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Herein, to improve the service life of die steels, many methods are used to improve their properties. However, some properties may be weakened after different heat treatments. In this study, a novel method of nanoparticle treatment is used to improve the service performance of high‐Cr steel (HCS), and the effect of nano‐TiC ceramic particles on its microstructures and properties under different heat‐treatment conditions is investigated. After forging and isothermal spheroidization, the nano‐TiC ceramic particles treatment HCS has a mixed grain with equiaxed grain and striated grain. Under different heat‐treatment conditions, the nano‐TiC reinforced HCS has refined martensite laths, carbides, and a higher content of retained austenite. In contrast, the nano‐TiC ceramic‐particles‐reinforced HCS that have higher strength and strain, the yield strength (σ0.2), tensile strength (σb), fracture strain, product of strength and strain, and impact toughness of HCS‐51 with nano‐TiC (HCSN‐51) are 1349 MPa (1531 MPa), 1662 MPa (1770 MPa), 9.4% (12.1%), 12 405 MPa% (18 766 MPa%), and 266 J cm−2 (445 J cm−2), which is 13.5%, 6.5%, 28.7%, 51.3%, and 67.3% higher, respectively. The primary strengthening mechanisms included fine‐grain strengthening and precipitation strengthening. The main toughness mechanism was fine‐grain and transformation‐induced plasticity. [ABSTRACT FROM AUTHOR]

In the general environment of lightweight automobiles, the integrated die-casting technology proposed by Tesla has become the general mode to better achieve weight reduction in automobiles. The die-casting mold required by integrated die-casting technology has the characteristics of large scale and complexity. Hence, higher requirements are put forward for the comprehensive performance of the die steel. Despite the stagnation in the progress of conventional strengthening methods, enhancing the performance of die steel has become increasingly challenging. Indeed, it necessitates exploring novel die steel and optimizing heat treatment and reinforcement technologies. This article summarizes and analyzes the development status of die steel and corresponding heat treatment and microstructure manipulation as well as strengthening methods and elaborates on an excellent nano-strengthening technology. Furthermore, this review will aid researchers in establishing a comprehensive understanding of the development status of die steel and the processes utilized for its strengthening. It will also assist them in developing die steel with improved comprehensive performance to meet the high demand for mold steel in the integrated die-casting technology of the new era. [ABSTRACT FROM AUTHOR]

We found that the high solid solution Al-9 Mg alloy with a bimodal grain structure processed by hard-plate rolling (HPR) exhibited enhanced thermal stability despite annealing at 275 °C for 24 hours. The notable thermal stability originates from the inherent stable deformation microstructure dominated by (101)-oriented coarse grains induced by a high solute Mg content, which further stabilizes the microstructure upon static annealing. Moreover, recovery occurs preferentially in coarse grains, leading to slow coarsening of the ultrafine grains. This paper provides a new way to improve thermal stability of severely deformed Al-Mg alloys by tailoring grain orientations. [ABSTRACT FROM AUTHOR]

We developed a facile and low-cost approach to prepare lightweight and high-strength magnesium-matrix composites with a nacre-inspired laminated structure. First, lamellar Mg2B2O5 whisker (Mg2B2O5w) scaffolds with initial solid loadings of 10, 15 and 20 vol% were prepared by ice templating. The wettability between a molten AZ91D alloy and the Mg2B2O5w scaffold was greatly improved by the incorporation of nano-SiO2 sol in the aqueous slurry, making the preparation of nacre-mimetic AZ91D/Mg2B2O5w composite by way of pressureless infiltration feasible. The SiO2 content in the Mg2B2O5w scaffold has a significant effect on the processing and the microstructure and properties of the composites. The optimum SiO2 content was about 6-8 wt% of the total ceramic loading. A lower SiO2 content resulted in incomplete infiltration, while a higher content led to the formation of a large quantity of Mg2Si in the composite. The flexural strength of the composites seemed independent of the initial ceramic loading (10-20 vol%), whereas the compressive strength and elastic modulus increased considerably and the crack-growth fracture toughness decreased with increasing ceramic content. The mechanism for such variations was addressed. [ABSTRACT FROM AUTHOR]

In this work, primary Mg2Si crystals shaped by {100} and {111} facets were successfully fabricated in Al–Mg–Si melts via the adsorption and poisoning of the Ca element. The modifier Ca plays an important role in determining the morphologies of primary Mg2Si, which can be transformed from dendrites (0 wt%) to crystals with a combination of eight {111} and four {100} facets (0.08 wt%), then to truncated cubes (0.1 wt%), and finally to cubes fully bounded by {100} facets (0.2 wt%) with increasing Ca content. The growth processes of cubic primary Mg2Si have been revealed. As the growth rates of {100} surfaces are diminished by adsorption of the Ca element, primary Mg2Si tends to form perfect cubes with exposed {100} facets. Moreover, by prudently adjusting the concentration of the Ca element, complex polyhedral crystals enclosed by {111} and {100} surfaces were designed and prepared. The results offer valuable insights into designing the modification effect of different modifying elements, which are critical to promoting the industrial application of light alloys with improved morphology and refined size of microstructures. [ABSTRACT FROM AUTHOR]

Functionally graded 2014Al/SiC composites (FGMs) with varying volume fractions (1-7%) of nano-SiC particulates (n-SiC) were fabricated by powder metallurgy. The effect of n-SiC content on corrosion and wear behaviors was studied. The microstructures of composites were characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy. The corrosion behavior of the composites was evaluated by potentiodynamic polarization scans in 3.5 wt.% NaCl solution. Corrosion results show that corrosion current of composite layer with 3 vol.% n-SiC was much lower than that of 2014Al matrix. Mechanical properties of the composites were assessed by microhardness tests and ball-on-disk wear tests. As the applied load changed from 15 to 30 N, wear rates of the composites increased significantly and the wear mechanism transformed from mild to severe wear regime. It also shows that 3 vol.% n-SiC/2014Al composite layer observed the lowest wear rate where adhesive and abrasive wear mechanisms played a major role. These results suggest that the n-SiC are effective candidates for fabricating FGMs for the applications demanding a tough core and a hard, wear or corrosion resisting surface. [ABSTRACT FROM AUTHOR]

The reaction pathway of combustion synthesis (CS) of Ti5 Si3 in Cu- Ti- Si system was explored through a delicate microstructure and phase analysis on the resultant products during differential thermal analysis ( DTA). The formation of Cu- Si eutectic liquids plays a key role in the reaction pathway, which provides easy route for reactant transfer and accelerates the occurrence of complete reaction. Cu initially reacted with Si to form Cu3 Si by a solid-state diffusion reaction, which further reacted with Cu to form Cu- Si liquids at the eutectic point of ~802°C; then Ti was dissolved into the surrounding Cu- Si liquids and led to the formation of Cu- Ti- Si ternary liquids; finally, Ti5 Si3 was precipitated out of the saturated liquids by a solution-reaction-precipitation mechanism. The reaction pathway in CS of titanium silicide ( Ti5 Si3) could be described briefly as: Cu(s) + Ti(s) + Si(s)→ Cu3 Si(s) + Ti(s) + Si(s)→( Cu- Si)(l) + Ti(s)→( Cu- Ti- Si)(l)→ Cu(l) + Ti5 Si3(s). [ABSTRACT FROM AUTHOR]

