Plastic Flow of L12 Ordered Alloys

1984 ◽  
Vol 39 ◽  
Author(s):  
D. P. Pope ◽  
V. Vitek
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Dislocation Core ◽  
Uniaxial Stress ◽  
Cross Slip ◽  
Slip Model ◽  
Unusual Behavior ◽  
Solid Solution Strengthening ◽  
Ordered Alloys ◽  
The Cross

ABSTRACTThe flow stress of many L12 ordered alloys has a very unusual temperature dependence: the flow stress increases with increasing temperature. This unusual behavior is related to the nature of dislocation dissociation and core structure. The flow stress increase is the result of thermally activated cross slip of [101] screw dislocations to the (010) plane which is accompanied by a transformation of the dislocation core from a glissile to a sessile form. Thus dislocations which are mobile on (111) planes become immobile after cross-slip into (010) planes. The dependence of the flow stress on temperature, orientation and sense of the applied uniaxial stress will be discussed in the light of this cross slip model for Ni3Al, Ni3Ga and for γ/γ′ nickel base superalloys.The response of Ni3Al to cyclic plastic strains (plastic strain controlled fatigue) will also be shown to be in accord with the cross slip model. The mean stress in such a test becomes compressive or tensile, depending on the orientation of the sample, even though the net plastic strain is zero after each cycle.The strengthening of Ni3Al by ternary additions will also be discussed. It will be shown that ordinary solid solution strengthening models are not applicable but that the cross slip model can also be applied.Finally, it will be shown that dislocation core simulation studies predict that there should also be a class of L12 ordered alloys that show a “normal” flow stress-temperature behavior, i.e., the flow stress increases at low temperatures. The results of our studies on Pt3Al will be used to illustrate this behavior.

Deformation Mechanisms and Solid-Solution Strengthening in Ordered Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
Dennis M. Dimiduk ◽  
Satish Rao
Keyword(s):  
Solid Solution ◽  
Flow Behavior ◽  
Stoichiometric Composition ◽  
Dislocation Core ◽  
Deformation Mechanisms ◽  
Solid Solution Hardening ◽  
Solid Solution Strengthening ◽  
Ordered Alloys ◽  
Solute Hardening

ABSTRACTFundamental to understanding the results of alloy design studies, is the need for understanding the intrinsic role of solutes in a particular compound. For many compounds such an understanding must be built from a systematic exploration of the role of deviations from the stoichiometric composition as well as the role of ternary solute additions on the variation of flow behavior. Within most intermetallic systems the problem is complicated since the fundamental mechanisms of flow are not well established and, in those systems where these mechanisms are known, thermal activation can lead to dislocation-core transformations and changes in the operative slip systems with temperature. In general, flow may be governed by more than one dislocation process at a given temperature and deformation twinning may be a major contributing deformation mechanism. The problem of isolating the mechanisms of solid-solution hardening may, therefore, require treatment as a problem of combined strengthening mechanisms operating in parallel. This paper reviews the key aspects of deformation mechanisms and solute strengthening in intermetallic alloys. Classical elastic theories of solute hardening serve as an origin, from which, the progress made to date in isolating the mechanisms of solute hardening in ordered alloys is discussed.

Strengthening of Ni3Al by Ternary Additions

1986 ◽  
Vol 81 ◽  
Author(s):  
F. Heredia ◽  
D. P. Pope
Keyword(s):  
Flow Stress ◽  
Dislocation Core ◽  
Uniaxial Stress ◽  
Lattice Parameter ◽  
Strength Increase ◽  
Dominant Mechanism ◽  
Wide Range ◽  
Stress Asymmetry ◽  
Ternary Additions ◽  
Octahedral Slip

