Showing papers on "Hardening (metallurgy) published in 1984"
TL;DR: In this article, a phenomenological treatment of plastic deformation is proposed which makes it possible to describe in a unified way the plastic behavior of a material both under dynamic loading and in creep.
1,310 citations
TL;DR: In this article, the validity of using an equivalence criterion to describe the plastic properties of polycrystals at large strains is addressed from the point of view of the microscopic properties of the constituent grains.
497 citations
TL;DR: In this paper, a new yield function for compressible P M materials has been derived based upon a yield criterion postulated by the authors, which was experimentally verified for the uniaxial state of compressive stress using the P M aluminum alloy X7091 as a model material, and excellent agreement was found between theoretical and experimental results for the density dependence of the yield and geometrical hardening.
350 citations
TL;DR: In this paper, it was shown that the occurrence of such an "anomaly" is not restricted to anisotropic plasticity, but also in the case of hypoelasticity and classical isotropic hardening plasticity theory.
153 citations
TL;DR: In this article, it was observed that during prolonged cycling in the so-called cyclic saturation regime, slow but significant microstructural changes continued to occur in the bulk, giving rise to secondary cyclic hardening.
143 citations
TL;DR: In this article, the authors apply Hill's self-consistent method to finite elastic-plastic deformations and estimate the overall moduli of polycrystalline solids, showing that small second-order quantities such as shape changes of grains and residual stresses have a first-order effect on the overall response, as they lead to a loss of the overall stability by localized deformation.
Abstract: Applying Hill's self-consistent method to finite elastic-plastic deformations, the overall moduli of polycrystalline solids are estimated. The model predicts a Bauschinger effect, hardening, and formation of vertex or corner on the yield surface for both microscopically non-hardening and hardening crystals. The changes in the instantaneous moduli with deformation are examined, and their asymptotic behavior, especially in relation to possible localization of deformations, is discussed. An interesting conclusion is that small second-order quantities, such as shape changes of grains and residual stresses (measured relative to the crystal elastic moduli), have a first-order effect on the overall response, as they lead to a loss of the overall stability by localized deformation. The predicted incipience of localization for a uniaxial deformation in two dimensions depends on the initial yield strain, but the orientation of localization is slightly less than 45 deg with respect to the tensile direction, although the numerical instability makes it very difficult to estimate this direction accurately.
137 citations
115 citations
TL;DR: In this article, the effect of strain hardening on the flow behavior of superplastic copper alloy Coronze 638 has been analyzed and it was shown that grain growth at low strain rates causes sufficient hardening to compensate for the low strain rate sensitivity, thus preventing the development of sharp necks.
111 citations
TL;DR: In this paper, a general procedure based on polynomial expansion of yield function in terms of invariants of the stress tensor is proposed in the context of associated plasticity for isotropic materials undergoing isotropically hardening.
Abstract: A general procedure based on polynomial expansion of yield function in terms of invariants of the stress tensor is proposed in the context of associated plasticity for isotropic materials undergoing isotropic hardening. The procedure can be used to evolve one or more models for a material by using appropriate laboratory test results. One of the functions showing invariance at ultimate and a single function to describe continuous yield and ultimate yield behavior is investigated in detail. Based on comprehensive series of bests on cubical specimens for different (geological) materials, a hardening or growth function is defined in terms of the trajectory of plastic strain and the ratio of deviatoric to total plastic strain. The predictions of the proposed model are verified with respect to the observed results from tests with different stress paths. The model provides highly satisfactory predictions for both stress‐strain and volumetric strain responses from various stress paths. The proposed model shows po...
85 citations
Abstract: The hardening model proposed by Z. Mroz based on the uniaxial fatigue behavior of many metals is adopted to derive an incremental constitutive equation for general three-dimensional problems. This constitutive law is then employed in the analysis of metal forming problems to assess the influence of loading cycles, of the types involved in standard forming processes, on the ultimate formability of sheet metals. The predicted forming limit curves differ quantitatively from results obtained via an isotropie hardening model and differ qualitatively from those obtained via a kinematic model. Also investigated are the effects of such loading cycles on material response to simple tensile loading, which is often used to characterize a material. Significant differences between the present model and the other two models considered are observed in such characterizers of simple tensile behavior as the stress-strain curve, the anisotropy parameter and the uniform elongation. These differences suggest a rather simple experiment to identify the proper material model to be used in analyses of problems which involve loading cycles. Comparisons with some experimental results reveal that the employment of an anisotropic hardening model, such as the generalized Mroz model derived herein, is indeed crucial in accurately predicting material response to complicated loading histories.
