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One of the major challenges of equiatomic CoCrFeMnNi HEA is to manufacture parts with complex geometry that have higher yield strength. Equiatomic CoCrFeMnNi HEA was successfully fabricated in the present study with selective laser melting. The unique microstructure and mechanical anisotropy that generally appear in additive manufactured materials were investigated. SLM-built HEA has strongly oriented grains, dislocation networks, and nano-sized oxides. In addition, the average grain sizes were measured as 15.66 μm, 12.93 μm, and 5.98 μm on the plane perpendicular to the scanning direction (SD), transverse direction (TD), and building direction (BD), respectively. A compressive test measured outstanding yield strengths (YS) of 778.4 MPa, 766.4 MPa, and 703.5 MPa in the loading axis of SD, TD, and BD, respectively. These outstanding YSs are the result of a combination of fine grain sizes, high dislocation density and nano-sized oxides. In addition, anisotropy in mechanical properties are result from different values of Taylor factor and grain size according to the loading axis. After a compression test, the geometrically necessary dislocation density was found to differ about 2.5 times on each plane parallel to the loading axis in the same macro strain. Based on such findings, the relationship among microstructure, mechanical anisotropy and deformation mechanism are discussed in the present paper. Furthermore, the mechanical properties of SLM-built equiatomic CoCrFeMnNi HEA are predicted by using multiple strengthening mechanisms considering the microstructural characteristics.

Three Ni-base powder metallurgy superalloys have been developed recently, and tensile tests at temperatures ranging from room temperature (RT) to 815 °C were conducted on them. The results conformed their excellent tensile properties, in comparison with several other existed polycrystalline superalloys. In this work, by means of microstructure characterization, thermal dynamic calculations, and theoretical modeling, different strengthening mechanisms including precipitation strengthening, grain boundary strengthening, solid solution strengthening, and Orowan strengthening, were found to contribute to the yield strength in different degrees, which would help to further enhance the tensile properties of these alloys through composition design and processing optimization thereafter.

Ceramic nanoparticles reinforced aluminum matrix composite is a kind of promising materials in industrial production. However, its preparation is difficult due to the poor wettability between Al melt and ceramic particles and severe particle aggregation tendency. In this paper, the in-situ NdB6/Al–5Cu-0.3Mn nanocomposites were successfully prepared with the aid of melt spinning technology and ultrasonic vibration. Optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used to observe the microstructures of nano-NdB6/Al ribbons and NdB6/Al–5Cu-0.3Mn nanocomposites. The observation results were as follows: (1) more than 80% of the prepared NdB6 particles were nanoscale; (2) the NdB6 particles could be uniformly distributed in the Al–5Cu-0.3Mn alloy; (3) the NdB6 particles had the effects of grain refinement and dispersion strengthening on the Al–5Cu-0.3Mn alloy; (4) the NdB6 particles had a certain orientation relationships with α-Al. The tensile strength of Al–5Cu-0.3Mn alloy strengthened by the NdB6 particles was improved significantly. The strengthening mechanisms were investigated in detail.

The aim of this study is to investigate the mechanical effect of graphene nanoparticles and boron carbide microparticles together on Al-17Si alloy. For this purpose, graphene nanoparticles were firstly attached to boron carbide surfaces by semi-powder method. The Al-17Si alloy was then infiltrated into these particles. Systematic characterization of produced composites, microstructure investigations, strengthening mechanisms were investigated respectively. The composites were systematically characterized by XRD, DSC, SEM and TEM. Their mechanical strength was determined experimentally by compression test. In addition, the contribution of these reinforcements to strength by using some models has been calculated theoretically and the results have been associated with the microstructure. According to these results, the yield strength of pure matrix was increased from 185 MPa to 547 MPa by increasing 195% with the reinforcement of 0.5 vol% GNPs + B4C at most. This result is also the case where the theoretical and experimental are the most compatible. In this case, it is thought that load transfer mechanism and dislocations make the most positive contribution while porosity makes the most negative effect.

The effect of 7.5 at.% Al addition in Al7.5CoCrNi medium-entropy alloy (MEA) was investigated. The recrystallized Al7.5CoCrNi exhibited the microstructure of fine-grain face-centered cubic (FCC) phase altogether with the formation of NiAl-rich B2-phase precipitate around the grain boundary and grain interior. The formation of NiAl-rich precipitate led to the significant grain size refinement compared to the Al-free CoCrNi MEA. The small addition of Al was also discovered to be able to significantly improve the mechanical properties of CoCrNi matrix, with a substantial yield strength increment from 400 MPa to 680 MPa was obtained. This increment occurs owing to the combination of several strengthening mechanisms by the addition of Al via substitutional solid solution, grain refinement, and the B2-phase precipitation strengthening that has a good agreement with the theoretical results. The presence of NiAl-rich B2 phase also changed the plastic deformation mechanism that the dislocation slip without e martensitic transformation was found to replace the deformation twinning mechanism which generally observed in a CoCrNi matrix during the plastic deformation.

In present work, the CoCrNi/Mo mixed powder was designed and fabricated by a novel coating method followed by the calcination and reduction processes. The results indicated that in-situ Mo particles distributed homogeneous among the CoCrNi gas atomized powder and no other drawbacks generated such as contamination and oxidation, the reduced Mo particles were nanoscale, and maximum size did not exceed ∼ 600 nm. The SPSed CoCrNi/Mo composite with significant amount of in-situ μ phases showed improved mechanical properties: the yield strength and hardness from 352 MPa to 159 HV to 815 MPa and 375 HV, compared with the pure CoCrNi MEA (medium entropy alloy). The improved properties are mainly attributed to synergistic effects of various strengthening mechanisms, including solid solution strengthening, load transfer effect, Orowan strengthening, grain refinement, especially thermal mismatch mechanism. In addition, this could give insights on the applications of other MEA or HEA-based composites fabricated by coating method.

Excellent high-temperature mechanical properties and high recrystallization temperature are crucial for molybdenum (Mo) alloys in practical applications. The microstructure and high-temperature mechanical properties of Mo-0.8%La2O3-2%ZrC alloys prepared by traditional powder metallurgy technology associated with cross rolling post treatment were investigated. Results showed that the Mo1950-rolled alloys had a fine grain size of about 1.65 μm due to hot cross rolling and high tensile strengths of 988 MPa and 189 MPa at room temperature and 1400 °C, respectively. SEM and TEM examinations indicated that although most of the large La2O3 and ZrC particles were distributed along the grain boundaries, some nano-sized particles were well dispersed in intragranular zones. Particularly, dislocations were found to intercepted by the second phase particles in tensile samples, which could effectively enhance both the tensile strength and recrystallization temperature. Dislocation, grain refining, and second phase particles were all found to play important roles in strengthening the alloys below the recrystallization temperature, while second phase particle strengthening was the only strengthening mechanisms above the recrystallization temperature.

