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Nanoindentation derived mechanical properties and strain rate sensitivity assessment of a set of stir cast metallic reinforced Aluminium-based composites, with an antecedence of anomalous stress oscillations and strain rate insensitivity during hot compression, was investigated in this study. For the evaluation, Al6063 based composites reinforced with 6 wt% CuZnAl, steel, nickel, and SiC particles were subjected to nanoindentation, and their strain rate sensitivity was assessed using strain rate jump test. The results show that the AMCs reinforced with the metallic particles, presented better mechanical properties than those reinforced with SiC. The CuZnAl reinforced AMC had the best hardness (1.25 ± 0.25 GPa) and elastic modulus (∼83GPa), which is opined to be on account of thermoelastic contributions to the basic strengthening mechanisms. The large scatter observed in the mechanical response of the AMCs is largely due to the inhomogeneous particle distribution. The higher indentation resistance with an increase in strain rate, coupled with the absence of displacement bursts, indicated that the composites largely exhibit positive strain rate sensitivity.

Microstructural evolution and strengthening mechanisms of Mg-3Sn-1Ca based alloys with additions of different amounts of AlN nano-particles were investigated. It was found that with increasing the amount of AlN nano-particles the grain size decreases obviously. The existence of AlN nano-particles could refine the primary crystal phases CaMgSn, which provided more heterogeneous nucleation sites for the formation of magnesium. Moreover, such nano-particles could also restrict the grain growth during solidification. After adding AlN nano-particles, both the tensile properties at room temperature and high temperature 250 °C and the hardness are largely improved. The improvement of strength is attributed to grain refinement and second phase refinement.

A powder thixoforging route combined with slurry based mixing process was proposed to fabricate graphene nanoplatelets (GNPs) reinforced magnesium matrix composites (MgMCs). The originally spherical and ball-milled ZK60 powders were used as matrices, respectively. The mixing of 0.05 wt.% GNPs with the spherical powder led to GNPs clusters and degraded the mechanical properties of the composite. In contrast, with the addition of an optimal content (0.1 wt.%) of GNPs, the composite fabricated from ball-milled powder achieved a joint enhancement in tensile yield strength (52%) and fracture toughness (19%), demonstrating a pronounced strengthening efficiency of 650% and a good balance between strength and toughness. The ball-milled powder endowed the composite with a homogenous distribution of GNPs and a denser microstructure with reduced Mg-Zn eutectics, and the thixoforging process offered a well-bonded Mg/GNP interface, making full use of the strengthening and toughening potential of GNPs. Theoretical predication based on a modified shear-lag model suggested that load transfer dominated the strengthening mechanisms. In-situ tensile tests verified that crack deflection, secondary cracks and GNPs bridging mainly accounted for the toughening mechanisms. A numerical model with consideration of GNPs orientations was also established to understand the toughening effect from GNPs bridging.

Through an investigation of the microstructure and mechanical properties of extruded Mg–5Bi–xSn (BT5x, x = 0, 2, 4, and 6 wt%) alloys, this study demonstrates that the addition of Sn to an Mg–5Bi binary alloy significantly improves the tensile strength of the extruded alloy. All the extruded alloys exhibit a typical basal fiber texture and a partially dynamically recrystallized (DRXed) microstructure consisting of fine DRXed grains and coarse unDRXed grains. As the Sn content increases from 0 wt% to 6 wt%, the average size of the DRXed grains decreases from 4.2 to 2.8 μm owing to the increase in the amount of precipitates via their grain-boundary pinning effect. The extruded B5 and BT52 alloys contain numerous Mg3Bi2 precipitates, but their size and number density are smaller and higher, respectively, in the latter alloy. Numerous Mg2Sn precipitates as well as Mg3Bi2 precipitates are present in the extruded BT54 and BT56 alloys, and the number density of the Mg2Sn precipitates is higher in the latter alloy because of its higher Sn content. The addition of 2 wt% Sn to the B5 alloy significantly improves the yield strength (YS) and ultimate tensile strength (UTS) of the extruded alloy—by 76 and 57 MPa, respectively. This drastic improvement is the combined outcome of enhanced grain-boundary hardening, precipitation hardening, and solid-solution hardening effects induced by the refined DRXed grains, numerous precipitates, and Sn solute atoms, respectively. The further addition of 2 wt% or 4 wt% Sn to the BT52 alloy leads to moderate increments in the YS and UTS of the extruded alloy. Specifically, each addition of 2 wt% Sn increases the YS and UTS by ~26 and ~20 MPa, respectively, which is attributed mainly to the additional precipitation hardening effect induced by the Mg2Sn precipitates.

Multi-direction impact forging (MDIF) was applied to the as-extruded ZK60 Mg alloy, and the microstructure, texture evolution and yield strength symmetry were investigated in the current study. The results showed that the average grain size of forged piece was greatly refined to 5.3 μm after 120 forging passes, which was ascribed to the segmenting effect of {10–12} twins and the subsequent multiple rounds of dynamic recrystallization (DRX). A great deal of {10–12} twins were activated at the beginning of MDIF process, which played an important role in grain refinement. With forging proceeding, continuous and discontinuous DRX were successively activated, resulting in the fully DRXed microstructure. Meanwhile, the forged piece exhibited a unique four-peak texture, and the initial //ED fiber texture component gradually evolved into multiple texture components composed of //FFD (first forging direction) and //FFD texture. The special strain path was the key to the formation of the unique four-peak texture. The {10–12} twinning and basal slip were two dominant factors to the evolution of texture during MDIF process. Grain strengthening and dislocation strengthening were two main strengthening mechanisms of the forged piece. Besides, the symmetry of yield strength was greatly improved by MDIF process.

Increasing the yield strength of austenitic steel without significantly sacrificing ductility has been a long-standing technical challenge. Here, we obtained an ultrahigh yield strength (∼1.4 GPa) and ductile (∼37% uniform elongation) austenitic steel through innovatively combining cold rolling, flash annealing, and tempering (CFT) processes. Such CFT steel shows a heterogeneous lamellar microstructure composed of reversed austenite and partially recrystallized austenite. The ultrahigh yield strength is attributed to the synergistic strengthening mechanisms induced by high-density dislocations, nano/ultrafine grains, and nanoscale precipitates. The achieved high ductility is associated with the pronounced transformation-induced plasticity (TRIP) effect induced by the high-density dislocations combined with the twinning-induced plasticity (TWIP) effect induced by grain refinement. Such a strengthening and plasticity mechanism paves the way for a processing route to achieve ultrahigh strength-high ductility combination in austenitic steel.