76 citations
TL;DR: In this paper, the surface instability of a semi-infinite layer of cohesive-frictional material under plane-strain uniaxial compression is analyzed and a deformation theory for rigid-plastic, incompressible material with a Mohr-Coulomb yield condition is presented.
TL;DR: In this article, the elastic limits of the steels (the stress at a strain of less than 5 × 10 −5 and the stress-strain curves at small plastic strains were measured using balanced electrical resistance strain gauges of high sensitivity.
TL;DR: In this paper, it was shown that the size and orientation of an imperfection is critical in determining whether or not localized necking is initiated along the imperfection, and the influence of strain hardening, strain rate hardening and plastic anisotropy on the occurrence of local necking of imperfect sheet is also examined.
Abstract: Localized necking in sheet metal has been examined for strain paths between uniaxial tension and plane strain (ie, the negative minor strain region of a forming limit diagram) The behavior of sheet with preexisting imperfections has been analyzed and is contrasted to that free of imperfections In particular, it is shown that the size and orientation of an imperfection is critical in determining whether or not localized necking is initiated along the imperfection The influence of strain hardening, strain rate hardening, and plastic anisotropy on localized necking of an imperfect sheet is also examined One of the most significant conclusions obtained from present analysis and from a reexamination of Hill’s theory is the prediction of a critical thickness strain criterion for the onset of localized necking at negative minor strains, regardless of whether or not an imperfection is present The critical thickness strain criterion is observed in Ti alloys, Al alloys, steels, and brass
TL;DR: Elaboration d'un modele pregnant, aux elements finis integres, applicable a la description and la comprehension, des phenomenes se produisant dans des materiaux incompressible as mentioned in this paper.
Abstract: Elaboration d'un modele pregnant, aux elements finis integres, applicable a la description et la comprehension, des phenomenes se produisant dans des materiaux incompressibles
TL;DR: The results of some new and previously published data from indentation hardness tests on natural and synthetic quartz as a function of temperature provide several interesting conclusions as mentioned in this paper, including that quartz hardness appears to be affected by the concentration of some cationic impurities but not by others.
Abstract: The results of some new and previously published data from indentation hardness tests on natural and synthetic quartz as a function of temperature provide several interesting conclusions. Indentation hardness appears to be affected by the concentration of some cationic impurities but not by others. A previous study showed that quartz hardness could be affected by electrolytically injecting lithium, but for the six natural quartz samples used in this study, no correlation between structural hydroxyl content and hardness existed. Several natural crystals showed hardening caused by heat treatments at temperatures of 600°C or higher for times of the order of several hours. Two synthetic crystals were tested, and samples from one showed a correlation of hardness with total hydroxyl content. The hardness of the weakest synthetic crystal was never less than 50% of the average of the natural quartz values at all temperatures up to 850°C.
TL;DR: In this paper, the surfaces of nodular and gray cast iron specimens have been modified by CO2 laser processing for enhanced hardness and erosion resistance by controlling resolidification of the laser melted layer through variations in laser beam/target interaction time and beam power density.
Abstract: The surfaces of nodular and gray cast iron specimens have been modified by CO2 laser processing for enhanced hardness and erosion resistance. Control of the near-surface microstructure was achieved primarily by controlling resolidification of the laser melted layer through variations in laser beam/target interaction time and beam power density. Typical interaction times and power densities used in this study were 5 msec and 500 kW/cm2. Analysis of the laser melted surface showed a dramatic increase in hardness and a greatly refined microstructure. Depending on the processing parameters, two basic kinds of microstructure can be produced in the laser hardened layer—a feathery microstructure with a very high hardness (up to 1245 HV) and a dendritic microstructure with a metastable, fully austenitic matrix and a lower hardness (600 to 800 HV). Erosion testing was done in a rotating paddle device using slurries of SiO2 or SiC in water. Weight loss and crater profile measurements were used to evaluate the erosion characteristics of the various microstructures. Both ductile and gray cast iron showed marked improvement in erosion resistance after laser processing.
TL;DR: In this article, a viscoplasticity theory which describes anisotropic hardening by using a Lagrangian deformation mapping of the elastic domain is applied to the quantitative modelling of observed yield surface deformation of 1100-0 aluminum subject to non-proportional loading in tension-torsion space.
