Search

The main point of successful manufacture of metallic composites by direct bonding of dissimilar materials is achieving a homogeneous interface bonding. Two different types of deformation techniques for fabrication of metal composites were investigated. The first one was developed on the basis of high pressure torsion associated with a high energy impact on the material where part of energy involved can be dissipated via non equilibrium phase transition realization. This deformation due to high shear deformations allows not only to form a nanostructure, but also to bond dissimilar metals. Moreover, this method allows for a relatively short time and in a number of compounds to receive in one step at room temperature monolithic composites of sufficient size to certify the structure and properties. The second technique is diffusion bonding which integrate one material with the other by pressure under high temperature. In order to clarify the bonding mechanism by plastic deformation of dissimilar materials, the microstructural and some mechanical properties were studied in the processed samples.

The pitting corrosion of an aluminum alloy AA1050 after being processed by continuous closed die forging (CCDF) was evaluated by cyclic potentiodynamic polarization (CPP). Microstructure evolution, mechanical and corrosion behaviors were studied as a function of the total strain imposed. The CCDF process was carried out at 0, 16 and 24 passes with loading times of 10 and 15¿s. The electron backscatter diffraction (EBSD) analysis revealed a grain refinement of 0.78¿µm after 24 passes, which promoted an increment in the yield strength (YS), ultimate tensile strength (UTS) and vickers hardness (HV) by a factor of 9, 3 and 2 respectively; but the uniform strain and strain to rupture decreased by 93% and 72% respectively. Resistance to corrosion after 16 and 24 passes was compared with the reference material (0 passes), using CPP in a Na2S04 0.1¿mol/l +100¿mg/l of NaCl electrolyte. Results showed that the specimens with 24 passes decreased its corrosion rate one order of magnitude. In addition, specimens with very fine grain sizes have shown nobler pitting potential and lower pitting volume fraction than coarse grain specimens.

Sandwich-like Al/Ti/Al-laminated composites have many advantages such as low density and high specific strength with value in mechanical manufacturing and aerospace engineering. Here, Al/Ti/Al-laminated composites were fabricated by hot roll bonding and subsequent processes: cryorolling (− 190 °C and − 100 °C), cold rolling (25 °C), and hot rolling (300 °C). Their bonding strength and mechanical properties were then studied by an Autograph AGS-X universal electronic testing machine. The results show that cryorolling can improve the interface bonding strength and tensile strength of Al/Ti/Al-laminated composites. For the Al/Ti/Al-laminated composites subjected to cryorolling at − 100 °C, they have the highest strength near 260 MPa—this is 48 MPa and 41 MPa higher than the laminated composites subjected to cold and hot rolling, respectively. These results also show the strongest peeling strength. Finally, the mechanisms of the enhancement of bonding strength and mechanical properties of Al/Ti/Al-laminated composites subjected to cryorolling were mainly discussed.

The particle size distribution significantly affects the material properties of the additively manufactured parts. In this work, the influence of bimodal powder containing nano- and micro-scale particles on microstructure and materials properties is studied. Moreover, to study the effect of the protective atmosphere, the test samples were additively manufactured from 316L stainless steel powder in argon and nitrogen. The samples fabricated from the bimodal powder demonstrate a finer subgrain structure, regardless of protective atmospheres and an increase in the Vickers microhardness, which is in accordance with the Hall-Petch relation. The porosity analysis revealed the deterioration in the quality of as-built parts due to the poor powder flowability. The surface roughness of fabricated samples was the same regardless of the powder feedstock materials used and protective atmospheres. The results suggest that the improvement of mechanical properties is achieved by adding a nano-dispersed fraction, which dramatically increases the total surface area, thereby contributing to the nitrogen absorption by the material.