In this study, surface mechanical attrition treatment was employed to sucessfully produce a gradient nanostructured layer on WE43 magnesium alloy. X-ray diffraction, energy dispersive X-ray spectrometer, and high-resolution transmission electron microscope observations were mainly performed to uncover the microstructure evolution responsible for the refinement mechanisms. It reveals that the grain refinement process consists of three transition stages along the depth direction from the core matrix to the topmost surface layer, i.e., dislocation cells and pile-ups, ultrafine subgrains, and randomly orientated nanograins with the grain size of ~40 nm. Noticeably, the original Mg3RE second phase is also experienced refinement and then re-dissolved into the α-Mg matrix phase, forming a supersaturated solid solution nanostructured α-Mg phase in the gradient refined layer. Due to the cooperative effects of grain refinement hardening, dislocation hardening, and supersaturated solid-solution hardening, the gradient nanostructured WE43 alloy contributes to the ultimate tensile strength of ~435 MPa and ductility of ~11.0%, showing an extraordinary strain hardening and mechanical properties among the reported severe plastic deformation-processed Mg alloys. This work provides a new strategy for the optimization of mechanical properties of Mg alloys via combining the gradient structure and supersaturated solid solution.

A Co-free as-cast AlCrFe2Ni2 medium entropy alloy (MEA) with multi-phases was remelted by fiber laser in this study. The effect of laser remelting on the microstructure, phase distribution and mechanical properties was investigated by characterizing the as-cast and the remelted AlCrFe2Ni2 alloy. The laser remelting process resulted in a significant decrease of grain size from about 780 μm to 58.89 μm (longitudinal section) and 15.87 μm (transverse section) and an increase of hardness from 4.72 ± 0.293 GPa to 6.40 ± 0.147 GPa (longitudinal section) and 7.55 ± 0.360 GPa (transverse section). It was also found that the long side plate-like microstructure composed of FCC phase, ordered B2 phase and disordered BCC phase in the as-cast alloy was transformed into nano-size weave-like microstructure consisting of alternating ordered B2 and disordered BCC phases. The mechanical properties were evaluated by the derived stress-strain relationship obtained from nano-indentation tests data. The results showed that the yield stress increased from 661.9 MPa to 1347.6 MPa (longitudinal section) and 1647.2 MPa (transverse section) after remelting. The individual contribution of four potential strengthening mechanisms to the yield strength of the remelted alloy was quantitatively evaluated, including grain boundary strengthening, dislocation strengthening, solid solution strengthening and precipitation strengthening. The calculation results indicated that dislocation and precipitation are dominant strengthening mechanisms in the laser remelted MEA.

Magnesium (Mg)-based biomaterials have gained acceptability in fracture fixation due to their ability to naturally degrade in the body after fulfilling the desired functions. However, pure Mg not only degrades rapidly in the physiological environment, but also evolves hydrogen gas during degradation. In this study, Mg0.5Zr and Mg0.5ZrxZn (x = 1–5 wt.%) matrix nanocomposites (MNCs) reinforced with different contents (0.1–0.5 wt.%) of graphene nanoplatelets (GNP) were manufactured via a powder metallurgy technique and their mechanical and corrosion properties were evaluated. The increase in GNP concentration from 0.2 wt.% to 0.5 wt.% added to Mg0.5Zr matrices resulted in decreases in the compressive yield strength and corrosion resistance in Hanks’ Balanced Salt Solution (HBSS). On the other hand, a higher concentration (4–5 wt.%) of Zn added to Mg0.5Zr0.1GNP resulted in an increase in ductility but a decrease in compressive yield strength. Overall, an addition of 0.1 wt.% GNPs to Mg0.5Zr3Zn matrices gave excellent ultimate compressive strength (387 MPa) and compressive yield strength (219 MPa). Mg0.5Zr1Zn0.1GNP and Mg0.5Zr3Zn0.1GNP nanocomposites exhibited 29% and 34% higher experimental yield strength, respectively, as compared to the theoretical yield strength of Mg0.5Zr0.1GNP calculated by synergistic strengthening mechanisms including the difference in thermal expansion, elastic modulus, and geometry of the particles, grain refinement, load transfer, and precipitation of GNPs in the Mg matrices. The corrosion rates of Mg0.5Zr1Zn0.1GNP, Mg0.5Zr3Zn0.1GNP, Mg0.5Zr4Zn0.1GNP, and Mg0.5Zr5Zn0.1GNP measured using potentiodynamic polarization were 7.5 mm/y, 4.1 mm/y, 6.1 mm/y, and 8.0 mm/y, respectively. Similarly, hydrogen gas evolution tests also demonstrated that Mg0.5Zr3Zn0.1GNP exhibited a lower corrosion rate (1.5 mm/y) than those of Mg0.5Zr1Zn0.1GNP (3.8 mm/y), Mg0.5Zr4Zn0.1GNP (1.9 mm/y), and Mg0.5Zr5Zn0.1GNP (2.2 mm/y). This study demonstrates the potential of GNPs as effective nano-reinforcement particulates for improving the mechanical and corrosion properties of Mg–Zr–Zn matrices.

A novel step grooving approach is proposed for the reinforcement incorporation before FSP, enabling the creation of through-thickness composition gradient with a higher volume fraction of reinforcement near the surface and relatively lower volume fraction in the core by using a single step of FSP. The overall tensile strength of Al-GNP functionally graded composite (FGC) is increased by ∼52% compared to pure aluminium. The localized Young's modulus and yield strength of the core region is increased by ∼12% and ∼54% compared to the surface region of the fabricated composite, respectively. The maximum strain in the core region is also decreased by ∼38% depicting its higher stiffness over the surface region. Contrastingly, the microhardness of the surface region is increased by ∼18% compared to the core region of the fabricated composite. Thus, a combination of higher surface hardness and excellent core tensile strength is achieved with the proposed methodology. The bending of graphene interlayers leading to the mechanical exfoliation of GNP increased the load sharing capability of the Al/GNP interface. The load sharing through interface and coefficient of thermal expansion mismatch between Al and GNP are identified as the dominant strengthening mechanisms in the fabricated composite.

Carbon nanotubes (CNT) are an extraordinary innovation for industrial applications. Remarkable characteristics of CNT considered as proper reinforcement in Aluminum (Al) based composites. Al - CNT composites possess energizing mechanical and thermal characteristics. Although characteristics improvements achieved by addition of CNTs in Aluminium metal matrix systems, the thermal mismatch and back stress strengthening mechanisms have not yet been clarified. Hence the purpose of this research paper to deal with the thermal mismatch and back stress strengthening mechanism of CNT-Al composites.

