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In this paper, the effect of deep cryogenic treatment (DCT) on the microstructure and properties of automotive 6063 aluminum alloy at different times was investigated with automotive 6063 aluminum alloy as the research object. The results show that under the conditions of deep cryogenic treatment, the lattice distortion occurs in the alloy matrix microstructure, and the resulting internal stress promotes the large proliferation of dislocations within the alloy and the increase of dislocation density; meanwhile, after the deep cryogenic treatment, the deformed grains are transformed into recrystallized and sub-crystals structural grains, the grains are refined, and the size of the grains is refined from the original 25.2 μm to 20.3 μm, with fine equiaxed crystals. Among them, the mechanical properties of the DCT36h specimen were the best, and its hardness, tensile strength, yield strength and elongation reached 142.44 HV, 328.32 MPa, 177.42 MPa, and 29.29%, which were 34.17%, 5.62%, 11.10%, and 32.77% higher than the original sample, respectively. We believe that the main mechanism for the increase in toughness is multiple reinforcement such as dislocation strengthening, grain refinement strengthening, precipitated phase strengthening and texture strengthening. [ABSTRACT FROM AUTHOR]

In this paper, perfect interface model of Al/AlCu alloy and defect interface model of Al/AlCu alloy after cracks were introduced at different positions of the interface were established by using cohesive zone modeling method. Classical molecular dynamics simulation was used to study the deformation behavior and microstructure evolution of Al/AlCu alloy interface model at a strain rate of 0.05 Å/ps and the temperature of 300 K. The simulation results show that perfect interface exhibits a uniform plastic deformation stage due to structural relaxation after yielding, while there is no structural relaxation during the deformation of defect interface and the tensile strength is much lower than that of perfect interface as well. In the process of deformation, stacking faults formed in perfect interface and cracks are generated and expanded in Al matrix, while there was no stacking faults forming along with the expansion and cracking at the position of introduced cracks in defect interface. Massive dislocation nucleation leads to the reduction in stress at the perfect and defect interfaces after yielding. The extension of Shockley partial dislocation and the nucleation of Stair-rod dislocation are the main mechanisms of interface deformation. Densities of Shockley partial dislocation and Stair-rod dislocation decrease with increasing strain before crack propagation. This study enriches the analysis of microstructure evolution of Al/AlCu alloy interface and similar interfaces during deformation. [ABSTRACT FROM AUTHOR]

TiAl alloy becomes a promising high-temperature structural material due to excellent mechanical properties at elevated temperature. However, the inherent brittleness makes it difficult to be processed by traditional technologies. Therefore, an innovative twin-wire plasma arc additive manufacturing (TW-PAAM) process is developed to fabricate TiAl alloy. Substrate heating is indispensable during additively manufactured TiAl alloy, which can alleviate its crack tendency. In this paper, crack-free TiAl alloy samples are fabricated using TW-PAAM, and the effect of substrate temperature (560, 620 and 680 °C) on as-deposited TiAl alloy is investigated in detail. With the increase in substrate temperature, microstructural lamellar spacing and colony size exhibit the tendency of increase. Also, α2 phase content, recrystallization degree and high Schmid factor frequency present the decrease tendency. These variations of microstructure characteristics further lead to the decrease in both microhardness and tensile properties of the deposit. These findings provide a valuable reference for optimizing microstructures and mechanical properties of additively manufactured TiAl alloys. [ABSTRACT FROM AUTHOR]

Al–Zn–Mg–Cu alloys can be fabricated by a series of thermo-mechanical processing methods (e.g., hot rolling, forging and extrusion), which is able to serve in aeronautic, automobile, and marine industries because of its excellent physical properties. However, reaching the balance between high strength and favorable ductility to present its high performance is still in progress, during which temperature and strain rate are two very important external variables. More importantly, the core lies in sophisticated microstructure evolution paths involved in hot deformation, which consists of different microstructure mechanisms and behaviors and can be expressed as various mechanical responses. Therefore, a fundamental review of microstructure mechanisms and behaviors, microstructure evolution and relevant mechanical responses of Al–Zn–Mg–Cu alloys during high-temperature deformation is of great significance. In present paper, first, various experimental methods have been introduced. Second, general trends of mechanical properties changing with temperature and strain rate have been summarized. Third, major microstructure mechanisms and behaviors have been discussed. Then, a schematic illustration originating from dislocations' movement has been depicted, which succeeding microstructure evolution and mechanical responses (including superplasticity) have been reviewed accordingly. Finally, further suggestions of hot deformation of Al–Zn–Mg–Cu alloys have been given. [ABSTRACT FROM AUTHOR]

This paper aims to unveil effects of α colony and α plate parameters on tensile properties and impact toughness of Ti-55531 alloy with multilevel lamellar microstructures. Microstructures with different α colony and α plate sizes were prepared using varied heat treatments and analyzed by X-ray diffraction, scanning electron microscopy, electron back-scattered diffraction, transmission electron microscopy. Relationships of microstructure and strength, plasticity and impact toughness were discussed. Results indicate that tensile strength increases, while plasticity and impact toughness of the alloy decline with decreasing effective sizes (width/length ratio) of α colony (dc) and α plate (dα) and increasing of volume fraction of α phase. Both dc and dα follow the Hall–Petch principle with strength, and dc was determined to be the critical controlling parameter of strength owing to higher interfacial strengthening effect induced by α colony. However, plasticity is primarily related to dα. Moreover, impact toughness for both dc and dα follows the linear relation, but the coefficient of dα is higher. Furthermore, impact toughness is more dependent on plasticity than strength. Larger α plates lead to more mechanical twins during impacting and result in higher plasticity and impact toughness. Therefore, the impact toughness should depend more on the size of α plates. In order to unveil the influence of α plate size on impact deformation and microcrack initiation behavior of Ti-55531 alloy, the microstructural deformation and crack nucleation characteristics in the impact crack nucleation region were detected by TEM in detail; then, the schematic illustration for microstructural deformation and crack nucleation characteristics was made according to experiment results. [ABSTRACT FROM AUTHOR]

