Showing papers on "Hardening (metallurgy) published in 2006"
TL;DR: An analytical model for predicting the yield strength of particulate-reinforced metal matrix nanocomposites has been developed in this article, where the strengthening effects involving Orowan strengthening effect, enhanced dislocation density due to the residual plastic strain caused by the difference in the coefficients of thermal expansion between the matrix and particles, and loadbearing effect have been taken into account in the model.
1,042 citations
TL;DR: It is observed that a nanostructured metal can be hardened by annealing and softened when subsequently deformed, which is in contrast to the typical behavior of a metal.
Abstract: We observe that a nanostructured metal can be hardened by annealing and softened when subsequently deformed, which is in contrast to the typical behavior of a metal. Microstructural investigation points to an effect of the structural scale on fundamental mechanisms of dislocation-dislocation and dislocation-interface reactions, such that heat treatment reduces the generation and interaction of dislocations, leading to an increase in strength and a reduction in ductility. A subsequent deformation step may restore the dislocation structure and facilitate the yielding process when the metal is stressed. As a consequence, the strength decreases and the ductility increases. These observations suggest that for materials such as the nanostructured aluminum studied here, deformation should be used as an optimizing procedure instead of annealing.
617 citations
TL;DR: In this article, the influence of texture and grain size on work hardening behavior and dynamic recovery of magnesium alloys was studied, in addition to the direct effect of texture through the change in the orientation factor for basal and prismatic slip, effects were found on dynamic recovery and the appearance of stage II of workhardening.
598 citations
TL;DR: By controlling the specimen aspect ratio and strain rate, compressive strains as high as 80% were obtained in an otherwise brittle metallic glass, and a systematic strain-induced softening was observed which contrasts sharply with the hardening typically observed in crystalline metals.
Abstract: By controlling the specimen aspect ratio and strain rate, compressive strains as high as 80% were obtained in an otherwise brittle metallic glass. Physical and mechanical properties were measured after deformation, and a systematic strain-induced softening was observed which contrasts sharply with the hardening typically observed in crystalline metals. If the deformed glass is treated as a composite of hard amorphous grains surrounded by soft shear-band boundaries, analogous to nanocrystalline materials that exhibit inverse Hall-Petch behavior, the correct functional form for the dependence of hardness on shear-band spacing is obtained. Deformation-induced softening leads naturally to shear localization and brittle fracture.
390 citations
05 Nov 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors examined the effect of Zn and Na additions to an age hardenable Mg-1.3 Sn (at.%) alloy using hardness measurements and transmission electron microscopy.
Abstract: Additions of Zn and Zn + Na to an age hardenable Mg–1.3 Sn (at.%) alloy have been examined using hardness measurements and transmission electron microscopy. Zn additions resulted in a substantial increase (300%) in the hardening increment after aging at 200 °C but the time to peak hardness was relatively unaffected. The additions were found to have little effect on the number density of precipitates formed and no effect on the identity of precipitates but significant changes to particle morphology were observed. Combined additions of Zn and Na (an element previously illustrated to be an effective microalloying element for the Mg–Sn system) showed features typical of separate additions of Na and Zn: a large increase in the observed hardening increment, an acceleration of the time to peak hardness and a change in particle morphology. Furthermore, the combined Zn + Na additions resulted in synergistic effects on precipitate stability during overaging and the time to peak hardness. The stability of Mg 2 Sn precipitates formed in the Mg–Sn–Zn–Na alloy was much greater than those usually observed in the Mg–Sn–Na system and the time to peak hardness was much reduced from ∼58 h in the Mg–Sn–Na alloy to 7 h in the Mg–Sn–Zn–Na alloy.
270 citations
TL;DR: In this article, a calculated method of hardness based on the Mulliken overlap population analysis in first principles has been presented, and the effects of stress strain on intrinsic hardness were studied, and a formula of hardness under stress was established.
Abstract: Intense theoretical and experimental interest has been focused on the possibility of new materials with hardness exceeding that of diamond. However, building the link between the information that first-principles calculations can produce and the hardness of materials remains one of the challenges of computational materials science. In this paper, a calculated method of hardness based on the Mulliken overlap population analysis in first principles has been presented. In particular, the effects of stress strain on intrinsic hardness were studied, and a formula of hardness under stress is established. It can be employed to explain the hardening phenomenon resulting from the stress of film and grain boundary and nanoeffects. The theoretical results revealed that nanodiamond films obtained by careful experiments can be harder than bulk single-crystal diamonds.
