Abnormal Grain Growth Research Articles

Complete Goss Secondary Recrystallization by Control of the Grain Size and Texture of Primary Recrystallization in Grain-Oriented Silicon Steel.

Matrix microstructure and texture controlling is an important way to optimize Goss ({110}<001>) abnormal grain growth (AGG) in high magnetic induction grain-oriented silicon (Hi-B) steel during primary recrystallization. In the present work, a matrix with homogeneous grain size and favorable texture components was obtained through two-stage normalized annealing followed by primary recrystallization. Furthermore, secondary recrystallization was performed for sharp Goss orientation by slow heating and purified annealing. It was found that plenty of island grains, which occurred and disappeared gradually, accompanied the process of AGG. Through analyzing the evolution of microstructure and texture, we realized that the formation of island grains was related to the large-size grains in matrix, and the elimination of that was attributed to the special grain boundaries which satisfied both coincident site lattice (CSL) and high-energy (HE) models. It was essential to control grain size and favorable orientations in matrix comprehensively for the high-efficient abnormal growing of sharp Goss orientation, through which excellent magnetic properties could be obtained simultaneously.

Fast Li-ion transport pathways via 3D continuous networks in homogeneous garnet-type electrolyte for solid-state lithium batteries

Solid-state lithium batteries (SSLBs) using solid-state electrolytes (SSEs) have attracted much attention due to their satisfying safety and high energy density. Towards further practical development, insufficient room temperature ionic conductivity in garnet-type Li6.5La3Zr1.5Ta0.5O12 (LLZTO) SSEs (usually ˂1×10−3 S‧cm−1) remains a significant challenge and calls for a giant leap. In this work, a novel solid-state sintering strategy is employed by introducing La2O3 nanoparticles to promote the homogenous distribution of the grains and construct 3D continuous Li-ion transport networks along the grain boundaries. The La2O3 nanoparticles are regarded as the second phase to inhibit the abnormal grain growth (AGG) of LLZTO grains and reduce the voids defect to improve the relative density. The LaLiO2 Li-ion conductor is synthesized by combining the excess La2O3 nanoparticles and the gas Li2O, providing continuous ionic pathways and enhancing the Li-ion conductivity. The Li-ion conductivity reaches 1.12×10−3 S•cm−1 (64 % higher than the pure LLZTO electrolyte) with a relative density of 98.1 %. The results presented here show that SSLBs with LiFePO4 cathode achieve a superior stable cycling performance with a high discharge capacity of 128.8 mA•h•g−1 and a Coulombic efficiency over 99% after 600 long-term cycles (0.5 C) at room temperature. The work provides a feasible solid-state sintering approach to creating SSEs with high performances for future applications of SSLBs.

Thermal stability of grain structure for Ag nanotwinned films sputtered with substrate bias

In this study, different grain growth paths after aging at various temperatures for 1 h were observed in Ag nanotwinned thin films with and without substrate bias voltage, which led to large differences in thermal stability. As-deposited Ag nanotwinned thin films with and without substrate bias voltage were characterized by FIB, EBSD, and TEM, which revealed thinner equiaxial fine-grained regions, higher amounts of (111)-oriented grains and denser nanotwin stacking perpendicular to the growth direction of columnar grains in thin films with -150 V substrate bias voltage. Due to the better lattice arrangement and densification of the crystal structure due to substrate bias voltage, the microstructures remained almost unchanged, except for a little equiaxial grain growth, even after aging at 450 °C for 1 h. However, in the Ag nanotwinned thin film without substrate bias voltage, severe abnormal grain growth (AGG) occurred after aging at only 250 °C for 1 h. Better understanding of the differences in thermal stability in nanotwinned thin films is provided in this study, and the findings will be beneficial for experimental design for further applications.