Despite significant gains on understanding strengthening mechanisms in precipitate strengthened materials, such as aluminum alloys, there persists a sizeable gap in the atomistic understanding of how different precipitate types and their morphology along with dislocation character affects the hardening mechanisms. Toward this, the paper examines nature of precipitation strengthening behavior observed in the Al-Cu alloys using atomistic simulations. Specifically, the critical resolved shear stress is quantified across a wide range of dislocation-precipitate interactions scenarios for both θ′ and θ phase of Al2Cu. Overall, the simulations reveal that the dislocation character (edge or screw) plays a key role in determining the predominant hardening mechanism (shearing vs. Orowan looping) employed to overcome the θ′ Al2Cu precipitate. Furthermore, the critical shear stress and mechanism to overcome the precipitate is sensitivity to the position of the glide plane with respect to the precipitate and its orientation. Interestingly in our findings, the θ Al2Cu precipitate conventionally regarded as un-shearable particle was overcome by shear cutting mechanism for small equivalent precipitate radius, which agrees with recent TEM observations. These findings provide necessary information for the development of atomistically informed precipitate hardening models for the traditional continuum scale modeling efforts.

Carbon nanotubes reinforced aluminum matrix nanocomposites were fabricated by friction stir processing. Raman spectroscopy, scanning electron microscope, transmission electron microscopy and tensile tests were used to characterize microstructures and mechanical properties of the nanocomposites. Effects of energy input during friction stir processing on microstructures and mechanical properties of the nanocomposites were investigated. It was found that the grain of aluminum matrix in the nanocomposites was coarsened slightly with the increase of energy input. Microstructure analysis showed that carbon nanotubes were successfully incorporated into aluminum matrix by friction stir processing and well bonded interfaces between the carbon nanotubes and aluminum matrix were formed. However, the carbon nanotubes dispersion and mechanical properties of the nanocomposites fabricated with different energy inputs were quite different, in which better carbon nanotubes dispersion and higher tensile strength could be obtained by applying higher energy input during the fabrication process. By applying the highest energy input, the tensile strength of the nanocomposite was 53.8% higher than that of the unreinforced aluminum. Meanwhile, the elongation of the nanocomposite was 31.2%, which showed an excellent ductility. The strengthening mechanisms were the synergy of Orowan looping, load transfer and grain refining. The present findings may provide the guidance on the optimization of the processing parameters during friction stir processing for fabricating the high performance aluminum/CNTs nanocomposites.

Hybrid (Ti5Si3 + TiCx) (x = 0.67) particles reinforced TC4 matrix composites were in-situ prepared by hot-press sintering, basing on the reactions between Ti3SiC2 and Ti. To research the effects of Ti3SiC2 content on the microstructures and mechanical properties, 1–10 wt% Ti3SiC2 were selected. When Ti3SiC2 content was less than 5 wt%, Si element dissolved in the matrix, and TiCx distributed in the matrix homogeneously. While the content exceeded 5 wt%, Si was precipitating as Ti5Si3 attaching to TiCx particles, which resulted in the aggregations of reinforcements. The micro-hardness of matrix was improved with the solid solubility of Si increasing in matrix, and the compressive strength was improved with Ti3SiC2 content increasing. The hardness was mainly affected by solid solution strengthening. The compressive strength was affected by the solid solution strengthening, fine-grain strengthening and the improvement effect of reinforcements. It was determined that solid solution strengthening played the major role by theoretical calculation.

A four-component equimolar high-entropy alloy (HEA) with the composition of HfNbTiZr and body-centered cubic (bcc) structure was processed by HPT at RT. The evolution of the dislocation density, the grain size and the hardness was monitored along the HPT-processed disk radius for different numbers of turns between ¼ and 20. It was found that most of the increase of the dislocation density and the refinement of the grain structure occurred up to the shear strain of ∼40. Between the strains of ∼40 and ∼700, only a slight grain size reduction was observed. The saturated dislocation density and grain size were ∼2.1 × 1016 m−2 and ∼30 nm, respectively. The saturation in hardness was obtained at ∼4450 MPa. These values were similar to the parameters determined in the literature for five-component HEAs processed by HPT. The analysis confirmed that the main component in the strength was given by the friction stress in the HPT-processed bcc HfNbTiZr HEA. It was also revealed that the contribution of the high dislocation density to the strength was significantly higher than the effect of the small grain size.

The current study explores Al-Zn-Mg alloy reinforced with a high weight fraction of B4C particles as a model system to elucidate the relationship between the microstructure and mechanical behavior of submicron-grained, precipitation strengthened Al-based metal matrix composites (MMCs). Our results indicate that the incorporation of high weight fraction of B4C reinforcement particles can lead to a high dislocation density within the Al grains. Under identical aging condition, this results in an acceleration of the global precipitation kinetics compared to those of the unreinforced counterparts. The microstructures of the consolidated material and heat-treated material were characterized by a high density of plate-like η/η′, and some coarse “fiber-like” precipitates. The “fiber-like” precipitates were identified to be incoherent η2 or η4 precipitates. To elucidate the mechanical behavior of the composite, the contributions from various strengthening mechanisms were estimated using existing relationships. In addition, the effects of the reinforcement particles and precipitates on the fracture mechanisms are discussed.

Relatively high strength and good ductility are rarely obtained simultaneously in aluminum matrix composites. In the present work, dual-phased TiCn-Al3Tim (n: nanosized TiC particles and m: micron-sized Al3Ti particles) particles were in situ synthesized in an Al-Ti-C system via the combustion synthesis method. Subsequently, (TiCn-Al3Tim)/Al hybrid composites were readily fabricated at high addition levels (0, 1, 3, 5 and 7 vol%) via the re-melting and diluting method assisted ultrasonic vibration. Then, the isolated influences of the dual-phased TiCn-Al3Tim particles on the solidification behaviors, microstructure evolution and mechanical properties, at both ambient- and elevated-temperatures, of aluminum alloys were systematically investigated. The experimental results revealed that the α-Al dendrites were substantially refined with a reduction of up to 4 times when compared with that of the unreinforced base alloy. Furthermore, at ambient temperature, 5 vol% (TiCn-Al3Tim)/Al exhibited the optimum comprehensive mechanical properties, and the yield and ultimate tensile strength were 124.3% and 165.2% higher than those of the unreinforced base alloy, whilst the fracture strain was not sacrificed. Theoretical calculations suggest that thermal-mismatch and Orowan strengthening effects contributed most to the yield strength increment, whereas the favourable fracture strain was achieved mainly due to grain refinement. Moreover, at elevated temperature (453 K), the yield strength and ultimate tensile strength were improved by 327.8% and 236.1%, respectively, whilst the fracture strain was still at a relatively high level of 29.2%. The improved thermal resistance primarily resulted from the pinning effects of the TiCn-Al3Tim particles on the grain boundaries and dislocations.