A ring-shaped Mg–8.5Gd–4Y–1Zn–0.4Zr (wt%) alloy was manufactured via centrifugal casting and ring-rolling process. The effects of accumulative ring-rolling reduction amount on the microstructure, texture, and tensile properties of the alloy were investigated. The results indicate that the microstructure of centrifugal cast alloy consists of equiaxed grains and network-like eutectic structure present at grain boundaries. The ring-rolled alloy exhibits a characteristic bimodal microstructure composed of fine dynamic recrystallized (DRXed) grains with weak basal texture and coarse un-DRXed grains with strong basal texture, along with the presence of LPSO phase. With increasing amount of accumulative ring-rolling reduction, the coarse un-DRXed grains are refined via the formation of increasing amount of fine DRXed grains. Meanwhile, the dynamic precipitation of Mg5RE phase occurs, generating a dispersion strengthening effect. A superior combination of strength and ductility is achieved in the ring-rolled alloy after an accumulative rolling reduction of 80%. The tensile strength of this ring-rolled alloy after peak aging is further enhanced, reaching 511 MPa, while keeping a reasonable ductility. The salient strengthening mechanisms identified include the grain boundary strengthening of fine DRXed grains, dispersion strengthening of dynamic precipitated Mg5RE phase, short fiber strengthening of LPSO lamellae/rods, and precipitation strengthening of nano-sized prismatic β′ precipitates and basal γ′ precipitates.

In this work, the Al2O3-reinforced high Nb–TiAl laminated composite is successfully fabricated by an innovative way of direct-current magnetron sputtering combined with the foil-foil metallurgy, with assistance of vacuum hot-pressed sintering. Here, the Nb-coated aluminum foil and titanium foil, microstructure evolution, the lamellar plane distribution and the mechanical performances are carefully studied. Specifically, the composite is composed of the α2-Ti3Al, γ-TiAl and α-Al2O3 phase, in which the high Nb–TiAl matrix has a fully lamellar microstructure and a high content (∼6.5%) of Nb. Taken the textured titanium foil as raw material, the multi-stage annealing process is proved to be an effective way to control the lamellar plane distribution in the high Nb–TiAl matrix, showing that 82.3% of the lamellar planes forms an angle less than 30° from the RD-ND plane of the composite. Moreover, the bending strength and fracture toughness of the composite reach 817 MPa and 12.41 MPa m1/2, respectively. Further, the toughening and strengthening mechanisms are also detailly discussed. We believe that the major findings in this work can provide a new idea to design the high strength-toughness intermetallic-ceramic composites.

The in-situ nanoscale TiC particles reinforced Ti6Al4V composites was prepared by selective laser melting (SLM) from the mixture of Ti6Al4V alloy powders and graphene powders, the microstructure and interface bonding of the composites were studied. The composites were mainly composed of α, α' martensite and α+β structures. More TiC were formed in the overlapping regions than that in the molten pool, the solidification rate in overlapping regions was slow, which was beneficial to TiC nucleation and growth. The TiC and Ti matrix displayed following orientation relationships: axis [0 0 1]β-Ti∥[-1 -1 1]TiC∥[0 -1 1 0 ]α-Ti, lattice plane (2 2 2)TiC //(0 0 0 2)α-Ti, lattice plane (1 1 1)TiC//(0 0 0 2)α-Ti, lattice plane (1 1 1)TiC//(1 0 -1 0)α-Ti. The TiC and Ti matrix have a small degree (6.2%) of mismatch between (1 1 1)TiC and (0 0 0 2)α-Ti, and the semi-coherent interface was occurred. TiC preferentially nucleated and grew up along its (1 1 1) plane. The situ synthesized TiC was added into the Ti6Al4V alloy, refined the grains, and increased the microhardness of the alloy. The microhardness of the composites was 13.6% higher than that of Ti6Al4V alloy. The TiC effectively pinned the dislocations and grain boundaries were responsible for the enhanced mechanical properties of the composites.

Melt-grown alumina-based composites are receiving increasing attention due to their potential for aerospace applications; however, the rapid preparation of high-performance components remains a challenge. Herein, a novel route for 3D printing dense (< 99.4%) high-performance melt-grown alumina-mullite/glass composites using directed laser deposition (DLD) is proposed. Key issues on the composites, including phase composition, microstructure formation/evolution, densification, and mechanical properties, are systematically investigated. The toughening and strengthening mechanisms are analyzed using classical fracture mechanics, Griffith strength theory, and solid/glass interface infiltration theory. It is demonstrated that the composites are composed of corundum, mullite, and glass, or corundum and glass. With the increase of alumina content in the initial powder, corundum grains gradually evolve from near-equiaxed dendrite to columnar dendrite and cellular structures due to the weakening of constitutional undercooling and small nucleation undercooling. The microhardness and fracture toughness are the highest at 92.5 mol% alumina, with 18.39±0.38 GPa and 3.07±0.13 MPa·m1/2, respectively. The maximum strength is 310.1±36.5 MPa at 95 mol% alumina. Strength enhancement is attributed to the improved densification due to the trace silica doping and the relief of residual stresses. The method unravels the potential of preparing dense high-performance melt-grown alumina-based composites by the DLD technology.

In this paper, the homogenized Mg-9Gd-2Nd-1.6Zn-1Zr (wt%) alloys were subjected to various equal channel angular pressing (ECAP) passes (1, 2, 4 and 8) with Bc route at 400 °C. Then, the microstructure evolution and strengthening mechanisms of alloys were systematically investigated. The results show that the coarse deformed grains are completely consumed by the dynamic recrystallized (DRX) grains, the number of dynamic precipitates gradually increases, and the intensity of basal texture of the alloy is gradually weakened with increasing ECAP passes. After 8 passes ECAP, the grain size is dramatically refined from 50 μm (homogenized) to 2.1 μm (8p-ECAPed), which is mainly due to the DRX, particle-stimulated nucleation (PSN) induced by broken eutectic phase and hinder grain growth of dynamic precipitates. The excellent comprehensive mechanical properties are achieved by 4 passes, and the corresponding yield strength (YS) and ultimate tensile strength (UTS) as well as elongation (EL) are 321 MPa, 378 MPa and 14.4％, respectively. This can be mainly ascribed to the combined effect of broken eutectic phase, DRX grains, kinked long period-stacking order (LPSO) and dynamic precipitates.

Refractory metal particles can potentially be used to reinforce titanium matrix composites. In this research, a titanium matrix composite reinforced by 20 wt.% tungsten particles (20WP/Ti) was fabricated by powder metallurgy. The mechanical properties of 20WP/Ti were then evaluated over a broad strain rate range of 10−3–4 × 103 s−1. The microstructure of the composite consisted of W particle reinforcements, W diffusion regions, and an alloyed Ti matrix. The interdiffusion between W and Ti atoms produced broad diffusion regions and the Kirkendall effect. The W diffusion regions were a complex multiple-phase mixture of micron-sized β-Ti grains, nanoscale ω-Ti and α″-Ti phases and W nanoparticles. 20WP/Ti exhibited excellent mechanical properties due to the presence of multiple strengthening mechanisms including reinforcing phase strengthening, solid solution strengthening, and precipitation strengthening. The addition of W particle reinforcing phases suppressed the adiabatic shear sensitivity of the composite. When the strain rate exceeded 1400 s−1, the dynamic strength of 20WP/Ti declined upon increasing the strain rate, attributing to a mass of Kirkendall pores and the thermal softening effect of the β-Ti phase in the W diffusion region at high strain rates.

