Increasing Deformation Strain Research Articles

Microstructure evolution and mechanical property of Mg-Gd-Y-Zn-Zr alloy wires prepared by hot drawing

This study examined the effects of hot drawing deformation on the microstructure, texture, and mechanical properties of an Mg-9.5Gd-4Y–2Zn-0.3Zr alloy. A Φ6 mm extruded alloy bar was hot drawn down to a Φ1.2 mm wire through multi-passes. The results revealed that the intergranular 18R-long period stacking ordered (LPSO) phase was gradually changed into elongated shapes distributing along the drawing direction with increasing deformation strain, while the 14H-LPSO phase precipitates in the α-Mg matrix are progressively fragmented. The average grain size in the wire first increased from 4.6 μm to 25.9 μm and then decreased to 6.7 μm, and the volume fraction of dynamic recrystallisation first decreased from 95.5% to 8.6% and then increased to 48.7%. The initial weak <0001>//ED anomalous texture gradually changed and strengthened into a <01-10>//DD dual basal texture. The Φ1.2 mm wire achieved a tensile strength of 553.5 MPa, a yield strength of 473.6 MPa, and an elongation of 2.5%. Calculations indicated that the high yield strength in Φ1.2 mm wire was mainly attributed to the high content of the large aspect ratio 18R-LPSO phase, high density of low angular grain boundaries, and strong basal texture.

Mechanisms of necklace recrystallization in a BCC Fe-Al-Ta alloy with strengthening Laves phase precipitates

A necklace structure composed of fine grains formed by dynamic recrystallization was uncommonly observed at the pre-existing grain boundaries during the hot compression of a BCC Fe-25Al-1.5Ta alloy containing C14 - (Fe, Al)2Ta Laves phase precipitates. Two possible mechanisms for necklace formation were proposed; particle-stimulated nucleation and grain boundary bulging, depending on whether the original grain boundaries are occupied by C14 particles, or they are free of them. Recrystallization was initiated preferentially around the clusters of large particles at the boundaries containing particles. In contrast, the bulging of the original grain boundaries by strain-induced boundary migration was observed as a preliminary stage for necklace formation at the particle-free boundaries. The necklace structure expanded into the deformed volume in such a way that low-angle subgrain boundaries decorating the necklace layers transformed into grains with increasing deformation strain.

Investigation of the relationship between microstructural evolution and mechanical properties in a metastable β-ZrTiAlV alloy

In this study, the relationship between microstructural evolution and mechanical properties of a metastable β-ZrTiAlV alloy during compression was investigated. Microstructure characterization revealed that three different morphologies of α′ martensite, 101¯2 twinned α′ martensite, untwinned α′ martensite and α′ martensite paired were triggered at the initial deformation stage. With increasing deformation strain, these three kinds of α′ martensite undergo a process of widening and merging, and eventually form the 101¯2twin-related α′ domains, normal α′ domains and connected α′ domains, respectively. Mechanical properties test shows that the alloy exhibits a relatively high yield strength of 900 MPa and a high work hardening rate (about 6000 MPa) during compression. This high yield strength is attributed to the high triggering stress of deformation-induced β to α′ martensite transformation at initial deformation stage and the high solid solution strengthening effect of large amount Ti. The activation of α′ martensite and 101¯2 internal twins brings about the transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects, giving the alloy a substantial high work hardening rate, and their evolution with increasing strain leads to nonlinear evolution of the work hardening rate.

Effect of pre-deformation before aging on discontinuous precipitation behaviour in Cu-Ni-Si alloys

ABSTRACT The effect of deformation before aging on discontinuous precipitation in Cu–4.75wt%Ni–1.13wt%Si and Cu–6wt%Ni–1.42wt%Si alloys after solution treatment was investigated. Two kinds of deformation, one under and the other over the uniform deformation limit were implemented after solution treatment. With increasing deformation strain in both alloys, the discontinuous precipitation is accelerated and the aging time for a fully covered region by discontinuous precipitation is shortened. However, the Cu–6wt%Ni–1.42wt%Si alloy deformed under the uniform deformation limits showed an enhanced discontinuous precipitation compared to that for the alloy deformed over the uniform deformation limit. The deformation defects including dislocations and shear bands play the role of encouraging discontinuous precipitation. The shear bands formed during prior deformation beyond the necking point could provide sites for discontinuous precipitation initiation in the early stages of annealing However, shear bands tend to hinder the advance of discontinuous precipitation with further aging in the Cu–Ni–Si alloy with a high content of Ni and Si.