The results presented in this paper make a contribution to investigation of the effects of electromagnetic on the segregation of C and Mn elements and the microstructure of in-situ granular γ+(Fe, Mn)3C eutectics reinforced steel matrix composites (abbreviated EAMC). Electromagnetic can enhance the segregation of C and Mn elements. The volume fraction of the granular eutectics increases largely with the electromagnetic process during solidification. Endogenetic austenite crystals appear in the matrix of EAMC, which results from the rupture of the dendrite of the primary austenite crystals during growing. The mechanism of the effects of electromagnetic on the microstructure was analyzed with the electromagnetic theory and non equilibrium solidification theory. The heating and stirring domino effects of electromagnetic decrease the efficient distribution coefficient (keff) of the solute in EAMC. It provides space-time, thermodynamics, and dynamics terms to the developed branching of primary austenite dendrites (γ-Fe), which is beneficial to the formation and increasing volume fraction of the granular eutectics. [ABSTRACT FROM AUTHOR]

Since the aluminum matrix composites prepared by additive manufacturing are prone to defects such as pores and cracks, the properties of the formed composites cannot be further improved. Therefore, the preparation of SiC/AlSi10Mg composites with high modulus and high strength by selective laser melting technology is of great significance for the wide application of aluminum matrix composites. This work will further investigate the defect formation, microstructure evolution, and solidification mechanism of the composites. The matrix microstructure of the composites can be efficiently refined by adding SiC. In addition, the 5 wt.% SiC/AlSi10Mg composites showed improvements in the tensile yield strength, microhardness, bending strength, elastic modulus, and ultimate tensile strength as compared to the AlSi10Mg alloy. These increases were 21.1 %, 18 %, 8.7 %, 23.2 % and 9.2 % respectively. The strengthening mechanisms at room temperature include fine grain strengthening, thermal mismatch strengthening, solid solution strengthening and precipitation strengthening. It is also mentioned that the primary causes of the decrease in toughness are stress concentration and the existence of the brittle precipitation phase (Al 4 C 3). The increase in high-temperature strength is attributed to the pinning role of SiC and precipitate phases relative to grain boundary and dislocation climbing. [ABSTRACT FROM AUTHOR]

The present work investigates the microstructure and tensile properties of a hot rolled 6061 alloy quenched by cold rolls (RQ) at different preheating temperatures. The preheating temperature strongly affects microstructure evolution and mechanical properties. Low preheating temperature (490 °C) resulted in both low strength and low elongation. The RQ alloy preheated at 540 °C exhibited improved ductility compared to those subjected to T6 and T8 temper, and comparable strength to that after T8 temper. The dynamic recovery during hot rolling contributed to the improved tensile elongation and retained work hardening. High preheating temperature also led to pronounced ageing hardening during short-term ageing. [ABSTRACT FROM AUTHOR]

Simultaneously improved impact toughness and wear resistance of high Cr tool and die steels (HCS) enable them to be widely used in the lightweight field. In this study, TiC + TiB 2 /HCS steel was prepared by pre-dispersed ceramic nanoparticles combined with specific heat treatment. The effects of ceramic nanoparticles on the microstructures, mechanical properties and wear resistance of TiC + TiB 2 /HCS steel were investigated by comparing it with shield machine tool steel (H13 steel). The results demonstrated that the introduction of ceramic nanoparticles refined the microstructure of the TiC + TiB 2 /HCS steel and uniformed the distribution of the precipitates. For TiC + TiB 2 /HCS steel and H13 steel with the equivalent hardness values, the impact toughness and the wear resistance of TiC + TiB 2 /HCS steel were 67.3 % and 39.5 % higher than that of H13 steels, respectively. Moreover, when the wear resistance was comparable, the impact toughness of TiC + TiB 2 /HCS steel was 89.1 % higher than that of H13 steel. This study provides an innovative solution to prepare high-service performing service life tools and die steels to replace shield machine tool steels. • Using pre-dispersed ceramic nanoparticles combing specific heat treatment to fabricate TiC + TiB 2 /HCS steel. • Refined matrix microstructure, finer carbides were obtained and more uniform dispersed of TiC + TiB 2 /HCS steel. • Comprehensive performance including hardness, toughness and wear resistance of TiC + TiB 2 /HCS steel was improved. [ABSTRACT FROM AUTHOR]

Bimodal hybrid in-situ nano-/micro-size TiC/Al composites were prepared with combustion synthesis of Al-Ti-C system and hot press consolidation. Attempt was made to obtain in-situ bimodal-size TiC particle reinforced dense Al matrix composites by using different carbon sources in the reaction process of hot pressing forming. Microstructure showed that the obtained composites exhibited reasonable bimodal-sized TiC distribution in the matrix and low porosity. With the increasing of the carbon nano tube (CNT) content from 0 to 100 wt. %, the average size of the TiC particles decreases and the compressive strength of the composite increase; while the fracture strain increases first and then decreases. The compressive properties of the bimodal-sized TiC/Al composites, especially the bimodal-sized composite synthesized by Al-Ti-C with 50 wt. % CNTs as carbon source, were improved compared with the composites reinforced with single sized TiC. The strengthening mechanism of the in-situ bimodal-sized particle reinforced aluminum matrix composites was revealed. [ABSTRACT FROM AUTHOR]

A high extrusion ratio of 166:1 was applied to commercial AZ61 alloy in one step with an extrusion speed of 2.1 m·min−1. The effects of DA (direct aging) treatment on the microstructure and tensile properties of extruded alloy were investigated. The extruded alloy exhibits fine DRXed grains and the average grain size is ~11 μm. After DA treatment at 170 °C, the tensile strength and 0.2% offset yield strength is enhanced from 314 to 336 MPa and from 169 to 191 MPa respectively, sacrificing elongation from 26.5% to 23.3%. The grain size and texture distribution of extruded AZ61 scarcely evolve during the post aging treatment. However, the enhanced strength in peak-aged alloy is mainly caused by the high-density elliptical Mg17Al12 precipitates distributing uniformly along the grain boundaries or within the grains, by precipitation and dispersion hardening. Furthermore, the nano-sized precipitates effectively inhibit grains from coarsening by triggering pinning effects along the grain boundaries at elevated temperature. As a result, the peak-aged alloy exhibits a better superplasticity of 306.5% compared with that of 231.8% of extruded sample. This work provides a practical one-step method for mass-producing Mg alloy sheets with excellent tensile strength and ductility compared with those fabricated by conventional extrusion methods. [ABSTRACT FROM AUTHOR]

Simultaneously improving the wear resistance and toughness can extend the service life of steel. In this study, nano-TiC-H13 steel was successfully fabricated by pre-dispersion nano-TiC/Al master alloy in conventional casting to simultaneously improve the wear resistance and toughness. The influence of nano-TiC ceramic particles on the microstructure, tensile properties, impact toughness, and wear behavior under the synergistic effect of high load and temperature was explored. Results indicated that nano-TiC ceramic particles can effectively refine the microstructure and promote the precipitation of the finer carbides, which significantly improved the properties of steel. The no-notch impact toughness (380.2 J/cm2), U-shaped notch impact toughness (36.6 J/cm2), and yield strength (1440 MPa) of nano-TiC-H13 increased by 12.7%, 31.2%, and 8.2%, respectively, compared with that of H13. Furthermore, the volumetric wear rate (8.2 × 10−10 m3/m) of nano-TiC-H13 under 450 °C and 30 N is decreased by 28.6% in contrast with H13. The high strength and plasticity in nano-TiC-H13 can resist the intrusion of debris and reduce plastic deformation. This work provides an innovative approach for the simultaneous improvement of the wear resistance and toughness of steel. • Nano-TiC refines the microstructure and promotes the finer precipitates distributed. • Finer microstructure inhibits stress concentration and improves strength and toughness. • Higher strength resists debris intrusion, resulting in wear resistance improvement. • Excellent toughness retards crack extension and delays failure of steel. [ABSTRACT FROM AUTHOR]

