Deformation behavior of 4;Mo alloys

Five polycrystalline nickel-molybdenum single-phase alloys (up to 10 at.% Mo) and pure nickel (INCO 270) were tested in compression at two temperatures. The molybdenum solutes contribute not only an additive friction stress, but also a multiplicative effect on the strain-hardening rate. This multiplicative effect is interpreted in terms of an influence of mobile solutes on the dislocation/dislocation interaction strength. Solute mobility was evidenced by the occurrence of static strain aging and of a strain-rate sensitivity that has a negative contribution. The total rate sensitivity, however, remained positive and jerky flow was not observed.     

Deformation properties of sintered tungsten-based heavy alloys

The deformation properties of tungsten-based sintered alloys are studied. Plasticity diagrams are plotted for these alloys at deformation temperatures up to 900°C and various state-of-stress schemes. The properties of the tungsten-based sintered alloys are determined during alternating deformation. The joint action of the temperature (up to 900°C) and the state of stress on the ductility of the tungsten-based sintered alloys is analyzed. The results obtained are used to simulate damage accumulation for various methods of strain hardening of heavy alloys (rotational reduction, hydraulic forging, rolling in multiroll passes). Hydraulic forging is considered, and the limiting reductions are determined using the condition of impossible irreversible metal microfracture.     

Deformation characteristics in Β phase Ti-Nb alloys

Deformation modes in Β-phase Ti-Nb alloys containing from 36 to 52 wt pct Nb have been investigated as a function of composition, crystallographic orientation, or deformation temperature using both two surface trace analysis and transmission electron microscopy. 332 (113) twinning occurs in the low niobium content alloys independent of orientation and temperature. With increasing niobium content, 332<113> twinning or (111) slip occurs dependent on orientation and temperature. The operative twinning systems are explained by considering both the polarization of twinning shear and the Schmid factor. The 332 (113) twinning is suppressed in the high niobium content alloys and also suppressed by aging or oxygen addition in the low niobium content alloy. These characteristics have previously been observed in Β phase Ti-V and Ti-Mo alloys. The occurrence of 332 (113) twinning in Β-phase Ti alloys is related to the instability of Β phase. Formerly Graduate Student of Tohoku University     

Deformation of rapidly solidified dispersion strengthened titanium alloys

The influence of erbium on the behavior of titanium and titanium-aluminum based alloys has been investigated over a range of strain rates and temperatures (25 to 775°C). Data from hotextruded bulk specimens indicate that, although oxide dispersion strengthening can be large under certain conditions, the strengthening is minimal in fine-grain material subjected to low strain rate deformation at high temperatures. Both microstructural observations and an analysis of the flow data indicate profuse grain boundary sliding under these conditions. Grain coarsening anneals, which also coarsen the dispersoids and increase their population along grain boundaries, result in significantly improved high temperature flow strengths, especially in the high temperature/low strain rate regime. S. L. Kampe of Michigan Technological University, Houghton, MI     

Deformation behavior of bimodal nanostructured 5083 Al alloys

Cryomilled 5083 Al alloys blended with volume fractions of 15, 30, and 50 pct unmilled 5083 Al were produced by consolidation of a mixture of cryomilled 5083 Al and unmilled 5083 Al powders. A bimodal grain size was achieved in the as-extruded alloys in which nanostructured regions had a grain size of 200 nm and coarse-grained regions had a grain size of 1 μm. Compression loading in the longitudinal direction resulted in elastic-perfectly plastic deformation behavior. An enhanced tensile elongation associated with the occurrence of a Lüders band was observed in the bimodal alloys. As the volume fraction of coarse grains was increased, tensile ductility increased and strength decreased. Enhanced tensile ductility was attributed to the occurrence of crack bridging as well as delamination between nanostructured and coarse-grained regions during plastic deformation.     

Deformation and fracture behavior of two Al-Mg-Si alloys

Deformation and fracture behavior of two Al-Mg-Si alloys in different aging conditions has been studied by tensile testing, transmission electron microscope (TEM), and scanning electron microscope (SEM) observation. Tensile test results show that the strain hardening exponents (n values) of the two alloys decrease sharply at the early stage of artificial aging and are only 0.045 and 0.06, respectively, in the overaged condition. The sharp decrease of work hardening rate is believed to be one major reason that results in the rapid decrease of elongation to failure at the early stage of artificial aging. In fully aged conditions, dislocations are concentrated in narrow bands during plastic deformation of these alloys, which is responsible for the very low n values of the Al-Mg-Si alloys in peak aged and overaged conditions. The Si particles formed in the interior of grains of the higher Si containing alloy reduce the inhomogeneous deformation behavior. The TEM results show that large precipitates and precipitate-free zones (PFZs) along grain boundaries are formed in peak aged and overaged conditions, and SEM observations demonstrate that the tensile fracture modes of the two alloys in these aging conditions are completely intergranular with many small cusps decorated on facets of the fractured grain boundaries. Thus, the fracture process of both alloys is suggested to be that in which the high local stresses, built up where the slip band impinges on the grain boundaries, nucleate voids at the grain boundary precipitates by decohesion of the particle/PFZ interface, and then coalescence of these voids within the PFZ leads to the final fracture of these alloys.     