The microstructure, compressive properties and in vitro degradation behavior of as-cast Mg alloys with high Zn or Ca content were investigated. The results showed that the addition of Ca (1 wt%) to Mg–5Zn or Zn (1 wt%) to Mg–5Ca changed the shape, distribution, volume fraction and the type of second phase. When 1 wt% Ca was added to Mg–5Zn alloy, the second phase changed from Mg7Zn3 to Ca2Mg6Zn3 phase and it was distributed from granular formation to a continuous network structure. While the second phase was changed from Mg2Ca in Mg–5Ca alloy to the coexistence of Mg2Ca(Zn) and slight Ca2Mg6Zn3 phase in Mg–5Ca–1Zn alloy. The second phase exhibited a continuous network distribution in both of Mg–5Ca and Mg–5Ca–1Zn alloys, but the width of Mg2Ca(Zn) phase was reduced obviously after adding 1 wt% Zn to Mg–5Ca alloy. The compressive test revealed that Zn element was contributed to the promotion of ultimate compressive strength and fracture elongation, while Ca element was beneficial for improving the yield strength of Mg alloys. The immersion test proved that the weight loss of Mg–5Zn–1Ca was the highest, followed by Mg–5Zn, Mg–5Ca and Mg–5Ca–1Zn alloy. The Mg–5Zn-based alloys suffered severe pitting, while Mg–5Ca-based alloy exhibited a relatively uniform corrosion. The Ca addition accelerated the corrosion of Mg–5Zn alloy due to the expansion of potential difference between second phase and Mg matrix, while Zn addition reduced the micro-galvanic corrosion of Mg–5Ca alloy due to the lowest potential difference between Mg2Ca(Zn) phase and Mg matrix. [ABSTRACT FROM AUTHOR]

Introducing of thermodynamically stable strengthening phases is an important means enhancing the properties of magnesium alloys. To introduce a stable Al2Nd strengthening phase, the Mg-Al-Nd alloys were prepared with a fixed atomic ratio of 2:1 for Al and Nd. The total content of Al and Nd was varied at 1%, 3%, 5%, and 7%, respectively. The effects of Al2Nd phase on the microstructure and mechanical properties of the Mg-Al-Nd alloys were systematically studied in this work. The experimental results indicated that the as-cast alloy primarily consisted of the acicular Al11Nd3 phase as a secondary phase. After undergoing a homogenization treatment at 500 °C for 12 h, the secondary phase underwent a transformation, resulting in the formation of short rod shape Al2Nd structures. Simultaneously, layered Al2Nd precipitated within the α-Mg matrix. The formation of twinning was inhibited, while the Al2Nd phase promoted recrystallization and refined the microstructure through the mechanism of particles stimulated nucleation (PSN), as the Al and Nd contents increased during thermal deformation. At the same time, the increases of Al2Nd phase can enhance the strength and the plasticity of the alloy. The mechanical properties of extruded Mg-1.36Al-3.64Nd (AE5) alloy were excellent with yield strength of 175 MPa, ultimate tensile strength of 249 MPa, and the elongation of 15.4%. The enhanced performance can be primarily attributed to the refined microstructure and the presence of Al2Nd precipitates with small size, which contributed to effective fine grain strengthening and secondary phase strengthening. [ABSTRACT FROM AUTHOR]

Hafnium (Hf) was added as an alloying element to enhance the strength in the NiCoCrAlYMoHf alloys, and the effects of Hf content on constituent phases, microstructural characteristics, and mechanical properties of the as-cast alloy were investigated. The experimental results showed that microstructure of the alloy with 1.0 wt.% Hf was composed of β phase and γ′ phase. The experimental results showed that microstructure of the alloy with 1.0 wt.% Hf was composed of β phase and γ′ phase. With increase in Hf content, the β phase content increased, while the γ′ phase content decreased, and σ phase gradually appeared and precipitated at grain boundary, which resulted in an increase in the hardness of alloys from 429 to 586 HV. The indentation hardness, Young's modulus, and compressive strength of NiCoCrAlYMoHf alloy with 4.0 wt.% Hf could reach 7.12 GPa, 185.52 GPa, and 2659 MPa, respectively, which means that more addition of Hf is beneficial for improving performances of NiCoCrAlYMoHf alloys. The microhardness value is 1.95 times higher than that of the Hf-free alloy. Furthermore, the nanoindentation hardness and Young's modulus are 1.05 and 1.75 times higher, respectively, than those of the Hf-free alloy. [ABSTRACT FROM AUTHOR]

In this study, the gradient microstructure of Mg-Y-Nd-Zr alloy processed by an ultrasonic surface rolling process (USRP) is characterized by electron backscatter diffraction analysis and transmission electron microscopy. The mechanism of microstructure evolution and its effect on mechanical properties of the alloy are discussed in detail. The grain size and orientation of Mg-Y-Nd-Zr alloy after USRP treatment changed gradually along the processing depth. The grain refinement mechanism was elucidated as follows: First, the coarse-grained matrix was subdivided by dislocation slip and twins and further refined into sub-structures by multiple techniques, such as mutual intersection and fragmentation between twins, the interaction between twins and dislocations, and the entanglement of dislocations. Finally, equiaxed nanocrystals with high-angle grain boundaries were formed by sub-grain rotation and recrystallization. The strength improvement of the alloy was mainly attributed to the contributions of grain refinement and dislocation strengthening. The synergistic deformation between the gradient structures is the main reason for the excellent strength and plasticity matching of the alloy. [ABSTRACT FROM AUTHOR]

Mg–8.7Gd–4.18Y–0.42Zr magnesium alloys are subjected to hot compressive tests at a strain rate of 0.002–2 s−1 and a compression temperature of 300–450 °C. Compared with strain rate, compression temperature appears to have a greater impact on dynamic precipitation. By virtue of the pinning effect, precipitates located immediately adjacent to the dynamic recrystallized (DRX) grain boundaries may greatly affect grain growth. As the compression temperature increases, DRX grains multiply rapidly. Nevertheless, the number of DRX grains is decreased owing to the increase in strain rate. However, further increasing the strain rate to 2 s−1, the increased energy stored generates stronger driving forces, causing dislocations to move, thereby raising the number of DRX grains by a considerable amount. With an increase in compression temperature and a decrease in strain rate, substructure development has been described as high-density dislocation → VLAGBs (sub-GBs) → LAGBs → HAGBs → DRX grains. It is DRX that is responsible for the predominant softening mechanism in this studied alloy, accompanied by a continuous dynamic recrystallization (CDRX) process characterized by transforming low-angle grain boundaries into high-angle grain boundaries, as well as discontinuous dynamic recrystallization (DDRX), which is characterized by bulging grain boundaries. [ABSTRACT FROM AUTHOR]