The size, distribution, and morphology of TiC particle in Fe–Ti–C system have a great influence on the mechanical properties of TiC/Fe composites. In this work, TiC/Fe composites were fabricated in the Fe–Ti–C system with different carbon source and molar ratio by combustion synthesis and hot-pressing method. Morphology and size of ceramic particles, as well as microstructure, interface bonding and mechanical properties of composites were compared. The results showed that the size of TiC particles decreased with increase of Fe content of Fe–Ti–C systems fabricated by the same carbon source, while the particles change from spherical shapes to cubic shapes which can reduce stress concentration between ceramic particles and matrix. Furthermore, TiC/Fe composites fabricated by 5Fe–Ti-carbon blacks (CBs) system exhibited superior yield strength (1523 MPa) compressive strength (2203 MPa) and microhardness (691.5 HV), caused by the high interface bonding strength and lamellar pearlite matrix which can commendably limit the dislocation slip. By comparison, TiC/Fe composites fabricated by 21Fe–Ti-carbon nanotubes (CNTs) system showed higher fracture strain (25.85%) on account of the ferrite matrix with favorable plastic. This work reveals the influence of carbon source and molar ratio of Fe–Ti–C system on TiC/Fe composites, which is helpful to further improve the properties of TiC/Fe composites. [ABSTRACT FROM AUTHOR]

Thermal fatigue failure is one of the main factors affecting the service life of hot work die steel. Achieving excellent thermal fatigue resistance for hot working die steels can benefit the industry economically. In this work, (TiC + TiB 2)/Al master alloys were used to add TiC–TiB 2 nanoparticles into high-Cr die steels, which achieves microstructure manipulation and obtains excellent thermal fatigue resistance and strength-plastic combination. The results showed that after being manipulated by 0.02 wt% TiC–TiB 2 nanoparticles, the surface oxidation zone of the high-Cr die steel after different thermal fatigue cycles is reduced than high-Cr die steel without manipulation. TiC–TiB 2 nanoparticles effectively refined the heat-treated microstructure of high-Cr die steel, promoting the Cr element and alloy carbides being more uniformly distributed in the matrix, which prevents the occurrence of oxidative pitting and conducive to the formation of a dense and uniform Cr 2 O 3 oxide layer, and further preventing the initiation of thermal fatigue cracks. Moreover, these finer and more uniformly distributed precipitates in TiC–TiB 2 nanoparticles manipulated high-Cr die steels will promote stress dispersion and hinder thermal fatigue crack propagation. This work provides a promising avenue for the design of low-cost, high-performance, and long-life die steels for industrial applications. • The microstructure has been manipulated with traces TiC–TiB 2. • Thermal fatigue cracks initiation are closely correlated to surface oxidative erosion. • Nanoparticle-reinforced steels have better thermal fatigue resistance. [ABSTRACT FROM AUTHOR]

Lightweight NiAl alloys are expected to replace high-density nickel-based superalloys, but their mechanical performance needs to be improved. In this work, NiAl–30Cr composites with a novel heterogeneous microstructure composed of fine NiAl matrix and Cr single-phase was successfully prepared. Nanoscale Cr particles with 15 nm in size precipitated in NiAl matrix are coherent with NiAl matrix owing to very low interplanar and interatomic spacing mismatch. Such a composite microstructure makes NiAl–30Cr exhibit high strength and high toughness. The yield strength (1207 MPa), ultimate compressive strength (2307 MPa), product of strength and plasticity (29.3 GPa%), and fracture toughness (10.76 MPa m1/2) of NiAl–30Cr increased by 96.6%, 85.6%, 55.1% and 19.7% respectively at room temperature compared to the corresponding ones of NiAl. At 1000 °C, the yield strength (144 MPa) of NiAl–30Cr was 85.9% higher than that of NiAl. Solution strengthening and precipitation strengthening were the key strengthening mechanisms at room temperature. The enhancement in toughness was attributed to grain refinement, increased crack propagation paths, weakened Ni–Al covalent bonding and coordinated deformation of Cr single-phase and NiAl matrix. By contrast, the main strengthening mechanism at 1000 °C is the solid solution Cr atoms hindering dislocation climbing and the stable interface bonding between the Cr nanoprecipitation phase and the NiAl matrix. This work provides new ideas for preparing high-strength and tough NiAl alloy. • NiAl–30Cr consists of NiAl and Cr single-phase, which can coordinate deformation. • Coherent Cr nano-precipitates distribute in NiAl matrix, and interface is stable. • The yield strength increased by 96.6% and 85.9% at 25 °C and 1000 °C. • The strengthening and toughening mechanisms are revealed. [ABSTRACT FROM AUTHOR]

Abstract Relatively high strength and good ductility are rarely obtained simultaneously in aluminum matrix composites. In the present work, dual-phased TiC n -Al 3 Ti m (n: nanosized TiC particles and m: micron-sized Al 3 Ti particles) particles were in situ synthesized in an Al-Ti-C system via the combustion synthesis method. Subsequently, (TiC n -Al 3 Ti m)/Al hybrid composites were readily fabricated at high addition levels (0, 1, 3, 5 and 7 vol%) via the re-melting and diluting method assisted ultrasonic vibration. Then, the isolated influences of the dual-phased TiC n -Al 3 Ti m particles on the solidification behaviors, microstructure evolution and mechanical properties, at both ambient- and elevated-temperatures, of aluminum alloys were systematically investigated. The experimental results revealed that the α-Al dendrites were substantially refined with a reduction of up to 4 times when compared with that of the unreinforced base alloy. Furthermore, at ambient temperature, 5 vol% (TiC n -Al 3 Ti m)/Al exhibited the optimum comprehensive mechanical properties, and the yield and ultimate tensile strength were 124.3% and 165.2% higher than those of the unreinforced base alloy, whilst the fracture strain was not sacrificed. Theoretical calculations suggest that thermal-mismatch and Orowan strengthening effects contributed most to the yield strength increment, whereas the favourable fracture strain was achieved mainly due to grain refinement. Moreover, at elevated temperature (453 K), the yield strength and ultimate tensile strength were improved by 327.8% and 236.1%, respectively, whilst the fracture strain was still at a relatively high level of 29.2%. The improved thermal resistance primarily resulted from the pinning effects of the TiC n -Al 3 Ti m particles on the grain boundaries and dislocations. Highlights • Novel dual-phased TiC n -Al 3 Ti m particles were in situ synthesized. • TiC n -Al 3 Ti m exerted refinement by heterogeneous nucleation and inhibited growth. • TiC n -Al 3 Ti m enhanced strength at 298 K by thermal mismatch and Orowan effects. • TiC n -Al 3 Ti m enhanced strength at 453 K by pinning and retarding effects. [ABSTRACT FROM AUTHOR]