Effects of abnormal grain growth at longitudinal weld on the aging behavior and mechanical properties of 2196 Al[sbnd]Cu[sbnd]Li alloy profile

Abnormal grain growth (AGG) at longitudinal weld of 2196 AlCuLi profile was observed during solution treatment, and the effects of AGG on the aging behavior and mechanical properties of the profile were investigated. The results show that the AGG area almost contained no low angle grain boundaries (LAGBs) while the fine extrusion fibers in the matrix area contained numerous LAGBs. The AGG structure at weld seam leads to precipitated phases coarsening, PFZ widening and a sharp decrease of elongation in profiles. During aging process, the AGG area precipitated more coarse S′/S and T2 phases and exhibited a faster age hardening rate than the matrix area, while the numerous LAGBs in the matrix area promoted the precipitation of strengthening phases (T1, δ′/β′) and suppressed the formation of coarse phases. The phases formed along the grain boundaries are mainly coarse quasi-crystal T2 phases while abundant fine T1 phases formed along the LAGBs of the matrix area, and the PFZ of AGG area is far wider than that in matrix area. During the pre-stretching process, the fine grains and LAGBs of the matrix area conduced to form and store more dislocations, which provided more nucleation sites for T1 phases.

Sintering behavior of Ni–Zn ferrite powders prepared by molten‐salt synthesis

AbstractNi0.5Zn0.5Fe2O4 powders were prepared by a novel molten‐salt synthesis method. The effects of calcination processes of the powders on their sintering behaviors were investigated. Compared with the synthesis by traditional solid‐state reaction, the proposed molten‐salt method can significantly reduce the synthesis temperature of Ni0.5Zn0.5Fe2O4 from 800 to 550°C below, and the prepared powders have relatively high sintering activity at low temperature, which can thus decrease the sintering temperature. However, the abnormal growth of grains is easy to occur during sintering, thus resulting in uneven grain size. In particular, during the molten‐salt synthesis, the holding time for calcination is a dominant factor affecting the activity and crystallization degree of the resultant powders. From the point of view of increasing the density of sintered bodies, the optimal conditions for synthesizing Ni0.5Zn0.5Fe2O4 powder by the proposed molten‐salt synthesis is 400°C for 6 h. In addition, the saturate magnetization of the finally obtained ferrite ceramics has nothing to do with the preparation processes, while their coercivity depends on their densification and grain size caused by their different processing routes.

Effect of Cr addition on the structure and electrical properties of CaCu3Ti4O12 NTC thermistor

In the present work, CaCu3-xCrxTi4O12 (CCCTO, 0 ≤ x ≤ 1) ceramics were prepared by a solid-state reaction. The influence of Cr on the structure and electrical properties of the CCCTO ceramics was investigated in detail. X-ray diffractometry (XRD) revealed that all samplesʼ main phases were CaCu3Ti4O12 (CCTO), but CuO and CaTiO3 phases were also found. Cr doping suppressed the abnormal growth of grains, thus the grain size distribution became more uniform with the increase of Cr doping content. The resistance-temperature analysis revealed that all CCCTO ceramics had a noticeable Negative Temperature Coefficient (NTC) effect. The resistivity ρ30 of the CCCTO ceramics decreased from 1.15 × 106 to 8.73 × 104 Ω cm with an increase in the value of x, along with a decrease in the thermal constant B from 6596 to 3267 K. It was also observed that both the grain and grain-boundary effects contributed to their NTC characteristics. The analysis revealed that the conductivity of the ceramics arose mainly from the electron hopping mechanism. All the samples showed an electrical relaxation behavior. The observations indicated that the structures and electrical properties of CCCTO ceramics could be attuned precisely by adjusting the concentration of the Cr2O3 doping agent.

Thermal Stability of Grain Structure for Ag Nanotwinned Films Sputtered With Substrate Bias

In this study, different grain growth paths after aging at various temperatures for 1 hour were observed in Ag nanotwinned thin films with and without substrate bias, which led to large differences in thermal stability. As-deposited Ag nanotwinned thin films with and without substrate bias were characterized by FIB, EBSD, and TEM, which revealed thinner equiaxial fine-grained regions, higher amounts of (111)-oriented grains and denser nanotwin stacking perpendicular to the growth direction of columnar grains in thin films with -150 V substrate bias voltage. Due to the better lattice arrangement and densification of the crystal structure due to substrate bias, the microstructures remained almost unchanged, except for a little equiaxial grain growth, even after aging at 450 °C for 1 hour. However, in the Ag nanotwinned thin film without substrate bias, severe abnormal grain growth (AGG) occurred after aging at only 250 °C for 1 hour. Better understanding of the differences in thermal stability in nanotwinned thin films is provided in this study, and the findings will be beneficial for experimental design for further applications.