This study investigated the effects of O content on microstructure and mechanical properties of cold-rolled Ti-34Nb-(0, 0.3, 0.6)O (wt.%) alloys during aging within a wide temperature range (300 °C ~ 550 °C) by means of TMA, XRD, TEM and SEM. With the increase of aging temperature, it is found that: (1) O suppresses the precipitation of ω phase, thereby delaying the precipitation of α phase, and increases the precipitation peak temperature of α phase; (2) O inhibits the growth, spheroidization and decomposition of α phase, and increases the (α + β)/β phase transformation temperature; (3) at the same aging temperature (400 °C ~ 550 °C), oxygen-enriched alloys have higher strength and elastic properties. The elastic allowable strain (σ0.2/E) of Ti-34Nb-(0.3, 0.6)O alloys after aging at 400 °C × 8 h is up to 1.8%, which makes them suitable for preparing heat-resistant and high-elastic components for aerospace field. Ti-34Nb-0.3O alloy after aging at 450 °C × 8 h exhibits lower elastic modulus, high strength and good elongation, and has a good application prospect in the field of human implant materials. [ABSTRACT FROM AUTHOR]

The fretting wear behaviors and mechanism of a high Nb–TiAl alloy with full lamellar microstructure at ambient temperature were investigated. The fretting wear mechanism of the alloy under different loads and displacement amplitudes was revealed using experiments and molecular dynamics simulations. The results showed that the load and displacement amplitude significantly affected fretting wear behaviors and the mechanism of the Ti–45Al–9Nb alloy. Higher load and lower displacement amplitude could effectively reduce the fretting wear of the alloy. Molecular dynamics simulation results showed that the order-twin lamellar interface hindered the deformation and dislocation movement of twins, improved the mechanical properties of the material, and improved the wear resistance of such alloy. The wear mechanism of Ti–45Al–9Nb alloy was adhesive wear and surface fatigue wear. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) techniques including laser powder bed fusion have been widely used to produce metallic components with microstructures and mechanical properties distinctly different from the conventionally manufactured counterparts. Understanding how AM parameters affect the evolution of microstructure, including texture, of these AM metallic components is critical for appropriate manipulation of their processing and therefore their mechanical properties. Here we conducted a systematic investigation of texture evolution of a face-centred cubic CrMnFeCoNi high-entropy alloy cuboid fabricated using laser powder bed fusion. Our results showed that the texture evolutions along the build direction were different between the corner and central parts of the sample. Detailed analysis suggested that the texture evolution is closely related to local thermal gradient, which is a property that can be manipulated through changing AM parameters. The different textures lead to the significant variations of mechanical properties within the sample. [ABSTRACT FROM AUTHOR]

Alloys processed by laser powder-bed fusion show distinct microstructures composed of dislocation cells, dispersed nanoparticles, and columnar grains. Upon post-build annealing, such alloys show sluggish recrystallization kinetics compared to the conventionally processed counterpart. To understand this behavior, AISI 316L stainless steel samples were constructed using the island scan strategy. Rhodonite-like (MnSiO3) nanoparticles and dislocation cells are found within weakly-textured grains in the as-built condition. Upon isothermal annealing at 1150 °C (up to 2880 min), the nucleation of recrystallization occurs along the center of the melt pool, where nuclei sites, high stored elastic energy, and local large misorientation are found in the as-built condition. The low value of the Avrami coefficient (n = 1.16) can be explained based on the non-random distribution of nucleation sites. The local interaction of the recrystallization front with nanoparticles speeds up their coarsening causing the decrease of the Zener-Smith pinning force. This allows the progression of recrystallization in LPBF alloys, although sluggish. These results allow us to understand the progress of recrystallization in LPBF 316L stainless steel, shedding light on the nucleation mechanisms and on the competition between driving and dragging pressures in non-conventional microstructures. They also help to understand the most relevant microstructural aspects applicable for tuning microstructures and designing new LPBF alloys. [ABSTRACT FROM AUTHOR]

Aluminum alloy is the optimum material for weight reduction and widely used in a lot of industries including automobile, rail transportation, aerospace, and so on. Ternary Ti3AlC2 powder was adopted in this study to improve the laser welding quality of 6061 Al alloy. Addition of the Ti3AlC2 powder could increase the width and stability of the molten pool, which was beneficial to inhibit the formation of defects such as pore, spatter, rugged surface, sagging, and undercut. Reaction products of Ti3AlC2 powders including Ti3AlxC2, TiAl3, and TiC impeded the growth of dendrites and could serve as nucleating agent, resulting in the formation of massive isometric crystals and dispersed precipitates. The refinement strengthening and dispersion strengthening could impede the extension of deformation and made up the influences of uneven melting loss of alloying elements, leading to the increase and uniformity of weld hardness from 53.1 HV0.2 to 74.9 HV0.2. Both of the welded joints with and without assistant powder fractured at the welds. Elimination of pores increased the loading area of weld while generation of precipitates impeded the extension and connection of dimples, leading to the improvement of tensile strengths from 191.0 to 232.5 MPa and displacements from 0.95 to 1.59 mm. [ABSTRACT FROM AUTHOR]

The microstructure evolution of an as-extruded WZ-A3 alloy compressed at 1080 °C/0.005 s−1 was investigated in this study. The results show that MSEB (middle-size extrusion bar) and LSEB (large-size extrusion bar) compression samples with 0.3 strain have the highest fraction of LAGBs (low-angle grain boundaries) and the lowest complete recrystallization zone fraction. MSEB and LSEB samples show similar area fraction of large γ′ phases (> 500 nm) during hot compression. But roughly 5% fine γ′ phases (< 500 nm) existed in interior of large grains during hot compression for MSEB sample and nearly none in LSEB sample. These fine γ′ phases can inhibit LAGBs migration and dislocation movement during hot compression. LSEB sample shows finer average grain size, lower ratio fraction of LAGBs and larger complete recrystallization fraction than those of MSEB sample during hot compression. The microstructure is more sensitive to strain for MSEB than for LSEB during hot compression. Large grains and fine γ′ phases can cause higher deformation resistance, more intense work hardening and DRX (dynamic recrystallization) softening behavior during hot compression while small grains are easy to trigger DRX under relatively small strain storage energy during hot compression. [ABSTRACT FROM AUTHOR]