Abstract Al–Si–Mg alloys manipulated by in-situ synthesized nanoparticles have been prepared by casting method in this work. The addition of different contents of refiners promoted the obvious grain refinement of the Al–Si–Mg alloys. It was found that 0.10 wt% refiners addition caused a significant and efficient refinement on α-Al (from 1675 µm to 199 µm) and Mg 2 Si in the inoculated Al–Si–Mg alloys. The morphology of the eutectic Si in the inoculated Al–Si–Mg alloys transformed from needle-like structure to a fibrous one, and the mean size sharply decreased (from 26.56 µm to 11.89 µm) and increased a little with the increase of FeBSi amorphous refiners content. Tensile property tests showed that both strength and ductility of the alloys were improved by the addition of FeBSi amorphous refiners. The yield strength, tensile strength, fracture strain and elongation of the alloy inoculated with 0.10 wt% FeBSi amorphous refiners for 20 min were 226 MPa, 343 MPa, 18.4% and 16.7%, compared to those of the uninoculated alloy (170 MPa, 289 MPa, 13.7% and 12.2%), respectively. It was found that the Fe 2 B and Fe 3 Si nano-sized particles which were crystallized from FeBSi amorphous refiner contributed to the grain refinement of α-Al, resulting in higher strength. Moreover, grain refinement shortened the atomic diffusion distance and refines Mg 2 Si. The grain refinement and spheroidization of eutectic Si enhance uniform deformation during tension, and reduce the possibility of crack initiation and expansion, thus improving the plasticity. Graphical abstract fx1 Highlights • The inoculated Al–7Si–0.3Mg alloy appeared as 199 µm fine grains. • The inoculated alloy reached 226 MPa, 343 MPa, 18.4%(δ) and 16.7%(ε f). • This work achieved the refinement of α-Al and Mg 2 Si and the spheroidization of eutectic Si. • The Fe 2 B, Fe 3 Si had better lattice mismatch with α-Al and eutectic Si. [ABSTRACT FROM AUTHOR]

Abstract The strength and toughness of a material are generally two mutually exclusive properties. Optimization of these properties can be realized by regulating microstructures based on a bio-inspired idea. Herein, we used gelatin as a pore-regulating agent to investigate the effect of microstructural transition from "nacre-like" lamellae to "honeycomb-like" reticulae on the mechanical properties of metal–ceramic composites. By introducing different quantities of gelatin into SiC slurries during freeze casting and infiltrating the sintered SiC scaffolds with pure molten Al, we prepared the Al/SiC (88/12 in volume) composites with variable yet controllable microstructures and further demonstrated that the desired properties could be achieved by tailoring their microstructures. Specifically, the Al/SiC composites with a fully laminated structure exhibited optimal fracture toughness (K Jc) of 51.9 ± 2.9 MPa m1/2 while those with a three-dimensional reticular structure displayed peak three-point flexural strength of 371 ± 6 MPa. The relationship between the microstructures and mechanical properties of the composites was addressed based on material strengthening and toughening mechanisms. [ABSTRACT FROM AUTHOR]

Abstract Zr and Sb are simultaneously added to refine and modify primary Mg 2 Si in Al–20Mg 2 Si alloys. Compared with single addition of Zr or Sb, the combined addition of Zr and Sb can result in an enhanced refinement and modification effect on primary Mg 2 Si. The unique co-modification effect is mainly derived from the synergistic combination of Sb and Zr. Sb can involve in the formation of Mg 3 (Sb, Si) 2 particles and thereby can act as heterogeneous nuclei of primary Mg 2 Si, resulting in the uniform distribution and refined particle size of primary Mg 2 Si crystals. The role of Zr is also indispensable as it can decrease the solidification temperature interval of the primary Mg 2 Si phase, which could further refine the primary Mg 2 Si crystals and promote their complete growth. Moreover, the wear resistance of Al–20Mg 2 Si alloys is also improved owing to the special co-modification effect of Zr and Sb. Since primary Mg 2 Si can be optimized by enhancing heterogeneous nucleation and decreasing solidification temperature interval, such idea can be extended to guide the microstructure control in other alloy systems. Graphical abstract Image 1 Highlights • Fined and polygonal primary Mg 2 Si particles were obtained by adding Zr-Sb. • The wear resistance of Al–20Mg 2 Si alloys was improved due to fined primary Mg 2 Si. • Mg 3 (Sb,Si) 2 particles act as nuclei of primary Mg 2 Si particles. • Zr decreases the solidification temperature interval of primary Mg 2 Si phase. [ABSTRACT FROM AUTHOR]

Abstract The performances of particulate–reinforced aluminum matrix composites are strongly dependent on alloying elements, precipitates and added particulates. To reveal the sole influence mechanisms of high volume fraction of nanosized particulates on the solidification behavior, microstructure and mechanical properties of aluminum alloys, nanosized SiC P (60 nm) was incorporated into commercial pure Al at different volume fractions (i.e., 0, 1, 3, 5, 7 and 9 vol%) by stir–casting assisted ultrasonic vibration. The results reveal that a fairly uniform dispersion of nanosized SiC P throughout the matrix was achieved at a volume fraction as high as 7 vol%. Average α–Al dendritic sizes were significantly refined from 270 µm for the matrix to 90 µm in the solidified microstructure of nanocomposites. Thermal analysis during solidification indicates that the presence of nanosized SiC P increased the nucleation temperature of α–Al, whilst recalescence during solidification process disappeared. Additionally, the yield and ultimate tensile strength of the nanosized SiC P /Al composites at both ambient temperature and 453 K were remarkably improved, whilst remaining suitable fracture strain. Theoretical analysis suggests that the significant strength increments induced by nanosized SiC P at ambient temperature could be attributed to thermal mismatch strengthening, Orowan strengthening and grain refinement strengthening, while the pinning effect of nanosized SiC P could predominantly account for the strengthening effect at 453 K. Highlights • Nanosized SiC P refined the microstructure via heterogeneous nucleation and inhibited growth. • SiC P enhanced strengths at 298 K mainly due to thermal mismatch and Orowan strengthening. • Pinning effects of SiC P on grain boundaries and dislocation climbing enhanced strengths at 453 K. [ABSTRACT FROM AUTHOR]

We prepared B 4 C/Al laminated composites via ice-templating and gas-aided pressure infiltration and investigated the effects of TiO 2 addition on the microstructures and mechanical properties of the composites. The incorporation of TiO 2 led to the formation of TiB 2 after sintering, reduced the formation of harmful phases and increased the strength of ceramic architectures. However, its excessive addition resulted in the cracking of ceramic layers and the formation of metal strips after Al infiltration. The bending strength, fracture toughness and work of fracture of the composites first increased and then decreased with increasing initial TiO 2 content, reaching maxima of 420 ± 20 MPa, 44 ± 2 MPa m 1/2 and 5002 ± 175 J m −2 , respectively. The specific strength and toughness are comparable to those of titanium alloys. Furthermore, fracture modes and toughening mechanisms were thoroughly addressed by analyzing crack propagation paths and fracture surface morphologies. Crack deflection and metal bridging are two primary extrinsic toughening mechanisms. [ABSTRACT FROM AUTHOR]