Fabrication and thermal shock behavior of ZrO2 toughened magnesia aggregates

MgO-based refractories have been regarded as ideal linings for various furnaces owing to high refractoriness and excellent corrosion resistance to basic slag. However, thermal shock damage resulting from poor thermal shock resistance (TSR) of magnesia is the common failing. The present work aimed at improving TSR of magnesia aggregates by introducing microscale monoclinic ZrO2. The results showed that the ZrO2 added could increase cation vacancy concentration and inhibit abnormal growth of MgO grains, which therefore enhanced densification of the specimens. However, when the ZrO2 amount exceeded 15 wt%, densification decreased slightly due to agglomeration of ZrO2 and formation of more microcracks at the MgO grain boundaries. With increasing ZrO2 content, although the flexural strength degraded, the fracture toughness increased constantly because of the toughening effects of crack deflection and crack branching. Besides, although the addition of ZrO2 decreased the thermal conductivity, TSR of the specimens was significantly improved with increasing ZrO2 content due to the increase in toughness and decrease in strength, thermal expansion coefficient as well as Young's modulus. After thermal shock tests, 15 wt% ZrO2 containing specimen exhibited the highest TSR, whose residual strength ratio was about triple of that of the pure magnesia specimen. However, further increasing ZrO2 content to 20 wt% reduced the TSR attributing to the spalling of intergranular ZrO2 agglomerations.

Microstructure, mechanical properties, and cutting performances of WC-Co cemented carbides with Ru additions

In this study, the microstructure, mechanical properties, and cutting performance of WC-8Co cemented carbide with different Ru additions were studied in detail. The results show that Ru can inhibit the abnormal growth of WC grains and the mean grain size of WC grains decreases. Ru can result in the lattice distortion of Co phases and promote the phase transition of Co from face-centered cubic (FCC) to hexagonal closepacked (HCP) as Ru can reduce the stacking fault energy of Co phases. The proportion of HCP Co phases increased from 14.4 to 39.6% with increasing Ru content. Meanwhile, among the five groups of cemented carbides with different Ru additions, cemented carbides with 1.5 wt% Ru exhibit the highest hardness of 1382 HV and transverse rupture strength (TRS) of 3790 MPa. The enhanced hardness and TRS were due to solid solution strengthening and phase transition of Co, respectively. The fracture toughness of cemented carbide was enhanced from 16 MPa m−1/2 with 0 wt% Ru to 19 MPa m−1/2 with 0.5 wt% Ru. Additionally, during the dry cutting of Ti–6Al–4V, the diffusion of Ti and Al elements is hindered. Therefore, the wear resistance of the tools is improved. The cutting lifetime of the cemented carbide tools with 0.5 wt% Ru increased three-fold compared to those without Ru addition.

Microstructure and mechanical properties of Zr3Al3C5-based ceramics synthesized by Al-Si melt infiltration

In this work, bulk Zr3Al3C5-based ceramics were synthesized by the infiltration of Al-Si melt into zirconium carbide (ZrC) perform. The phase composition, microstructure, and mechanical properties of as-fabricated ceramics were studied. The results demonstrate that Si is more effective to reduce the twin boundary energy of ZrC than Al, and thus promotes the decrease of formation temperature of Zr3Al3C5. With the infiltration temperatures increasing from 1200 to 1500 °C, the Zr3Al3C5 content increases from 10 to 49 vol%, which is contributed to the increase of flexural strength from 62±9 to 222±10 MPa, and fracture toughness (KIC) from 2.8±0.2 to 4.1±0.3 MPa·m1/2. The decrease of mechanical properties for the samples fabricated at 1600 °C is ascribed to the abnormal growth of Zr3Al3C5 grains.

Influence of WC content on microstructure and mechanical properties of Mo2FeB2-based cermets fabricated by multi-step sintering