A superior combination of yield strength (1001 MPa) and − 20 °C impact toughness (166 J) was obtained in Nb–V–Ti-microalloyed Ni–Cr–Mo–Cu steel treated by direct quenching and tempering route (DQT). The tested steels treated by DQT route and re-austenitization and tempering route (QT) were compared with each other in terms of mechanical properties and microstructures characterized by optical microscopy, transmission electron microscopy, X-ray diffraction, electron back-scattered diffraction method and so on. Strength and Vickers hardness of the tested steel treated by the above two routes vary with isothermal aging temperature (400–600 °C), shown as under-aged state, peak-aged state and over-aged state. All DQT specimens show higher strength and Vickers hardness than QT specimens with the same aging condition. Furthermore, the largest difference of yield strength between DQT and QT specimens was shown in DQT600 and QT600 specimens. DQT600 or QT600 specimens refers to direct quenched (DQ) or quenched (Q) specimens isothermally aged at 600 °C. The main disparities in quenched microstructure between DQ and Q specimens are mainly in morphology of prior austenite grains, dislocation density of martensite matrix and solution amount of Nb and Mo elements dissolving in martensite matrix, which play key roles in affecting microstructure and mechanical properties of DQT and QT specimens. Higher dislocation density of matrix and finer average diameter of both MC (M is any combination of Nb, Mo and V) and Cu-rich particles were shown in DQT600 specimens than in QT600 specimens. Strengthening from dislocations and nanosized MC and Cu-rich particles mainly leads to the largest difference of yield strength between DQT600 and QT600 specimens. In addition, strong dislocation strengthening and precipitation strengthening in DQT600 specimen also elevated its ductile-to-brittle-transition-temperature, compared with QT600 specimen.

In this work, novel bioinspired polyurethane (PU) scaffolds were fabricated via freeze casting for PU-based Pancreatic Ductal Adenocarcinoma (PDAC) model. In order to reproduce the tumour micro-environment that facilitates cellular kinetics, the PU scaffolds were surface modified with extracellular matrix (ECM) proteins including collagen and fibronectin (Col and FN). Synchrotron-based small- and wide-angle X-ray scattering (SAXS/WAXS) techniques were applied to probe structural evolution during in situ mechanical testing. Strains at macroscopic, nano-, and lattice scales were obtained to investigate the effects of ECM proteins and pancreatic cell activities to PU scaffolds. Significant mechanical strengthening across length scales of PU scaffolds was observed in specimens surface modified by FN. A model of stiffness modulation via enhanced interlamellar recruitment is proposed to explain the multi-scale strengthening mechanisms. Understanding multi-scale deformation mechanisms of a series of PU scaffolds opens an opportunity in developing a novel pancreatic cancer model for studying cancer evolution and predicting outcomes of drug/treatments.

In this study, a novel fine-grained AZ31 magnesium (Mg) alloy reinforced with sub-micron vanadium particles (VP) was prepared by powder metallurgy (P/M). It was found that VP could accelerate the pile-up of dislocations and the refinement of Mg crystallite sizes during the milling process. The Mg matrix was refined to nanocrystalline scale after milling for 90 h, and the ultimate average crystallite size was only 25 nm. Meanwhile, a homogeneous distribution of the sub-micron VP in Mg matrix was achieved. After hot-extrusion process, the average grain size of Mg matrix was 3.08 μm, which reached fine-grained scale. Additionally, the AZ31-2.5 wt % VP composite exhibited competitive mechanical properties. Compared to the as-cast AZ31 Mg alloy, the microhardness, yield strength, ultimate tensile strength and elongation of AZ31-2.5 wt % VP composite increased by 102%, 128%, 59% and 10%, respectively. The grain boundary strengthening played a dominant role in improvement of strength. Simultaneously, the strengthening mechanisms of thermal mismatch, Orowan strengthening and load transfer also made a contribution. Besides that, the fracture mechanism of the AZ31-2.5 wt % VP composite included ductile and brittle fracture mode.

Fire–resistant properties of Mo-/Nb-added structural steels were evaluated using hot tension tests and constant-load tests. Hot tension tests showed that an increase in the Mo and Nb contents led to a slow decrease in the strength as the holding time increased at a high temperature (600 °C), enhancing the fire resistance. Transmission electron microscopy (TEM) and atom probe tomography analyses revealed that this improved fire resistance stemmed from the annihilation of dislocations at high temperatures, which was suppressed by the solid solution of Mo atoms and fine precipitation of Ti/Nb-enriched MC carbides. Meanwhile, an increase in Ti content decreased fire resistance via precipitation of coarse TiC particles, i.e., in-situ TEM observations showed that dislocations moved easily along the surface of coarse particles by climb, indicating that coarse particles did not play a role in disturbing dislocation movement during deformation at high temperatures. Next, constant-load tests were carried out with a constant load of 50% of the yield strength, while the temperature was increased linearly until failure. The results were in good agreement with the results of the hot tension tests; i.e., the failure temperature increased with an increase in the Mo and Nb contents, indicating improvement in fire resistance.

In order to overcome the interfacial incompatibility of carbon fiber reinforced magnesium matrix (Cf/Mg) composites, a double-layer interface (ZrO2–MgO) is designed in this work. Carbon fiber was modified with ZrO2 coating by sol-gel process. Microstructural examination reveals that MgO layer forms on the surface of ZrO2 coating by ZrO2 reacting with Mg during the composite fabrication. Such double-layer interface could inhibit Al4C3 and hence prevent fiber damage. Meanwhile, the wettability was improved for the reaction between ZrO2 and Mg. Thus the tensile strength of ZrO2-Cf/AZ91D composite was 68.0% higher than that of the unmodified one. Due to the fiber bundle pull-out, debonding and crack deflection, the toughness of Cf/Mg composite with double-layer interface is increased simultaneously.

Mg-2.6Sm-1.3Gd-0.6Zn-0.5Zr (wt.%) alloy is prepared with metal mold casting and followed hot extruded at 400°C with the extrusion ratio of 25:1. Microstructure and mechanical properties of the as-extruded alloy are investigated using optical microscope (OM), scanning electron microscope (SEM) with electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM). The results show that the as-extruded alloy is fully dynamically recrystallized, which develops rare earth (RE) texture component. The as-extruded alloy shows an age-hardening response at 200°C, in which there are numerous nano-scale plate strengthening phase β′ precipitated in the matrix. The as-extruded alloy in the peak-aged condition exhibits ultimate tensile strength, yield strength, and elongation of 332 MPa, 220 MPa and 22.7% at room temperature, respectively. The dominant strengthening mechanisms of the investigated alloy are fine-grain strengthening, solid solution strengthening and precipitate strengthening.

