High True Strain Research Articles

Ionic Strength of Methylcellulose-Based Films: An Alternative for Modulating Mechanical Performance and Hydrophobicity for Potential Food Packaging Application

The growing environmental concern with the inappropriate disposal of conventional plastics has driven the development of eco-friendly food packaging. However, the intrinsic characteristics of polymers of a renewable origin, e.g., poor mechanical properties, continue to render their practical application difficult. For this, the present work studied the influence of ionic strength (IS) from 0 to 500 mM to modulate the physicochemical properties of methylcellulose (MC). Moreover, for protection against biological risks, Nisin-Z was incorporated into MC’s polymeric matrices, providing an active function. The incorporation of salts (LiCl and MgCl2) promoted an increase in the equilibrium moisture content in the polymer matrix, which in turn acted as a plasticizing agent. In this way, films with a hydrophobic surface (98°), high true strain (85%), and low stiffness (1.6 mPa) can be manufactured by addition of salts, modulating the IS to 500 mM. Furthermore, films with an IS of 500 mM, established with LiCl, catalyzed antibacterial activity against E. coli, conferring synergism and extending protection against biological hazards. Therefore, we demonstrated that the IS control of MC dispersion presents a new alternative to achieve films with the synergism of antibacterial activity against Gram-negative bacteria in addition to flexibility, elasticity, and hydrophobicity required in various applications in food packaging.

Effect of single-crystal orientation on the molybdenum structure and hardness upon high pressure torsion

The effect of the initial orientation on structure development upon severe plastic deformation performed by high pressure torsion at room temperature has been investigated on molybdenum single crystals of two orientations (110) and (113). The initial orientation of molybdenum has been found to affect its deformability, texture, and the size of structural elements significantly only at the initial stages of deformation. Single crystal with the (113) orientation is more stable to deformation. Its fragmentation starts at a higher true strain than the fragmentation of the single crystal with the (110) orientation. An increase in the true strain above 6 completely neutralizes the effect of the initial orientation on the structure development.

Refinement of Ti18Zr15Nb alloy structure exposed to accumulative high-pressure torsion deformation

The strain γ processing at high-pressure torsion (HPT) deformation for many hard materials is really much smaller than expected. This is a result of slippage of sample surface and surface of anvils. In this context, the authors develop a new method- “accumulative high-pressure torsion” (ACC HPT). This method enables producing much higher true strains in metallic and alloys than the traditional HPT method. HPT and ACC HPT were applied to β-Ti-alloys Ti-18Zr-15Nb. As TEM studies showed, the size of grains after HPT n = 10 revolutions is about 40 nm while the size of grains after ACC HPT with n = 10 revolutions (in total) is about 20 nm.

Effects of Deformation Processing Parameters on the Microstructure Evolution and Microhardness of GH4169 Superalloy during Annealing Treatment

Effects of deformation processing parameters on the microstructural evolution and microhardness of deformed samples during annealing treatment were analyzed. The results show that the initial aging time has the greatest influence on the refinement of annealed grain compared with other processing parameters. This attributes to more δ phases precipitating with the improving initial aging time. The high content of δ phase hinders the quick dynamic recrystallization (DRX) grain growth during annealing. Thus, the high strain rate helps to refine deformed grain by annealing treatment due to a high content of δ phase retained after deformation. Additionally, the massive appearance of recrystallized nuclei/grains also hinders adjacent grain growth. The appearance of many DRX nuclei at high deformation temperature or true strain will cause the fine annealed grain, although the dissolution of δ phase is enhanced. Thus, the grain deformed at 950–1010 °C can be refined to 11–14 μm during annealing. Furthermore, the high true strain is beneficial to obtain fine and homogeneous microstructure during annealing because the high deformation energy promotes static recrystallization (SRX) nucleation. Besides, the microhardness of GH4169 superalloy depends on the grain size and retained content of δ phase due to the fine‐grain and γ″ phase strengthening.