It is well known that a balance between the generation of low-angle and high-angle grain boundaries (LABG and HAGB) is achieved in materials undergoing a severe plastic deformation (SPD) process. It is also observed that most annealed materials evolve from a substantial fraction of LAGB at the early deformation steps towards a steady state in which an equilibrium between LAGB and HAGB fractions is attained. In the present work, such a balance is analyzed for different alloys, i.e., Cu, Al, and Fe based. A mathematical expression is proposed for the amount of LAGB and HAGB as a function of the strain impaired which in turn can be used to predict the number of passes (especially for ECAP) or the amount of total deformation for any SPD process necessary to attain a steady microstructure. The model seeks to serve as a first approximation of the mechanical and microstructural properties of ultrafine grain metal materials.

A novel continuous process of severe plastic deformation (SPD) named continuous close die forging (CCDF) is presented. The CCDF process combines all favorite advances of multidirectional forging and other SPD methods, and it can be easily scaled up for industrial use. Keeping constant both the cross section and the length of the sample, the new method promotes a refinement of the microstructure. The grain refinement and mechanical properties of commercially pure aluminum (AA1050) were studied as a function of the number of CCDF repetitive passes and the previous conditioning heat treatment. In particular, two different pre-annealing treatments were applied. The first one consisted of a reheating to 623 K (350 &deg, C) for 1 h aimed at eliminating the effect of the deformation applied during the bar extrusion. The second pre-annealing consisted on a reheating to 903 K (630 &deg, C) for 48 h plus cooling down to 573 K (300 &deg, C) at 66 K/h. At this latter temperature, the material remained for 3 h prior to a final cooling to room temperature within the furnace, i.e., slow cooling rate. This treatment aimed at increasing the elongation and formability of the material. No visible cracking was detected in the workpiece of AA1050 processed up to 16 passes at room temperature after the first conditioning heat treatment, and 24 passes were able to be applied when the material was subjected to the second heat treatment. After processing through 16 passes for the low temperature pre-annealed samples, the microstructure was refined down to a mean grain size of 0.82 &micro, m and the grain size was further reduced to 0.72 &micro, m after 24 passes, applied after the high temperature heat treatment. Tensile tests showed the best mechanical properties after the high temperature pre-annealing and 24 passes of the novel CCDF method. A yield strength and ultimate tensile strength of 180 and 226 MPa, respectively, were obtained. Elongation to fracture was 18%. The microstructure and grain boundary nature are discussed in relation to the mechanical properties attained by the current ultrafine-grained (UFG) AA1050 processed by this new method.

Aluminum alloys can be used in the fabrication of intricate geometry and curved parts for a wide range of uses in aerospace and automotive sectors, where high stiffness and low weight are necessitated. This paper outlines a review of various research investigations on the superplastic behavior of aluminum alloys that have taken place mainly over the past two decades. The influencing factors on aluminum alloys superplasticity, such as initial grain size, deformation temperature, strain rate, microstructure refinement techniques, and addition of trace elements in aluminum alloys, are analyzed here. Since grain boundary sliding is one of the dominant features of aluminum alloys superplasticity, its deformation mechanism and the corresponding value of activation energy are included as a part of discussion. Dislocation motion, diffusion in grains, and near-grain boundary regions being major features of superplasticity, are discussed as important issues. Moreover, the paper also discusses the corresponding values of grain size exponent, stress exponent, solute drag creep and power law creep. Constitutive equations, which are essential for commercial applications and play a vital role in predicting and analyzing the superplastic behavior, are also reviewed here.

Effect of ultrasonic treatment (UST) with an amplitude of oscillating tension-compression stresses 100 MPa on the characteristics of superplastic deformation of Ti-6Al-4V alloy with an ultrafine grained (UFG) structure processed by equal-channel angular pressing (ECAP) is studied. During tensile tests at 600°C with initial strain rates in the interval from 10-4 to 10-3 s-1, ultrasonically irradiated samples exhibit a reduced flow stress, higher values of the strain rate sensitivity coefficient and elongation to failure as compared to the samples tested directly after ECAP. Detailed studies of the microstructure of samples subjected to ECAP only and ECAP followed by UST revealed no considerable differences. It is suggested that the UST affected fine structure of the material bringing them to a state with a higher ability of relaxation of deformation-induced defects.