In prior works, a novel method for continuously obtaining Al-Zr master alloys from oxide raw materials by electrolysis of a low-melting electrolyte based on the KF-NaF-AlF3-ZrO2 system at 800 °C to 820 °C was proposed. In the present work, the method for preparing the Al-Zr master alloy proceeded in an enlarged 100 A electrolyzer and the obtained master alloy was applied for grain refinement and improvement of its aluminum alloy properties. The modifying ability of the master alloy was studied, drawing on the example of the Al-Si-Fe alloy. Different amounts of the Al-Zr master alloy with a content of 10 wt pct zirconium were added to the Al-Si-Fe alloy at 900 °C. The effect of the zirconium content in the aluminum alloy and its cooling rate on its structure and properties was revealed. It was found that the addition of zirconium to the alloy refined the grain by 4 to 5 times without changing its shape or structure. A study of the joint effect of alloying and rate cooling indicated that a grain size reduction of up to 5 mkm can be achieved by these procedures.

Nanoceramic composites exhibit superior properties over their microcounterparts due to their microstructural differences. However, achieving grain size reduction in these composites through grain suppression is limited. Therefore, the use of nanopowders (both matrix and reinforcement) at the starting level itself and an attempt to further reduce the grain size may yield extraordinary properties. Thus, the present research aims to investigate the tribological and mechanical properties of ZTA nanocomposites reinforced with nano-MgO/MWCNT. The composites were developed separately through spark plasma sintering (SPS) and microwave sintering. The experimental results showed that with increase in the normal load and sliding velocity, the COF decreases, while the wear rate increases. Further, both the COF and wear rate increased with increase in the normal load and sliding velocity beyond a certain point. Moreover, when the normal load is increased beyond 65N, the wear rate of the composites increases rapidly irrespective of the sliding velocities. The addition of MgO increased the hardness through a secondary phase and pinning effect of the composites, while the addition of MWCNTs increased their fracture toughness through crack branching. The wear rate and the COF of the SPS composites were better than their MW-sintered counterparts.

Background Polymer hydrogels have attracted considerable attention as functional materials. The conventional single network hydrogels (SNs) are mechanically either too soft or brittle to be used as load-bearing substances. Therefore, the interpenetrating network hydrogels (IPNs) with unique physical characteristics paid more and more attention and they have shown great potentials in fabricating a variety of food structures with desired functionalities. Scope and approach This review provided a summary of the latest developments and applications of IPNs in terms of synthesis strategies (heating-cooling, enzymatic, and ionic-induced technique), physical performance (mechanical property, water holding capacity, swelling capacity, and thermal property), formation and strengthening mechanisms, as well as food applications. The major future trends of IPNs in food systems were also discussed. Key findings and conclusions As compared with SNs, IPNs generally exhibited more favorable mechanical performance, water holding capacity and thermal stability. The strengthening mechanisms of IPNs were mainly attributed to the filling of polysaccharides in other biopolymers, the increased density of entangled network, and the possible interactions between individual networks. IPNs with tunable mechanical property could be fabricated, showing great potential for various food applications such as edible films, three-dimensional printing, delivery of bioactive/aroma compounds, as well as fat replacers.

Mechanical milling presents an effective solution in producing a homogenous structure for composites. The present study focused on the production of 0.5 wt% yttria nanoparticle reinforced 7075 aluminum alloy composite in order to examine the effects of yttria dispersion and interfacial bonding by ball milling technique. The 7075 aluminum alloy powders and yttria were mechanically alloyed with different milling times. The milled composites powders were then consolidated with the help of hot pressing. Hardness, density, and tensile tests were carried out for characterizing the mechanical properties of the composite. The milled powder and the microstructural evolution of the composites were analyzed utilizing scanning and transmission electron microscopy. A striking enhancement of 164% and 90% in hardness and ultimate tensile strength, respectively, were found compared with the reference 7075 aluminum alloy fabricated with the same producing history. The origins of the observed increase in hardness and strength were discussed within the strengthening mechanisms' framework.

TiB2 particles clusters evolution, mechanical properties and strengthening mechanisms of in situ 6wt% TiB2/Al–Zn–Mg–Cu composites subjected by two-step deformation process were studied. The results suggest that large TiB2 clusters and belts can hinder elements dissolution and diffusion, leading to partial transformation from T phase to S phase. Two-step orthogonal deformation can effectively break the TiB2 clusters to release the wrapped phases, which is conductive to solution process. Low fraction of residual T and S phases, broken brittle phases and uniform TiB2 distribution are in favor of mechanical properties. In T6 state, η’ and GP II are the main reinforcement phases, which can contribute to yield strength about 355.30 MPa estimated by strengthening model, dislocation reinforcement contribution is about 112.70 MPa. The 6wt% TiB2/Al–Zn–Mg–Cu composite subjected two-step deformation owns an excellent mechanical performance, 616.96 MPa (UTS), 552.00 MPa (YS), 9.67% (EL). Comparably, UTS, YS and EL of that improve by 16%, 15%, 265% in radial direction and 12%, 18%, 87% in axial direction than forged composite. The 6wt% TiB2/Al–Zn–Mg–Cu composite subjected two-step orthogonal deformation owns an excellent mechanical performance, 616.96 MPa (UTS), 552 MPa (YS), 9.67% (EL). Comparably, the UTS, YS and EL of that improve by 16%, 15%, 265% in radial direction and 12%, 18%, 87% in axial direction than forged composite, respectively.

The microstructure and mechanical behavior of low-carbon ultrafine grain steel (UFG; 0.165 wt pct carbon) after niobium (Nb) addition were investigated. It was found that the addition of 0.028 wt pct of Nb resulted in the optimal tensile strength of 990.8 MPa with an adequate elongation of 15.5 pct. In comparison to the normal UFG steel (without Nb), the strength of Nb-UFG steel was substantially enhanced without any sacrifice of its elongation. The main increased strengthening mechanisms of Nb-UFG steel were precipitation and dislocation strengthening. The improved work hardening and adequate elongation of Nb-UFG steel could be ascribed to geometrically necessary dislocations and heterogeneous ferrite grains. Discontinuous static recrystallization occurred by a small rolling reduction on hardened martensite laths, resulting in the formation of heterogeneous ferrite grains. Ultrafine ferrite grains were surrounded by high-angle grain boundaries, and nanoscale Nb(C, N) carbonitrides providing precipitation strengthening were precipitated mainly in the α-phase.

Both the dual-phase and multi-phase high-entropy alloys show excellent mechanical properties. The dual-phase FeCoCrMn alloy consisted of alternating lamellar face-centered-cubic (FCC) and sigma (σ) phases was developed in this work. The FCC and σ phase were identified to be FeCoMn-rich and Cr-rich phase, respectively. The alloy showed high compression yield strength of 1431 MPa at room temperature, which was attributed to the specific lamellar structure and high volume fraction σ phase (46%). The ductility was limited (compression strain was about 1%), due mainly to the inherent brittleness of σ phase. The compression properties at elevated temperatures were also evaluated. The yield strength and compression strain at 400 °C were 758 MPa and 12.6%, respectively. The yield strength at 800 °C was 181 MPa. The strengthening mechanisms of the alloy at different temperatures were discussed based on the microstructural characterization. The improved thermal activation process and the strength decline of both the FCC and σ phases at the elevated temperatures may be responsible for the decreased yield strength and increased ductility. In addition, the comparison of yield strength between FeCoCrMn alloy and other high-entropy alloys was also made.