268 citations
TL;DR: In this paper, the effect of deformation twinning on the mechanical response of high-purity α-titanium deformed at room temperature was investigated and it was shown that the newly formed deformation twins were harder than the matrix.
Abstract: Novel experiments were conducted to elucidate the effect of deformation twinning on the mechanical response of high-purity α-titanium deformed at room temperature. Orientation-imaging microscopy (OIM), microhardness, and nanohardness evaluations were employed in conjunction with optical microscopy and quasi-static compression testing to obtain insight into the deformation mechanisms. Hardness measurements revealed that the newly formed deformation twins were harder than the matrix. This observation is perhaps the first experimental evidence for the Basinski mechanism for hardening associated with twinning, arising from the transition of glissile dislocations to a sessile configuration upon the lattice reorientation by twinning shear. This work also provided direct evidence for two competing effects of deformation twinning on the overall stress-strain response: (1) hardening via both a reduction of the effective slip length (Hall-Petch effect) and an increase in the hardness of twinned regions (Basinski mechanism) and (2) softening due to the lattice reorientation of the twinned regions.
224 citations
TL;DR: In this paper, the precipitation sequence on artificial ageing of a stretched Al-Cu-Mg alloy was studied using transmission electron microscopy, differential scanning calorimetry and hardness tests, which showed that the second stage hardening is dominated by S phase, which forms a dense precipitate structure at the peak hardness stage, whilst no significant amounts of other phases or zones are detected.
213 citations
TL;DR: In this paper, the effect of strain rate on stress-strain behavior of austenitic stainless steel 309 and 304L was investigated, where tensile tests were conducted at room temperature at strain rates ranging from 1.25×10−4s−1 to 400 s−1.
Abstract: The effect of strain rate on stress-strain behavior of austenitic stainless steel 309 and 304L was investigated. Tensile tests were conducted at room temperature at strain rates ranging from 1.25×10−4s−1 to 400 s−1. The evolution of volume fraction martensite that formed during plastic deformation was measured with X-ray diffraction and characterized with light microscopy. Alloy 304L was found to transform readily with strain, with martensite nucleating on slip bands and at slip band intersections. Alloy 309 did not exhibit strain-induced transformation. Variations in ductility and strength with strain rate are explained in terms of the competition between hardening, from the martensitic transformation and a positive strain rate sensitivity, and softening due to deformational heating. Existing models used to predict the increase in volume fraction martensite with strain were examined and modified to fit the experimental data of this study as well as recent data for alloys 304 and 301LN obtained from the literature.
207 citations
TL;DR: In this article, the effect of the particle size, codeposition percentage of SiC and type of imposed current on microhardness as well as on the microstructure of the electrodeposits were investigated.
Abstract: Pure Ni and nickel matrix composite electrocoatings containing micron- and nano-SiC particles (1 μm and 20 nm respectively) were produced under direct and pulse current conditions from an additive-free Watts type bath. The effect of the particle size, codeposition percentage of SiC and type of imposed current on the microhardness as well as on the microstructure of the electrodeposits were investigated. Ni/SiC composite deposits prepared under either direct or pulse current conditions exhibited a considerable strengthening effect with respect to pure Ni coatings. The improved hardness of composite coatings was associated to specific structural modifications of Ni crystallites provoked by the adsorption of H+ on the surface of SiC particles, thus leading to a (211) texture mode of Ni crystal growth. Pulse electrodeposition significantly improved the hardness of the Ni/SiC composite coatings, especially at low duty cycles, in which grain refinement and higher SiC incorporation (vol. %) was achieved. The enhanced hardness of Ni/nano-SiC deposits, as compared to Ni/micron-SiC composites, was attributed to the increasing values of the number density of embedded SiC particles in the nickel matrix with decreasing particle size. In addition, the observed hardening effects of the SiC particles might be associated to the different embedding mechanisms of the particles, which could be characterized as inter-crystalline for micron-SiC and partially intra-crystalline for nano-SiC particles.
200 citations
TL;DR: In this article, the effects of loading rate, peak/valley strain or stress holds, ambient temperature and non-proportional loading path on the cyclic softening/hardening and ratchetting behaviors of the material were discussed.
15 Dec 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of tool traverse and rotation speeds on the residual stresses are quantified for welds between non-age-hardening AA5083 and age-hardened AA6082 and compared to single alloy joints made from each of the two constituents.