The microstructure evolution during the annealing treatment of a recycled copper after cold rolling to total strain of 2.6 was investigated. The cold deformation resulted in the elongation of initial grains along rolling direction and the strain-induced formation of subboundaries. Annealing recovery occurred in the temperature range 100-250 °C. The recrystallized microstructures were observed after annealing at 300-400 °C. The hardness of partially recrystallized copper samples was interpreted in terms of dislocation strengthening. The recrystallization kinetics was estimated according to a Johnson–Mehl–Avrami–Kolmogorov equation using different methods for recrystallized fraction determination, i.e., the fractional softening, the grain orientation spread, and the Kernel average misorientation.

There is a large number of methods for severe plastic deformation (SPD). Multidirectional forging (MDF) is probably one of the most easily scalable for industrial application. In general, two main conditions need to be fulfilled for successful SPD processing: constant sample geometry and application of a quasi-hydrostatic pressure. The first condition is necessary for strain accumulation by repetitive deformation and the second one helps preventing cracking in the specimens with high accumulated strain. However, MDF is not providing quasi-hydrostatic condition in the processed sample. This paper reports a novel method for severe plastic deformation, namely continuous closed die forging (CCDF), which fulfils both requirements for the successful deformation of samples to a very high accumulated strain. Commercially pure aluminum (1050) was processed to a total strain of 24 by CCDF. After processing, the microstructure was refined down to a mean grain size of 0.78 μm. Tensile testing showed good mechanical properties: yield strength and ultimate tensile strength of the ultrafine-grained aluminum were 180 and 226 MPa, respectively. Elongation to rupture was about 18%. The microstructure, microhardness and grain boundary statistics are discussed with regard to the high mechanical properties of the UFG aluminum processed by this novel method.

Physical simulation of the stress-strain state and microstructure evolution, which are similar to that occurring during asymmetric rolling with a large strain, is very important for design of technologies of producing ultra fine grained metallic materials. This paper presents the results of optimization of specimen geometry and a special multi-cycle shear-compression technique for the physical simulation of asymmetric rolling with a large strain up to e ~ 4. The specimen consisted of a parallelepiped having an inclined gauge section created by two diametrically opposed semi-circular slots which were machined at 45°. The specimen was compressed between two flat dies during shear-compression testing in accordance to the special multi-cycle scheme. Each cycle of the shear-compression testing consisted of two steps. The first step included height reduction of specimen, after that specimen was rotated by 90º. The second step included length reduction of the specimen for getting the quasi original shape of a parallelepiped. The specimen provided simultaneous pure and simple shear in an inclined gauge-section. The level of effective strain was controlled through adjustment of the specimen geometry, height reduction, load application direction and number of cycles of shear-compression. Gauge thickness, width and radius of the specimen were optimized by FEM with using of software DEFORM 3D. Numerical simulation and comparison of the stress-strain state during shear-compression testing and asymmetric rolling of low-carbon steel AISI 1010 were performed. Results of FEM analysis of the applicability of the multi-cycle shear-compression testing to the modeling of asymmetric rolling were discussed.

Changes in the structure of coarse-grained nickel due to ultrasonic treatment (UST) are studied. For this purpose, commercially pure nickel was annealed at a temperature of 1300 °C for 1 h to obtain a coarse-grained structure with a low dislocation density. On the electrolytically polished surface of the sample, a 2 × 2 mm2 sized area was marked and investigated by EBSD analysis. Further, the sample was subjected to UST with an oscillating stress amplitude of 20 MPa, and the marked area was polished and scanned again. X-ray diffraction analysis and microhardness measurements were carried out before and after UST as well. It is shown that UST leads to dislocation generation, an increase in the fraction of low-angle boundaries, changes in the shape of twins and grain boundaries. The dependence of structural parameters and microhardness on the UST amplitude is also described.

