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Primary Mg2Si with a truncated octahedral morphology and size over a range of 8–15 μm were prepared by simultaneously adding Ca and Sb into the Al–Mg–Si melt. It is revealed for the first time that CaSb2 can act as the nucleus of primary Mg2Si during solidification, which changes the morphology and refines the size of primary Mg2Si significantly. It is useful for improving the mechanical properties of the Al–Mg–Si alloy. The skeleton-type growth processes of truncated octahedral primary Mg2Si crystals were identified by observation of the three-dimensional (3-D) morphologies of the crystals extracted from the Al–Mg–Si alloy. The content of Ca and Sb plays an important role in determining the morphologies of primary Mg2Si, which can be transformed from coarse dendrites to defective truncated octahedra and finally to the coexistence of perfect truncated octahedra and flat truncated octahedra with increasing the content from 0 to 0.2 and then to 0.5 wt%. Our study provided a one-step less-cost method to change the morphologies and sizes of primary Mg2Si, which is important to tailor new light-weight alloys with high strength and toughness. [ABSTRACT FROM AUTHOR]

Using 3 wt% TiO nanopowders as sintering aid, we prepared porous lamellar AlO-ZrO composites with an initial solid loading of 30 vol% and the AlO/ZrO weight ratios of 1:9, 3:7, 5:5, 7:3, and 9:1 by freeze casting. The viscosity of water-based slurries decreased with increasing AlO content while the porosity and the wavelength of the lamellae in the sintered scaffolds showed first an increase and then decrease with maximum values appearing at AlO:ZrO = 5:5. A relatively large amount of tetragonal (t) ZrO transformed to monoclinic (m) ZrO with the increase in the AlO content and sintering temperature, thus reducing stress-induced phase transformation effect during loading. The compressive strength of the sintered scaffolds depended on sintering temperature, porosity, and the phase composition in the composites. A maximum value of 105 ± 10 MPa was achieved in the scaffolds with a composition of AlO:ZrO = 3:7 after sintering at 1450 °C for 2 h. [ABSTRACT FROM AUTHOR]

Uniaxial tensile tests were performed on fine-grained, rolled AT33 alloy at strain rates of 1.0 × 10-4-1.0 × 10-1 s-1 and temperatures of 25-250 °C. The rolled AT33 alloy with an average grain size of 7mm was produced by cast-rolling and hot-rolling. The relative deformation mechanisms at high temperature were investigated in this study. It was found that the strain rate sensitivity increases from 0.01 at room temperature to 0.13 at 250 °C. The average stress exponent and the activation energy have been calculated to be 6.5 and 145 kJ mol-1, respectively, indicating that the dominant tensile deformation mechanism is dislocation climb-controlled creep profiting from the lattice self-diffusion. The dispersed nano-sized Mg2Sn particles in the rolled AT33 alloy increase dislocation accumulation, which not only contributes to a promising tensile strength at high temperature but also provides a high driving force for the dynamic recrystallization (DRX). It has found that DRX is mainly responsible for the obtained high tensile ductility of 76-205% at temperatures of 200-250 °C. [ABSTRACT FROM AUTHOR]

Co-doped Zn2SnO4 -- graphene -- carbon nanocomposites have been prepared for the first time through a convenient one-step hydrothermal method. The size of Co-doped Zn2SnO4 nanoparticles is about 3-5 nm and they are well dispersed on graphene nanosheets and carbon layer. L-Ascorbic acid is introduced to serve as a reductant for GO and carbon sources. The doping of Co can enhance the crystalline degree of Zn2SnO4 nanoparticles. When evaluated as anode materials for lithium ion batteries, the Co -- ZTO -- G -- C nanocomposites exhibited a significantly higher reversible capacity of 699 mA h g-1 after 50 cycles at 100 mA g-1 and an improved cycling stability of 461 mA h g-1 after 200 cycles at 500 mA g-1 compared with Co -- ZTO -- G and ZTO -- G -- C nanocomposites. Moreover, even at a high current density of 1000 mA g-1, the reversible capacity of 418 mA h g-1 still remained. The improved electrochemical performance can be attributed to the synergy of the graphene substrate, the protective carbon layer, the uniform ultrafine Zn2SnO4 nanoparticles and Co doping. Therefore, Co -- ZTO -- G -- C nanocomposites show great prospect as anodes for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The wetting of (100), (110), and (111) MgO single crystals by molten Mg was studied in a flowing Ar atmosphere at 1073 K using an improved sessile drop method. The results show that the contact angle and work of adhesion are mildly dependent on MgO substrate orientation. However, the work of separation calculated by density functional theory shows a sequence of (100) < (110) < (111). This discrepancy was explained by a model considering the possible effects of evaporation and deposition of Mg at the substrate surface on the interfacial adhesion. For Mg on the clean MgO surfaces, the adhesion consists primarily of Mg-O ionic bonds with some Mg-Mg metallic bonds. In addition, a small amount of covalent bonds are present in the metal slab adjacent to the Mg/MgO (110) and Mg/MgO (111) interfaces. The different work of separation at three interfaces depends on the strength and amounts of Mg-O and Mg-Mg bonds as well as on the surface free energy of respective planes. For the MgO surfaces pre-deposited by a monolayer of Mg atoms, the interfaces are dominated by the Mg-Mg bonds, thus mitigating the effect of substrate orientation on the wettability and adhesion. [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 formation enthalpy, electronic structures, and elastic moduli of the intermetallic compound Ti5Si3 with substitutions Zr, V, Nb, and Cr are investigated by using first-principles methods based on the density-functional theory. Our calculation shows that the site occupancy behaviors of alloying elements in Ti5Si3, determined by their atom radius, are consistent with the available experimental observations. Furthermore, using the Voigt-Reuss-Hill (VRH) approximation method, we obtained the bulk modulus B, shear modulus G, and the Young's modulus E. Among these four substitutions, the V, Nb, and Cr substitutions can improve the ductility of Ti5Si3 effectively, while Zr substitution has little effect on the elastic properties of T15S13. The elastic property variations of Ti5Si3 due to different substitutions are found to be correlated with the Me4d-Me4d antibonding and the strengthened Me-Si bonding in the solids. [ABSTRACT FROM AUTHOR]