Friction stir processing (FSP) has emerged as an effective secondary processing technique to improve the microstructure and properties of aluminum matrix composites (AMCs). Al/(0–15 wt%) Al3Fe AMCs were prepared by adding pure iron powder to molten aluminum and subjected to FSP. The microstructural changes before and after FSP were studied using OM, SEM, EBSD and TEM. Cast composites exhibited coarse grains, segregation, pores and sharp-edged particles. The distribution of particles was rearranged into a homogeneous distribution after FSP. Casting defects such as pores were eliminated. The sharp edges of Al3Fe particles were removed and rounded into near spherical shape. The grain size reduced remarkably due to severe plastic deformation and the pinning effect of reinforced particles. The density of dislocations increased considerably after FSP. The microstructural changes resulted in an improvement of tensile strength and ductility. The possible strengthening mechanisms were reported.

Current work reports on the development of A357 alloy composite which is reinforced with dual size SiC particles by stir casting route. Influence of different weight fractions (3% coarse+ 3% fine, 4% coarse + 2% fine, and 2% coarse + 4% fine) of dual size SiC particles on mechanical properties and wear resistance of A357 composites is the focus of this work. Hardness and tensile properties were studied for dual size composites and then were compared with A357 alloy. Microstructural study, fractured surface and worn surface investigation were carried out using optical and scanning electron microscopes respectively. Microstructural analysis showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. Compared to A357 alloy, the composites showed improvement in hardness, yield, and tensile strength. In particular, composite with 4 wt. % of fine and 2 wt. % of large SiC particles displayed the highest tensile strength while composite with 4 wt. % of large and 2 wt. % of fine SiC particles exhibited high hardness and wear resistance among A357 alloy and dual particle size composites. The strengthening mechanisms that contributed to improvement in strength values were effective load transfer and dislocation strengthening due to thermal mismatch.

In this research, a novel nitinol shape memory alloy particulate (NiTip) reinforced aluminum matrix composites (AMCs) with fine-grained structure was prepared by underwater friction stir processing (UFSP). Microstructure observation and NiTip/Al interfacial composition analysis showed that UFSP resulted in an uniform dispersion of NiTip in the simultaneously created fine-grained 5083Al matrix, with no additional intermetallics formed at well-bonded NiTip/Al interfaces. The addition of NiTip could accelerate dynamic recovery (DRV) by increasing matrix deformation and promote dynamic recrystallization (DRX) by particle stimulated nucleation (PSN). Due to lack of serious NiTip/Al interfacial diffusion deteriorating their shape memory effect, the introduced NiTip in the resulting AMCs still exhibited a one-stage reversible phase transformation between martensite and austenite. Also, the shape memory effect of NiTip can be activated through pre-deforming in martensite state and then reheating above austenite transformation temperature, thereby introducing compressive residual stress into the matrix. The fine-grained structure with homogeneous NiTip distribution and well-bonded NiTip/Al interfaces in UFSP AMCs, significantly improved strength without adversely affecting the ductility. A detailed analysis on various strengthening mechanisms contributing to the strength of the UFSP AMCs was carried out. Fine grain strengthening, geometrically necessary dislocation strengthening and load transfer effect were demonstrated to be three main contributors to the improved strength of the UFSP AMCs.

The 0.5 vol% Ni-CNTs/Cu nanocomposites with magnetic alignment were prepared by depositing nickel onto CNTs, flake ball milling (FBM), magnetic alignment treatment (MAT) and spark plasma sintering (SPS). The experiment results proved that the properties of the 0.5 vol% Ni-CNTs/Cu nanocomposites with magnetic alignment were anisotropic and the longitudinal properties (parallel to the axial direction of CNT) were the best with the tensile strength up to 292 MPa, the longitudinal elongation rate of about 34%, the longitudinal electronic conductivity of 93% IACS (3% higher than that of SPSed pure copper), and the longitudinal thermal conductivity of 339.8 W/mk (10% higher than that of SPSed pure copper). TEM analysis confirmed that the CNTs were aligned along the axial direction and dispersed uniformly in the Cu matrix. A small amount of Cu2O nanocrystals formed by in-situ reactions between hydroxylic or carboxylic groups of CNT and Cu atoms led to a strong CNT-Cu2O-Cu chemical bonded interface. The interface of the Ni-CNTs/Cu nanocomposites might be the strong CNT-Cu2O-Cu chemical bonding and the oxygen-mediated bonding (Cu-O-C/Ni-O-C). The strengthening mechanisms in the 0.5 vol% Ni-CNTs/Cu nanocomposites with magnetic alignment were ascribed to fiber strengthening through Cu/CNTs interfacial load transfer and strain hardening by CNT dislocation interaction.

Friction stir processing (FSP) has emerged as an effective secondary processing technique to improve the microstructure and properties of aluminum matrix composites (AMCs). Al/(0–15 wt.%) Al2Cu AMCs were prepared by adding pure copper powder to molten aluminum and subjected to FSP. The microstructural changes before and after FSP were studied using OM, SEM, EBSD and TEM. Cast composites exhibited coarse grains, segregation, pores and large polygonal shape particles. The distribution of particles was rearranged into a homogeneous distribution after FSP. Casting defects such as pores were eliminated. The large Al2Cu particles were broken into fine sized particles. The grain size reduced remarkably due to severe plastic deformation and the pinning effect of the reinforced particles. The density of dislocations increased considerably after FSP. The microstructural changes resulted in an improvement of tensile strength and ductility. The possible strengthening mechanisms were reported.

Ni-Mn-Ga-Co-Cu melt spun ribbons were investigated in the as-cast and annealed states. The initial microstructure of the ribbons was highly anisotropic along the growing direction and was characterized by three different regions of equiaxed, columnar and dendritic grains. At ambient temperature, the microstructure was composed of two martensitic phases, i.e. non-modulated and seven-layer modulated, and the high temperature L21 austenite phase. The stabilization of the austenite phase was a consequence of a strong grain size reduction, especially close to the “contact” side of the ribbons. Subsequent annealing at 823 K triggered atomic ordering, which promoted an improvement in the magnetization. Additional annealing at 1173 K brought about a substantial refinement of the microstructure. The ribbon structure changed to a single non-modulated martensite phase, whereas on a microstructural level, the grains and martensitic plates coarsened considerably. The annealed ribbons resembled oligo-crystalline materials and may cause interest for magnetic field-induced strain applications.