Grain refinement by severe plastic deformation can make conventional metallic materials several times stronger, but it leads to dramatic loss of their ductility. Gradient structure through the thickness of processed material represents a new strategy for producing a superior combination of high strength and good ductility. In gradient metallic materials the grain size increases gradually from nanoscale at the surface to coarse-grained in the core. Strain gradient can be considered as a mechanism of creating of such microstructures. Providing of predetermined strain gradient in the metallic materials can be achieved by asymmetric rolling (AR), when circumferential speeds of the top and bottom work rolls are different. Since the AR is a continuous process, it has great potential for industrial production of large-scaled sheets. Searching the optimal process parameters which can provide special strain gradients through sheet thickness is very important. This paper presents the distributions of the effective strain through sheet thickness of low-carbon steel AISI 1015 processed by a single-pass AR. Influence of process parameters was investigated by the finite element method with using software DEFORM 2D. Extremely high strain gradient e ≈ 4...8 through sheet thickness during a single-pass AR was found. FE analysis of the deformation characteristics, presented in this study, can be used for optimization of the AR process as a method of fabrication of metallic materials with gradient microstructures.

Commercially pure nickel was processed by equal channel angular pressing (ECAP) through route Bc for 12 passes to obtain an ultrafine grained (UFG) microstructure and further subjected to an ultrasonic treatment (UST) which introduced a maximum amplitude equivalent to anormal stresses of 100 MPa in a steady state regime. It was observed that the microstructure of UFG Ni can be differently altered depending on the position in the sample, i.e. on the amplitude of the ultrasonic wave. The microstructural analysis demonstrated a lower dislocation density (due to the activation of recovery) at the cross section of the specimen subjected to UST at an amplitude equal to 0.8 of the maximum one, plus enhanced hardening in the cross section at the maximum amplitude.

Grain refinement is an effective approach to improve mechanical properties of conventionally-manufactured high entropy alloys (HEAs). Additive manufacturing of HEAs is a new materials challenge and increasing reports are available for exploring the optimal processing parameters and post-manufacturing treatments to advance the physical and mechanical properties of additively-manufactured (AM) HEAs. At the current stage of the development of AM HEAs, it is necessary to investigate the significance of grain refinement on their mechanical properties and structures. In the present study, a CoCrFeNi HEA is manufactured by a laser powder-bed fusion technique using pre-alloyed HEA powders on which grain refinement was conducted by high-pressure torsion for up to 8 turns under 6 GPa at room temperature. The results from nanoindentation and Vickers microhardness testing demonstrate high strain hardening capability and increased plasticity, thus potentially high ductility, in the nanostructured AM CoCrFeNi HEA. X-ray diffraction analysis demonstrates the structural evolution with decreasing crystallite size, increasing microstrain and expanding lattice parameter with grain refinement in the HEA. The structural changes justify the estimation by nanoindentation of the rate-controlling mechanism of the grain boundary-mediated dislocation activity for the nanostructured AM HEA. This study provides advantages of nanostructuring for current developments in the AM technology of HEAs.

The ultrafine-grained microstructures, mechanical properties and electrical conductivity of a Cu–0.3%Cr–0.5%Zr alloy subjected to equal channel angular pressing (ECAP) at a temperature of 400 °C to a total strain of 1, 2, and 4 were investigated. The ultrafine-grained microstructure resulting from progressive increase in the misorientations of strain-induced low-angle boundaries during the multiple ECAP process is considered as a type of continuous dynamic recrystallization. The multiple ECAP process resulted in substantial strengthening of the alloy. The yield stress of CuCrZr alloy in the initial solution treated condition (ST) increased from 65 MPa to 476 MPa after four ECAP passes at 400 °C. For the aged condition (AT), the yield stress increased from 170 MPa to 511 MPa after four passes. The strengthening was attributed to the grain refinement and high dislocation densities evolved via large strain deformation. Bacon–Kocks–Scattergood modification of the Orowan model is sufficient for acceptable description of the precipitation hardening of AT specimens during ECAP processing; this finding is in excellent agreement with the experimental data. The discrepancy between the experiment and model for ST specimens disappears after taking into consideration additional precipitating of the supersaturated solid solution during preheating and ECAP processing.