We prepared a large-scale aligned structure in Al 2 O 3 porous ceramics by a simple and novel bidirectional freeze-casting technique. This technique uses a side metal plate to achieve cold-surface cooling from the bottom to generate dual temperature gradients to control the nucleation and growth of ice crystals. By recording the slurry temperature in situ, we obtained various temperature gradients for the samples prepared by this technique using 3 mm thick copper, aluminium and stainless-steel plates as the cold surfaces. The architectures of the scaffolds produced under these freezing conditions were investigated to determine the effect of the temperature gradients on the morphology of the microstructure. Finally, a model was proposed to account for the temperature gradient regulatory mechanism of the transition from a dendritic structure to a parallel structure. [ABSTRACT FROM AUTHOR]

In this work we proposed a novel strategy for spontaneous infiltration of molten Al into a porous lamellar Y 2 O 3 partially stabilized ZrO 2 (PSZ) architecture prepared by using an ice-templating method. The kinetics of liquid spreading and infiltration under the application of a 10 mA current was investigated. The electrochemically-induced improvement in wettability greatly facilitated the spontaneous infiltration. [ABSTRACT FROM AUTHOR]

In the present study, the application of hard–plate rolling (HPR) on the hard-to-deform Mg–7Al–5Zn (AZ75) alloy resulted in a homogeneous fine grained (∼6 μm) microstructure, where numerous micron/nano Mg 17 (Al, Zn) 12 precipitates with spherical morphology uniformly dispersed both at grain boundaries and within grain interiors. More importantly, the HPRed AZ75 alloy exhibited superior mechanical properties with a simultaneous high strength and ductility at room temperature, i.e. yield strength (YS) of ∼218 MPa, ultimate tensile strength (UTS) of ∼345 MPa and elongation of ∼19%, which was comparable to the commercial wrought magnesium alloys. According to the contribution from the several strengthening mechanisms estimated by simplified models, the grain boundary strengthening is the predominant mechanism for the high YS of the alloy. The high ductility is benefited from the strong work-hardening capacity resulted from Zn solid solutes and the presence of numerous well-dispersed nanosized precipitates as well as weakened texture. Moreover, the fine grained AZ75 alloy exhibits an optimum superplasticity of ∼615% at 300 °C at 1 × 10 −3 s −1 . It is attributed to the enhanced grain boundary slip (GBS) promoted by a well maintained fine grain structure resulted from the pining effect by numerous Mg 17 (Al, Zn) 12 particles segregating along grain boundaries during tension. The results will be helpful for the development and processing of high alloying element content Mg alloys with high strength and ductility as well as enhanced formability. [ABSTRACT FROM AUTHOR]

The coarse segregative eutectic phases, emerged in the twin roll casting (TRC) process of Mg strips, which cannot be resolved solely by controlling the processing variables or post heat treatment, are detrimental to the subsequent rolling deformation. Considering it, we introduce the pre-rolling steps on the TRC Mg-4Al-2Sn-1Zn (ATZ421) alloys, which is expected to facilitate the dissolution of these segregative phases by increasing distortion of crystal lattices and rolling stress, and further investigate the effect of a single pass or two passes pre-rolling on the microstructure evolution and tensile properties. It indicates that the pre-rolled alloy with two passes presents more uniform precipitates and higher twinning density in comparison with that using a single pass. The uniform distribution of precipitates in two passes pre-rolling is due to the increase in density of dislocations and deformed twins, which results in more distortion of crystal lattices with more stored energy, facilitating the diffusion of solutes. Moreover, the pre-rolling of two passes introduces more rolling stress into Mg matrix, which is beneficial for the crush of coarse eutectic phases, and further accelerates the sufficient dissolution of second phases. After the subsequent rolling and annealing processes, the sheet with pre-rolling deformation of two passes shows finer microstructure, which mainly benefits from the pinning effects of uniform nano-sized precipitates. As a result, the annealed sheet with two-pass pre-rolling deformation exhibits an advantageous combination of high strength and high ductility with fine microstructure, showing an ultimate tensile strength of ~297 MPa, a yield strength of ~ 205 MPa and an elongation of 25.0%. This work provides an effective method of dissolving the coarse segregative phases in the TRC Mg alloys with significant potential for industrial production. [ABSTRACT FROM AUTHOR]

Different dendritic grain morphology of an Al-Cu alloy was obtained by adjusting the casting parameters. Compared to the equiaxed dendritic grains, the tortuous dendritic grains led to increased tensile elongation (from 10.4% to 16.8%) and work of fracture (from 11.2 J/mm 2 to 17.2 J/mm 2 ) by more than 50%, respectively. Meanwhile, the high tensile strength (∼540 MPa) and grain size (∼80 μm) were unchanged. The intergranular fracture crack zigzagged along tortuous grain boundaries, reducing the stress concentration at the crack tip and increasing the propagation resistance and path, leading to increased toughness and elongation. The zigzag morphology of grain boundaries was attributed to tortuous dendritic grains. [ABSTRACT FROM AUTHOR]

Achieving bimodal grain structure via cold rolling remains a challenge for Al–Mg alloys. In the present work, a high tensile strength (∼525 MPa) and ductile (∼14%) Al–9Mg alloy was fabricated by a novel hard-plate rolling (HPR) route with a single-pass thickness reduction of 75%. Increasing solute Mg content promotes a bimodal structure and a high dislocation density in the HPRed Al–Mg alloys due to the severely retarding effect of Mg solutes on dynamic recovery/recrystallization. The simultaneous high ductility and strength is due mainly to the strong work hardening ability deriving from the bimodal grain structure and the high solute Mg content. [ABSTRACT FROM AUTHOR]

The overall microstructure-manipulated Al-13Si-5Cu-0.6 Mg alloy was successfully fabricated via introducing 0.1 wt% Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator with short time of 60 s, to determine its suitability for applications at room and higher temperatures. The microstructure manipulation mechanism, mechanical properties and strengthening mechanism in manipulated Al-13Si-5Cu-0.6 Mg alloy were discussed. The Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator provides more nucleation sites in the formation of primary Si, Al Si eutectic and Al 2 Cu. As a result, the optimal microstructure is composed of finer α-Al grains, Al 2 Cu and more rounded primary and eutectic Si, with sizes decreased to ∼52%, 13%, 73% and 42%, respectively. The yield strength, tensile strength, elongation and fracture strain of manipulated Al-13Si-5Cu-0.6 Mg alloy are improved by 22.9%, 16.8%, 58.2% and 47.7% at room temperature than those of the unmanipulated Al-13Si-5Cu-0.6 Mg alloy, respectively. The improved tensile properties at room temperature are attributed to the significant strengthening effect of smaller precipitates and grain refinement while the excellent plasticity is derived from finer α-Al grain, round-corner primary Si and eutectic Si spheroidization. The yield strength and tensile strength are increased by 28.1% and 15.3% at 250 °C, and 28.3% and 10.8% at 300 °C, respectively. The strengthening mechanism at high temperature is mainly the second phase strengthening and the effect of finer eutectic Si on the pinning grain boundary. The overall microstructure manipulation in this work provides better comprehensive mechanical properties and a practicable method to fabricate the Al-Si-Cu-Mg alloy with superior strength and ductility, especially for die-casting alloy with short-time and high-efficiency. [Display omitted] • Fully microstructure-manipulated alloy was made via adding trace nanoparticles. • Nanosized ZrCu(B2) and Zr 2 Cu have ideal lattice mismatch with Si, α-Al and Al 2 Cu. • The sizes of primary Si, α-Al, eutectic Si and Al 2 Cu decreased simultaneously. • The tensile strength and elongation of manipulated alloy are greatly improved. [ABSTRACT FROM AUTHOR]