The microstructures and mechanical properties of a Mg−8Ho−0.6Zn−0.5Zr alloy were thoroughly investigated. The results reveal five kinds of intermetallic phases, namely the 14H long-period stacking ordered (LPSO) phase, the 18R LPSO phase, Mg24Ho5, Mg0.5Ho1.5, and Mg3Ho. Ordinarily, the 18R LPSO phase locates at a lamellae grain boundary with the misorientation angle of 136.9° and is simultaneously coherent with two α-Mg grains. The corresponding orientation relationships are as (001)18R//(0001)α1 and [010]18R//〈11 2 ¯ 0〉α1, and (001)18R about 43.1° from (0001)α2 and [010]18R//〈11 2 ¯ 0〉α2. After hot-extrusion, the disintegrated intermetallic phases composed of Mg24Ho5 and Mg3Ho mainly distribute at extrusion stringers while the LPSO phases mainly locate in un-recrystallized regions. In addition, amounts of fine spherical intermetallic particles were formed when many parallelly distributed LPSO plates precipitated in a part of the recrystallized grains. The as-extruded Mg−8Ho−0.6Zn−0.5Zr alloy exhibits excellent combination of high strength and high ductility. The underlying strengthening mechanisms were revealed as fine-grain strengthening and dispersion strengthening.

In this paper, an accumulative roll bonding (ARB) process is exploited to produce high-strength, fine dispersed and uniform distribution of Al-5vol.%SiC nanocomposite. The microstructure illustrates and validates a good distribution of SiC reinforced in the Al 1050 matrix. It is observed that, an increasing of ARB passes tends to decrease and refine the size of SiC particle to nanoscale. It is concluded from tensile test that, as number of passes increases, strengths of Al ARBed and composite samples are improved. However, their ductility decreases at initial ARB pass and then increased. The Al-SiC tensile strength of nanocomposite sample is greater 5 times than the annealed Al 1050 used as the original raw material. The strengthening of composite sample occurs due to grain refinement, uniformity, reinforcing role of particles, strain work hardening, and bonding quality. From hardness test, after the initial pass, the hardness improved quickly, then dwindled and finally saturated by further rolling. Experimental data is exploited to derive governing equations describe the effect of the number of ARB passes on the tensile strength and elongation of manufactured nanocomposite samples. It is found that, the tensile strength and elongation can be described as an exponential function that depends on the number of passes. Numerical results from these equation are more consistent with experimental investigation.

The gradient nanograined metals have the unexpected combination of high strength and high ductility. However, the detailed dynamic and continuous process of deformation mechanism at nanoscale need to be further understood. Herein, we report the deformation behavior and microstructure evolution of gradient-nanograined body-centred cubic alloys using molecular dynamics simulations. An analytical model is also established to predict the strength for nanograined alloys. The results show that the alloying can soften the gradient-grained and random-nanograined Fe-based alloys. With the increasing Ni concentration, dislocation density decreases, due to the fact that the Ni solute increases stacking fault energy and the deformation twinning acts as a strong obstacle to suppress dislocation motion. The gradient distributions of strain and stress in gradient-nanograined metals occur due to the plastic incompatibilities, resulting in the inhomogeneous deformation of gradient-nanograined Fe and alloys. In addition, the inverse gradient-nanograined distribution, including large grain in the top surface and small grain in the central region, generates in random-nanograined alloys. It is owing to the grain growth in surface layer, resulting in the gradient strain and stress. Interestingly, the nucleated dislocation network and the deformation twinning considered as a reduction of dislocation mean free path decline rapidly with the increasing grain size for gradient-nanograined structure. The theoretical modeling determines the total strength derived from the individual contributions of different strengthening mechanisms, revealing that the grain boundaries dominate the yield strength and the back stress contributes the most to the straining hardening in nanograined materials.

The W-1.5 wt%ZrO2 alloys were prepared through azeotropic distillation method and then fabricated by four different processing techniques. The effect mechanisms of original solutions containing different acidity on the physical characteristics of the doped tungsten powders were analyzed. The doped tungsten powders with lower degree of particle agglomerates can be prepared under the condition of the original solution with the pH value of 2. Hot isostatic pressing process is beneficial to obtain higher microhardness and excellent wear resistance compared to conventional sintering, vertical sintering and hot swaging process. Meanwhile, the vertical sintering process can fabricate alloy with the compressive strength of 2090 MPa and the critical fracture strain of 0.35, approximately 24.4% and 45.8% higher than those of the swaged W-ZrO2 alloy, and approximately 55.3% and 98.1% higher than those of the swaged pure W, respectively. After swaging, though the swaged alloy has the highest density, the compressive strength and critical failure strain both decrease due to the growth of grain after annealing. The strengthening mechanisms of W-1.5%ZrO2 alloys prepared by different techniques were discussed.

A promising Mg-Zn-Y alloy with the long-period stacking ordered (LPSO) second phase has been developed for about twenty years. Because the LPSO phase has the unique 18R crystal structure, particularly for its packing sequence along [0001], as well as it plays an important role in strengthening mechanisms, it is interesting to clarify in terms of mechanical properties and deformation mechanisms. In this study, uniaxial micro-pillar compression tests are conducted on LPSO along the [0001] direction. At the same time, nanoindentation system equipped with the Berkovich tip is used to extract the basic mechanical properties of (0001) plane. The basal dislocations are found to be activated first, causing the bending of the sample. The bending would lead to the shear stress field downward and thus would cause the nucleation and movement of prism dislocations with [0001] Burgers vector. Prism dislocations can form the fatal 45° slip trace inside the micro-pillar and finally go through the whole sample causing fracture. The basal dislocations are found at the Zn6Y8-Mg interface which might be originated from the local strain field between them.

The Mg-12Gd-2Er-0.4Zr (GE122K) is fabricated by double extrusion, and the effects of grain refinement and precipitate evolution on the mechanical performance of the extruded alloys are deeply analyzed. Scanning electron microscope results spectacle that some bulky precipitates in the single extruded alloy are fragmented to fine precipitates during double extrusion and distribute linearly along the extrusion direction (ED). The fine precipitates exhibit the strongest dispersion strengthening effect, whereas the bulky precipitates act as crack resources and decrease the elongation. After double extrusion, a refined grain structure with an average grain size of 2.7 μm is achieved, which is attributed to dynamic recrystallization (DRX). Moreover, double extrusion boosts the content of rare-earth elements into the matrix by dissolving the fine precipitates. During aging, extensive β′ precipitates form in the double extruded alloy than in the single extrude alloy. As a result, refined grains and strong precipitation strengthening make a significant contribution to a high yield strength (YS) of 422±1.59 MPa with an elongation (EL) of 6.5±0.89% in the double extruded+peak-aged alloy (ACX2). The possible strengthening mechanisms are discussed, and it is found that grain refinement and precipitate strengthening are the main contributors to the high strength of the GE122K alloy.