Abstract: The effect of tool traverse and rotation speeds on the residual stresses are quantified for welds between non-age-hardening AA5083 and age-hardening AA6082 and compared to single alloy joints made from each of the two constituents. The residual stresses have been characterised non-destructively by neutron diffraction and synchrotron X-ray diffraction. The region around the weld line was characterised by significant tensile residual stress fields which are balanced by compressive stresses in the parent material. The rotation speed of the tool has been found to have a substantially greater influence than the transverse speed on the properties and residual stresses in the welds, particularly on the AA5083 side where the location of the peak stress moves from the stir zone to beyond the edge of the tool shoulder. The changes in residual stress are related to microstructural and hardness changes as determined in a previous study [1,2]. In particular the larger stresses under the weld tool on the AA5083 side compared to the AA6082 side are related to a transient reduction in yield stress due to dissolution of the hardening precipitates during welding prior to natural aging after welding.
TL;DR: In this paper, an anisotropic model that captures the influence of evolving texture on the plastic response of hexagonal close-packed (hcp) metals is proposed, which is further applied to the description of the mechanical behavior of high-purity zirconium at room temperature.
TL;DR: A temperature-dependent anisotropic material model for use in a coupled thermo-mechanical finite element analysis of the forming of aluminum sheets was developed in this article, where the anisotropy properties of the aluminum alloy sheet AA3003-H111 were characterized for a range of temperatures 25 −260 −C (77 −500 −F) and for different strain rates.
TL;DR: In this paper, a semianalytical Sachs-type equation for the flow stress of magnesium-base alloys is developed using the Schmid law, power law hardening, and a sigmoidal increase in the twinning volume fraction with strain.
Abstract: A semianalytical Sachs-type equation for the flow stress of magnesium-base alloys is developed using the Schmid law, power law hardening, and a sigmoidal increase in the twinning volume fraction with strain. Average Schmid factors were estimated from electron backscattered diffraction (EBSD) data. With these, the equation provides a reasonable description of the flow curves obtained in compression and tension for samples of Mg-3Al-1Zn cut in different orientations from rolled plate. The model illustrates the general importance of basal slip and twinning in magnesium alloys. The significance of prismatic slip in room temperature tension testing is also highlighted. This is supported with EBSD slip line trace analysis and rationalized in terms of a possible sensitivity of the critical resolved shear stress for prismatic (cross) slip to the stress on the basal plane.
TL;DR: In this article, low-temperature gas-phase carburization has been used to generate very high surface interstitial carbon contents, up to ∼12 at.%, in a 316L austenitic stainless steel.
TL;DR: The microstructure and hardness of binary Al-Zn and Al-Mg alloys were studied both in the as-cast state and after high-pressure torsion (HPT) with 5 torsions (shear strain about 6).
25 May 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors used the electron back scattering diffraction technique to reveal changes of bulk microstructure due to cyclic loading and minor changes of dislocation microstructures were detected by transmission electron microscopy, which was attributed to high stability of the grain structure and lower purity of the examined ultrafine-grained copper.
Abstract: Fatigue lifetime under stress control of ultrafine-grained Cu of 99.9% purity prepared by equal channel angular pressing is shown to exceed that of conventionally grained cold worked counterparts by a factor of 1.7 in the low-, high- and very-high-cycle region. The electron back scattering diffraction technique did not reveal changes of bulk microstructure due to cyclic loading. Minor changes of dislocation microstructure were detected by transmission electron microscopy. Qualitative change from moderate cyclic hardening to cyclic softening was observed with increasing stress amplitude. Comparison of S–N data with those available in literature shows substantially higher lifetime of the material studied in this work in the high- and very-high-cycle region. This effect is attributed to the high stability of the grain structure and lower purity of the examined ultrafine-grained copper.
TL;DR: In this paper, two expanding cavity models (ECMs) are developed for describing indentation deformations of elastic power-law hardening and elastic linear-hardening materials, which explicitly show that for a given indenter geometry indentation hardness depends on Young's modulus, yield stress and strainhardening index of the indented material.
TL;DR: In this paper, the interaction between twinning and slip in clock-rolled zirconium plate and the role that it plays in the hardening response was investigated, and it was shown that twins influence the reload behavior by either reorienting material for easy slip or by providing barriers to slip.
15 Jan 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The low-cycle fatigue behavior of SUS304-HP austenitic stainless steel was investigated systematically using tension-compression cycling under fully reversed total strain amplitude control conditions at room temperature in laboratory air.