The effects of increasing deformation strain on the microstructural evolution of a metastable β-Zr alloy

In this study, we investigated the morphology evolution of deformation-induced α', α″ martensite and retained β phase with increasing deformation strain in metastable β-Zr-43.2Ti-4.5Al-4.2V (wt. %) alloy by ex-situ and regular compression tests. Three types of deformation-induced α' martensite have been observed for the first time during deformation, namely, twinned α' martensite, untwinned α' martensite and paired α' martensite. Transitions in morphology of twinned α' martensite from thin plate to twinned plate and to widened twinned plate, eventually to {101¯2} twin-related domains and of untwinned α' martensite from thin plate to widened plate to domain have been observed with increasing deformation strains. The paired α' martensite is undergone a process in which the α' martensite impacted grain boundaries stimulating the nucleation of new α' martensite in neighboring grains, and then leading to martensite growth on both sides grow simultaneously. With progressive deformation, the nano-size deformation-induced α″ martensite changes from long thin plate to ladder-shaped plate to 90° rotation domains. The morphology evolution of untwinned α' martensite, paired α' martensite and α″ martensite are mainly related to the self-accommodation mechanism, while the morphology evolution of twinned α' martensite is mainly related to the plastic accommodation mechanism. The average hardness increased with increase in deformation strains, owing to the martensitic transformation strengthening along with dislocation multiplication strengthening.

A phenomenon of strain induced bainitic transformation and its effect on strength enhancement in a lightweight transformation-induced-plasticity steel

Microstructure evolution, transformation behavior and mechanical property are examined for a Fe-0.35C-1.1Mn-4.1Al-0.38Si (in wt%) ferrite-based lightweight transformation induced plasticity (TRIP) steel under tensile deformation at room temperature (25 °C) to 450 °C. The influence of deformation temperature and strain on mechanical stability of retained austenite leads to the occurrence of various transformations in the TRIP steel. From room temperature towards 150 °C, strain induced martensitic transformation (SIMT) takes place resulting in the formation of twin-type martensite, and it is progressively suppressed with increasing deformation temperature. A phenomenon of strain induced bainitic transformation (SIBT) of retained austenite is observed at higher deformation temperatures, and it is enhanced with increasing deformation strain and temperature ranging from 150 °C to 300 °C. During the SIBT, the formation of carbide-free bainite with high dislocation density is primarily attributed to the increased carbon diffusivity. The occurrence of the SIBT reveals the significant importance of the diffusion-associated mechanism for the bainitic transformation. Above 300 °C, the activation of dislocation movement in retained austenite gradually replaces the SIBT with increasing deformation temperature. The highest tensile strength obtained at 300 °C indicates the strength enhancement due to the SIBT.

Precipitation behaviors of 14H LPSO lamellae in Mg96Gd3Zn0.5Ni0.5 alloys during severe plastic deformation

A high-performance extruded Mg96Gd3Zn0.5Ni0.5 alloy containing 14H LPSO phases and two different dynamic recrystallization (DRX) grains was successfully fabricated, which exhibited superior ultimate tensile strength (400 MPa) and outstanding elongation (20%). Meanwhile, the results show that the substitution of 0.5 at.% Zn with Ni element can refine the grain size of as-cast Mg96Gd3Zn1 alloy significantly. While limited 14H LPSO lamellae are formed near the block 14H LPSO phases due to Ni addition during solution treatment, copious 14H LPSO lamellae induced by external force are precipitated in α-Mg matrix after subsequent hot extrusion in the Mg96Gd3Zn0.5Ni0.5 alloy. Furthermore, two different DRX phenomena are successively stimulated with increasing deformation strain. Discontinuous DRX emerges first at the interface of block 14H LPSO phases, and then continuous DRX occurs in the kink bands of 14H LPSO lamellae. The precipitation behaviors of 14H LPSO lamellae and two types of DRX grains contribute to the excellent mechanical properties.