The study of microstructure and mechanical properties formation of A2024 alloy obtained by the multipass radial-shear rolling (RSR) method is discussed in this article. FEM simulation was carried out that made it possible to evaluate the influence degree of rolling temperature–velocity parameters on the strain state of material. It has been found the increase in rotary velocity of rolls significantly influences on the deformation heating of bar after RSR (predominantly in its surface layer). The combination of rolling temperature–velocity conditions at selection of deformation regime has complex effect on structure and properties formation. The analysis of sizes and distribution of phase particles has shown that the rolling at lower temperatures allowed to increase the mechanical strength due to the more intensive refinement of undissolved Fe-containing phase. The gradual decrease in the rolling temperature in each pass makes possible to achieve the high strength (UTS ~ 430 MPa and YS ~ 255 MPa) while maintaining the ductility level ~ 15%, that are comparable to ones obtained at some severe plastic deformation (SPD) methods. [ABSTRACT FROM AUTHOR]

Ti–26Nb–2Fe–(0, 2, 4, 6, 8)Sn alloys were prepared by arc melting and subjected to homogenization, cold rolling, and solution treatment. The β phase stability of the alloys increased with the addition of Sn. Ti–26Nb–2Fe comprised ω + β phases, whereas a single β phase was detected in Ti–26Nb–2Fe–(2, 4, 6, 8)Sn. With an increase in Sn, the Young's modulus first decreased from 83 GPa in Ti–26Nb–2Fe to 58 GPa in Ti–26Nb–2Fe–4Sn and increased to 63 GPa in Ti–26Nb–2Fe–8Sn. Sn suppressed twinning during tension. Although the work-hardening rate decreased with the decrease of twinning, Sn was beneficial for maintaining a low work-hardening rate and postponed necking. All the alloys exhibited remarkably high plasticity. A strong solid solution strengthening effect of Sn was not observed in the studied Ti–Nb–Fe–Sn alloys. Ti–26Nb–2Fe–4Sn with a good combination of high tensile strength (yield strength of 592 MPa and tensile strength of 622 MPa) and low Young's modulus (58 GPa) exhibited significantly higher cell viability than that of the control group after a 7-day culturing, indicating that it is a suitable candidate for biomaterials. [ABSTRACT FROM AUTHOR]

In this study, the effects of different Sc + Zr compound addition on the tensile properties, impact toughness, stress corrosion cracking (SCC) properties, polarization curves, electrochemical impedance spectroscopy (EIS), and pitting corrosion (PC) of Al–Zn–Mg alloys are investigated. The results show that the Sc + Zr co-addition significantly inhibits the recrystallization behavior, refines the grain structure, and improves the tensile properties and impact toughness of the studied alloys. In fact, 0.43 wt% Sc + Zr-containing alloy achieves the maximum tensile properties, the tensile strength and yield strength are increased by 60.4 and 71.5 MPa, respectively. The impact toughness of 0.30 wt% Sc + Zr-containing alloy is 36.5 J/cm2, which is increased by 6.4 J/cm2. The Sc + Zr co-addition significantly reduces the SCC sensitivity, increases the charge transfer resistance, decreases the corrosion current density, and improves the PC resistance of Al–Zn–Mg alloys. The results of the strengthening model show that the main strength mechanism of Al–Zn–Mg alloys is precipitation strengthening of conventional η′ phases. The high toughness and corrosion resistance of alloys with Sc + Zr co-addition associated with the recrystallization resistance and the grain structures yielded by coherent Al3ScxZr1-x particles. [ABSTRACT FROM AUTHOR]

The microstructure, corrosion behavior and corrosive film formation of as-extruded Mg–2Zn–0.4Mn–0.1Sr–xGd alloys (x = 0, 0.5, 1 and 2 wt%) in Hank's solution were studied. Microstructure was investigated by scanning electron microscopy (SEM), scanning Kelvin probe force microscopy (SKPFM), X-ray photoelectron spectroscopy (XPS). Corrosion behavior was evaluated by immersion and electrochemical tests. The microstructural observations indicated that the addition of 0.5–2 wt% Gd led to the formation of Mg3Zn3Gd2 phase and grain refinement. SKPFM results showed that the Gd-rich (Mg3Zn3Gd2) phase was nobler than the α-Mg matrix in Gd-containing alloys and formed micro-galvanic corrosion. The alloy with 0.5–1 wt% Gd addition had better corrosion resistance and displayed uniform corrosion behavior than that Gd-free alloy. However, excessive Gd addition (2 wt%) decreased the corrosion rate and caused severe localized corrosion due to massive cathode Gd-rich particles. Combined with mechanical properties and corrosion resistance, the alloy with 1 wt% Gd exhibited a potential for degradable implant applications. The obtained superior corrosion resistance was due to the refined microstructure and the compactness of Gd-containing corrosion products film. In addition, a systematic discussion of corrosion behavior and corrosion film formation was provided by means of schematic illustration. [ABSTRACT FROM AUTHOR]

This work underscores the effect of local microstructural configuration on the dislocation movement and micro-mechanical behaviour in fine/ultra-fine-grained (< 2 μm), cold-rolled, and annealed 301L austenitic stainless steel by site-specific nanoindentation experiments. Indentation loading, holding, and unloading behaviour have been studied separately for five different microstructural categories. Hardness and modulus vary proportionally from one indentation to another. It has been observed that a large density of high-angle boundaries most competently restricts the dislocation motion (strain hardening) resulting in high hardness. However, the back stress generated by the dislocation pile-up aids recovery during holding/unloading. Contrarily, the coarse grain reveals lower hardness attributed to easy dislocation transmission and a lesser elastic recovery during holding/unloading owing to an insufficient back stress in the absence of a favourable dislocation pile-up. The observation is against the general expectation considering the grain size dependence of the formation of pile-ups in ductile materials subjected to large-scale deformation. Interestingly, low-angle boundaries interact more with the dislocations and form such a defect structure that the strain locally reaches the critical value for the formation of deformation-induced martensite following Kurdjumov–Sachs orientation relationship with the parent austenite. [ABSTRACT FROM AUTHOR]