The ignition and reaction processes of the thermal explosion reaction from the Ti–B4C system in air were studied. The thermal explosion reaction for the formation of TiC and TiB2 can be initiated at a relatively low temperature with the incorporation of air. Generally, the ignition process in air is suggested to be a chemical oven rather than gas transport, and the reaction process is proposed to be dissolution and precipitation. [ABSTRACT FROM AUTHOR]

Compared with the Ti–C system, the additions of metals (Fe, Al, and Cu) can increase the lattice parameter and stoichiometry of TiC x by forming metal–Ti intermediate phases (for C/Ti≤0.8). But for C/Ti>0.8, the Fe addition can decrease the lattice parameter and stoichiometry of TiC x by the formation of Fe–C solid solutions due to the hindrance of atom diffusion and the decrease of combustion temperature, while the additions of Al and Cu can increase them by the formation of Al–Ti and Cu–Ti solid solutions due to the dilution of Al and Cu. [ABSTRACT FROM AUTHOR]

Based on pin on disc dry sliding tests and scanning electron microscopy (SEM) observation, the sliding wear behaviors of granular &gamma+(Fe, Mn)3C eutectics reinforced austenite matrix composites (abbreviated EAMC) under dry wear condition were studied. The wear testing shows that the wear process of EAMC can be divided into running-in and steady state regimes. The serious plastic deformation and flow occur to austenite matrix of EAMCin the running-in regime. The dominant wear mechanism of EAMC is the delamination wear at the steady state regime. The &gamma+(Fe, Mn)3Ceutectic particles, as the main body against the normal load and abrasive wear, can delay the formation of dislocation depleted zone and accumulation of abrasive on the counterpart surfaces. Therefore, the probability of the debris formation and flaked decreases, which results in the decrement of wear rate for EAMC and the increment of critical normal load above which severe wear occurs to EAMC. The criterion on the critical normal load for particulate reinforced composites was revised. The calculated results agree well with the experimental ones for EAMC. [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]

Al-Mg alloys are widely used as important engineering structural materials in aerospace engineering, transportation systems, and structural constructions due to their low density, high specific strength, corrosion resistance, welding capability, fatigue strength, and cost-effectiveness. However, the conventional Al-Mg alloys can no longer fully satisfy the demands of practical production due to difficulties caused by many defects. The high strength of Al-Mg alloys as non-heat treatment precipitation-strengthened alloys is achieved primarily by solid solution strengthening along with work hardening rather than precipitation strengthening. Therefore, severe plastic deformation (SPD) techniques can be often used to produce ultrafine-grained structures to fabricate ultra-high strength aluminum alloys. However, this approach often achieves the strengthening of material at the cost of reduced ductility. This paper comprehensively summarizes the various approaches of ultrafine/nanocrystalline materials for enhancing their plasticity, elaborates on the creation of a bimodal microstructure within the alloy, and discusses the formation of a nanotwin microstructure within the alloy and the incorporation of dispersed nanoparticles. The mechanisms underlying both the strengthening and toughening during large plastic deformation in aluminum alloys are summarized, and the future research direction of high-performance ultrafine crystalline and nanocrystalline Al-Mg aluminum alloys is prospected. [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]