Deformation behavior of submicrocrystalline aluminum alloys during dynamic loading

The structure and the mechanical properties of aluminum V95 and AMts alloys with various grain sizes (from micron to submicron) are studied in a wide range of strain rates (from 10^–3 to 10⁵ s^–1). Submicrocrystalline (200–600 nm) materials are formed by dynamic channel-angular pressing at a strain rate of 10⁵ s^–1 using a pulsed power source.     

Deformation behavior in quenched and aged beta Ti-V alloys

The deformation characteristics of quenched and aged Ti-V alloys in the composition range 20 to 40 wt pct vanadium have been examined by optical metallography and transmission electron microscopy. A coarse lenticular deformation product similar in appearance to previously reported strain induced “martensites” was found to be associated with the occurrence of the omega phase. These features proved to be {112}〈111〉 twins. In the omega bearing alloys prolonged aging resulted in a transition of the deformation mode from twinning to slip at a point which corresponded either to the onset of embrittlement or alpha phase precipitation.     

Deformation behavior and texture development in beta Ti-V alloys

Beta phase titanium-vanadium alloys in the composition range 20 to 40 wt pct vanadium were studied to determine the dependence of mechanical properties and texture formation on deformation modes. Changes in twinning probability and slip characteristics with vanadium content are reflected in wide variations in sheet textures in both as-rolled and rolled and recrystallized samples. These sheet textures exhibit strongly anisotropic strength properties which may be qualitatively related to the type of texture.     

Deformation and microstructure in L10 type Ti-Al-V alloys

The addition of vanadium to polycrystalline, single-phase γ-TiAl significantly enhances stiffness from room temperature (RT) to 1173 K. The maximum yield stress in Ti-55A1-10V alloy is centered near 1073 K, in contrast with those of single-crystal Ti-54A1 at 873 and 1073 K, depending upon deformation orientation. The effect of strain rate on yield stress is present over the entire temperature range, but it is more prominent above 873 K, while the effect becomes significantly small between 673 and 873 K, similar to that observed in Ll₂ type Ni₃Al. The microstructure of deformed Ti-55A1-10V and Ti-49.5A1-10V alloys evolved by slip, twinning, and formation of stacking faults. Twinning is a major deformation mode in Ti-49.5-10V alloy and a minor mode in Ti-55A1-10V alloy. It appears that the amount of twins for a given deformation decreases with increasing Al content. The twin structures in both alloys were found to be true twins of {111}〈112]. No pseudotwinning was observed in the alloys deformed in the temperature range of RT to 1273 K. The stacking faults found in the deformed alloys had an extrinsic character. No intrinsic type of stacking faults were found in these alloys. In addition to the cross slip of superdislocations, the anomalous hardening up to 1073 K appears attributable to an ordinary superdislocation pinning structure, dislocation loops, and nonglissile “square shaped dislocations,” which are products of super-superdislocation reaction. These nonglissile or pinning structures are unwinded in the deformed Ti-55A1-10V alloy at 1273 K, consistent with the softening behavior at this temperature.     

Deformation and transition behavior associated with theR-phase in Ti-Ni alloys

Deformation behavior associated with theR-phase (rhombohedral phase) transition and the subsequent martensitic transformation was studied systematically in Ti-Ni alloys by tensile testing over a wide temperature range covering belowM _f to aboveT′ _R (>A_f). Since the deformation and transition characteristics showed a strong dependence on thermo-mechanical treatment and Ni-content, internal structures were examined by electron microscopy in specimens with various Ni-content and thermo-mechanical treatment. As a result precipitates and/or dislocations were revealed in the specimens in which theR-phase transition occurs. Based on the above results, the effects of thermo-mechanical treatment and Ni-content on the deformation and transition characteristics were clarified for both theR-phase transition and the martensitic transformation.     