This study demonstrates the evolution of microstructure and mechanical properties of a hypoeutectic Al–7Si–0.4Mg (A356) alloy processed by accumulative back extrusion (ABE) at temperatures ranging from 200 to 500 °C. ABE processing is one of the new severe plastic deformation techniques enabling one to produce relatively large ultrafine-grained materials in a cylindrical shape. One complete pass of ABE was estimated to introduce a reasonably homogeneous effective strain of ~3 as calculated by finite element analysis. Microstructural observation showed that globular α-Al primary phase was subdivided into fine substructures and Si particles having a fibrous shape were fragmented and spheroidized within the eutectic constituent through ABE processing. There was no evidence of homogeneous distribution of the fine Si particles in the α-Al phase after ABE. Mechanical testing at room temperature showed that both yield strength and ultimate tensile strength of the A356 alloy dramatically increased through ABE, especially at lower processing temperatures, as compared with the as-cast condition whereas there was no significant reduction in ductility at all processing temperatures. The experimental results were discussed with emphasis on the microstructure evolution involving dynamic recrystallization and deformation behavior including strengthening mechanisms and strain hardening in the Al–Si alloy.

Although superplasticity has intensively been studied for half century, few observations have been reported for pure metals due to fast grain growth at temperatures required for superplasticity. With developing of nanocrystalline materials, there was a hope that superplasticity could be obtained in a number of pure metals. Indeed, low temperature superplasticity in pure nickel was reported in pioneering work in 1999, later superplastic feature of nanonickel was attributed to sulfur presence in grain boundaries. Recently, it was concluded that superplasticity it is not related to the presence of sulfur at grain boundaries or a liquid phase at grain boundaries. Thereby, the phenomenon of superplasticity in pure metals is still far away for our understanding and it requires future work. This report is devoted to reassessment of superplastic behavior of nanonickel and it provides new results on enhanced plasticity of pure nickel processed by HPT consolidation of rapid quenched ribbons.

Solid state joints were obtained for the first time by ultrasonic welding (USW) of ultrafine-grained (UFG) thin disks of Ni processed by high pressure torsion (HPT). Samples of two types were studied: the ones for lap shear mechanical tests were prepared by joining two disks superimposed on each other under static loads of 4.5 and 6.0 kN, and the other type samples for structural characterization were obtained by sequential welding (consolidation) of four disks. The welding time for both type samples was equal to 1 s. The structure of consolidated samples was studied in their cross section by SEM, EBSD analysis, and also their Vickers microhardness was measured.

The results of studies on the development of instruments for ultrasonic welding (USW) of metals, which is the basic process for ultrasonic additive manufacturing, are presented. The influence of process parameters (static loading and welding time) on the microstructure and strength of joints produced by USW of commercially pure copper, nickel and titanium is studied. Preliminary results of the first studies on the USW of metals in an ultrafine grained (UFG) state are presented and the prospects of using UFG metals in the ultrasonic additive manufacturing are evaluated.

Bulk nickel-graphene (Ni-Gr) composites are in the high demand for most of the engineering applications. Despite many efforts made, the main problem remains the homogeneous dispersion of graphene into the Ni matrix without destroying the structural integrity of Gr. The present paper addresses the fabrication, structural features and mechanical characteristics of bulk Ni-Gr composites, manufactured from nanosized nickel powder and exfoliated graphite platelets (GP) via modified powder metallurgy procedure including micromechanical GP splitting. The combination of XRD, SEM, Raman spectroscopy and EBSD analysis revealed homogeneous distribution of Gr in Ni matrix and the significant grain refinement observed for Ni-0.1 wt% Gr composite. Bimodal grain size distributions were obtained for all samples studied, and the mean grain size depends on Gr content. Raman spectroscopy proved the complete GP-to-graphene conversion for composite with 0.1 wt% Gr. Bulk nickel specimen and composites exhibit ∼3 times higher hardness and moderate tensile strength values compared to Ni, manufactured from micron-sized powders.