The microstructural evolutions and properties variations of a CuCrZrY alloy processed by equal channel angular pressing (ECAP) with different passes were studied systematically. After 4 passes of ECAP, the average grain size was decreased to 500 nm, and the grain size distribution became more uniform during the subsequent processing. After 8 passes ECAP-ed and aged at 400 °C for 7 h, the samples’ tensile strength and electrical conductivity are 560 MPa and 86.4%IACS. The main strengthening mechanisms are precipitation strengthening, low-angle grain boundary strengthening, and high-angle grain boundary strengthening (about 82% in total). Finite element simulation was carried out through ABAQUS to obtain the equivalent strain distribution diagram of ECAP, resulting in that the strain force of the outer region was less than that of the inner one. The inconsistency of deformation leads to the inhomogeneity of microstructure. These findings will effectively guide researchers to develop high-strength high-electrical conductivity copper alloys.

Two novel aluminum alloys were designed and studied by incorporating concepts of high entropy and conventional aluminum alloys. The alloys: Al–4Zn–4Mg and Al–4.5Zn–4.5Mg (mol.%) have a single-phase FCC matrix with a maximized concentration of the alloying elements. CALculation of PHAse Diagrams (CALPHAD) approach was applied to determine the compositions and the design of heat treatment schedules. Both alloys show high stiffness and high strength after solution treatment and have excellent impact-resistance after artificial aging. The phase stabilities and strengthening mechanisms were investigated using Optical Microscopy (OM), Scanning Transmission Electron Microscopy (STEM), and X-Ray Diffraction (XRD). The results show that the GP zones and T-phase nanoparticles are mainly responsible for the high stiffness-high strength and impact resistance properties.

Aluminum matrix Boron carbide composites is an important thermal neutron shielding material. In order to prepare 12 wt% B4C/6061Al composite with higher mechanical properties by powder metallurgy method, the new composite reinforced by Nano-Al2O3 particles was fabricated by hot isostatic pressing in the semi-solid temperature range. The tensile properties and strengthening effects of the composite were investigated in this research. The tensile stress-strain curve of the composites was tested by material testing machine, and the microstructure and tensile fracture morphology of composites were analyzed by scanning electron microscopy (SEM) and transmission electron microscopes (TEM). The results indicated that the tensile strength of the composite was greatly improved by the addition of Nano-Al2O3, but the elongation decreased obviously. Nano-Al2O3 particles had seriously affected the microstructure and fracture morphology of the composite and lead to the more obvious brittle fracture characteristics. Strengthening mechanisms of Nano-Al2O3 particles reinforced 6061Al/B4C composite have been discussed, which reveals that grain boundary strengthening mainly plays the most important role.

The high-temperature properties of the molybdenum sheet doped with 1.0 wt%Al2O3 particles were investigated. The Al2O3 particles have a good bond with the Mo matrix and there exists an amorphous transition layer at the interface between Al2O3 particles and Mo matrix in the as-rolled sheet. The tensile strength of the Al2O3-doped Mo sheet is higher 23–62% than that of the pure Mo sheet at room and high temperatures, with its recrystallization temperature increased by about 200 °C than that of the pure Mo sheet. Furthermore, the fracture and strengthening mechanisms were discussed.

Manufacturing copper metal matrix composite (CMMCs) through stir casting method results in numerous desirable benefits. This research is dedicated on fabricating Cu with 0, 3, 6 and 9 wt% TiO2 and 1% Gr CMMCs. The reinforcement particles were added to Cu molten metal at 1200 °C. The cast CMMCs have been analysed using advanced characterization method viz. XRD, FESEM and EDAX. XRD peaks confirm the presence of hard ceramic TiO2 particles in the matrix. Grain refinement takes place in the composite due to TiO2 particles. Two kinds of distribution are observed in the micrographs. By increasing the content of TiO2 and Gr, agglomeration occurs within the grain boundaries and reduces the grain size. As a result, hardness and ultimate tensile strength are improved by the incorporation of TiO2 particles and the corresponding strengthening mechanisms involved have been discussed.

The bulk ultrafine grained (UFG) AA6063/4 wt.%SiC composite sheets with varying reinforcement size of SiC (12 μm (coarse), 1 μm (fine) and 45 nm (nano)) have been developed with a novel hybrid process of stir casting and cryo-severe plastic deformation process (cryorolling). The influence of SiC particle size during development of UFG composites and its effect on microstructural modification, strengthening mechanism and failure mechanism was studied in detail. The resultant effect of cryorolling and size of SiC particles has resulted in significant microstructural refinement (less than 350 nm in all UFG composites) and accumulation of high dislocation density; which resulted in improvement in tensile strength as 88%, 108% and 141% in UFG composites reinforced with coarse, fine and nano particles respectively as compared to the unreinforced base alloy. A good agreement in theoretical and experiment yield strength of UFG coarse and fine composites is observed with a variation in UFG nano composite.

A Ti-6Al-6V-2Sn alloy reinforced with two different volume fractions of TiC particles was subjected to tensile deformation at 750 °C during in-situ high energy synchrotron diffraction to study the load partition between the α-, β-, and TiC phases. Elastic anisotropies and stress differences are shown for the different phases. Possible strengthening mechanisms are analysed and quantified to explain the differences observed in the peak stresses between the matrix and the composites. TiC particles, with an inhomogeneous distribution within the matrix, are capable of bearing load. Although this can be considered as the main strengthening mechanism, it has negligible effect up to the peak stress of the matrix. The evolution of the microstructure during the hot deformation is also analysed and related to the load partition and the damage of the composite.

Nano alumina whiskers (Al2O3w) were in-situ synthesized in carbon nanotubes (CNTs) reinforced aluminum matrix nanocomposites (AMNCs) which were fabricated by flake powder metallurgy (P/M). To study the strengthening effect of nano Al2O3w on CNTs reinforced AMNCs and clarify the strengthening mechanisms, the microstructures and mechanical properties of AMNCs are investigated. It is found that CNTs-Al2O3w reinforcements have a significant hybrid strengthening effect on tensile strength due to their uniform dispersion and good interfacial bonding with Al matrix. The strengthening mechanisms of CNTs-Al2O3w reinforcements are considered as a sum of load transfer, grain refinement, thermal mismatch and Orowan looping theory. The experimental strengths of AMNCs containing 0.25 and 0.5 vol% CNTs are well matched with the theoretical values calculated by the strengthening mechanisms. And the differences between them are less than 2.9%, which is highly effective for predicting the mechanical properties of CNTs-Al2O3w reinforced AMNCs. The predicted values indicate that load transfer mechanism from both CNTs and Al2O3w is dominant, improving UTS of 0.5CNTs reinforced flake AMNCs (228 MPa) by more than 79.5% in comparison with pure Al.