AbstractIt is important for a number of reasons to have a basic understanding of the mechanisms by which ternary additions strengthen Ni3Al. First of all, since the basic strength-controlling mechanisms in pure Ni3Al are different from those in pure metals and substitutional solid solutions, it is expected that the mechanisms of solid solution strengthening will also be different in Ni3Al. Secondly, such an understanding will provide valuable insights into the properties of nickel-base superalloys in which Ni3Al is a key constituent. In addition, since new alloys based on an ordered Ni3Al matrix are being developed, it is important to understand the strengthening mechanisms in such alloys. In the present study, flow stress measurements have been performed on single crystals of Ni3Al containing additions of Hf and Ta, and on binary Ni rich, Ni3A1 used as a reference alloy. The data have been collected over a wide range of temperatures, for different orientations within the unit triangle, and as a function of the sense of the applied uniaxial stress. The effect of such additions on the critical resolved shear stress (CRSS) for octahedral slip has been determined and combined with previous data. An attempt is then made to clarify whether a lattice parameter/modulus mismatch effect or a dislocation core effect is the dominant mechanism for the strength increase with compositional changes. It appears that a lattice parameter/modulus mismatch is the dominant mechanism for orientations in which the tension/compression flow stress asymmetry disappears.

An Overview of the Temperature Dependence of the Strength of the Ni3Al System

1986 ◽  
Vol 81 ◽  
Author(s):  
John K. Tien ◽  
Sandra Eng ◽  
Juan M. Sanchez
Keyword(s):  
Temperature Dependence ◽  
Antiphase Boundary ◽  
Research Community ◽  
Cross Slip ◽  
Slip Model ◽  
Anomalous Temperature Dependence ◽  
Anomalous Temperature ◽  
Ordered Alloys ◽  
Strength Dependence ◽  
Intermetallic System

AbstractMany L12 ordered alloys including the Ni3Al intermetallic system are noted for their anomalous temperature dependence of strength. It is also generally accepted that this dependence is due to a thermally assisted cross-slip, work hardening based model [1,2]. An alternative antiphase boundary (APB) based model has long been dismissed by the research community because prior calculations of APB energy, and some measurements, have shown that the appropriate APB energy of Ni3Al should remain constant with temperature [3]. These aspects will be reviewed briefly and will serve as a basis for a presentation of some more recent results. These will include the strain rate insensitivity of strength versus temperature in the increasing strength temperature region, a result that is, in our view, rather contradictory to the thermally assisted cross-slip model. Some very recent calculations of equilibrium APB energies will also be reviewed in the context of the strength dependence issue. These results show that the equilibrium APB energy increases with temperature. The question of what role, if any, equilibrium APB plays in the deformation and strengthening process will be discussed.

Dislocation Core Structure and the Anomalous Yield Behavior of Li2 Ordered Alloys At Elevated Temperatures

1984 ◽  
Vol 39 ◽  
Author(s):  
V. Vitek ◽  
D. P. Pope
Keyword(s):  
Flow Stress ◽  
Elevated Temperatures ◽  
Computer Modelling ◽  
Dislocation Core ◽  
Core Structure ◽  
Anomalous Increase ◽  
Screw Dislocations ◽  
Ordered Alloys ◽  
Dislocation Core Structure ◽  
Increasing Temperature

ABSTRACTIn many LI2 ordered alloys the flow stress increases with increasing temperature and is in this “anomalous” regime strongly dependent on orientation and sense of the applied stress. These dependences can be predicted from the nature of the dissociation and core structure of the 1/2<101> screw superpartials in these alloys. Computer modelling shows that two different configurations, a glissile one on {lll} planes and a sessile one on {010} planes, exist and both are described here in detail. The anomalous increase of the flow stress may then be explained by an increasing amount of core transformations from the glissile to sessile forms as the temperature increases. The theoretical model for the immobilization of screw dislocations by this mechanism is then discussed and its validity illustrated by comparison with experimental results on Ni3 (Al, Ta) single crystals.