The analysis of severely deformed pure Fe structure aided by X-ray diffraction profile

Pure Fe was severely deformed by a combination of shaped cold rolling and cold drawing. X-ray diffraction profiles analysis was applied in accordance with the Williamson-Hall (WH) and modified Williamson-Hall (MWH) methods to identify crystallite sizes of the deformed specimens. It was found that some differences exist between the results of WH and MWH procedures using the hkl dependent Young’s modulus or considering the average dislocation contrast factor. The latter method is more accurate and enables the determination of the character of dislocations in plastically deformed Fe. It was shown that by increasing deformation strain, the screw dislocations dominated. The enhancement of hardness occurs in the deformed Fe due to grain refinement, dislocation accumulation and deformation-induced vacancies.

Investigation of texture, microstructure, and mechanical properties of a magnesium–lanthanum alloy after thermo-mechanical processing

Abstract The texture, microstructure, and mechanical properties of Mg-1.33La (wt.%) alloy after hot rolling and cold plane strain compression were investigated by using X-ray diffraction, optical microscopy, and micro-hardness measurements. This thermo-mechanical processing resulted in a relative weakening of the texture that was mainly a basal type. The microstructures after hot rolling and cold plane strain compression revealed the presence of a second phase (Mg17La2), mostly at grain boundaries. Twins were profuse, and their morphologies were quite different after hot rolling and cold plane strain compression. The Mg-1.33La (wt.%) alloy exhibited good room temperature formability and an increase in strength. The alloy's hardness increased with increasing deformation strain. Such properties were explained by the effect of both the Mg17La2 phase precipitation and the sample's texture.

Strain-induced dynamic precipitation of Mg17Al12 phases in Mg–8Al alloys sheets rolled at 748 K

Strain-induced dynamic precipitation of Mg17Al12 phases was observed in large strain hot rolling of Mg–8Al alloys sheets. Our results show that Mg17Al12 phase precipitates in dynamic recrystallization of grains due to severe plastic deformation and the amount of secondary particles increases with increasing deformation strain. Two types of nanoscale Mg17Al12 phases precipitated inside dynamic recrystallized grains were observed. The growth of dynamic recrystallized grains is constricted by the pinning effect of β phase. The mechanical properties of rolled sheets are largely influenced by the increase of the deformation strain. It shows that the increase of ultimate tensile strength of rolled sheets can be segregated into two different stages, which are similar to the enhancement of dynamic recrystallization. The tendency of mechanical properties evolution of rolled sheets reveals that strain-induced precipitates have excellent hardening behavior and it can be considered as a promising way in improving mechanical properties of Mg alloys.

Free Volume Study of Severely Plastic Deformed Pure Fe

There is a growing interest for investigation of free-volume type defects in SPD-processed ultrafine-grained materials. In the present work, excess free volume in pure Fe prepared by shaped rolling is studied by high-resolution differential dilatometer as well as Archimedes method. The results show the formation of excess volume with increasing deformation strain. The volume fraction of free volume detected by dilatometer is below the evaluation of Archimedes method maybe because of the existence of void in the deformed metal. Microstructural study by field emission type scanning electron microscope confirms the presence of voids.

Strain-induced refinement and thermal stability of a nanocrystalline steel produced by surface mechanical attritiontreatment

A surface layer with a depth-dependent nanocrystalline microstructure was formed on reduced activation ferrite-martensitic (RAFM) steel by means of surface mechanical attrition treatment (SMAT). Equiaxed nano-sized grains in the surface layer were characterized by XRD, SEM and TEM, and the result indicated that the grain size decreased gradually with increasing deformation strain and strain rate. Compared with the size and number of carbides in the matrix, smaller and fewer carbides were detected in the SMAT layer, which indicated the refining and dissolving process of carbide during the drastic deformation in the SMAT process. Sub-grain boundaries (sub-GB) and high dense dislocation walls (DDWs) in ferrite were found in deformation layer, and dislocation accumulation, rearrangement and annihilation during the drastic deformation were discussed in detail. Both TEM images and XRD results demonstrate that the nanocrystalline layer has excellent thermal stability after annealing at 823K.