In this study, nanocrystalline Fe-Ni permalloy and Fe-Ni-TiO2 composite coatings were prepared by pulse electrodeposition technique and the effect of current density at five levels was investigated. Morphology of the surface, chemical composition, microstructure, magnetic behavior, hardness and wear properties of the coatings were studied by means of SEM, EDS, XRD, VSM, Vickers microhardness tester and the wear testing instrument of pin-on-disk type. The results showed the mixture morphologies of small needles and fine cauliflower for the coatings prepared at low current densities. Ni content increased in expense of Fe content due to anomalous deposition at higher current densities and the amount of TiO2 nanoparticles in the coatings were also increased. X-ray diffraction patterns showed BCC structure as the dominant phase. However, by increasing the current density, two phase structures of BCC and FCC were detected. It was observed that the current density has a positive effect on grain refinement of Fe-Ni and Fe-Ni-TiO2 coatings. The results of VSM measurements demonstrated that the saturation magnetization (Ms) decreased and coercivity (Hc) increased by increasing the current density due to a reduction of Fe content and grain size. The highest saturation magnetization and lowest coercivity were obtained at 10 mA/cm2 for all coatings. Saturation magnetization values for the Fe-Ni-TiO2 coatings were lower than those of the Fe-Ni coatings. Moreover, the wear resistance and hardness of the coatings can be largely improved by reducing the grain size and Fe content in Fe-Ni matrix. Also, the friction coefficient and the wear rate values of Fe-Ni-TiO2 coatings were lower than those of Fe-Ni coatings due to the grain refinement and dispersion strengthening mechanisms. The adhesive type mechanism and the wear debris were observed on the worn surface of Fe-Ni coatings. While by increasing the TiO2 nanoparticles, the abrasive grooves and wear debris on the worn surface were reduced and the worn surfaces of coatings showed both adhesive and abrasive wear mechanisms.

In the present study, Al-4%SiC nanocomposite was manufactured with homogeneous and uniform distribution of SiC particles in Al matrix using accumulative roll bonding (ARB) technique. In addition high strength Al sheets were manufactured using ARB technique with the aim of comparison. Tensile test and microhardness were used to characterize the produced nanocomposite. Moreover, 3D FE model is presented to predict microhardness of the manufactured nanocomposite. The results show that at the initial stages of ARB process, particle free zones as well as particle clusters were observed in the microstructure of the nanocomposite. After 9 ARB passes, Al-4%SiC nanocomposite with uniform distribution of particles was produced. The tensile strength for ARBed Al and Al-4%SiC nanocomposite after nine passes is 3.19 and 4.09 times of the annealed Al 1050, respectively. Moreover, microhardness of ARBed Al and Al-4%SiC nanocomposite after nine passes is 3.63 and 4.76 times of the annealed Al 1050, respectively. Interestingly, the main strengthening mechanism is the grain refinement and dislocation strengthening due to rolling process, while the addition of SiC nanoparticles acts as a secondary strengthening source. Finally, the microhardness results predicted by the presented 3D FE model correlate well with the experimental results.

In this paper gas tungsten arc welding (GTAW) was applied to dissimilar lap joining of Al6061 and Zn-coated galvanized low carbon steels using Al-5 wt% Si filler metal. The joining mechanism was based on a hybrid brazing/welding mechanism. Three factors contributed to the joint strength including (i) low heat input rate of GTAW process which reduce the intermetallic compound layer growth during joining, (ii) the special role of Si in the filler metal which was able to change the nature of reaction layer from predominantly η-Al5Fe2 phase to predominately less brittle Al-Fe-Si phase and (iii) the flux-like action of Zn-coating which ensures complete wetting of steel surface by Al melt. It was found that there is a critical heat input which when exceeded caused degradation of the mechanical strength of the joint due to increased intermetallic compound growth.

This study demonstrates that the addition of 4 wt% Al to Mg-7Sn-1Zn alloy effectively promotes the dynamic recrystallization and dynamic precipitation behaviors during extrusion and significantly improves the tensile properties of the extruded alloy. The Al addition dramatically increases the area fraction of the dynamically recrystallized (DRXed) grains of the extruded alloy. This is mainly attributed to the particle-stimulated nucleation effect induced by undissolved Mg2Sn particles, the increased amount of grain boundaries owing to grain refinement of the billet, and the increase in stress applied during extrusion. The amount of fine Mg2Sn precipitates of the extruded alloy also increases with the Al addition, owing to an increased number of nucleation sites for precipitation; this, in turn, leads to a reduction in the grain size of the extruded alloy through the enhanced grain-boundary pinning effect caused by the precipitates. As a result, the tensile and compressive strengths of the extruded alloy considerably improved with Al addition, which is due to the combined effects of Al solute atoms, undissolved Mg2Sn particles, more Mg2Sn precipitates, and reduced grain size. Furthermore, the grain size reduction caused by the Al addition suppresses the formation of twins—which can act as cracking sites—during tensile deformation; this results in a considerable increase in the tensile elongation of the extruded alloy.

We report on an investigation of the influence of sintering temperature on microstructure and mechanical behaviors of the Al matrix composites. In this paper, the ultrafine grained AA7075/B4C composites was synthesized via cryomilling and one-step consolidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized for characterization of the grain size of the AA7075/B4C composites consolidated at various sintering temperatures. Our results indicated that the grain size increased gradually from ∼73.1 nm to ∼184.7 nm with the sintering temperature increasing from 350 °C to 450 °C. The formation of abnormal grain growth was observed in the AA7075/B4C composite consolidated at 500 °C B4C particles distributed homogenously, discretely and randomly in the Al matrix based on the observation in Field-emission scanning electron microscopy (FESEM). The porosities were found to decrease in the AA7075/B4C composites with the rising of sintering temperature. The Vickers hardness, compressive yield strength and fracture strength of the AA7075/B4C consolidated at 450 °C were 233 HV, 724.9 MPa and 834.5 MPa, respectively. The analysis of strengthening mechanisms revealed that increasing of sintering temperature resulted in the sacrifice of grain-boundary strengthening and dislocation strengthening.

The present study aims to understand the effect of physio-chemically functionalized graphene nanoplatelet (GNP) reinforcement on tensile properties of aluminum nanocomposite synthesized via spark plasma sintering (SPS). Aluminum matrix was reinforced with different weight percentage of functionalized GNPs (0.25, 0.5 and 1.0 wt%). The novel GNP dispersion technique, i.e. the physio-chemical functionalization of GNPs along with improvised Al powder – GNP particle mixing method resulted in homogeneous distribution of GNPs throughout the Al matrix. The optimization of SPS parameters assisted in achieving a very good densification (up to 99%) in the nanocomposite. Tensile test revealed 98% increment in yield strength of Al-0.5 wt% GNP nanocomposite. Further increase in GNP content (1.0 wt%) resulted in deterioration in the tensile properties attributed to agglomeration of GNPs in the Al matrix. A theoretical prediction of the yield strength of the Al-GNP nanocomposites was carried out considering the various strengthening mechanisms. Fractographs of pure Al and Al-GNP nano composites indicate change of fracture mode from ductile to brittle with increase in the GNP amount.