Herein, Mo2FeB2-based cermets, with nominal composition of Mo2FeB2-2.06Fe-2.9Ni-2.5Cr-xWC-0.04C (x = 0, 2.5, 5, 10 wt %), are fabricated by multi-step sintering to investigate influence of tungsten carbide (WC) content on microstructure and mechanical properties. Results reveal that the microstructure of WC-free cermets resembles that of traditional cermets. However, microstructure of WC-containing cermets (x = 2.5 wt %) is composed of fine black core/grey rim Mo2FeB2 grains and coarse white-colored coreless Fe3(W,Mo)3C grains. Furthermore, at x ≥ 5 wt %, most of white coreless Fe3(W,Mo)3C grains are transformed into a white core/black rim structure. From these observations, it can be concluded that growth of nearly round-shaped Mo2FeB2 grains is through diffusion-control, leading to normal grain growth (NGG), whereas the growth of polyhedral Fe3(W,Mo)3C grains is dictated by the interfacial reactions, resulting in 2D nucleation and partially abnormal grain growth (AGG). In addition, grain size distribution of WC-containing cermets exhibits distinct bimodal characteristics, where average grain size is smaller than that of WC-free cermets. More importantly, presence of WC significantly improves the mechanical properties, resulting in superior fracture toughness of 25.1 ± 0.5 MPa m1/2 and hardness of 90.3 ± 0.1 HRA, at x = 5 wt %, without compromising much of transverse rupture strength.

Microstructural Stability of Extruded Mg-Mn-Ce Hollow Profiles with Weld Seams

Despite aluminum profiles, magnesium profiles have not been well developed due to the low formability. Furthermore, extruded magnesium profiles show a strong dependence on the mechanical properties, according to the loading direction. This is caused by a strong basal texture, which is directly dependent on the process parameters during the extrusion and the subsequent aging. Thus, the present paper focuses on the analysis of the microstructure and its evolution of extruded magnesium hollow profiles, which were subjected to a series of heat treatments at 475 °C up to one hour. The hollow profiles were extruded through a porthole die, thus, containing longitudinal weld seams. These were formed by material that underwent heavy shearing along the tool surface based on the friction conditions in the porthole die. Three extrusion ratios (ER = 8:1, ER = 16:1, ER = 30:1) were applied, resulting in three different wall thicknesses of the profiles. The microstructure of the profiles was analyzed using light-optical microscopy (LOM) and scanning electron microscopy (SEM) coupled with electron backscatter diffraction (EBSD). The analysis revealed no change of the microstructure of the profiles extruded at the two higher extrusion ratios within the time frame of the heat treatment. In contrast, the microstructure and, thus, the micro-texture of the profile with the lowest extrusion ratio (ER = 8:1) has been affected to a great extent. While only small changes in microstructure in the weld-free area were observed, the initial microstructure in the weld seam was transformed from fine recrystallized grains into a significantly bimodal microstructure mainly due to an abnormal grain growth (AGG). These changes were accompanied by a promotion of the rare-earth (RE) texture component for the weld-free material and a change of the overall texture from RE to a typical non-RE double fiber texture for the weld seam due to the intense AGG within the short-time heat treatments. In addition, the influence of the extrusion ratio on particle size and distribution as well as the character of the microstructure governing the behavior during heat treatments was analyzed and discussed.

Effect of bimodal WC particle size and binder composition on the morphology of WC grains in WC–Co–Ni3Al cemented carbides

In addition to dispersed nanoparticles in the binder phase, the effect of Ni3Al on the growth mechanism of tungsten carbide (WC) grains is also essential for the fabrication of high-quality of cemented carbides. In this work, WC–Co–Ni3Al cemented carbides with different combinations of Co and Ni3Al binders was studied by using the original artificial bimodal WC grain size distribution. The WC particle sizes of medium 4 μm, fine 1 μm and ultrafine 0.2 μm were adopted. A series of WC–Co–Ni3Al alloys were firstly designed based on thermodynamic calculations and then liquid-sintered at 1450 °C for 1 h. Subsequently, the morphology and grain size distribution of WC grains were studied. By increasing the proportion of Ni3Al in the Co–Ni3Al composite binder phase, the solid–liquid interfacial energy increases significantly, which may provide a higher driving force for abnormal grain growth (AGG) through 2-dimension (2D) nucleation. However, the increase of Ni3Al proportion conversely greatly raises the energy barrier for the migration of W and C atoms into liquid binder phase, which finally retards the AGG of WC. Consequently, the AGG of WC decreases and the number of crystallites with blunt faces increases on WC particles with the increase of Ni3Al proportion, which can be well accounted for by the presently detected WC morphology evolution.