Impact of short range ordering on the anomalous four-stage strain hardening behavior of low solid-solution hardening Ni–Cr alloys

The effect of short range ordering (SRO) on the strain hardening behavior of low solid-solution hardening Ni–Cr alloys with high stacking fault energies (SFEs) was systematically investigated under uniaxial compression to a high true strain ε t of 0.9 at room temperature. An unexpected four-stage (including Stages A, B, C and D) changing law in strain hardening rate was revealed, which is completely different from the case of conventional high-SFE alloys whose strain hardening rate just monotonously declines as the strain increases. Observations on the deformation microstructures strongly demonstrate that the recovery of strain hardening rate in Ni–Cr alloys (Cr ≥ 20 at.%) at Stages B (0.11 < ε t < 0.21) and D ( ε t ≥ 0.65) should be ascribed to the transformation in dislocation slip mode from wavy slip to planar slip, and the occurrence of the extensive deformation twins (DTs) together with the secondary DTs, respectively. Besides, in the later period of Stage C (0.21 < ε t < 0.65), microbands (MBs) and DTs have been locally formed in the Ni–Cr alloys with high SRO degree, which delays the decrease of strain hardening rate to a certain extent. Based on these experimental observations, the impacts of SRO on the formation of planar slip bands, MBs and DTs are analyzed, and the effect of SRO on the four-stage strain hardening behavior is also discussed systematically based on the different deformation mechanisms. In brief, an enhancement of SRO in low solid-solution hardening Ni–Cr alloys with high SFEs has been convincingly confirmed to be capable of improving the strain hardening capacity.

Mechanical anisotropy and microstructural changes during cryorolling of Al–Mg–Si alloy

Rolling was performed on Al–Mg–Si alloy sheets to true strain values of 0.69 and 1.38 at both room temperature and at cryogenic (liquid nitrogen) temperature and the influence of rolling temperature on microstructure and mechanical properties was studied. At both the reductions, cryorolled samples exhibited enhanced hardness and strength compared to room temperature rolled samples. The enhanced properties of cryorolled samples are attributed to the high dislocation density, increased microstrain and a reduced crystallite size compared to room temperature rolled samples. Besides, at high true strain condition, anisotropy behaviour was studied and correlated with X-ray bulk texture components. Evaluation of the percentage volume fraction of individual texture components revealed that cryorolled samples exhibited ~16% and ~33% increase in S and brass deformation texture components, respectively compared to room temperature rolled samples. Cryorolled samples also showed an enhanced texture index value compared to room temperature rolled samples.

Promoting Ti4C2S2 strain induced precipitation during asymmetrical hot rolling to improve r value and advantaged texture in Ti stabilized IF steel

The kinetic of Ti4C2S2 strain induced precipitation in a Ti stabilized IF steel was investigated using two stage interrupted compression test with high true strain (0.5). The PTT (precipitation–time–temperature) diagram was obtained by plotting 1/Ar–time curves. TEM (transmission electron microscopy) observation confirmed that the evolution of Ti4C2S2 precipitate in the quenched samples of thermal simulation is in good agreement with the PTT diagram. Hot strips were produced at three different rolling temperatures with high strain and slight shear deformation. It was found that hot rolling at the nose temperature of the Ps line of the PTT diagram can effectively promote the precipitation of Ti4C2S2 and retard the precipitation of TiC. Cold rolled and annealed sheets from hot strip containing higher volume fraction of Ti4C2S2 exhibited higher r value and stronger γ fiber texture with equal {111}〈112〉 and {111}〈110〉 components. By contrast, cold rolled and annealed sheets from hot strips containing lower volume fraction of Ti4C2S2 represented lower r values and weaker γ fiber texture with significant drops from {111}〈112〉 to {111}〈110〉 component.