A novel equimolar CrMnFeVTi high-entropy alloy (HEA) was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). The phase formation and microstructure in the milled powders and in the sintered bulk HEA were characterized using a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that a body-centered cubic (BCC) phase formed gradually in the milled powders during MA. After SPS, a very small fraction of the BCC phase transformed into a face-centered cubic (FCC) phase. Thus, the sintered bulk CrMnFeVTi HEA exhibits a dual-phase structure of BCC and FCC phases, with an average nano-scale grain size of ∼97 nm. Thermodynamic analysis demonstrates that it is the high concentration of titanium in the bulk CrMnFeVTi HEA that stabilizes this dual-phase microstructure over a single-phase microstructure. Titanium has the largest atomic radius and the highest enthalpy of mixing with the other elements, leading to a phase transformation from the BCC phase to FCC phase during SPS. The bulk CrMnFeVTi HEA exhibits extremely high values of compressive strength (2279.53 MPa) and hardness (835 HV), which are significantly higher than those reported for most single-phase BCC structured HEAs. Calculations performed for the contributions of different strengthening mechanisms in this HEA indicate that dislocation and grain boundary strengthening play the most significant roles, whereas the effect of solid solution strengthening effect is very limited because of the release of lattice distortion energy during the BCC to FCC phase transformation in the SPS process.

To improve its strength and ductility, a novel microduplex Mg-7.28Li-2.19Al-0.091Y alloy was designed; its sheets 2 mm in thickness were fabricated by casting, homogenization, and rolling. Mechanical properties and microstructural evolution were investigated by tensile tester, hardness tester, optical microscope, transmission electron microscopy (TEM), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). Tensile tests reveal that the ultimate tensile strength of 299 MPa and elongation of 15.7% were demonstrated in the cold-rolled alloy; the ultimate tensile strength of 211 MPa and elongation of 26.5% were demonstrated in the annealed alloy. Hardness tests indicate that the microhardness of α-Mg phase reaches HV 85. TEM examination reveals that high-density dislocations, dislocation pile-up, dislocation tangle, and interaction between dislocations and particles result in dislocation strengthening and second phase strengthening in the cold-rolled alloy. TEM and XRD results show that α-Mg, β-Li, AlLi, MgLi2Al, and Al2Y phases exist in the cold-rolled alloy while α-Mg, β-Li, MgLi2Al, and Al2Y phases exist in the annealed alloy. SEM observation shows that the fracture mode in the cold-rolled state is a ductile and brittle mixed fracture, and the fracture mode in the annealed state is a ductile fracture. The elongations in both cases are consistent with the fracture morphologies. Strengthening mechanisms were analyzed via crystal defect strengthening models. A strengthening sequence was proposed in this alloy as follows: dislocation strengthening > solid solution strengthening > grain boundary strengthening > lattice friction strengthening > second phase strengthening.

The effects of micro Al2O3 particles additions on microstructures and thermal and mechanical properties of the Sn-9Zn-1Al2O3 nanoparticles on low temperature wetting and soldering of 6061 aluminum alloys are investigated in this study. The results show that the melting temperature of the alloys firstly slightly decreases and then slightly increases with the increase in the micro Al2O3 particles concentration, while the pasty ranges of the alloys are simultaneously increased. The spreading coefficient of Sn-9Zn-1Al2O3-0.25microAl2O3 is about 13.75%, and is increased to about 41.5% of Sn-9Zn-1Al2O3-0.75microAl2O3. Both the surface diffusion, rapid adsorption and phase flow contribute to the formation of precursor film. When micro Al2O3 is added to the composite solder alloys, acicular Sn-Zn eutectic structures are smaller in size from acicular to acicular or circular spot. The strengthening mechanisms with bimodal size Al2O3 particles are on account of grain refinement and load transfer effect of bimodal sized Al2O3. The strength induced by particles is a very important part, which it can account for 21% of the total tensile strength of the solder.

In the present study, the application of hard–plate rolling (HPR) on the hard-to-deform Mg–7Al–5Zn (AZ75) alloy resulted in a homogeneous fine grained (∼6 μm) microstructure, where numerous micron/nano Mg17(Al, Zn)12 precipitates with spherical morphology uniformly dispersed both at grain boundaries and within grain interiors. More importantly, the HPRed AZ75 alloy exhibited superior mechanical properties with a simultaneous high strength and ductility at room temperature, i.e. yield strength (YS) of ∼218 MPa, ultimate tensile strength (UTS) of ∼345 MPa and elongation of ∼19%, which was comparable to the commercial wrought magnesium alloys. According to the contribution from the several strengthening mechanisms estimated by simplified models, the grain boundary strengthening is the predominant mechanism for the high YS of the alloy. The high ductility is benefited from the strong work-hardening capacity resulted from Zn solid solutes and the presence of numerous well-dispersed nanosized precipitates as well as weakened texture. Moreover, the fine grained AZ75 alloy exhibits an optimum superplasticity of ∼615% at 300 °C at 1 × 10−3 s−1. It is attributed to the enhanced grain boundary slip (GBS) promoted by a well maintained fine grain structure resulted from the pining effect by numerous Mg17(Al, Zn)12 particles segregating along grain boundaries during tension. The results will be helpful for the development and processing of high alloying element content Mg alloys with high strength and ductility as well as enhanced formability.

Effects of samarium (Sm) addition on microstructures and tensile properties of Mg−6.0Zn−0.5Zr (ZK60) alloy under both as-cast and as-extruded states were thoroughly investigated. Similar to some other rare earth (RE) additions, the grains of the as-cast ZK60 alloy were refined and the dominant intermetallic phase was changed from MgZn 2 to Mg 3 Sm 2 Zn 3 (W) phase by Sm addition. After extrusion, the ZK60 sample with Sm addition owns much finer dynamic recrystallization (DRX) grains due to the widely spaced large particles and the fine particles on DRX grain boundaries. Furthermore, some other intermetallic phases were examined in the as-extruded samples such as Mg 4 Zn 7 and Mg 7 Zn 3 in ZK60 sample, Mg 22 Zn 64 Sm 14 (Z) and Mg 21 Zn 62 Sm 17 (W′) in ZK60+Sm sample. Thirdly, Sm addition results in much finer, much more and more stable spherical nano-scale precipitates in matrix. Finally, Sm addition further improves the strength of ZK60 alloy, with the dominant strengthening mechanisms being revealed as both fine grain strengthening and precipitation strengthening.