Abstract: Extensive experimental evidence indicates that yield surfaces exhibit significant anisotropic hardening. Subsequent yield surfaces are both translated and deformed in stress space. A viscoplasticity theory which describes anisotropic hardening by using a Lagrangian deformation mapping of the elastic domain is applied to the quantitative modelling of observed yield surface deformation of 1100-0 aluminum subject to non-proportional loading in tension-torsion space.
TL;DR: In this article, the effect of prior cold deformation on the martensitic hardening response is discussed, which results in finer austenite grains, which produces accelerated carbide dissolution and alloy enrichment compared to un worked, soft annealed structures.
Abstract: Numerous publications refer to the phase transformations and properties of SAE 52100 steel, and this paper concerns itself with the effect of prior cold deformation on the martensitic hardening response. TheAc1 and Ac3 temperatures are lowered due to cold work as is theMs with a resultant increase in the retained austenite content for a given hardening cycle. Significantly, the prior cold deformation results in a refinement of the austenite grain size. The low angle dislocation cells produced by the cold deformation recover during the heating to the austenitizing temperature to form fine ferrite subgrains. The intersections of the fine ferrite subgrains with the spheroidal carbides in the soft annealed microstructures are preferential sites for nucleation of austenite. This results in finer austėnite grains, which produces accelerated carbide dissolution and austenite alloy enrichment compared to un worked, soft annealed structures. The mechanism for the accelerated austenitization is significant in predicting heat treatment response from published phase transformation data for SAE 52100 steel.
TL;DR: In this paper, the authors present some experimental results on 316 L stainless steel at room temperature and show that the additional hardening due to multiaxiality is present every time that the strain (or stress) path is non-proportional.
TL;DR: In this article, two processes are identified which lead to this hardening of chalks: consolidation, which leads to a reduction in porosity to about 40%, and pressure solution/cementation which will occur only after consolidation has increased the effective stress.
Abstract: Chalk exhibits mechanical properties ranging from those akin to a stiff soil to those akin to a strong rock, depending on its diagenetic and deformation history. Two processes are identified which lead to this hardening of chalks: consolidation, which leads to a reduction in porosity to about 40%; and pressure solution/cementation which will occur only after consolidation has increased the effective stress. Both of these processes are restricted by low permeabilities so that during hardening it is necessary for the deformation to maintain permeable pathways to dissipate any excess pore fluid pressure. This is facilitated by fracturing or by the development of open stylolites which permit fluid flow. In the Isle of Purbeck (Dorset) a lateral gradient in chalk hardness across the Purbeck Axis reflects the increasing deformation of the chalk. Both consolidation and pressure solution/cementation have occurred, with complete cementation being restricted to the most highly strained chalk which is also the most fractured. The Purbeck Chalk provides a model for both diagenetic and localized deformation hardening in chalks generally.
TL;DR: In this paper, the influence of the strain path upon the formability of the sheet is investigated using different types of forming limit diagrams under complex strain paths, and the effect of material strain hardening and strain-rate hardening is examined for several strain paths.
Abstract: Forming limit diagrams (FLDs) in simple and complex deformation paths are determined using a theoretical model of localized necking due to an initial heterogeneity of the sheet. The influence of the strain path upon the formability of the sheet is investigated using different types of FLDs under complex strain paths.The effect of material strain hardening and strain-rate hardening is examined for several strain paths. The influence of the imperfection level on the FLDs is presented. Computer simulation of the evolution of rheological parameters during deformation and their dependence on the strain path is carried out.The model is compared with previous experimental works, and a good agreement is obtained between theoretical results and experimental forming limit diagrams.The mathematical model developed in this work is shown to be a powerful tool to understand and predict the plastic behaviour of metal under simple and complex strain paths.
TL;DR: In this article, an extensive theoretical investigation of f.c. crystals under [110] loading in the channel die compression test is presented, and two lattice orientations known from experiment to be stable relative to the channel axes, through large deformations, are investigated for each of four hardening laws.
Abstract: An extensive theoretical investigation of f.c.c. crystals under [110] loading in the channel die compression test is presented. Two lattice orientations known from experiment to be stable relative to the channel axes, through large deformations, are investigated for each of four hardening laws. These are Taylor's classical isotropic hardening rule, a 2-parameter empirical rule from the metallurgical literature, the “simple theory” of anisotropic latent hardening( Havner and Shalaby , Proc. R. Soc. A 358 ,47 (1977)), and a modification of the simple theory proposed by pfirce et al., Acta Met. 30 , 1087 (1982). Predictions of active systems, equal multiple-slip and consequent lattice stability, finite shape change, and lateral constraint stress are the same for all theories, corresponding to minimum rate of plastic work, and are in general agreement with experiments on copper crystals by Wonsiewicz and Chin , Met. Trans. 1 , 2715 (1970) and Wonsiewicz et al. , Met. Trans. 2 , 2093 (1971). The predictions of latent hardening differ among the theories, however, depending upon whether there is relative rotation of material and lattice. The potential significance of experimental studies of latent hardening in these particular stable lattice orientations is emphasized.