Deformation inhomogeneity and representative volume in Pb/Sn solder alloys

To verify whether the deformation of the bulk test specimens represents that of small solder joints, we have used the concept of “representative volume.” The representative volume is defined as the smallest volume which represents the average inelastic and inhomogeneous deformation of the entire body. We have performed the first set of experiments to determine this representative volume by measuring the microscopic deformations of a large Pb/Sn eutectic alloy specimen as a function of applied strain. The results show that the representative volume of the specimen is very large compared to the size of the solder joints. Formerly with IBM T.J. Watson Research Center, Yorktown Heights, NY 10598     

Deformation behavior of Zr3Al-Nb alloys II: Indentation creep studies

The high-temperature mechanical properties of Zr₃Al, Zr₃Al-3Nb, and Zr₃Al-10Nb alloys were assessed using the indentation hardness method. All three alloys showed negligible creep up to 500 K. Using Sargent and Ashby’s approach, different creep parameters such as stress exponent, activation energy, and activation area were estimated. Using the data generated in the present study and those available in the literature, a deformation creep curve was developed. The relationship between hardness and temperature in the high-temperature region can be expressed in terms of an Arrhenious equation. The activation energy estimated from this relationship was found to be in good agreement with that obtained from the indentation creep curve. On comparing the creep behavior of Zr₃Al-Nb alloys with some other intermetallics, it was observed that Zr₃Al-based intermetallics have better creep resistance compared to other intemetallics.     

Deformation behavior of Zr3Al-Nb alloys I: Room-temperature and high-temperature deformation study

The deformation behavior of the Zr₃Al-Nb alloys was studied by measuring hardness at different temperatures, by hot rolling, and by hot pressing. Using the hardness data, elasticity and plasticity parameters were estimated and were used to determine the suitable temperature range of deformation for these alloys. Hot rolling and hot pressing were applied to determine the optimum temperatures and annealing time for carrying out deformation successfully in these alloys. Microstrural investigation of the hotdeformed samples revealed that the matrix β phase has undergone substantial deformation and the second intermetallic phase, Zr₂(Al,Nb), underwent dissolution and re-precipitation. The hardness of the fully annealed Zr₃Al-Nb alloys showed two types of temperature dependence. Transition temperatures for the change in behavior, intrinsic hardness, and softening coefficient were determined. The hardness of the fully annealed alloys rolled to different extent at various temperatures and subsequently heat treated was used to study the recovery process. The microstructural study of room-temperature deformed binary Zr₃Al alloy showed the splitting of the superlattice dislocations into partials containing superlattice intrinsic stacking faults.     

Deformation and heat treatment of NiAl-Y2O3-based powder alloys: I. Deformation and production of various pressed sections

The effect of a hot extrusion regime for workpieces produced by calcium hydride reduction (CHR) of mechanically activated powders of an NiAl intermetallic alloy and an NiAl-Y₂O₃ alloy composite on their deformability is studied to form various (round, flat, lens-shaped) sections. The extrusion regimes that make it possible to produce defect-free samples of the NiAl-Y₂O₃ alloy composite with a metal-deformed structure without traces of dynamic recrystallization are developed. Deformed semifinished samples are formed.     

Deformation and heat treatment of NiAl-Y2O3-based powder alloys: III. Directional recrystallization

The effect of recrystallization annealing of various sections produced by twofold extrusion with a total reduction λ = 28 and blade profiles produced by isothermal stamping on the formation of a directional structure with a low fraction of transverse boundaries has been studied in NiAl-Y₂O₃ (2.5 and 7.5 vol %) alloys. Annealing at temperatures of (0.89–0.95)T _m of NiAl is performed under isothermal conditions or in a temperature field with a temperature gradient along the product length. It is shown that Y₂O₃ particles of irregular shapes introduced during mechanical activation into the NiAl powder prepared by hydride-calcium reduction take a rounded shape during deformation and heat treatment. As a result of mechanical activation, extrusion, and subsequent directional recrystallization (DR), complex oxides form. The crystallographic texture of the extruded and recrystallized rods and profiles is studied. It is shown that hot extrusion and subsequent DR result in the formation of a quasi-single-crystal structure in a NiAl matrix with coarse elongated recrystallized grains.     

Deformation and heat treatment of NiAl-Y2O3-based powder alloys: II. fabrication of parts

Hydrostatic pressing of mechanically activated calcium hydride reduction (CHR) powders of plain intermetallic compound NiAl is used to fabricate parts of a complex shape that have a density and strength that allow the application of mechanical processing. The sections of a nozzle blade from an aviation gas turbine engine are produced from mechanically activated CHR mixtures of NiAl-2.5% Y₂O₃ powders by isothermal forging.