Al-Cu matrix composites containing nano-sized SiC p were successfully prepared by dispersing nano-sized SiC p /Al master alloy into the molten Al-Cu alloy with combined semi-solid stir casting and hot extrusion processes. Microstructures of nano-sized SiC p /Al-Cu composites and their tensile properties were investigated. Results show that the α-Al dendrites became finer and better formed and nano-sized SiC p was formed in the α-Al grains. With nano-sized SiC p adding to the Al-Cu matrix, the tensile strength of the described composites increased remarkably especially under the temperature of 453 K, while their plasticity were still high. Nano-sized SiC p particles had been uniformly dispersed in the Al alloy, yielding composites with high strength at elevated temperatures. The strengthening mechanisms of nano-sized SiC p were also discussed. This will raise the probability of using Al matrix composites as lightweight materials for structural applications at elevated temperatures. [ABSTRACT FROM AUTHOR]

Effects of Zn addition on the microstructure and tensile properties of as-extruded Mg-8Al-2Sn (AT82) alloy were investigated in the present work. All the extruded AT82 alloys exhibited a fully dynamically recrystallized (DRXed) microstructure, while the grains were slightly refined with Zn addition. Moreover, second phase particles (Mg 2 Sn and Mg 17 Al 12 ) increased significantly in amount with increasing Zn content. It was found the ultimate tensile strength (UTS) and yield strength (YS) gradually increased with increasing Zn content from 0 to 1.5 wt%, meanwhile the elongation maintained unchanged at a high level, i.e. ~17–19%. In particular, the as-extruded AT82-1.0Zn alloy exhibited both a high strength and high ductility at room temperature, e.g. UTS of ~357 MPa and elongation of ~19%. The superior combination of strength and ductility is mainly benefited from the enhanced work-hardening ability resulted from Zn solid solutes and the presence of more well-dispersed fine particles in AT82-1.0Zn alloy. [ABSTRACT FROM AUTHOR]

In the present study, Mg-6Zn-1Zr (ZK60) alloy with a homogeneous fine-grained structure (~5 µm) was produced by hot extrusion. The influence of temperature on tensile properties anisotropy and the associated change in deformation mechanisms in the range of 25–275 °C of the fine-grained ZK60 alloy were investigated. Under room temperature, the fine-grained ZK60 alloy exhibited a high tensile strength of ~269–327 MPa and high ductility of ~15–39% when tested at three different directions, indicating a high anisotropy. With increasing testing temperature to 150 °C and further to 275 °C, the alloy showed a gradual decrease in anisotropy. Especially, the fine-grained ZK60 alloy exhibited superplasticity of ~376–434% when tested at 275 °C, which should be due to the increasing role of grain boundary sliding (GBS), as the strong basal texture associated with room temperature deformation became almost random at elevated temperatures. Moreover, the abrupt decrease in tensile anisotropy and associated change in texture with increasing temperature correlates closely to the transformation of deformation mode from a dislocation-dominated behavior to a GBS-mediated one. [ABSTRACT FROM AUTHOR]

The Al2014 composites reinforced with uncoated and Ti 5 Si 3 -coated SiC P were fabricated by stir-casting. The results suggested that the Ti 5 Si 3 -coated SiC P /Al2014 composites exhibited more uniform dispersion of SiC P , higher elastic modulus and tensile properties than uncoated ones. Additionally, the nano-sized Ti 3 AlC 2 interfacial layer was detected between the Ti 5 Si 3 -coated SiC P and α-Al. [ABSTRACT FROM AUTHOR]

Forging and welding are common necessary procedures for AA6××× alloys, and recrystallization is an inevitable process. However, it is still difficult to realize the control of the recrystallization behavior, while realizing the strengthening of mechanical properties of the base metal and welded joint. In this study, we overcome this problem through 0.5 wt% TiC–TiB 2 nanoparticles, and fully reveal the influence of the nanoparticles on the recrystallization behavior of the base metal and nugget zone of a friction-stir-welded (FSW)-ed joint from the perspectives of dislocation rearrangement and grain boundary motion. The strengthening mechanisms of the base metal and FSW-ed joint are clarified. The recrystallization driving force of the base metal and nugget zone was increased. Dislocations with a higher density rearranged and formed more grain boundaries in the nugget zone. Besides, nanoparticles distributed on the grain boundaries restrained the vanishing of low-angle grain boundaries. The nugget zone microstructures were refined from 3.1 to 2.3 μm, and the recrystallization ratio was increased from 7.2% to 10.4% at 800 rpm. The grains in the nugget zone were refined from 2.2 to 1.9 μm, and the recrystallization ratio was increased from 16.1% to 18.4% at 1200 rpm. The promoted recrystallization in the nugget zone accelerated the release of stress. Nanoparticles weakened the precipitate coarsening in the nugget zone. After strengthening, the ultimate tensile strength and plastic strain of the FSW-ed joint at 800 rpm were increased by 4.7% and 18.8%, respectively. This study provides new approaches for a systematic microstructure evolution control in FSW-ed 6061 Al alloys. • Trace nanoparticles double the recrystallization driving force of base metal. • More dislocation tangles promoted recrystallization of nugget zone. • Nanoparticle also inhibited grain coarsening of nugget zone. • Precipitate coarsening in the nugget zone was weakened. • FSW-ed joint softening was alleviated and the mechanical properties were enhanced. [ABSTRACT FROM AUTHOR]

The use of nanoparticles to efficiently manipulate the microstructure of steel and improve its mechanical properties has considerable practical relevance and application value. This study proposes the novel manufacturing process of dispersing nanoparticles within the melt through master alloys and investigates the effect on the microstructure and properties of the TiC-nanoparticle-reinforced H13 steel through this nanoparticles-dispersion process in synergy with the forging and heat treatment. As a consequence of the nanoparticles-dispersion process, the microstructure was significantly refined, the grain size and the length of martensite lath were both reduced, and the precipitates were more homodispersed. The finer microstructures could prevent stress concentration, promote synergy between grains, and mainly induce grain refinement, and second-phase strengthening, resulting in an unprecedented enhancement in strength and toughness. The tensile yield strength, ultimate strength, fracture strain, no-notch, and U-shaped-notch impact toughness in 0.02 wt% TiC-nanoparticle-reinforced H13 were 1453 MPa, 1724 MPa, 13.1%, 376.9 J/cm2, and 36.4 J/cm2, which were 8.1%, 12.1%, 12.9%, 17.5%, and 23.8% higher than those of H13. This research overcomes a critical technology bottleneck in the preparation of nanoparticle-strengthened steel and offers a novel approach to manufacturing high-performance steel. • Using TiC/Al master alloy to introduce nano-TiC uniformly dispersed in H13 steel. • The master alloy method prevents agglomeration and surface contamination of particles. • Finer microstructures were obtained and carbides were more uniformly dispersed. • Excellent strength and toughness are obtained in H13 through master alloy method. [ABSTRACT FROM AUTHOR]