Design of a new Ni-free austenitic stainless steel with unique ultrahigh strength-high ductility synergy

A conceptual approach was used to design a new Ni-free austenitic stainless steel with a unique combination of ultrahigh strength and ductility. The concept was based on the alloying of the 0.05C–18Cr–12Mn (wt.%) steel by 0.39%N and heavy warm rolling (84% reduction) at 1173K (900°C) to achieve the yield strength of minimum 1GPa and high tensile strength and elongation due to a proper stability of the austenite as a result of the optimized stacking fault energy (SFE). The yield strength of 1010MPa, tensile strength of 1150MPa and high fracture strain of 70% were measured for the steel designed. Dislocation and solid solution hardening mechanisms are introduced as the main contributors for the ultrahigh yield strength of the steel. The strain hardening is gradual and the hardening rate reaches a high level of ∼2400MPa at a high true strain of 40% due to slow α′-martensitic transformation and mechanical twinning. Consequently, the ductility of the designed steel is excellent.

Adaptive characterization of recrystallization kinetics in IF steel by electron backscatter diffraction

In this study, a rigorous methodology for quantifying recrystallization kinetics by electron backscatter diffraction is proposed in order to reduce errors associated with the operator's skill. An adaptive criterion to determine adjustable grain orientation spread depending on the recrystallization stage is proposed to better identify the recrystallized grains in the partially recrystallized microstructure. The proposed method was applied in characterizing the microstructure evolution during annealing of interstitial-free steel cold rolled to low and high true strain levels of 0.7 and 1.6, respectively. The recrystallization kinetics determined by the proposed method was found to be consistent with the standard method of Vickers microhardness. The application of the proposed method to the overall recrystallization stages showed that it can be used for the rigorous characterization of progressive microstructure evolution, especially for the severely deformed material.

Elevated-temperature deformation at forming rates of 10−2 to 102 s−1

In the hot working at constant strain rate ( $$\dot \varepsilon $$ ) of Al and α Fe alloys at 0.5 to 0.9 T M (absolute melting temperature), steady-state deformation is achieved in similarity to creep, which is usually at constant stress. After an initial strain-hardening transient, the flow stress becomes constant in association with a substructure which remainsequiaxed and constant in the spacing of sub-boundaries and of dislocations in both walls and subgrains. All these spacings become larger at higher temperature (T) and lower $$\dot \varepsilon $$ values as well as with lower stress, being fully consistent with the relationships established in creep. Because hot working can proceed to a much higher true strain in torsion (∼100) and compression (∼2) as well as in extrusion (∼20) and rolling (∼5), it is possible to confirm that grains continue to elongate while the subgrains within them remain equiaxed and constant in size. When the thickness of grains reaches about 2 subgrain diameters (d s), the grain boundaries with serrations (∼d s) begin to impinge and the grains pinch off, becoming somewhat indistinguishable from the subgrains; this has been called geometric dynamic recrystallization (DRX). In polycrystals as at 20 °C, deformation bands form and rotate during hot working according to the Taylor theory, developing textures very similar to those in cold working. In metals of lower dynamic recoverability such as Cu, Ni, and γ Fe, new grains nucleate and grow (discontinuous DRX), leading to a steady state related to frequently renewed equiaxed grains, containing an equiaxed substructure that develops to a constant character and defines the flow stress.

Deformation-induced martensitic characteristics in 304 and 316 stainless steels during room-temperature rolling

The effect of grain size on the deformation-induced martensite (α′) in 304 and 316 stainless steels (SS) during room-temperature rolling has been studied. Samples of four grain sizes of 52, 180, 229, and 285 μ in 304 and three grain sizes of 77, 125, and 200 /μm in 316 SS have been rolled from 16 to 63 pct reduction in thicknesses to characterize the microstructures during the rolling deformation. The amount of α′ formed increases with increase in the amount of deformation in both SS for a given grain size. The volume fraction of martensite formed increases with a decrease in grain size in 304 SS, while the α’ martensite formation has been found to be grain size insensitive in 316 SS. The volume fraction of α’ formed in 304 SS is always higher than that in 316 SS for a fixed percent reduction in thickness and grain size. This is attributed to the higher number of shear band intersections observed in 304 SS, which are considered to be the nucleation sites for the α’ embryos. The lath martensite obtained at small true rolling strains changes to blocky type at higher true strains. The morphology of α′ formed has been discussed and its characteristics obtained from rolling deformation have been compared with those earlier reported from the room-temperature tensile deformation.