were measured as a function of the atomic fraction of iron (x) within the range of 0≤x≤0.45 at 1700±5 K, using a laboratory-built, high-temperature isoperibolic calorimeter. The minimum integral enthalphy of mixing at x=0.5 is about −820±45 J mol⁻¹. The enthalpy of formation of solid γ-Fe-Mn alloys with 30.0, 40.0, 50.0, and 57.0 at. pct Mn was determined indirectly, using the same calorimeter, by dissolving these alloys in liquid aluminium at 1409±3 K, and the minimum value amounts to −1940±70 J mol⁻¹ at x=0.5. The heat capacities of these alloys as well as the heat capacity of pure iron and α-Fe-Mn alloys with 0.95, 2.03, 2.73, and 4.30 at. pct Mn, were measured by a differential thermal analysis (DTA) technique and are described using a new analytical representation of the magnetic contribution. The composition dependencies of heat content, Curie and Neél temperatures, enthalpy of formation of α-Fe-Mn alloys, magnetic contribution to the enthalpy of pure Fe and its change due to the addition of Mn, as well as the change of enthalpy upon the γ → α transformation, were deduced from the experimental data. The results obtained were compared with experimental information available in the literature.     

Role of Si in Improving the Shape Recovery of FeMnSiCrNi Shape Memory Alloys

The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe₅Ni₃Si₂ type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si.     

Effects of cold work on precipitation in Al-Cu-Mg-(Ag) and Al-Cu-Li-(Mg-Ag) alloys

A study has been made of the effects of cold work prior to aging on precipitation hardening in selected Al-Cu-Mg-(Ag) and Al-Cu-Li-(Mg-Ag) alloys. General aging characteristics have been determined by differential scanning calorimetry, and response to hardening has been correlated with microstructure using transmission electron microscopy (TEM), selected area electron dif-fraction (SAED), and quantitative stereology. Particular attention has been given to the phases Ω andT ₁ that form on the {111 }_α planes, although information on the precipitates θ′,S′ (orS), and δ′ is also reported. Although Ω andT ₁, have similar morphologies and habit planes, their response to cold work prior to aging is different. Deformation promotesT ₁ formation at the expense of the δ′ phase in Al-Cu-Li alloys and at the expense of δ′, θ′, andS′ in Al-Cu-Li-Mg-Ag alloys. On the other hand, in Al-Cu-Mg-Ag alloys, deformation assists precipitation of θ′ at the expense of Ω phase, and some decrease is recorded in the hardening response. Prior cold work is also found to reduce the response during natural aging in most alloys. These results are discussed in terms of the role of particular alloying additions. Formerly Research Fellow, Department of Materials Engineering, Monash University     

Lattice spacings and stacking fault probabilities in Ag−Cd−In alloys

Lattice spacing values in ternary Ag−Cd−In alloys containing 5 to 30 at. pct Cd and 5 to 15 at. pct In have been determined from X-ray powder patterns using the Nelson-Riley extrapolation procedure. The values are shown to lie, in a ternary plot, on iso-parameter lines obtained by joining equal lattice spacing values in the relevant binary alloys. The intrinsic stacking fault probabilities (α) in these alloys obtained from measurement of X-ray peak displacements are found to follow the empirical relation α=α₀ expk|ΔZ|p, where α₀ is the intrinsic fault probability in Ag, |ΔZ| is the weighted mean of solvent-solute valence differences,p is the combined solute content, andk is a constant approximately equal to 0.08 in agreement with the value found earlier for binary alloys based on silver.     

Microstructural characteristics of Ni-Sb eutectic alloys under substantial undercooling and containerless solidification conditions

Both Ni-36 wt pct Sb and Ni-52.8 wt pct Sb eutectic alloys were highly undercooled and rapidly solidified with the glass-fluxing method and drop-tube technique. Bulk samples of Ni-36 pct Sb and Ni-52.8 pct Sb eutectic alloys were undercooled by up to 225 K (0.16 T _E ) and 218 K (0.16 T _E ), respectively, with the glass-fluxing method. A transition from lamellar eutectic to anomalous eutectic was revealed beyond a critical undercooling ΔT ₁*, which was complete at an undercooling of ΔT ₂*. For Ni-36 pct Sb, ΔT ₁*≈60 K and ΔT ₂*≈218 K; for Ni-52.8 pct Sb, ΔT ₁*≈40 K and ΔT ₂*≈139 K. Under a drop-tube containerless solidification condition, the eutectic microstructures of these two eutectic alloys also exhibit such a “lamellar eutectic-anomalous eutectic” morphology transition. Meanwhile, a kind of spherical anomalous eutectic grain was found in a Ni-36 pct Sb eutectic alloy processed by the drop-tube technique, which was ascribed to the good spatial symmetry of the temperature field and concentration field caused by a reduced gravity condition during free fall. During the rapid solidification of a Ni-52.8 pct Sb eutectic alloy, surface nucleation dominates the nucleation event, even when the undercooling is relatively large. Theoretical calculations on the basis of the current eutectic growth and dendritic growth models reveal that γ-Ni₅Sb₂ dendritic growth displaces eutectic growth at large undercoolings in these two eutectic alloys. The tendency of independent nucleation of the two eutectic phases and their cooperative dendrite growth are responsible for the lamellar eutectic-anomalous eutectic microstructural transition.     