A Modified Peric Model for Al-Mg Alloy Sheet with Rate-Independent Initial Yield Stress at Warm Temperatures

2019 ◽  
Vol 287 ◽  
pp. 3-7
Author(s):  
Yong Zhang ◽  
Qing Zhang ◽  
Yuan Tao Sun ◽  
Xian Rong Qin
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Strain Rate ◽  
Yield Stress ◽  
Constitutive Models ◽  
Mg Alloy ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Rate Dependent ◽  
Dependent Flow

The constitutive modeling of aluminum alloy under warm forming conditions generally considers the influence of temperature and strain rate. It has been shown by published flow stress curves of Al-Mg alloy that there is nearly no effect of strain rate on initial yield stress at various temperatures. However, most constitutive models ignored this phenomenon and may lead to inaccurate description. In order to capture the rate-independent initial yield stress, Peric model is modified via introducing plastic strain to multiply the strain rate, for eliminating the effect of strain rate when the plastic strain is zero. Other constitutive models including the Wagoner, modified Hockett–Sherby and Peric are also considered and compared. The results show that the modified Peric model could not only describe the temperature-and rate-dependent flow stress, but also capture the rate-independent initial yield stress, while the Wagoner, modified Hockett–Sherby and Peric model can only describe the temperature-and rate-dependent flow stress. Moreover, the modified Peric model could obtain proper static yield stress more naturally, and this property may have potential applications in rate-dependent simulations.

Effect of Hydrogen on the Development of Superplastic Deformation in the Submicrocrystalline Ti–6Al–4V Alloy

2016 ◽  
Vol 838-839 ◽  
pp. 344-349 ◽  
Author(s):  
Galina P. Grabovetskaya ◽  
Ekaterina N. Stepanova ◽  
Ilya V. Ratochka ◽  
I.P. Mishin ◽  
Olga V. Zabudchenko
Keyword(s):  
Solid Solution ◽  
Plastic Deformation ◽  
Flow Stress ◽  
Superplastic Deformation ◽  
Deformation Localization ◽  
Solid Solution Strengthening ◽  
Solution Strengthening ◽  
Hydrogenation Effect

Hydrogenation effect on the development of superplastic deformation in the submicrocrystalline Ti–6Al–4V alloy at temperatures (0.4–0.5)Тmelt is investigated. Hydrogenation of the submicrocrystalline Ti–6Al–4V alloy to 0.26 mass% during superplastic deformation is found to result in solid solution strengthening, plastic deformation localization, and as a consequence, decrease of the deformation to failure. Possible reasons for the decrease of the flow stress and increase of the deformation to failure in the submicrocrystalline Ti–6Al–4V–0.26H alloy during deformation under conditions of superplasticity and simultaneous hydrogen degassing from the alloy are discussed.

scholarly journals The Prospects for Mechanical Ratcheting of Bulk Metallic Glasses

2003 ◽  
Vol 806 ◽  
Author(s):  
Wendelin J. Wright ◽  
R. H. Dauskardt ◽  
W. D. Nix
Keyword(s):  
Plastic Strain ◽  
Metallic Glasses ◽  
Room Temperature ◽  
Tensile Axis ◽  
Uniaxial Stress ◽  
Temperature Deformation ◽  
Steel Alloys ◽  
Cyclic Torsion ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic

ABSTRACTThe major mechanical shortcoming of metallic glasses is their limited ductility at room temperature. Monolithic metallic glasses sustain only a few percent plastic strain when subjected to uniaxial compression and essentially no plastic strain under tension. Here we describe a room temperature deformation process that may have the potential to overcome the limited ductility of monolithic metallic glasses and achieve large plastic strains. By subjecting a metallic glass sample to cyclic torsion, the glass is brought to the yield surface; the superposition of a small uniaxial stress (much smaller than the yield stress) should then produce increments in plastic strain along the tensile axis. This accumulation of strain during cyclic loading, commonly known as ratcheting, has been extensively investigated in stainless and carbon steel alloys, but has not been previously studied in metallic glasses. We have successfully demonstrated the application of this ratcheting technique of cyclic torsion with superimposed tension for polycrystalline Ti–6Al–4V. Our stability analyses indicate that the plastic deformation of materials exhibiting elastic–perfectly plastic constitutive behavior such as metallic glasses should be stable under cyclic torsion, however, results obtained thus far are inconclusive.

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