Avoiding abnormal grain growth in thick 7XXX aluminium alloy friction stir welds during T6 post heat treatments

Abstract Friction stir welding (FSW) is becoming an essential welding technique in the aerospace industry. However, friction stir welds are usually weaker than the parent material. The dissipated heat causes a softening of the 7XXX series aluminium alloys. Post-welding heat treatments are used to restore the highest strength after welding. The reference treatment is composed of two-steps heating: a solution heat treatment typically at 470 °C for 30 min, quench in water followed by artificial aging 120 °C for 24 h. These treatments are responsible for very significant grain coarsening in the weld nugget zone known as secondary recrystallization, sometimes leading to abnormal grain growth (AGG). This is particularly true for thick plates. This secondary recrystallization phenomenon is detrimental for tensile performances. A detailed analysis of the conditions leading to secondary recrystallization during post-welding heat treatments is provided. A procedure to avoid secondary recrystallization in FSWed joints is then highlighted. Thermal cycles during welding are controlled by welding on a low thermal conductivity backing plate (i.e. stainless steel) which avoids very fine grains in the bottom of the weld nugget. This new procedure opens the path to excellent welds presenting at least the strength and ductility of the T6 base material.

Influence of Sintering Process Conditions on Microstructural and Mechanical Properties of Boron Carbide Ceramics Synthesized by Spark Plasma Sintering.

Boron carbide (B4C) ceramics were synthesized by spark plasma sintering at a temperature between 1600 and 2050 °C without employing any sintering additives. The effect of sintering process parameters, such as temperature, holding time, pressure, hearting rate, and pulsed electric current, and the particle size of the raw powder on the densification behavior and mechanical properties of B4C ceramics, were comprehensively and systematically investigated. Hardness and fracture toughness of B4C that has a density close to the theoretical value were found to be 33.5 ± 0.2 GPa and 3.21 ± 0.13 MPa·m1/2, respectively. Electron backscatter diffraction (EBSD) analysis revealed no abnormal growth of grains due to an increase in holding time and pressure. Twin structures present in ceramics are beneficial for their mechanical performance.

Experimental investigations to find the effect of post weld heat treatment (PWHT) on the microstructure and mechanical properties of FSW dissimilar joints of AA2024-T351 and AA7075-T651

In this present study, a Friction stir weld (FSW) technique is applied to fabricate the FSW joints of aluminium alloy plates of 2024-T351 and 7075-T651 in butt-joint arrangement using a FSW tool of shape taper threaded cylindrical (TTC). The FSW joints are produced using constant FSW parameters of tool rotation speed (TRS) of 650 rpm, tool traverse speed (TTS) of 150 mm/min and tool plunge depth (TPD) of 6.20 mm. Tensile and microstructure specimens are removed from the weld joint in the direction perpendicular to the tool traverse and across the weld region. Initially, each of these specimens are heat treated to solution temperature (400, 420, 440, 460, 480, 500 °C) for 1 h and tested for tensile properties. The heat-treated microstructure samples are examined for the presence of abnormal grain growth (AGG) in the weld nugget zone (WNZ), thermally affected zone (TMAZ), heat affected zone (HAZ) of the weld region using stereo-zoom microscope and scanning electron microscope (SEM). Microstructure specimens subjected to solution heat treatment up to 480 °C are stable and reveals no AGG. However, for 500 °C the microstructures are not stable and the presence of AGG in the weld regions are observed. At 480 °C, the tested specimen shows homogeneity in hardness distribution across the weld regions. Thus, solution temperature of 480 °C is chosen as an optimizing solution temperature. Further, the tensile specimens are subjected to ageing temperature with constant temperature of 180 °C for various durations range 5, 8 and 12 h. Thus, these experimental investigations indicate that the specimen subjected to solution treatment at 480 °C followed by ageing temperature of 180 °C for 12 h show higher ultimate tensile strength (UTS) of 435 MPa and percentage increase of 6.8% compared to the specimens without heat treatment having UTS of 407 MPa.

Revealing the underlying mechanism of abnormal grain growth in sub-rapid solidified Al-Mg-Si-Fe alloy

The dependence of abnormal grain growth (AGG) on initial solidification microstructure in the Al-Mg-Si-Fe alloy was investigated. The AGG was more prone to occur during annealing in the sample following the sub-rapid solidification (SRS, cooling rate ~ 200 K/s) route as compared to the counterpart undergoing conventional solidification (CS, ~18 K/s). It was verified to be closely related to the {100} 〈310〉 grain clusters containing high-mobility grain boundaries based on quasi in-situ microstructure analysis and the refined Mg2Si particles that can be easily dissolved in the SRS sample. This research provides insights for better understanding the close relationship between the AGG and SRS process.