Copper and its alloys have been in the service of humankind earlier than any other metal throughout history. In the present review, all aspects of the SPS of copper and its alloys are comprehensively investigated, and their potential effects on the microstructure and properties of alloys are thoroughly reviewed. In this regard, the densification phenomenon during SPS treatment is fully investigated. The effects of raw powder characteristics involving particle size, contamination content, and powder morphology on the sinterability of these materials are examined. Then, the influence of SPS operation parameters consisting of pressure, heating rate, dwelling time, pulsed electrical current, electrical pulses pattern, sintering temperature, and sintering tooling on densification of these materials is extensively discussed. Furthermore, the microstructure evolution and grain growth behaviors during SPS are explored. In addition, current challenges and future perspectives of this field are addressed. [ABSTRACT FROM AUTHOR]

Al-Mg alloys are normally prone to lose part of their yield and tensile strength at high temperatures due to insufficient thermal stability of the microstructure. Here, we present a Ca-modified Al–Mg–Sc alloy demonstrating high strength at elevated temperatures. The microstructure contains Al4Ca phases distributed as a network along the grain boundary and Al3(Sc,Zr) nano-particles dispersed within the grains. The microstructure evolution and age-hardening analysis indicate that the combination of an Al4Ca network and Sc-rich nano-particles leads to excellent thermal stability even upon aging at 300 °C. The tensile strength of the alloy for temperatures up to 250 °C is significantly improved by an aging treatment and is comparable with the commercial heat-resistant aluminum alloys, i.e., A356 and A319. At a high temperature of 300 °C, the tensile strength is superior to the above-mentioned commercial alloys, even more so when expressed as the specific strength due to the low density of Ca-modified Al–Mg–Sc alloy. The excellent high-temperature strength results from a synergistic effect of solid solution strengthening, grain boundary strengthening and nanoparticle order strengthening. [ABSTRACT FROM AUTHOR]

Peritectic solidification has attracted increasing attention as a lot of important binary alloys, such as Fe–Ni, Zn–Cu, Fe–C and Ti–Al, exhibit peritectic reaction during solidification. In order to investigate the solidification behavior of Zn-rich Zn–Cu peritectic alloy containing nominally up to 7.8 wt.% Cu, a series of laser surface remelting experiments were performed. With the increase in growth velocity, Zn–Cu alloys with Cu content below 3.0wt.% showed an evolutional sequence from low-velocity η planar interface → lamellar structures → η shallow cells and finally to high-velocity η planar interface. The Zn-4.0 wt.%Cu alloy showed a similar transitional sequence except that irregular η cells appeared when low-velocity planar interface became unstable. In contrast, ε cell/dendrite was the typical microstructure of the Zn-7.8 wt.% Cu alloy within the whole scanning velocity range. Based on the maximum interface temperature criterion, a eutectic growth model under rapid solidification conditions (TMK model) and a self-consistent numerical model for the cellular and dendrite growth were applied to establish a phase and microstructure pattern selection map, which drew a clear whole picture of the relationship between phase/microstructure and solidification conditions of this series of alloys. Regarding the microstructure feature, our investigation revealed the range of the solidification velocity and chemical composition of lamellar structures as dominant microstructure and their lamellar spacing displayed a considerable range of the average value as a function of growth velocity. The relationship between the lamellar spacing and the growth velocity was further analyzed by using the TMK eutectic model, and the results showed the same overall trend as the experimental results. A phase and microstructure pattern selection map of Zn-rich Zn–Cu peritectic alloys. Regression analysis of the average spacing of lamellar structures. [ABSTRACT FROM AUTHOR]

The ω-phase in metastable β-titanium (Ti) alloys attracts great research interests owing to the metastability and the involved microstructural complexity upon straining, while the fundamental understanding on its formation mechanism is still insufficient. In this study, deformation-induced ω-plates have been systematically investigated using Ti-10 wt% Cr metastable β-Ti alloy containing athermal ω-precipitates. It is found that single-variant ω-plates form either along {332}β twin interfaces or in the twin interiors, which closely depends on twin morphologies. For the acicular β-twin, the ω-plate appears in the twin interiors accompanied by high density of parallel straight dislocations, while for the lenticular twin, the ω-plate attaches to the twin interface without the surrounding dense parallel straight dislocations. These unique formation characteristics result from local stress field induced by the twinning itself and the passive transformation of athermal ω-precipitates. It is further revealed that the passive transformation of athermal ω-precipitates dominates the formation of ω-plates inside the acicular twins, while it is the locally preferential twin thickening that promotes the ω-plates to form along the lenticular twin interfaces. These findings provide new insight into deformation-induced ω-phase transformation and the intricate deformation microstructures in metastable β-Ti alloys. [ABSTRACT FROM AUTHOR]

A CoCrCuNiAl0.5 high-entropy alloy (HEA) was prepared by spark plasma sintering (SPS). The effect of plasma transferred arc (PTA) remelting on the microstructures and properties of the SPS-ed HEA was studied. The results showed that, after PTA remelting, the microstructures transformed from randomly-oriented equiaxed grains to dendrites with a directional solidified morphology. The coarse plate-like precipitates (~ 130 nm in diameter and ~ 20 nm in thickness) containing ordered L12 and disordered FCC structures inside the matrix grains were replaced by the disordered FCC spherical Cu-rich precipitates with several nanometers within the dendritic matrix. In the intergranular region, the size of the L12 cubic precipitates was decreased from ~ 55 nm to ~ 2 nm, and dislocations and lattice distortions were also observed. In addition, the brittle B2 phase was disappeared, and the extent of Cu segregation was decreased in the interdendritic region. The SPS-ed sample has a compressive yield strength of 913.8 MPa and a fracture strain of 21.7%. However, the PTA remelted sample exhibits a much higher fracture strain (> 70%, without fracture) and an appreciable yield strength of 739.4 MPa, which indicates an excellent balance between strength and ductility was achieved after PTA remelting. Furthermore, the corrosion resistance of the PTA remelted sample was higher than that of the SPS-ed sample, which was mainly due to the decreased elemental segregation, and the reduced sizes and types of the precipitates. [ABSTRACT FROM AUTHOR]