A comparative study was carried out on the synthesis of ZrB2-25 vol.% SiC-(5, 10 and 15 vol.%) TiC composites through microwave sintering (MS) and spark plasma sintering (SPS). The effects of TiC inclusion on sinterability, microstructures, phase analysis and mechanical characteristics of ZrB2-SiC composites processed through MS and SPS were examined and compared. The structural integrity of ZrB2-based composites was enhanced by TiC addition due to generation of lower tensile residual stresses in the matrix phase and higher compressive residual stresses in the reinforcement phase. The composites developed by SPS exhibited higher relative density, hardness and compressive strength, whereas higher fracture toughness was observed for composites developed by MS. Results indicated that SPS sintered Z25S10T composite exhibited maximum relative density, microhardness, compressive strength and minimum open porosity of 99.38 ± 0.26%, 24.78 ± 1.06 GPa, 349.01 ± 16.72 MPa and 0.37 ± 0.11%, respectively. The maximum fracture toughness of 6.36 ± 0.296 MPa m1/2 along with maximum critical energy release rate of 93.275 ± 4.64 J/m2 was obtained for Z25S15T composite developed through MS. The higher fracture toughness of microwave sintered composites could be attributed to the activation of several strengthening mechanisms like deflection, bridging and impeding of cracks.

Due to its electro-mechanical properties, commercially pure aluminium wires have attracted the interest of automotive industry representing a functional and efficient economic solution to reduce vehicle’s weight leading to the diminishing of energy consumption and emissions in today’s society. However, to consolidate its use in this sector and in new market realities, it is necessary to increase the flexibility of the aluminium conductor wires, consenting their installation in very small spaces and with high curvatures, avoiding any failure and electrical conductivity decrease. Thus, the evolution of microstructure and service performance need to be investigated and controlled to improve the service safety. The present research shows a new approach to efficiently continuously manufacture long wires with smaller diameters and fine grains at room temperature. It is studied the strengthening effects (yield and tensile strength, plasticity, hardness), the electrical conductivity and the microstructural changes of commercial 1370 pure aluminium (99.7% Al) when traditional wire drawing process is combined with equal channel angular drawing (ECAD) technique. The results of this proposed procedure of deformation “drawing-ECAD-drawing” show an evident benefit, compared to the classic technology of production of aluminium wire, obtaining fine grain structure product with superior mechanical strength and not influenced electrical conductivity. The proposed manufacturing approach leads to fine wires enhancing the material mechanical properties by microstructural evolution (i.e. grain size reduction) avoiding the traditional post manufacturing thermal treatments requiring a high amount of energy and time and careful steps.

Micro- to nano-indentation hardness-based stress–strain computations made for Berkovich spherically-tipped impressions put into (001) MgO crystal surfaces show an exceptional plastic strain hardeni...

High strength and large ductility of existing Mn-containing brass alloys need to be further improved when used as slippers of friction-pair materials, which could be achieved by tuning alloy composition and thermomechanical treatments appropriately. The present work optimized the amount of minor-alloying elements M (M = Mn, Fe, Si) in Cu-Zn alloy via a cluster formula approach and then investigated the microstructural evolution of the designed alloy with different thermomechanical treatments. As-cast alloy ingots were solid-solutioned at 1093 K (820 °C) for 3 h, hot-rolled at 923 ~ 1023 K (650 ~ 750 °C), and then aged at 673 ~ 723 K (400 ~ 450 °C) for 1 ~ 2 h, respectively. It is found that the alloy matrix consists of the main FCC-α phase plus a small amount of BCC-β and M5Si3 phases, among which the M5Si3 exhibits three types of primary, fine, and nano-scaled particles. The mechanical property varies with the thermomechanical treatments due to diverse microstructures (especially the morphology of M5Si3 particles), in which the high strength (σUTS > 580 MPa) and large ductility (δ = 16.3 ~ 29.4%) could be achieved simultaneously in 673 K (400 °C). The optimal matching of high strength and large ductility makes the current alloy more suitable as an alternative slipper material. The strengthening effect was further discussed in light of various strengthening mechanisms, and the calculated strength increment is well consistent with the experimentally measured yield strength.

Increasing nanoparticle volume fraction has been proved to be effective in improving the strength of nanoparticle reinforced Al matrix nanocomposite. However, the underlying mechanisms for the ultrahigh strength of those nanocomposites with high volume fraction (> 10 vol.%) nanoparticles are short of experimental research. In this study, the strengthening mechanisms of high strength Al matrix nanocomposite reinforced with 15 vol.% Al2O3 nanoparticles were investigated experimentally and analyzed theoretically. The results show that the thermal mismatch induced geometrically necessary dislocations exhibit a negligible strengthening effect, because of their low density in the nanocomposite that is contradiction to the conventional dislocation punch model. Orowan mechanism makes a major strengthening contribution in view of the deformation process dominated by nanoparticle-dislocation interactions due to the extreme pinning effect of nanoparticles on dislocation motion. In addition, the several mechanisms including grain boundary strengthening, load transfer strengthening, and elastic modulus mismatch induced dislocation strengthening contribute to the strength increase.

TiC/Fe0.6MnNi1.4 medium entropy alloy matrix composites with different volume fractions of TiC particles (i.e., 5, 10 and 15 vol%) were prepared by induction melting method. The experimental results showed that both the base alloy and the composite matrix possess face-centered cubic structure. The in-situ TiC reinforcement phase can significantly increase the mechanical properties of the composites at room temperature. In particular, the hardness, yield strength and ultimate tensile strength of the 10 vol%TiC/Fe0.6MnNi1.4 composite are found respectively to be 528 HV, 345.1 MPa and 716.7 MPa, representing a marked increase by 51.7%, 41.1% and 30.7% in comparison with the Fe0.6MnNi1.4 medium entropy alloy. The ductility of the composite in terms of the elongation to failure is reduced from 65.8% to 36.6% with the increase of the TiC content, which remains attractive for load-bearing structural applications. The strength improvement is underpinned by a combination of the load-bearing effect, Orowan process, dislocation interactions and solid solution effect.

The strength-ductility trade-off problem of carbon nanotube (CNT) reinforced aluminum matrix nanocomposites (AMNCs) restricts its further application. Hence, we report the fabrication of nano-Al4C3 reinforced AMNCs through friction stir processing (FSP) on CNT/Al composites which can simultaneously elevate the ductility of the composite and maintain the original strength. The microstructure evolution and the dispersion of reinforcement are investigated. Tensile tests show that the elongation of the Al4C3/Al composites fabricated via FSP at a rotation rate of 800 rpm increased by 1.6 times than that of CNT/Al composite and the yield strength retained 95%. The improvement of the mechanical properties is due to the strong Al4C3–Al interface, homogeneous dispersion, nano size, and dynamic recrystallization during FSP. Grain refinement and Orowan strengthening are the main strengthening mechanisms of Al4C3/Al composites. This research shares an approach to preparing a nano-Al4C3 reinforced aluminum matrix composite with well strength and outstanding ductility.