Influences of Solution Treatment, Deformation Strain, and Nanometric Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Particulate on Dry Wear Properties for Nanometric Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Particulate Reinforced Al Alloy Matrix Composites Manufactured by Casting

The influences of solution treatment, deformation strain, and nanometric Al2O3 particulate on dry wear properties for nanometric Al2O3 particulate reinforced Al alloy matrix Composites manufactured by casting were investigated. The result showed that both the wear resistance of AL matrix and the composites increased rapidly with increasing solution temperatures. The wear resistance increased slightly with increasing deformation strain for the composites. The wear resistance of the composites is higher than the AL matrix after the same deformation and heat treatment. Microstructure observation revealed that the grain sizes of the composites increased with increasing solution temperature and decreased with more severe deformation. Abrasive wear was the main wear mechanism both for the AL matrix and the composites.

A study of deformation-induced phosphorus grain boundary segregation in an interstitial free steel

Phosphorus grain boundary segregation in an interstitial free (IF) steel deformed at different temperatures and strain rates is measured by virtue of Auger electron spectroscopy (AES). The results reveal that the deformation-induced phosphorus grain boundary segregation has a non-equilibrium characteristic and increases with increasing deformation strain until reaching a steady value. In addition, the segregation of phosphorus increases more apparently for the specimen deformed at a lower temperature or a higher strain rate. Predictions with a kinetic model developed recently show a reasonable fit between the predictions and the observations, which indicates that the model is effective in the prediction of deformation-induced grain boundary segregation.

Influences of Solution Treatment, Deformation Strain and Nanometric Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Particulate on Hardness for Nanometric Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Particulate Reinforced Al Alloy Matrix Composites Manufactured by Casting

The influences of solution treatment, deformation strain, and nanometric Al2O3 particulate on hardness for nanometric Al2O3 particulate reinforced Al alloy matrix Composites manufactured by casting were investigated. The result showed that both the hardness of AL matrix and the hardness of the composites increased dramatically with increasing solution temperatures. The hardness increased slightly with increasing deformation strain for the composites. The hardness of the composites is higher than the AL matrix after the same deformation and heat treatment. Microstructure observation revealed that the grain sizes of the composites increased with increasing solution temperature and decreased with more severe deformation.

Influences of phase composition and thermomechanical conditions on shape memory properties of segmented polyurethanes with amorphous reversible phase

AbstractWe synthesized series of shape memory polyurethanes with amorphous reversible phase (Tg‐SMPUs) and systematically studied their microphase structure and shape memory properties. The Tg‐SMPUs having no or less hard phase showed lower shape recovery. When the volume fraction of hard phase was in the range of 20–30%, the Tg‐SMPUs exhibited the highest shape recovery. As the fraction of hard phase increased further the shape recovery decreased, because more polymer components with higher glass transition temperatures (Tgs) would participate in strain storage. For the Tg‐SMPUs having similar Tgs, those polymers having higher volume fraction of hard phase exhibited higher shape fixity, broader shape recovery region, and larger recovery stress. Increasing deformation strain could raise shape fixity and recovery stress but broaden shape recovery region. The highest recovery stress of a material could be achieved when the deformation occurred at its glass transition temperature below which decreasing deformation temperature could not increase recovery stress further. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Flow behavior and microstructure evolution of a P/M TiAl alloy during high temperature deformation