Examination of solidification pathways and the liquidus surface in the Nb-Ti-Al system

The solidification pathways, subsequent solid-state transformations, and the liquidus surface in the Nb-Ti-Al system have been examined as part of a larger investigation of phase equilibria in Nb-Ti-Al intermetallic alloys. Fifteen alloys ranging in composition from 15 to 40 at. pct Al, with Nb to Ti ratios of 4:1, 2:1, 1.5:1, 1:1, and 1:1.5, were prepared by arc melting and the as-cast microstructures were characterized by optical microscopy (OM), microhardness, X-ray diffraction (XRD), differential thermal analysis (DTA), backscattered electron imaging (BSEI), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). The results indicate that the range of primary β solidification is much wider than that indicated in previously reported liquidus surfaces, both experimental and calculated. Differential thermal analysis has identified the existence of a β to σ+γ transformation in three alloys where it was previously thought not to exist; confirmation was provided by high-temperature vacuum heat treatments in the single-phase β region followed by rapid quenching. The location of the boundary between the β, σ, and δ primary solidification fields has been redefined. A massive β → δ transformation, which was observed in the cast microstructure of a Nb-25Ti-25Al alloy, was repeatable through cooling following homogenization. A β → δ+σ eutectoid-like transformation in the 25 at. pct Al alloys, was detected by DTA and evaluated through microstructural analysis of heat-treated samples. Trends in the β phase with variations in composition were established for both lattice parameters and microhardness. As a result of this wider extent of the primary β solidification field, a greater possibility exists for microstructural control through thermal processing for alloys consisting of either σ+γ, β+σ, or β+δ phases. An erratum to this article is available at .     

Microstructure and mechanical behavior of spray-deposited Al-Cu-Mg(-Ag-Mn) alloys

The effect of alloy composition on the microstructure and mechanical behavior of four spray-deposited Al-Cu-Mg(-Ag-Mn) alloys was investigated. Precipitation kinetics for the alloys was determined using differential scanning calorimetry (DSC) and artificial aging studies coupled with transmission electron microscopy (TEM) analysis. DSC/TEM analysis revealed that the spray-deposited alloys displayed similar precipitation behavior to that found in previously published studies on ingot alloys, with the Ag containing alloys exhibiting the presence of two peaks corresponding to precipitation of both Ω-Al₂Cu and θ′-Al₂Cu and the Ag-free alloy exhibiting only one peak for precipitation of θ′. The TEM analysis of each of the Ag-containing alloys revealed increasing amounts of Al₂₀Mn₃Cu₂ with increasing Mn. In the peak and over-aged conditions, Ag-containing alloys revealed the presence of Ω, with some precipitation of θ′ for alloys 248 and 251. Tensile tests on each of the alloys in the peak-aged and overaged (1000 hours at 160 °C) conditions were performed at both room and elevated temperatures. These tests revealed that the peak-aged alloys exhibited relatively high stability up to 160 °C, with greater reductions in strength being observed at 200 °C (especially for the high Mn, low Cu/Mg ratio (6.7) alloy 251). The greatest stability of tensile strength following extended exposure at 160 °C was exhibited by the high Cu/Mg ratio (14) alloy 248, which revealed reductions in yield strength of about 2.5 pct, with respect to the peak-aged condition, for the alloys tested at both room temperature and 160 °C.     

Stress induced hydrogen redistribution in commercial titanium alloys

The change in hydrogen concentration as a function of applied strain has been studied in commercial titanium alloys that included threeβ-phase, twoα-phase, and an (α + β)-phase Ti-6Al-4V alloy with differingα/β morphologies.Insitu measurements were made using a nondestructive nuclear technique on samples for which uniaxial compressive and tensile stresses were applied by four-point bending. Theβ-phase alloys exhibited hydrogen redistribution under an elastic stress gradient, but no further change was discernible accompanying plastic deformation. The extent of hydrogen concentration change for theβ-phase alloys was of the order of 4 to 6 pct for a 620 MPa stress gradient. This is less than would be predicted based on available data for the partial molal volume of hydrogen. Diffusion coefficients in a stress gradient were also determined and are consistent with those measured inβ-phase titanium at elevated and room temperatures. Within the experimental sensitivities there was no evidence of hydrogen redistribution with applied stress for theα-phase and Ti-6Al-4V alloys.