High-entropy alloys (HEAs) have attracted great research interest owing to their good combination of high strength and ductility at both room and cryogenic temperatures. However, expensive raw materials are always added to overcome the strength-ductility trade-off at low temperatures, leading to an increased production cost for the cryogenically used alloys. In this work, a series of nitrogen-doped FeMnCoCr HEAs have been processed by homogenization annealing, cold rolling and recrystallization annealing followed by water quenching. The microstructural evolution and mechanical properties of the alloys are studied systematically. The Fe49Mn30Co10Cr10N1 alloy shows excellent mechanical properties at both 293 K and 77 K. Particularly, the yield and ultimate tensile strength of 1078 and 1630 MPa are achieved at the cryogenic temperature, respectively, while a satisfactory uniform elongation of 33.5 % is maintained. The ultrahigh yield strength results from the microstructure refinement caused by the activation of athermal martensitic transformation and mechanical twinning that occur in the elastic regime together with the increased lattice friction due to the cryogenic environment. In the plastic regime, the dynamic Hall-Petch effect caused by twinning, martensitic transformation, and reverse transformation together with the high barrier to dislocation motion jointly contribute to the ultrahigh tensile strength. Simultaneously, the transformation induced plasticity (TRIP) and the twinning induced plasticity (TWIP) effects jointly contribute to the ductility. The design strategy for attaining superior mechanical properties at low temperatures, i.e. by adjusting stacking fault energy in the interstitial metastable HEAs, guides the development of high-performance and low-cost alloys for cryogenic applications.

Fe–Al–Mn–C steels have superior mechanical properties, such as high yield and tensile strengths and low density, which make them suitable for applications in the automotive and defense industries. In particular, the aging of these steels at certain temperatures and times results in the formation of nanoscale precipitates such as κ-carbide, which can significantly affect their mechanical properties. Therefore, the precise estimation of the size and amount of κ-carbide precipitates is necessary to predict and control the mechanical properties of lightweight steels. However, because κ-carbides precipitate rapidly, it is difficult to detect subtle changes early in the precipitation process. Furthermore, it is difficult to experimentally observe and quantify nanoscale precipitates. We conducted thermokinetic simulations of the aging of lightweight steel specimens to predict the phase fraction and size of the precipitated κ-carbides after various aging times and validated these results by comparison with experimental data. Next, we assessed models of precipitation strengthening based on different mechanisms. Additionally, the total yield strength was predicted by calculating the precipitation strengthening effect and estimating all the strengthening mechanisms affecting the yield strength, for example, grain boundary strengthening, solid solution strengthening, and dislocation strengthening.

The strengthening mechanisms of Al-TiAl3 nanocomposite, fabricated using cold roll bonding, annealing, and accumulative roll bonding (ARB) on Al sheets sandwiching with pure Ti powder were investigated in the present study. With annealing at 590 ℃ for 2 h, TiAl3 intermetallic compound was formed. After subsequent ARB process up to 5 cycles, final composite consists of ultrafine Al grains of less than 500 nm with TiAl3 particles larger than 200 nm. The strength and hardness of the final composite are 2.5 and 3.5 times the initial values, with an ultimate tensile strength of 400 MPa, which is dominated by grain-boundary strengthening due to the ultrafine Al grains, and Orowan strengthening due to the small TiAl3 particles. For comparison, an alternative fabrication route of cold roll bonding–ARB–annealing was also studied. This study showed that annealing before ARB is a critical factor in producing an ultrafine grain structure containing TiAl3 particles.

Carbon nanotubes (CNTs) are regarded as an excellent reinforcement for reinforcing metal matrix composites. However, they are extremely difficult to disperse since nano-scaled CNTs have large specific surface area, generally leading to agglomeration due to the large van der Waals attractive forces. In this study, CNTs as carbon sources were added into Ti6Al4V matrix, a dry jar-milling process without milling balls was performed to greatly reduce the structural damage of CNTs and simultaneously meet the requirements of dispersion homogeneity. In situ synthesized TiC and unreacted CNTs reinforced Ti6Al4V matrix composites (TMCs) were successfully prepared by the fast manufacturing process via spark plasma sintering. The microstructures and mechanical properties including microhardness, compressive yield strength, ultimate compressive strength and plastic strain of the Ti6Al4V alloy and the TMCs prepared by different CNTs content were studied to evaluate the strengthening effects of the reinforcements on Ti6Al4V matrix.

A MoNbTiWZr refractory multi-principal element alloy with N and O impurities was sintered by mechanical alloying (MA) followed by the hot-press sintering (HPS). The results demonstrated that the as-sintered samples were composed of two homogeneous body-centered cubic (BCC1 plus BCC2) structural phases with a small quantity of face-centered cubic (FCC) (Zr,Ti)O oxide inclusions. Subsequently, the alloy was sintered at 1500 °C for 45 min to give a BCC phase with an average grain size of 7.27 μm and oxide inclusions of approximately 0.86 μm, and the resulting material exhibited a remarkable microhardness of 634 HV, compressive yield strength of 2660 MPa and plastic strain of 2.5% at ambient temperature. The superior mechanical properties of the as-prepared MoNbTiWZr were principally attributed to interstitial solid solution strengthening and grain boundary strengthening. Furthermore, the large difference in the yield strength between the experimental and theoretical values revealed that excessive oxides significantly impaired the contribution of precipitation strengthening to the yield strength. The synergistic effect of the various strengthening mechanisms can be optimized by controlling the size and volume fraction of the oxide precipitates to below 1 μm and 7%, respectively.

A novel Al0.5V0.1FeCrMnNi0.9 high-entropy alloy was designed to achieve enhanced strength and plasticity. The as-cast Al0.5V0.1FeCrMnNi0.9 alloy shows a typical dendritic microstructure consisting of a body-centered cubic-structured matrix phase and a B2-structured nanoprecipitate phase. Nanoprecipitates are homogeneous and dispersed in the matrix. The as-cast Al0.5V0.1FeCrMnNi0.9 alloy exhibits a compressive yield strength of 1.104 GPa, a fracture strength of 2.926 GPa, and a fracture strain of 45.7%. The product of strength and plasticity of this alloy is 133.72 GPa%, which is superior to that of most of the reported high-entropy alloys. The strengthening mechanisms were evaluated in detail, which indicates that the coherent precipitation enhancement contributes to the unusually high strength and plasticity.