Multilayer laminates comprising thirteen layers of Ti–6Al–4V alloy were produced by diffusion bonding. The influence of the processing conditions on the microstructure and mechanical properties of laminates were determined. The multilayer laminates were tested at room and liquid-nitrogen temperatures under impact bending tests with recording of dynamic loading diagrams. The influence of the interfaces pores on the total energy of fracture, the energy of crack initiation and the energy of crack propagation was analyzed. The impact strength value of the laminate decreased by 1.7 times for the crack divider orientation, and it increased by 14 times for the crack arrester orientation with the relative length of pores increasing from 1 to 30%.

Already for fifteen years many researchers have been trying to discover metallic materials with unusual combinations of strength and ductility: with high strength and enhanced ductility . This combination may be achieved through different ways: alloying, nanostructuring, etc. This report is an attempt to analyze the influence of inhomogeneity of different types (structural, phase and space) on mechanical properties of commercially pure ti tanium (bulk and powder) subjected to high- pressure torsion. Experimental results for HPT bulk and powder titanium have demonstrated that mechanical behavior of CP titanium strongly depends on phase inhomogeneity (alpha + omega phases), structural inhomoge neity (bimodal grain size distribution) and space inhomogeneity (retained porosity) in case of cold consolidated Ti powder. High strength in HPT bulk titanium due to the formation of hard omega phase during HPT processing at room temperature was detected. The strong omega phase transforms back to nanograined alpha phase domains during short annealing at elevated temperature. HPT consolidation of titanium powder leads to the formation of brittle specimens showing high strength but almost zero plasticity

An investigation has been conducted on AZ91 magnesium alloy processed in high-pressure torsion (HPT) at 296, 423 and 473 K for different numbers of turns. The microstructure has altered significantly after processing at all processing temperatures. Extensive grain refinement has been observed in the alloy processed at 296 K with apparent grain sizes reduced down to 35 nm. Segmentation of coarse grains by twinning has been observed in the alloy processed at 423 K and 473 K with average apparent grain sizes of 180 nm and 250 nm. Substantial homogeneity in microhardness has been observed in the alloy processed at 296 K compared to that found at 423 K and 473 K. The ultrafine-grained AZ91 alloy exhibited a significant dependence of the yield strength on grain size as shown by the microhardness measurements, and it obeys the expected Hall–Petch relationship. The alloying elements, fraction of nano-sized particles of β-phase, and the dominance of basal slip and pyramidal modes have additional effects on the strengthening of the alloy processed at 296 K.

Disks of commercial Al-1050 and ZK60A alloys were stacked together and then processed by conventional high-pressure torsion (HPT) through 1 and 5 turns at room temperature to investigate the synthesis of an Al–Mg alloy system. Measurements of microhardness and observations of the microstructures and local compositions after processing through 5 turns revealed the formation of an ultrafine multi-layered structure in the central region of the disk but with an intermetallic ?-Al3Mg2 phase in the form of nano-layers in the nanostructured Al matrix near the edge of the disk. The activation energy for diffusion bonding of the Al and Mg phases was estimated and it is shown that this value is low and consistent with surface diffusion due to the very high density of vacancy-type defects introduced by HPT processing. The results demonstrate a significant potential for making use of HPT processing in the preparation of new alloy systems.

An investigation was conducted to evaluate the dependence on grain size of the compressive deformation of commercial purity (CP) Ti. Tests were performed at room temperature using grain sizes from coarse-grained CG (20 ?m) to ultrafine-grained UFG (500 nm) and nanocrystalline NC (90 nm) with testing strain rates in the range from 0.01 to 10 s?1. The results show the flow stress and the strain rate sensitivity of CP Ti increase with decreasing grain size. Work hardening dominates at all strain rates in CG Ti but it balances with flow softening at 0.01 and 0.1 s?1 in UFG and NC Ti and there is obvious flow softening in these two materials at 10 s?1.