Recent advances in the kinetics of normal/abnormal grain growth: a review

Recent progress in the kinetics of grain coarsening and abnormal grain growth (AGG) is presented in this overview article. The factors affecting the kinetics of grain growth is reviewed with the emphasis on the recent findings on the solute drag and Zener pinning effects as well as the special case of duplex alloys, where the latter is discussed for the behavior of dual-phase steels during intercritical annealing. The common isothermal kinetics models for grain growth are listed, which is followed by the critical discussion on the simplifications and the commonly used methods for the determination of grain growth exponent (n) and activation energy (Q). The obtained values of n and Q for several classes of important engineering alloys such as microalloyed steels, stainless steels, magnesium alloys, aluminum alloys, titanium alloys, and high-entropy alloys are summarized with the discussion on the obtained values of kinetics parameters and their deviation from the theoretical expectations. Finally, the factors leading to AGG (such as the coarsening and dissolution of pinning particles and the crystallographic texture), the proposed mechanisms (such as the solid-state wetting and the grain boundary faceting/defaceting phenomena), and the kinetics of AGG (based on the empirical power law and the similarity of AGG to primary recrystallization in the form of secondary recrystallization) are reviewed. This overview can shed light on the understanding of grain growth and its effects.

Abnormal grain growth of 2196 Al-Cu-Li alloy weld seams during extrusion and heat treatment

The porthole die extrusion processes of 2196 Al-Cu-Li alloy were carried out at billet temperatures of 420–510 °C and ram speeds of 0.25–5.0 mm/s, then the extruded profiles were subjected to the solution and aging treatment. Abnormal grain growth (AGG) was observed along longitudinal weld of profiles during the extrusion and solution treatment. The fine equiaxed grains with Copper orientation were formed in the welding area when extruded at low temperature and low extrusion speed, and some Copper orientated grains transformed into recrystallization textures with the increase of deformation temperature. When extruded at high temperature and speed, AGG occurred in the junction area of Copper texture and recrystallization textures, and some strain-free Cube orientated grains in this area transformed into AGG structures due to the high growth-driving force and growth priority. During the solution treatment, the migration and annihilation of dislocations were repeated inside the equiaxed grains of the welding area, resulting in the coalescence of the subgrains and the formation of AGG. The abnormal grains formed during extrusion were mainly Cube orientated, while those occurred during solution treatment were randomly orientated. The weld seam had higher thermal stability during solution treatment if profiles were extruded at higher extrusion temperature and speed. In the matrix area, most of the dislocations migrated along the same direction, and the dislocations were hard to meet and annihilate. Besides, little driving force for grain growth could be provided by the flat grain boundaries of the matrix area. Hence, the Brass orientated grains in the matrix area possessed high thermal stability during the extrusion and solution treatment. The AGG structure led to the intergranular fracture and poor elongation of samples in the tensile test.

Abnormal grain growth in a Zn-0.8Ag alloy after processing by high-pressure torsion

Abnormal grain growth (AGG) in a Zn-0.8Ag (wt%) alloy, produced through the application of high-pressure torsion (HPT), was systematically investigated using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), high-resolution transmission electron microscopy (HR-TEM) and microhardness testing. The HPT-deformed alloy exhibits AGG at room temperature without any additional heat treatment. Analysis by EBSD revealed oriented grain nucleation in a {112¯0}〈0001〉 direction from the initial (0001) fibre texture which agrees with the maximum energy release model. New grains were oriented according to the minimal Young's modulus direction (c-axis), parallel to the shearing direction. The strain-induced dissolution of nanocrystalline Zn3Ag precipitates was identified as the main driving force for AGG in this alloy. The strains necessary for the initiation and termination of AGG were determined as ~4.0 and ~5.0, respectively. The increase in solid-solution strengthening caused an increase in hardness from ~47 HK in the fine-grained centre to ~84 HK in the coarse-grained region. A Hall-Petch investigation revealed grain refinement softening below a grain size of 23 µm. These results provide the first comprehensive description of AGG in metallic materials processed by a severe plastic deformation method at room temperature.