Innovative in-situ synthesis tactics of devising Al-Cu 4 /Al-Mg 1 alloy inoculated with Fe 80 -B 11 -Si 9 (at.%) metallic glasses were proposed to achieve comprehensive multiscale inoculation of the microstructure. The effects of inoculant on the solidification behaviors were studied, and calculated the mismatch between α-Al and Fe 2 B/Fe 3 Si according to the E2EM model. Formation of nano-Fe 2 B particles exerts low mismatch with α-Al was effective in stimulating heterogeneous nucleation. In the meanwhile, nano-Fe 3 Si particle and nano-Fe 2 B particle that is not trapped in α-Al dendrites hinder the movement of the S/L interface through adsorption, thus hindering the growth of α-Al dendrites. With inoculation, the grains of Al Cu 4 and Al Mg 1 got significantly refined. The manipulation of microstructure also includes weakening of element segregation and refinement of precipitation, which is ultimately accounted for the improvement of comprehensive mechanical properties. The various strengthening mechanisms of inoculated Al Cu 4 and Al Mg 1 alloy are explored, which offers an innovative idea for broadening the industrial utilization of metallic glass. [Display omitted] • Fe 2 B phases stimulated the heterogeneous nucleation of α-Al dendrites and inhibited its growth. • The Al-Cu/Al-Mg eutectic reaction was promoted. • The addition of Fe-B-Si metallic glass significantly refined the size of precipitates. • The comprehensive mechanical properties of Al-Cu 4 /Al-Mg 1 were enhanced by Fe-B-Si metallic glass. [ABSTRACT FROM AUTHOR]

Silicate-bonded porous SiC scaffolds with lamellar structures were prepared by freeze casting and liquid-phase sintering. It was found that the viscosity and solidification velocity of SiC water-based slurries with 30 vol% solid loading decreased with increasing Al 2 O 3 –MgO (AM) addition. As the AM content increased from 10 to 30 wt%, the lamellae of the sintered scaffolds became denser and the porosity decreased from 69±0.5% to 62±0.5%, while the compressive strength improved from 25±2 to 51±2 MPa. The dynamics of pressureless infiltration for an Al–12 Si–10 Mg alloy on the SiC porous scaffold was measured and the composites with lamellar-interpenetrated structures were successfully produced. Both the compressive strength and the elastic modulus of the composites increased with increasing AM content. The maximum strength reached 952±24 MPa and the highest elastic modulus about 156 GPa, respectively, in a longitudinal direction, increasing about 32% and 11% as compared with those of the composites without AM. [ABSTRACT FROM AUTHOR]

The nano-sized TiC p /Al-Cu composites were fabricated using the self-propagating high-temperature synthesis (SHS) reaction of Al-Ti-CNT master alloys in molten aluminum alloys. The tensile strength and ductility of the alloys were simultaneously improved by the addition of nano-sized TiC particles. The yield strength, ultimate tensile strength and fracture strain of the 0.3 wt% nano-sized TiC particles reinforced Al-Cu matrix composite increased to 350 MPa, 554 MPa and 14.75%, improved by 15.5%, 14.2% and 123.5%, respectively, compared with the unreinforced Al-Cu alloy (303 MPa, 485 MPa and 6.6%). The enhanced mechanical properties are attributed to the refined α-Al dendrites, a larger amount of smaller θ′ precipitates and the dispersed nano-sized TiC particulates. This study provides a feasible method to fabricate the nano-sized TiC p /Al-Cu composites with superior strength and ductility. [ABSTRACT FROM AUTHOR]

This work was carried out to investigate the relationship between microstructures and mechanical properties of extruded Al–20Mg 2 Si–4Cu alloys unmodified and modified with 0.5 wt% Sb addition at room and high temperatures. Various techniques including metallography, field emission scanning electron microscope, differential thermal analysis and scanning electron microscopy were used to characterize the microstructure, tensile behavior and fracture mechanism of the alloys. It was found that 0.5 wt% Sb additions were highly effective in refining microstructures by changing the morphology of primary Mg 2 Si from coarse dendrite into smaller polyhedral shape with average size less than 20 µm. Tensile test showed that ultimate tensile strength (UTS) of the modified alloy increased dramatically to 283 MPa at room temperature and 213 MPa at 150 °C, evidently higher than the 220 MPa and 185 MPa for the unmodified alloy, respectively. Fracture surface examinations revealed a transition from particle fracture of primary Mg 2 Si in the unmodified alloy to particle–matrix interface debonding in the modified alloy. The transformation of primary Mg 2 Si from coarse dendrites to refined polygonal shapes contributes to the enhanced strength and ductility of the modified alloy, since the polygonal primary Mg 2 Si particles dispersed uniformly in modified alloy, impeding dislocation motions and freeing stress concentrations. A schematic map was established to further elucidate the mechanisms of fracture behavior during stretching process. [ABSTRACT FROM AUTHOR]

It is challenging to concurrently control the microstructure evolutions after undergoing casting, sheet forming and welding. This study successfully addressed this challenge via trace TiC–TiB 2 nanoparticles in the amelioration of solidification-rolling-welding microstructural evolution. Nanoparticles refined the solidified microstructures and significantly increased the net driving force for recrystallization, promoting the precipitation of nanoscale Guinier–Preston zones and β'' phases. The coarsening of the fusion and heat-affected zones was also effectively suppressed. The yield strength (YS) and ultimate tensile strength (UTS) of the rolled plates were enhanced by 31.3% and 16.3%, respectively, without significantly sacrificing ductility. Additionally, the YS and UTS of the as-welded welding joints were enhanced by 30.2% and 7.8%, respectively. The amelioration mechanism of TiC–TiB 2 throughout the microstructural evolution and strengthening process was systematically investigated. This study provides a typical model for the complete amelioration of microstructural evolution in aluminum alloys under multiple processing conditions. • The nucleation of solidified phases is promoted, and their growth is hindered. • Recrystallization and formation of coherent nanoscale precipitates are promoted. • Coarsening of fusion zone and heat affected zone is suppressed. • Building better microstructure configuration for improved properties. [ABSTRACT FROM AUTHOR]

A fine-grained (∼3.6 μm) Mg–6Al–3Sn (AT63) alloy prepared by a hot rolled method is subjected to uniaxial tensile tests within the temperature range of 25–250 °C. Mg 2 Sn and Mg 17 Al 12 precipitates at grain boundaries effectively retard the growth of dynamically recrystallized (DRXed) grains. Grain boundary sliding (GBS) is activated at 250 °C, which is indicated by the stable DRXed grain size and agglomeration of the precipitates at grain boundaries. Moreover, Mg 2 Sn and Mg 17 Al 12 precipitates promote the formation of dynamic recrystallization (DRX). Both the DRX and GBS result in the high elongation (151.4%) of the AT63 alloy at 250 °C. Results obtained here will shed some light on elevated temperature deformation mechanisms of a new type of Mg–Al–Sn system, which is critical to the development of new Mg alloys with potential for applications at elevated temperatures. [ABSTRACT FROM AUTHOR]