An investigation has been conducted on the tensile properties of a fine–grained AZ91 magnesium alloy processed at room temperature by high pressure torsion (HPT). Tensile testing was carried out at 423 K, 473 K and 573 K using strain rates from 1×10–1 s–1 to 1×10–4 s–1 for samples processed in HPT for N = 1, 3, 5 and 10 turns. After testing was completed, the microstructures were investigated by scanning electron microscopy and energy dispersive spectroscopy. The alloy processed at room temperature in HPT exhibited excellent superplastic behaviour with elongations higher than elongations reported previously for fine–grained AZ91 alloy produced by other severe plastic deformation processes, e.g. HPT, ECAP and EX–ECAP. A maximum elongation of 1308 % was achieved at a testing temperature of 573 K using a strain rate of 1×10–4 s–1, which is the highest value of elongation reported to date in this alloy. Excellent high–strain rate superplasticity (HSRSP) was achieved with maximum elongations of 590 % and 860 % at temperatures of 473 K and 573 K, respectively, using a strain rate of 1×10–2 s–1. The alloy exhibited low–temperature superplasticity (LTSP) with maximum elongations of 660 % and 760 % at a temperature of 423 K and using strain rates of 1×10–3 s–1 and 1×10–4 s–1, respectively. Grain–boundary sliding (GBS) was identified as the deformation mechanism during HSRSP, and the glide–dislocation creep accommodated by GBS dominated during LTSP. Grain–boundary sliding accommodated with diffusion creep was the deformation mechanism at high test temperature and slow strain rates. An enhanced thermal stability of the microstructure consisting of fine equiaxed grains during deformation at elevated temperature was attributed to the extremely fine grains produced in HPT at room temperature, a high volume fraction of nano ?–particles, and the formation of ?–phase filaments.

Commercial purity (CP) Ti was processed by a two-step procedure of ECAP and drawing to give a nanocrystalline (NC) grain size of ~90 nm. Samples were tested in compression at a strain rate of 10 s −1 over the temperature range of 298−673 K. The results show the high stored energy and high interface energy promote the process of static recrystallization (SRX) when the NC Ti is heated above 573 K. Migration dynamic recrystallization (m-DRX) operates during compressive deformation at temperatures of 298−573 K giving a homogeneous microstructure. The compressive yield strength and peak stress at 298 K were measured as 1230 and 1330 MPa, respectively. When the test temperature is increased from 298 to 673 K, the yield strength and peak stress decrease and the work hardening rate and dynamic softening rate are also reduced.

The strengthening of metals is essentially controlled by the microstructures of the metal solids and it is well understood that smaller grain sizes lead to higher hardness and increased strength. Nevertheless, true bulk nanostructured materials are difficult to produce using established engineering techniques, especially when considering the practical and societal needs of materials selection. Lightweight Al and Mg are conventional metals having excellent physico-chemical and mechanical properties and with good strength/weight ratios in the finished products. However, the fabrication of high-strength metals consisting of these elements, using mechanical alloying and milling and cladding-type metal working, generally involves long-term processing conducted under extreme conditions using special facilities. The present study demonstrates the very rapid synthesis of a metal matrix nanocomposite (MMNC) of the Al–Mg system which was achieved by stacking metal disks of the two pure metals and processing by high-pressure torsion at ambient temperature for 10 turns. An exceptionally high hardness was achieved, similar to many steels, through rapid stress-induced diffusion of Mg and the simultaneous formation of intermetallic nano-layers and a nanostructured intermetallic compound with a supersaturated solid solution. This unexpected result suggests a potential for simply and expeditiously fabricating a wide range of MMNCs.