The relationship between microstructure evolution and mechanical performance of Al–Zn–Mg–Cu alloys with varying Cu/Mg ratios was discussed in detail under different two-step aging (T7X). The results showed that the undissolved second-phase particles including σ-Al7Cu2Fe and T-Al2Mg3Zn occurred in the quenched Al–Zn–Mg–Cu alloys. When the Cu/Mg ratio approaches 1.64, the S-Al2CuMg phase was also observed. Although the Cu/Mg ratio did not change the precipitation sequence of the Al–Zn–Mg–Cu alloys, it changed the coarsening rate and precipitate size distribution during aging process. The Al–Zn–Mg–Cu alloy with the lowest Cu/Mg ratio has the slowest coarsening rate and the highest strength (655 MPa). The fracture morphology of Al–Zn–Mg–Cu alloys changes from the typical brittle fracture to the intergranular-dominated mixed fracture mode or ductile fracture when the Cu/Mg ratios increases. Besides, the T79-aged alloys with varying Cu/Mg ratios have similar grain boundary precipitates (GBPs) and precipitate-free zones (PFZs). The T74-aged alloys with higher Cu/Mg ratio have more coarser GBPs and wider PFZs. [ABSTRACT FROM AUTHOR]

The effects of annealing temperature and heating rate on the microstructure, magnetic, and mechanical properties of melt-spun Fe81.7−xSi4B13Cu1.3Nbx (x = 0–4) alloy ribbons have been investigated. With increasing the annealing temperature, a ductile–brittle transition occurs during amorphous structure relaxation, the brittleness becomes severe with more α-Fe precipitation, and the hardness rises continuously. After annealing at respective optimum temperatures under the heating rate of 20 K/min, as the Nb content increases from 0 to 4 at.%, average grain size (Dα-Fe) and volume fraction (Vα-Fe) of the α-Fe in the nanocrystalline alloys decrease gradually from 53.3 nm and 52% to 8.7 nm and 42%, respectively; the strain at fracture (εf) representing ductile level increases from 1.33 to 1.72%; and the coercivity (Hc), saturation magnetic flux densities (Bs), and Vickers hardness (Hv) all decrease gradually. As the heating rate rises from 10 to 400 K/min, the Dα-Fe of the Fe81.7Si4B13Cu1.3 alloy decreases from 45.7 to 28.4 nm without considerable variation of the Vα-Fe; the Hc lowers from 235 to 25 A/m, the εf increases from 1.10 to 1.66%, and the Bs and Hv change slightly. Enriching of Nb weakens the dependence of nanostructure, magnetic softness, and annealing embrittlement on the heating rate. A correlation of εf ∝ Dα-Fen is found for the nanocrystalline alloys, where the n rises from − 1 to − 1/2 with enriching of Nb from 0 to 4 at.%. The mechanisms by which nanostructure affects magnetic and mechanical properties have been discussed. [ABSTRACT FROM AUTHOR]

The Mg–Zn–Ca–Sr alloy has good application prospects as a bone implant material; however, the as-cast alloy has both poor plasticity and formability, and there are few studies on its deformation properties. In this study, the microstructure, deformation behavior, textural evolution, and processing map of an Mg–3wt%Zn–1wt%Ca–0.5wt%Sr alloy were studied via a compression test using a Gleeble 1500D thermo-mechanical simulator. The mean apparent activation energy of the hot compression deformation of the Mg–3wt%Zn–1wt%Ca–0.5wt%Sr alloy was 250.44 kJ/mol. With an increase in temperature, both the grain size and the degree of dynamic recrystallization increased. Dynamically recrystallized grains predominantly nucleated near the grain boundary and the secondary phases. After compression, the alloy had a strong basal texture, and its textural strength decreased at first and then increased slightly as the deformation temperature rose. The optimal process parameters of the as-cast Mg–Zn–Ca–Sr alloy involved deformation temperatures of 603–633 K and strain rates of 0.03–0.005 s–1. [ABSTRACT FROM AUTHOR]

The intergranular corrosion (IGC) behavior of an extruded 6005A alloy profile with the coexisting of peripheral coarse grain (PCG) structure and partial recrystallized grain (PRG) structure was investigated by using an accelerated corrosion test, electrochemical impedance spectroscopy and a quasi in situ examination of IGC process. PCG structure was found to have a unique IGC behavior that pitting corrosion and subsequent IGC are less severe and will not be transformed into intragranular corrosion as they were found in PRG structure. Microstructure characterization reveals that the microstructural differences in grain boundary precipitates, primary α-AlFeMnSi intermetallic particles and grain characteristic between PCG structure and PRG structure are the reason for these phenomena. Further analysis indicates that the grain boundaries decorated with more AlFeMnSi particles and Q phase precipitates are more sensitive to corrosion, where Q phase precipitates are the primary cathodes and the most important factor affecting IGC; AlFeMnSi particles are supposed to initiate pitting corrosion since they are dissolved as anodes in the early stage of corrosion. With the development of corrosion, they are transformed into cathodes and become the bridges of IGC propagation by connecting the Q phase precipitates at grain boundary. In addition, grain characteristic was also found to have great effects on IGC. With the decrease in grain size and the increase in the frequency of high-angle grain boundaries and the dislocation density, corrosion becomes more severe and more likely to be transformed into intragranular corrosion. [ABSTRACT FROM AUTHOR]

Alloys with melting points < 150 °C are required for the development of flexible consumer devices. While the eutectic In–48Sn alloy is a promising candidate for these applications, its low tensile strength and low creep resistance during solid-state aging are of concern. The addition of Ag can address this issue to some extent; however, the effect of added Ag on the properties of the alloy is not well understood. Here, we studied the effects of added xAg (x = 0.5, 1.0, 1.5 wt.%) on the fusion start temperature, microstructure, and mechanical properties of the In–Sn eutectic alloy and found that the fusion start temperature of the In–48Sn–xAg alloy was reduced to around 113 °C due to the ternary eutectic reaction of In–Sn–Ag, in which ε-AgIn2 only formed in the In–48Sn–xAg alloys. In addition, smaller β-In3Sn and γ-InSn4 phases were produced through the formation of ε-AgIn2, which affected the mechanical properties of the alloy. In–48Sn–1.5Ag, with the smallest grains, exhibited the highest tensile strength of 12.5 MPa via boundary strengthening. In–48Sn–1.5Ag fractured in transgranular mode, which is different from the intergranular fracturing of the eutectic alloy with relatively large grains. Conversely, In–48Sn–0.5Ag, with the highest soft-β-In3Sn/hard-γ-InSn4 ratio, showed the longest elongation of 64%, which is twice that of the eutectic In–48Sn alloy. [ABSTRACT FROM AUTHOR]