Patent•
25 Jan 1984
TL;DR: Organopolysiloxane compositions which rapidly harden to the elastomeric state, even at ambient temperatures, are comprised of polyhydroxylated polysiloxanes, polyacyloxysilane cross-linking agent, and a hardening accelerator comprising an alkali or alkaline earth metal hydroxide.
Abstract: Organopolysiloxane compositions which rapidly harden to the elastomeric state, even at ambient temperatures, are comprised of (i) a polyhydroxylated polysiloxane, (ii) a polyacyloxysilane cross-linking agent therefor, and (iii) a hardening accelerator comprising an alkali or alkaline earth metal hydroxide. The subject compositions are useful, inter alia, for providing elastomeric seals.
TL;DR: A comprehensive review of current efforts on design of ductile polycrystalline Ni3 AI alloys can be found in this paper, where boron is used to improve the ductility and fabricability of Ni3 Al.
Abstract: This paper provides a comprehensive review of current efforts on design of ductile polycrystalline Ni3 AI alloys. Microalloying has proven to be very effective in alleviating the grain-boundary emibrittlement problem. The ductility and fabricability of Ni3 Al (24 at. % Al) are dramatically improved by adding a few hundred parts per million of boron. The beneficial effect of boron is related to its unusual segregation behavior as predicted from the theory of grain-boundary cohesion developed by Rice, based on thermodynamic analyses. Alloy stoichiometry strongly influences grain-boundary chemistry, which, in turn, affects the boundary cohesion and overall ductility of Ni3 Al. The solid-solution hardening of Ni3 AI depends on the substitutional behavior of alloying elements, atomic size misfit, and the degree of nonstoichiometry of the alloy. Hafnium additions are very effective in improving high-temperature properties of ternary Ni3Al (Al + Hf = 24 at. %) doped with boron. Alloying with <2% Hf substantially increases the yield stress and raises the peak-strength temperature. In addition, hafnium substantially improves creep properties and oxidation resistance. The Ni3 Al aluminides truly represent a new series of heat resistant materials which do not depend on chromium for oxidation resistance.
TL;DR: In this paper, Annealed specimens of AISI 304 and 316 were irradiated in the EBR-II fast reactor at ~400°C over a range of neutron fluxes and energy spectra.
TL;DR: In this article, the influence of the cooling intensity during hardening was investigated and the possibilities and limits of accelerating the cooling rate were studied, and the importance of the transformation heat was discussed.
TL;DR: In this paper, a constitutive model based on the concept of kinematic hardening is proposed to simulate monotonic and cyclic creep deformation in pure copper tubes subjected to combined tension and torsion at 300°C.
TL;DR: In this article, the structure and morphology of high purity alloys Fe-Mo-C and Fe-V-C during aging at 550°C are studied by electron diffraction, electron and field ion microscopy, X-ray measurements of α Fe matrix unit cell dimensions, and Mossbauer spectroscopy.
Abstract: The structure and morphology of Mo2C and VC resulting in secondary hardening of high purity alloys Fe-Mo-C and Fe-V-C during aging at 550°C are studied by electron diffraction, electron and field ion microscopy, X-ray measurements of α Fe matrix unit cell dimensions, and Mossbauer spectroscopy. It is stated that in the early stages of aging, when a sharp decrease in hardness occurs, the process takes place in two directions simultaneously, namely, the formation of cementite particles and the formation of globular clusters of alloying element atoms, the latter being mainly on dislocations and at grain boundaries. During the period of hardness increase, cementite particles are dissolving, and the content, shape, and location of alloying element clusters are changing. The alloying element clusters are mixed zones of M and C atoms, disclike in shape, the discs lying on {100}α planes. Special carbides having the fcc structure are observed at peak hardness in all the alloys investigated. The fcc struct...
TL;DR: In this article, the authors studied the creep flow rules of 316L stainless steel in tensile and axial-torsion experiments and showed that at low creep values of ϵkT I DGb a single kinematical variable: the internal stress takes a part in these laws.