Hot compression tests of a P/M Ti-47Al-2Cr-2Nb-0.2W-0.15B (at. pct) alloy were carried out on a Gleeble-3800 simulator at the temperatures ranging from 950 degrees C to 1250 degrees C with the strain rates ranging from 10 s(-1) to 10(-3) s(-1). Optical microscope, electron backscatter diffraction technique, and transmission electron microscope were employed to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization. It was found that the flow behavior is a function of the deformation temperature and strain rate. The dependence of the peak stress on the deformation temperature and strain rate can be expressed by a hyperbolic-sine type equation. The activation energy for the alloy is calculated to be 315 kJ/mol. The size of the dynamically recrystallized grains decreased with increasing the value of parameter Z. However, the size of dynamically recrystallized grains almost remains constant with increasing deformation strain. At the early stage the dominant nucleation mechanism of dynamic recrystallization in the alloy is the discontinuous dynamic recrystallization, which is characterized by the bulging of the original grain boundaries and the deformation twinning. As the deformation strain increased, the continuous dynamic recrystallization characterized by progressive subgrain rotation occurred. Twinning was observed under all deformation conditions. The spheroidization of the alpha(2) took place at the compression temperature 950 degrees C and the strain rate 10(-3) s(-1). (C) 2011 Elsevier B.V. All rights reserved.

The microstructure evolution and nucleation mechanisms of dynamic recrystallization in hot-deformed Inconel 625 superalloy

Hot compressions tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator at different strains between 900 °C and 1200 °C with a strain rate of 0.1 s −1. Optical microscope, transmission electron microscope and electron backscatter diffraction technique were employed to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization. It was found that both the size and fraction of dynamically recrystallized grains increase with increasing deformation temperature. However, the size of dynamically recrystallized grains almost remains constant with increasing deformation strain. The dominant nucleation mechanism of dynamic recrystallization in Inconel 625 superalloy deformed at 1150 °C is the discontinuous dynamic recrystallization, which is characterized by the bulging of the original grain boundaries accompanied with twining. The continuous dynamic recrystallization characterized by progressive subgrain rotation occurs simultaneously in dynamic recrystallization process, although it can only be considered as an assistant nucleation mechanism at the early stage of hot deformation.

Microstructure and texture evolution in cryorolled Al 7075 alloy

The present work investigates the microstructure and texture evolution of cryorolled Al 7075 alloy using FE-SEM, TEM, and neutron diffraction, respectively. The solution treated bulk Al 7075 alloy is subjected to rolling at liquid nitrogen temperature to produce sheets with different thickness reductions such as 35%, 50%, 70%, and 90%, respectively. It is evident from the microstructural characterisations of cryorolled samples that with the increasing deformation strain induced in the materials, the grains are fragmented and produce high amount of dislocation density due the suppression of dynamic recovery. The texture analysis of the cryorolled Al 7075 alloy has shown that the ideal fibres observed in the starting solution treated alloy has been destroyed during rolling. The Goss/Brass orientation of the cryorolled Al alloy is shifting towards the Brass components with increasing deformation strain induced in the samples. The orientation distribution functions of the cryorolled Al 7075 alloy clearly indicate the progressive weakening of the texture components, during cryorolling, with increasing strain, therefore, fragmentation and reorientation of micron sized grains occurs easily for the formation of subgrains and ultrafine-grained microstructures as evident from EBSD and TEM micrographs.

Shape memory effects of poly(L-lactide) and its copolymer with poly(ε-caprolactone)

The thermal properties, crystalline structure and shape memory effects of poly(L-lactide) (PLLA) and its copolymer with poly(e-caprolactone) (PCL) are systematically investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tensile tests. The influences of composition and intrinsic viscosity on structure and shape memory effects are also revealed. It is found that the PLLA homopolymer and poly(L-lactide-co-e-caprolactone) (PCLA) copolymers exhibit good shape memory effects. The existence of PLLA crystal and amorphous phase play very important roles for shape memory effects. The intrinsic viscosity obviously affects the crystallinity of polymers and further affects the shape memory effects. The shape recovery rate decreases with increasing deformation strain, which is relate to the deformation of PLLA crystal. The recovery stress increase with the increase of the e-CL content and maximum recovery stress is 3.54MPa obtained in the PCLA804 (20wt% e-CL content, Mw=304,400). With the increase of cyclic testing number, the shape recovery rates decrease and the shape retention rates increase at the beginning and then approach to a steady value.