Diamond-like carbon (DLC) coatings have attracted much attention due to their excellent hardness, low friction, and superior corrosion resistance. Unfortunately, the poor adhesion caused by internal stress limits the typical thickness to below 3–5 μm. This paper presents a novel interlayer design and interface engineering and the induced excellent adhesion of thick diamond-like carbon (DLC) coatings on a high speed steel substrate. The interlayer has fundamentally a graded Cr/CrCx/CrC/DLC structure, but various treatments to the hetero-interfaces have been conducted including sequential energetic ion bombardments with Cr at the substrate/Cr interface using high-power impulse magnetron sputtering (HiPIMS) and with C at the CrC/DLC interface using an anode layer ion source. It has been observed that the critical load has been improved from 18 N for a single Cr interlayer to 77 N for a Cr/CrCx/CrC interlayer for thick DLC coatings of 13 μm. Using the same design, a very high critical load of 73 N has been achieved on the ultra-thick DLC coating of 50 μm. This interlayer design has allowed the deposition of a DLC coating that is not only thick but also hard with excellent tribological properties. The DLC coatings have a high hardness of >18 GPa, a low friction coefficient of 0.12 and a low wear rate of (1.7 ± 0.2) × 10−15 m3/N·m. This paper discusses the effect of the ion bombardment of the interlayer on the coating adhesion and the strengthening mechanisms.

Preparing aluminum matrix composites (AMCs) using in situ method results in many desirable benefits. This paper is focused on preparing AA2024/(0, 2.5, 5, 7.5 and 10 wt%) ZrB2 AMCs by Al–K2ZrF6–KBF4 reaction system. The inorganic salts were added to molten aluminum alloy at an elevated temperature of 850OC. The prepared AMCs were studied by applying conventional microcopy and advanced characterization techniques. XRD peaks confirmed the successful synthesize of ZrB2 particles. No other phases such as Al3Zr and AlB2 were detected in appreciable quantity. There was a refinement of grains in the composite due to ZrB2 particles. Two kind of distribution was observed in the micrographs. Particle clusters trapped within the grain boundaries were observed with increased weight fraction of particles. ZrB2 particles were observed to be sub–micron and nano level in size and characterized by proper interfacial bonding with the aluminum matrix. The thermal misfit generated lot of strain fields in the aluminum matrix. The mechanical properties were improved remarkably by the incorporation of ZrB2 particles and the possible strengthening mechanisms were discussed.

The effect of nitrogen on the structure and mechanical behavior of a CoCrFeMnNi high-entropy alloy after rolling and subsequent annealing was examined. The as-cast alloys doped with 0.5, 1.0, and 2.0 at% N were cold rolled to 80% thickness reduction. Further annealing in the temperature range of 700–1000 °C for 1 h has resulted in (i) development of recrystallization in the fcc matrix and (ii) precipitation of the M2N type nitrides in the alloys with 1.0 and 2.0 at% N. The recrystallization onset temperature lowered with an increase in the N content. Besides, the fcc grain size in the alloy with 2.0 at% N was considerably smaller than that in the alloys with a lower nitrogen content due to a strong pinning effect of the nitride particles. The cold-rolled alloys had high strength, but very limited ductility. The recrystallized microstructure has resulted in a much better strength-ductility synergy when tested at 293 K. For example, the alloy with 2.0 at% N after annealing at 900 °C had the yield strength of 673 MPa, ultimate tensile strength of 1021 MPa, and ductility of 47%. A decrease in the testing temperature to 77 K has resulted in a considerable increase in strength. For example, the same alloy had the yield strength and ultimate tensile strength of 1097 and 1548 MPa, respectively. The quantitative analysis of the strengthening mechanisms has revealed that (i) grain boundary strengthening provides the highest contribution at 293 K (ii) the increase in strength at 77 K is mostly associated with the lattice friction and interstitial solid solution hardening.

Copper matrix nanocomposite reinforced by steel particles was prepared by the casting method. The disc mill and ball mill instruments were used to produce the steel particles from machining chips. The effects of the reinforcement particles' content on the microstructure, mechanical properties, fracture mechanisms, and electrical conductivity of the produced nanocomposite material were investigated. An analytical model is developed to predict the mechanical strength of the nanocomposites. The strengthening mechanisms of the reinforcement particles on the matrix and the adverse effects of the agglomeration of the particles on the composite mechanical strength are studied using the developed model. Results of the mechanical show that adding 2.5 wt% steal particles increases the yield strength, the tensile strength, the Brinell Hardness, and the Sharpy impact energy of the pure copper about 48%, 21%, 23.5%, and 300%, respectively. Elongation and ductility almost continuously increase by increasing the content of the particles. The results demonstrate the capacity of steel particles as cost-effective reinforcement material to enhance the copper matrix strength and toughness simultaneously. Furthermore, the addition of steel particles shows little adverse effect on the electrical conductivity.

Involving rare-earth-free Mg alloys, developing microstructure of nanocrystalline matrix and dispersing stable nano-scale precipitates, being a great challenge, is the key to achieve ultra-high strength. In this work, bulk nanocrystalline magnesium alloy was prepared by mechanical milling and subsequent vacuum hot pressing. The effect of hot pressing temperature on microstructure, densification and mechanical properties was analyzed. After hot pressing at 723 K for 60 min, the powders got densified and the average grain size of magnesium matrix was ~76 nm. Nano-scale Ti3Al precipitates with a particle size of ~10 nm were detected by X-ray diffractometer and high-resolution electron microscope. After that, annealing treatment was carried out at 573 K for various times. Both strength and ductility got improved evidently. After annealing at 573 K for 80 h, the yield strength, compressive strength, fracture strain and hardness were 498 MPa, 553 MPa, 4.9% and 1.44 GPa, respectively. Based on analysis on strengthening mechanisms, the contribution rates owing to grain boundary strengthening effect, Orowan effect and load transfer effect were calculated to be 64%, 33% and 3%. It was certified that nanocrystalline magnesium phase together with nano-scale Ti3Al precipitates play a crucial role in realizing ultra-high strength.

The effects of cold rolling and post deformation annealing (CR‐PDA) process on the comprehensive mechanical and corrosion properties of CrMnFeCoNi high entropy alloy (HEA) were investigated. The results indicate that the grain size was obviously refined from 207.5 µm to 4.6 µm. Moreover, the microhardness, yield strength and ultimate tensile strength increased by 28%, 68% and 24%, respectively. However, the elongation decreased from 59.3% to 43.8%. The strengthening mechanisms are mainly fine grain and dislocation density strengthening. Furthermore, the corrosion potential increased and the corrosion current density decreased after the CR-PDA process, indicating that the corrosion resistance of the alloy was improved, possibly because of the grain refinement and residual compressive stress. In conclusion, the CR-PDA process improves the comprehensive mechanical and corrosion properties of CrMnFeCoNi HEA.