In this study, an innovative method, wherein trace in situ synthesized nano-(TiC+TiB 2) particles are added forged H13 steel, was designed and used to manipulate its microstructure. This refined the grains and laths martensite, increased the retained austenite and carbides, and controlled the carbide segregation. Thus, the strength, plasticity, and toughness of the steel were simultaneously improved. Among the samples, the H13 steel, manipulated by 0.02 wt% nano-(TiC+TiB 2) particles, exhibited the best mechanical properties. Its yield strength, tensile strength, elongation, unnotched impact toughness and U-notch impact toughness increased by 11.6%, 7.6%, 14.2%, 35.0% and 33.8%, respectively, and reached 1142 MPa, 1426 MPa, 16.9%, 449.3 J/cm2, and 41.39 J/cm2, respectively. The main strengthening mechanisms were grain boundary strengthening, dislocation strengthening and dispersion strengthening. This study provides a new method for the bonding between ceramic nanoparticles and steel and provides a novel idea for the development of high-performance and low-cost steel. • The nano-(TiC+TiB 2) particles (NPs) are beneficial to nucleation of γ-Fe/α-Fe. • The trace nano-(TiC+TiB 2) particles inhibited carbide segregation of H13 steel. • More and fine carbides and austenite are yielded by adding trace nanoparticles. • The H13 steel with high comprehensive properties is prepared by adding trace NPs. [ABSTRACT FROM AUTHOR]

Abstract: Many experimental and theoretical studies indicated that the decrease of the size of the reinforcing particles can lead to substantial improvements in the mechanical performance of the composites. However, the investigations on the addition of the nano particles into conventional metal materials are still rare, especially the nano-TiC p into the Al–Cu alloys. In this study, the Ni coated nano-TiC p reinforced Al–Cu matrix composites were successfully fabricated by a casting route. It was found that the nano-TiC p was in the α-Al grains. The α-Al dendrites became finer and more developed. Moreover, the θ′ precipitates in the Al–Cu matrix were finer and uniformly distributed. The tensile strength and elongation of the composites increased simultaneously. After T6 heat treatment, compared with the unreinforced Al–Cu alloy, the tensile strength and elongation of the 0.8wt.% nano-sized TiC p /Al–Cu composite increased from 485MPa and 6.6% to 573MPa and 12.4%, respectively. [Copyright &y& Elsevier]

Abstract: Mg–5Sn alloy are successfully fabricated by a horizontal centrifugal casting method. Developed columnar dendritic crystals under the gravity casting condition can be mostly transformed into fine equiaxed grains by the centrifugal casting. Compared with the gravity casting, compression strength, yield strength and elongation-to-failure are significantly improved by the centrifugal casting, which increase from 181.6 to 257.5MPa, 38.7 to 52.3MPa and 14.9% to 21.2% on position r 1 (centrifugal radius r 1=0.05m), respectively. Moreover, the centrifugal casting also enhances work-hardening ability of the alloy. The transformation of crystals results in the enhancement of the compression properties and work-hardening ability. The results obtained here will shed some light on special casting methods of Mg alloys, which is potential to develop new light alloys with high strength and elongation. [Copyright &y& Elsevier]

Wetting of hot-pressed polycrystalline WC substrates by a Zr55Cu30Al10Ni5 bulk metallic glass (BMG)-forming alloy was investigated at 1133–1253 K in a high vacuum using a modified sessile drop method. The alloy melt spread rapidly on the WC surface, reaching no more than 30° within 3 s, and then slowly (at T < 1213 K) or even remained steady (at T ≥ 1213 K) in the subsequent isothermal dwelling stage. The final equilibrium contact angles were between 11° and 20°, slightly increasing with rising temperature and thus presenting an appreciably anomalous temperature-dependent behavior. The reaction between WC and the Zr-base melt was moderate, slightly enhancing with increasing temperature, and yielded W, ZrC and W5Zr3 at the interface. The wetting, in principle, was driven by the formation of a precursor film in front of the triple line as a result of the adsorption of active atoms (primarily Zr) rather than by the interfacial reaction. From the viewpoint of the wettability and reactivity, WC is a good reinforcement for the preparation of the Zr-base BMG matrix composites. [ABSTRACT FROM AUTHOR]

Abstract: The plastic deformation behavior of as-cast Mg–3Sn–1Zn (TZ31) alloy was investigated at room temperature, which exhibits strong strain hardening ability (i.e. n=0.55 and H c=3.62) and high elongation (ε p=19.1%). The generalized stacking fault (GSF) energy of TZ31 alloy is reduced owing to dopings of Sn and Zn atoms, which is beneficial to improving activity of basal slip, activation of non-basal slips and formation of numerous deformation twins. The high density of twins significantly restricts dislocation motion, leading to strong strain hardening ability of the TZ31 alloy. Results obtained here will shed some light on deformation mechanisms of Mg–Sn–Zn alloys, critical to the development of new high-plastic magnesium alloys. [Copyright &y& Elsevier]

Metal-ceramic composites generally exhibit limited strength-plasticity synergy due to pronounced difference in elastic and plastic deformation between "soft phase" and "hard phase", bottlenecking their applications. This work proposes a novel microstructure design concept using refractory metals and intermetallics to offer compromises between "soft phase" and "hard phase". A cost-effective fabrication method was used to produce 70 vol% (TiC + Al 6 MoTi + Mo)/Al cermet. The cermet is composed of submicron-TiC, micron-Al 6 MoTi and nano-Mo particles separated by Al in homogeneous microstructure. This multiple length-scale microstructure could delocalize stress concentration, enhance work hardening and deformation compatibility in cermet, resulting in unprecedentedly enhanced strength-plasticity synergy. Ultimate compressive strength, plastic strain and product of strength and plasticity of (TiC + Al 6 MoTi + Mo)/Al at room temperature and 573 K respectively are 1227 MPa, 6.9%, 7445 MPa·% and 781 MPa, 15.0%, 10021 MPa·%, which are increased by ~30%, ~25%, ~60% and ~37%, ~9%, 41% respectively compared with those for traditional 70 vol% TiC/Al. This work opens new perspectives for the design and application of metal-ceramic composites with high strength and plasticity synergy. [Display omitted] • A new strategy is proposed for develop metal-ceramic composites with multiple length-scale microstructure. • This multiple length-scale microstructure could enhance deformation compatibility. • 70 vol% (TiC + Al 6 MoTi + Mo)/Al cermet with unprecedentedly enhanced and plasticity synergy were fabricated. [ABSTRACT FROM AUTHOR]

Abstract: The modification of Mg2Si in Mg–5Si alloys with KBF4 was investigated in detail. With the increase of KBF4 content, the alloys exhibited sub-modified and fully modified microstructures, but no over-modified microstructure was found. In the fully modified alloys, most of the primary Mg2Si particles exhibited the morphology of octahedrons. It is believed that B which came from the decomposition of KBF4 effectively confined the growth of primary Mg2Si to the octahedron morphology. [Copyright &y& Elsevier]

Abstract: The magnesium matrix composites reinforced with 2, 5 and 7.5 wt.% fine TiB2 (∼7 μm) particulates were fabricated by a novel two-step processing method, i.e. adding a TiB2–Al compact mixed with fine TiB2 and Al powders to magnesium melt and using a semi-solid slurry stirring technique. The microstructure and properties such as porosity, hardness and wear resistance of the composites were investigated. The distribution of fine TiB2 particulates is relatively homogeneous throughout the Mg matrix. As compared with as-cast AZ91, the hardness and wear resistance of the Mg composite was higher and increased with increasing of TiB2 content, but the porosity of the composites was relatively higher and increased with increasing of TiB2 content. [Copyright &y& Elsevier]