Abstract: The low-cycle fatigue (LCF) behaviour of SUS304-HP austenitic stainless steel was investigated systematically using tension-compression cycling under fully reversed total strain amplitude control conditions at room temperature in laboratory air. In addition to tests at constant strain amplitudes, incremental step tests (IST) were also carried out. Cyclic stress response, during companion specimen tests (CST), revealed combinations of a variable cyclic hardening, stable behaviour and softening, depending on the applied cyclic strain amplitude, while during incremental step tests it exhibited cyclic hardening character at all strain levels. Microstructure observations using optical and transmission electron microscopy (TEM) revealed that with increasing total strain amplitudes the slip band density increased and the dislocation structure changed from a planar array to a more cellular-like structure. Cyclic deformation-induced austenite/martensite transformation was observed at higher cyclic strain amplitudes. The change in microstructures during cycling is responsible for the fatigue hardening/softening behaviour of the material. The SEM micrographs revealed that at low-strain amplitudes the inclusion-type nucleation occurred near the surface, while at the higher strain amplitudes crack initiation characterized by cleavage cracking occurred not only near the surface but also in the interior of the specimen. Linear or single-slope behaviour was seen both in cyclic stress–strain and Coffin-Mason plots. Masing cyclic stress–strain behaviour was presented only in the IST method but not in the CST method.
TL;DR: Based on thermodynamic calculations, a die-cast Mg-1.6, Ca-3.2, Zn alloy was solution treated at 465°C and aged at 150, 175, 200 and 225°C for up to 32 days as mentioned in this paper.
TL;DR: Canning et al. as mentioned in this paper investigated the quasi-static and dynamic compressive behavior of pyramidal truss cores made of 304 stainless steel using a combination of experimental techniques and provided a quantification of load-deformation response and associated failure modes across the sample.
TL;DR: In this paper, the effect of nanoparticles on the creep resistance of polyamide 66 was investigated under different stress levels (20, 30 and 40 MPa) at room and elevated temperatures (23, 50 and 80 8C), respectively.
15 Apr 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: A new high strength and high conductivity Cu-Fe-P-B-Ce alloy strengthened by cold working and aging was designed in this article, which exhibits excellent combination property that the tensile strength ( σ b ) is 509 MPa, the elongation ( δ ) is 16% and the conductivity is 80% IACS
Abstract: A new high-strength and high-conductivity Cu–Fe–P–B–Ce alloy strengthened by cold working and aging was designed The mechanical properties and electrical conductivity of Cu–Fe–P and Cu–Fe–P–B–Ce alloys were measured, and the microstructures of the samples were analyzed with optical microscope and by transmission electron microscopy Results showed that the recrystallization temperature of Cu–Fe–P alloy was greatly raised by adding trace B and Ce Thus, the good strengthening effect processed by both precipitation hardening and cold working hardening was obtained This novel Cu–Fe–P–B–Ce alloy exhibits excellent combination property that the tensile strength ( σ b ) is 509 MPa, the elongation ( δ ) is 16% and the conductivity is 80% IACS
TL;DR: In this article, the authors used phenomenological-empirical fitting models to assess the dose (displacement-per-atom, dpa), irradiation temperature (Ti) and test temperature (Tt) dependence of yield stress changes (Δσy), as well as the corresponding dependence of sub-sized Charpy V-notch impact test transition temperature shifts (�Tc).
TL;DR: In this paper, a model to predict the austenite decomposition into ferrite, pearlite, bainite and martensite during arbitrary cooling paths for thin sheet boron steel is used.
TL;DR: In this paper, a commercial purity aluminum nano-powder has been consolidated by the hot isostatic pressing technique, and the material yielded at 390 MPa -10 times the flow stress of the coarse-grained counterpart material.
TL;DR: In this paper, the role of different constituents of dual phase steel during the BH effect was investigated in detail by means of precision dilatometry and X-Ray Diffraction (XRD).
Abstract: The increase in the yield stress of dual phase (DP) steels, resulting from the static strain ageing phenomenon, commonly referred to as bake hardening (BH), gives an important contribution to the additional in-service strength of outer auto body parts, e.g. with respect to the dent resistance of the components made with DP steel. In order to understand this large BH effect, the role of the different constituents of the DP steel during this process needs to be considered. The various stages of tempering phenomena taking place in the martensite phase were investigated in detail by means of precision dilatometry and X-Ray Diffraction (XRD). The succession of the various tempering reactions that are characterised by typical volume changes was determined using both constant heating rate and isothermal dilatometric tests. The measurements made it possible to distinguish five distinct stages of structural changes during tempering: (I) the redistribution of carbon atoms, (II) the precipitation of η- or e-carbide, (III) the formation of Hag-carbide, (IV) the decomposition of retained austenite, and (V) the transformation of transition carbides to cementite.
TL;DR: In this paper, the deformation microstructures of an Fe-27% Cr-9% Ni dual-phase stainless steel, which was bar rolled/swaged to a total strain of 6.9 at ambient temperature, were studied.