Microstructure, texture modification and mechanical anisotropy of the high strain rate rolled Mg–xGa alloys (x = 1, 2, 3 and 5, in wt%) were carefully investigated by EBSD, XRD, tensile testing, etc. The Ga addition can promote the transformation from the substructure to the recrystallized grains in the process of dynamic crystallization (DRX) so as to obtain the uniform microstructure and enhance the formation of twinning during deformation, which weakens the texture of the sheet and eventually forms the higher scatter texture. Moreover, the Mg–2Ga alloy shows the lowest texture intensity and thus exhibits the best combination of strength and plasticity and excellent plasticity, with the elongation-to-failure from 31.1 to 34.5% in three testing directions. The higher Ga content brings about the bigger work hardening index (n value) of the alloy sheet. The n value in the RD direction rises from 0.18 to 0.27 with the increasing Ga addition from 1 to 5%. The Mg–Ga alloys have very low plastic anisotropy and their plastic strain ratios are about 1. The Mg–2Ga alloy shows the lowest r value (1.07) and its ∆r value is 0.02. The wrought Mg–Ga alloys can achieve both high plasticity and low plastic anisotropy, which are promising for the industrial applications. [ABSTRACT FROM AUTHOR]

Phase precipitation and recrystallization process of Al0.45CoCrFeNi high-entropy alloys (HEAs) were investigated by calculation of phase diagram and electron backscattered diffraction. To reveal the influences of microstructures on the response of mechanical behaviors, the tensile properties, hardness, elastic modulus, and fracture characteristics were thoroughly studied here. The as-processed duplex microstructures demonstrate that intercritical annealing treatments in the dual-phase filed could greatly slow down the recrystallization kinetics, attributing to the in situ precipitation of Ni, Al-rich phase formed initiatively along grain boundary. A series of fine-grained dual-phase HEAs, accompanying with yield strength widely ranging from 558 to 1223 MPa, were well fabricated via annealing the cold-rolled HEAs. Surprisingly, present HEAs exhibit excellent resistance to anneal softening, together with a relatively high recrystallization temperature of 900 °C (~ 0.63 Tm). Additionally, the coupled effect of fine-grain strengthening and precipitation strengthening is successful in manipulating the properties of face-centered-cubic HEA system. [ABSTRACT FROM AUTHOR]

FeCoCrNiAlMox (x = 0, 0.25, 0.5, 0.75, 1.0, molar ratio) alloy coatings were prepared on 2Cr13 steel substrates by wide-beam laser cladding, aiming to investigate the effects of different Mo addition amounts on the microstructure, phase composition, microhardness, and corrosion resistance of the coatings. The results show that all the coatings are of good quality without cracks or pores. Due to the dilution of the substrate, the actual composition of the coatings deviates from the designed composition to different degrees. The main constituent phase of different coatings was body-centered cubic solid solutions, which does not change with increasing Mo content. The middle part of the Mo0, Mo0.75, and Mo1.0 coatings consists of columnar crystal and Cr-rich needle-like precipitates, but the middle part of Mo0.25 and Mo0.5 coatings has a typical dendrite structure. There is not much difference in the alloy composition between dendrite and interdendrite, and the hardness and corrosion resistance of Mo0.25 and Mo0.5 coatings are basically the same. Among the coatings investigated in our study, the Mo1.0 coating has the greatest hardness and best corrosion resistance in 0.5 mol/L HCl solution. [ABSTRACT FROM AUTHOR]

Alloy 690 was diffusion-bonded and exposed to the high-temperature supercritical CO2 environment, and the effect of exposure on the microstructure and mechanical properties was investigated. In the as-bonded joint, some small carbides are discontinuously arranged along the bonding line. After exposure at 550 °C and 600 °C, the continuous carbides are developed and occupy all the grain boundaries and bonding line. The continuous carbides transform into the discrete large particles when the exposure temperature further increases to 650 °C. With the increase in exposure temperature, the tensile strength and microhardness of the joints decrease, while the elongation first slightly increases and then decreases at 650 °C. For the as-bonded joint and the joints exposed at 550 °C and 600 °C, the fracture occurs at the parent Alloy 690 and the main fracture mode is the ductile dimple fracture. However, for the joint exposed at 650 °C, the fracture occurs at the bond line with a manner of brittle fracture. The degradation of strengths and elongation after exposure to supercritical CO2 at 650 °C were associated with the growth of carbides along the bond line. [ABSTRACT FROM AUTHOR]

Magnesium-based alloys presented great potential for biodegradable implant materials. However, the poor mechanical properties and high corrosion rate blocked its extensive application. In this study, a new biodegradable Mg–Zn–Y–Gd–Zr alloy was fabricated and extruded. The microstructure, corrosion morphologies and corrosion products film of the as-cast, homogenized and as-extruded alloys were characterized by optical micrographs, scanning electron microscopy, X-ray diffraction and laser scanning confocal microscopy. Moreover, the corrosion mechanisms of the as-cast and as-extruded alloys were proposed, and the influencing factors of corrosion properties were discussed. The electrochemical test, immersion tests and corrosion morphologies demonstrated that the as-extruded alloy exhibited favorable corrosion properties. The as-cast and homogenized alloys displayed localized corrosion mode, and the as-extruded alloy displayed uniform corrosion mode. The Volta potential of the Mg3(Y,Gd)2Zn3 phase relative to Mg matrix was measured by using Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

Al/graphite composites with small amounts of Al–Si alloy were consolidated by spark plasma sintering and hot-extrusion processes. The effect of Al–Si alloy addition on densification behavior, microstructure, thermal conductivity (TC), coefficient of thermal expansion (CTE), and compressive strength has been systematically investigated. The results showed that the addition of Al–Si alloy resulted in improvements in relative density of the composites, interfacial bonding between Al and graphite, and orientation degree of graphite. The composites with Al–Si alloy showed improved TC and reduced CTE values in comparison with those without Al–Si alloy. For example, the 450 °C-extruded Al/60 vol% graphite/9 vol% Al–Si composite showed a maximum TC of 297 W m−1 K−1 and a minimum CTE of 7.95 ppm K−1. Moreover, the hot-extruded Al/graphite composites containing Al–Si alloy exhibited higher compressive strength compared to conventional squeeze-cast composites and hot-extruded composites without Al–Si alloy. [ABSTRACT FROM AUTHOR]