The main objective of the present study is to develop AA 7017 alloy matrix reinforced with yttrium oxide (Y2O3, rare earth element) nanocomposites by mechanical alloying (MA) and hot pressing (HP) techniques for armor applications. AA 7017+10 vol % Y2O3 nanocomposites were synthesized in a high-energy ball mill with different milling times (0, 5, 10, and 20 h) to explore the structural refinement effect. The phase analysis and homogeneous dispersion of Y2O3 in AA 7017 nanocrystallite matrix were investigated by X-ray diffraction (XRD), various electron microscopes (HRSEM, and HRTEM), Particle Size Analyzer (PSA), and Differential Thermal Analysis (DTA). The nanostructured powders were hot-pressed at 500 MPa pressure with a temperature of 673k for 1hr. The consolidated sample results revealed significant grain refinement and the enhanced mechanical properties with the function of milling time in which the 20h sample exhibited improvement in the hardness (142 VHN - 260 VHN) and ultimate compressive strength (514 MPa–906.45 MPa) due to effective dispersion of Y2O3. The various strengthening mechanisms namely, grain boundary (27.02–32.69 MPa), solid solution (57.21 MPa), precipitate (189.79–374.62 MPa), Orowan (135.68–206.92 MPa), and dislocation strengthening (84.99–149.82 MPa) were determined and correlated to the total strength.

High-Entropy Alloys (HEAs) are a promising class of metallic materials that have allured the world of material science and engineering. These intriguing materials are proving their worth in the coatings for severe ambient and demanding conditions. Laser cladding (LC) is a non-linear complex, multidisciplinary and modern technology applied for surface modification. Nobler properties of HEAs as compared to traditional alloys permitted the research community to explore Laser-Cladded High-Entropy Alloy Coatings (LC-HEACs). Here, this article provides a review and recent trends of LC-HEACs, aiming to address the use of LC technology for HEA materials, the influence of process parameters on the geometric and metallurgical characteristics of the LC-HEACs. Common defects not limited to microcracks and residual stresses, and techniques to improve the quality of the LC-HEACs are elucidated. Furthermore, thermo-kinetics effect, thermomechanical behavior, microstructural evolution, and strengthening mechanisms are illustrated for a better understanding of laser-material interaction. The potential applications of the LC-HEACs are outlined considering wear, corrosion, erosion, and oxidation resistance and their corresponding substrates. The article also highlights the research gaps, current trends, and possible future directions in the context of critical challenges that need to be catered, before the actual implementation of LC-HEACs in industries. Owing to the variety of element constitution for HEAs design as well as excellent mechanical and functional properties, LC-HEACs will blossom in the years to come.

The microstructural evolution and mechanical properties of ultrafine-grained (UFG) CP-Ti after an innovative large-volume equal channel angular pressing (L-ECAP) and multi-directional forging (MDF) were systematically examined using monotonic tensile tests combined with transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) techniques. Substantially refined and homogeneous microstructures were achieved after L-ECAP (8-pass and 12-pass) and MDF (2-cycle and 3-cycle), respectively, where the grain size distribution conformed to lognormal distribution. The grain refinement of 450 °C L-ECAP is dominated by dynamic recrystallization (DRX) and dynamic recovery (DRV), while that of MDF is dominated by DRX. The iron impurities promote recrystallization by pinning-induced dislocation accumulation so that DRX is prone to occur at iron segregation regions during L-ECAP. The monotonic tensile results show that the strain hardening rate of CP-Ti increases with the decrease of grain size, while the continuous strain hardening ability decreases. The relationship between the average grain size and yield strength is in accordance with Hall-Petch relationship. Meanwhile, the individual strengthening mechanisms were quantitatively examined by the modified model. The results indicate that the strengthening contribution of dislocation accumulation to yield strength is greater than that of grain refinement.

Molybdenum (Mo) and its alloy have great potential in the nuclear power field, but the low strength of fusion welding joints limits its engineering application. By adding two alloying elements in combination, namely carbon (C) and titanium (Ti), this study fulfilled the goal of improving properties of the heat affected zone (HAZ) while strengthening the fusion zone (FZ) of the joint. The alloying process is as follows: the base metal (BM) was first carburized then Ti foil was preset at the welding position and finally laser welding was carried out. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and nanoindentation were utilized to analyze mechanical properties and microstructures of the FZ and HAZ of the joint obtained by combined alloying with C and Ti. Moreover, the joint obtained by combined alloying was comparatively analyzed with those alloying only by C or Ti. Combined alloying can increase the maximum tensile strength to 406.6 MPa and strain to 6.6%, respectively. TiC phases as spherical particles with diameter ranging from tens to one hundred of nanometers can be precipitated in the FZ obtained by combined alloying playing a role of second-phase strengthening in Mo. Furthermore, Mo2C phases can be clearly observed at the grain boundary in the HAZ of the joint obtained by combined alloying. Mo2C is coherent or semi-coherent with the Mo matrix and can also have the second-phase strengthening effect. Combined alloying shows a new idea to strengthen Mo and its alloy welded joints.

The effects of TiB2 and Zr on the microstructure, aging response and mechanical properties of hot-extruded Al–Zn–Mg–Cu based materials were investigated and compared by multi-scale microstructure characterization techniques. The results showed that proper addition of TiB2 particles could refine grain size during solidification, promote dynamic recrystallization during extrusion, and inhibit grain growth during solution treatment. Meanwhile, Zr addition had minor influence on the grain refinement during solidification, but could effectively suppress recrystallization and grain growth compared with the Zr-free alloy. Furthermore, the TiB2 addition could simultaneously enhance the aging kinetics and peak-aged hardness of the materials. Comparatively, Zr addition could also improve the peak-aged hardness with minor effect on the aging kinetics of the materials. Finally, the quench sensitivity, elastic modulus and tensile properties of the materials were compared and studied. Specifically, the relationship between the microstructure and mechanical properties, and the strengthening mechanisms were discussed in detail.

Low ductility limits the extensive application of high volume fraction (>30 vol%) ceramic particle-reinforced metal matrix composites, and the simultaneous improvement of strength and ductility is still a challenge owing to the smaller amount of matrix contained in such composites. In this paper, the effects of various contents of Mg or Zn (0, 6, 10 and 14 wt%) on the interface mismatch and compression properties of 50 vol% TiB2/Al composite fabricated in situ are comparatively studied. The results indicate that Mg has a better refinement effect than Zn on the TiB2 ceramic particles. Mg can reduce the crystallographic mismatch degree of the Al/TiB2 interface. 6 wt% Mg simultaneously increases the σ0.2, σUCS and ef of the composite into 780 MPa, 1162 MPa and 10.68%, compared with the composite without the addition of Mg, increasing 8.5%, 2.8% and 30.6%, respectively. However, the addition of Zn leads to serious distortion of the Al lattice and deteriorates the interface matching degree of Al/TiB2, so the addition of Zn generally improves the σ0.2 and σUCS while sacrifices the plasticity simultaneously. Furthermore, the contributions of various strengthening mechanisms of the matrix in the high volume fraction TiB2/Al composites are analyzed through a comparative study.