A self-consistent thermodynamic description of the Zn–Al–Cu–Mg quaternary alloy system is developed. The as-cast microstructures of key Zn–Al–Cu–Mg samples in the low-alloyed range are studied experimentally. These are interpreted by computational thermodynamic analysis applying both Scheil and equilibrium simulations. Contradictions concerning the variation of apparent fraction of primary (Zn) phase, the eutectic structure and visibly larger fractions of eutectoid structure with increasing Mg content can be resolved by these detailed calculations. Two series of dedicated experimental work found in this journal on as-cast microstructures of such quaternary Zn alloys in the high-alloyed range, including also thermal analysis data, were also analyzed. The viability of this computational thermodynamic approach is demonstrated by providing a detailed analysis going beyond the explanations and interpretations in the original publications. The coverage of a larger Zn alloy composition range suggests a predictive capability of this approach. [ABSTRACT FROM AUTHOR]

The effects of varying Mg and Si levels on the microstructural inhomogeneity and eutectic Mg2Si morphology in die-cast Al-Mg-Si alloys have been investigated. It was found both Mg and Si additions decreased the microstructural inhomogeneity by producing more well distribution of primary α-Al and Al-Mg2Si eutectics, but had contrary effects on eutectic Mg2Si morphology. The increasing Mg level transformed eutectic Mg2Si from rod or lamellae to curved flake with larger eutectic spacing λ, while the increasing Si level promoted the formation of rod-like or lamellar eutectic Mg2Si with smaller λ. The reason for the above evolutions can be traced back to alloys' solidification behaviour. Thermodynamic calculation indicates that both Mg and Si decrease the liquidus temperature and suppress the precipitation of coarse primary α-Al grains (which tend to agglomerate in centre zone of samples) during the first solidification in shot sleeve, thus reducing the microstructural inhomogeneity. Mg addition shifts the eutectic point to lower Mg2Si concentration and induces a slower eutectic growth rate, causing a lower Mg2Si volume fraction in Al-Mg2Si eutectic cell. On the contrary, Si addition increased the Mg2Si volume fraction in eutectic cell by raising the Mg2Si eutectic concentration and the eutectic growth rate. To minimize the interfacial energy, Al-Mg2Si eutectics with different Mg2Si volume fractions exhibit various morphologies. The tensile test results show that both Mg and Si improved the strength at the cost of ductility. However, due to the formation of fine Al-Mg2Si eutectics, Si induced less ductility sacrifice than Mg when achieving the same strength improvement. [ABSTRACT FROM AUTHOR]

This study investigates the effects of the extrusion ratio and annealing treatment on the microstructure, texture and mechanical properties of an as-extruded Mg -11Gd -4.5Y -1Nd -1.5Zn -0.5Zr (wt%) alloy. A high extrusion ratio (30:1) results in a homogeneous microstructure with fine dynamic recrystallized (DRXed) grains, while a low extrusion ratio (6:1) leads to a bimodal microstructure with un-DRXed regions and DRXed grains. The bimodal microstructure can be removed by subsequent annealing. This alloy contains several long-period stacking ordered (LPSO) and MgRE phases (RE: rare earth). The extrusion ratio and annealing process have negligible effects on the volume fraction of the LPSO phase but have significant effects on the MgRE phase. The volume fraction of the MgRE phase decreases as the extrusion ratio and annealing time increase. Cuboid precipitates form in the alloy extruded at low extrusion ratios after annealing. The alloy exhibits a bimodal texture with <0001> and < $$ 10\overline{1} 0 $$ > components. The presence of the <0001> component is determined by a critical grain size. The texture evolution (such as the degree of grain growth) is not influenced by the extrusion ratio, but it is affected by the annealing time, which is related to the MgRE phase rather than the LPSO phase. The grain refinement, the MgRE and LPSO phases, and the texture contribute to the alloy strengthening. Finally, a high-strength extruded Mg bar with a diameter of 32 mm (an extrusion ratio of 6:1) was successfully produced. [ABSTRACT FROM AUTHOR]

Microstructures and tensile properties were investigated in metastable β-type Ti-10Mo, Ti-15Mo, and Ti-20Mo alloys after solution treatment. In addition to β phase, different martensitic structures with various sizes and morphologies were found in these alloys. In the Ti-10Mo alloy, acicular α″ plates were uniformly distributed in the β matrix. Transmission electron microscopy (TEM) revealed {111} α″-type twins had formed in α″ plates, and the orientation relationship between the β and α″ is close to (110) β//(001) α″, ( $$ 1\bar{1}2 $$ ) β//(110) α″, and [ $$ \bar{1}11 $$ ] β//[ $$ \bar{1}10 $$ ] α″. In the Ti-15Mo alloy, nanoparticles of athermal ω phase containing {112} β-type twins were observed in the β matrix. Smaller ω particles were found in the Ti-20Mo alloy than in the Ti-15Mo alloy. When tensile tested, the Ti-10Mo and Ti-15Mo alloys exhibited large plastic strains of 24 and 29 %, respectively, with ultimate tensile stresses of 756 and 739 MPa. The Ti-20Mo alloy displayed a higher ultimate tensile stress of 792 MPa but much smaller plastic strain (2 %). Although β phase dominates in all the metastable β-type Ti-Mo alloys, the nanostructured martensites also play an important role in the mechanical properties of the alloys. [ABSTRACT FROM AUTHOR]

In the present study, an attempt is made for the first time to reinforce long-period stacking ordered (LPSO) MgYZnAl (at.%) alloy with 0.5, 1.0, and 1.5 vol% of nano-AlO particles to form nanocomposites. Microstructure characterization revealed the ability of nano-AlO in inhibiting the formation of 14H LPSO phases in the nanocomposites during solidification. Homogenization at 723 K (450 °C) for 2 h led to the subsequent precipitation of fine Mg-Y-Zn-Al precipitates (≤1 µm) in the nanocomposites. The fine Mg-Y-Zn-Al precipitates and nano-AlO particles were established to be active in promoting dynamic recrystallization (DRX) of α-Mg via particle-simulated nucleation during extrusion, which was responsible for weakening the basal texture in the nanocomposites and improving failure strain. As a result, failure strain was significantly increased from 10.8 % in the monolithic alloy to beyond 15 % in the nanocomposites with the highest strength among nanocomposites achieved in NC5 (nanocomposite reinforced with 0.5 vol% of nano-AlO particles). [ABSTRACT FROM AUTHOR]