As an important part of die steels, hot-work die steels are mainly used to manufacture molds made of solid metal or high-temperature liquid metal from heating to recrystallization temperature. In view of the requirements for mechanical properties and service life for hot-work die steel, it is conducive to improve the thermal fatigue resistance, wear resistance, and oxidation resistance of hot work die steel. In this review, the main failure modes of hot-work die steel were analyzed. Four traditional methods of strengthening and toughening die steel were summarized, including optimizing alloying elements, electroslag remelting, increasing the forging ratio, and heat treatment process enhancement. A new nano-strengthening method was introduced that aimed to refine the microstructure of hot-work abrasive steel and improve its service performance by adding nanoparticles into molten steel to achieve uniform dispersion. This review provides an overview to improve the service performance and service life of hot work die steel. [ABSTRACT FROM AUTHOR]

It is widely known that the special performances and extensive applications of the nanoscale materials are determined by their as-synthesized structures, especially their growth sizes and morphologies. Hereinto, titanium carbides, which show brilliant comprehensive properties, have attracted considerable attention from researchers. How to give full play to their potentials in the light-weight manufacture, microwave absorption, electromagnetic protection, energy conversion and catalyst areas has been widely studied. In this summarized article, the synthesis methods and mechanisms, corresponding growth morphologies of titanium carbides and their further applications were briefly reviewed and analyzed according to their different morphological dimensions, including one-dimensional nanostructures, two-dimensional nanosheets and three-dimensional nanoparticles. It is believed that through the investigation of the crystal structures, synthesis methods, growth mechanisms, and morphology characterizations of those titanium carbides, new lights could be shed on the regulation and control of the ceramic phase specific morphologies to meet with their excellent properties and applications. In addition, the corresponding development prospects and challenges of titanium carbides with various growth morphologies were also summarized. [ABSTRACT FROM AUTHOR]

Magnesium matrix composites are essential lightweight metal matrix composites, following aluminum matrix composites, with outstanding application prospects in automotive, aerospace lightweight and biomedical materials because of their high specific strength, low density and specific stiffness, good casting performance and rich resources. However, the inherent low plasticity and poor fatigue resistance of magnesium hamper its further application to a certain extent. Many researchers have tried many strengthening methods to improve the properties of magnesium alloys, while the relationship between wear resistance and plasticity still needs to be further improved. The nanoparticles added exhibit a good strengthening effect, especially the ceramic nanoparticles. Nanoparticle-reinforced magnesium matrix composites not only exhibit a high impact toughness, but also maintain the high strength and wear resistance of ceramic materials, effectively balancing the restriction between the strength and toughness. Therefore, this work aims to provide a review of the state of the art of research on the matrix, reinforcement, design, properties and potential applications of nano-reinforced phase-reinforced magnesium matrix composites (especially ceramic nanoparticle-reinforced ones). The conventional and potential matrices for the fabrication of magnesium matrix composites are introduced. The classification and influence of ceramic reinforcements are assessed, and the factors influencing interface bonding strength between reinforcements and matrix, regulation and design, performance and application are analyzed. Finally, the scope of future research in this field is discussed. [ABSTRACT FROM AUTHOR]

The authors prepare nacre‐mimetic Al−7Si−5Cu/Al2O3−ZrO2 composites with alternately arranged soft‐hard phases and different ceramic compositions using freeze casting and gas‐pressure infiltration techniques and investigate their dry abrasive wear resistance. These composites exhibit excellent and anisotropic wear resistance when worn along different directions. The wear rates of the composite with Al2O3:ZrO2 = 1:9 against 400‐grit, 240‐grit, and 100‐grit SiC sandpapers are approx. 1/78, 1/37, and 1/27 of those of the Al−7Si−5Cu alloy. The underlying mechanisms for the excellent wear resistance of these nacre‐mimetic composites are ascribed to the "self‐sharpen" effect in the early running‐in period and the formation of friction films in the later wear period. Moreover, the anisotropic wear resistance is interpreted by the different stress states that the interface is subjected to. This paper presents the structures and wear properties of nacre‐inspired Al–7Si–5Cu/Al2O3–ZrO2 composites. The composites exhibit excellent wear resistance but distinct anisotropy when they are worn along different directions. The excellent wear resistance is ascribed to "self‐sharpen" effect and formation of friction films, while the anisotropy to the different stress states that the metal‐ceramic interface is subjected to. [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]

Nacre-inspired laminated composites have been proven to possess a unique combination of strength and toughness. In this study, we fabricated nacre-mimetic Cu/TiC composites via unidirectional freezing of aqueous TiC slurries containing different amounts of NiO additives, followed by ice sublimation, carbothermal reduction of NiO to Ni during sintering and then gas-pressure infiltration of the Cu melt. The introduction of Ni greatly facilitated the densification of ceramic lamellae and enhanced the interfacial bonding between Cu and TiC. The resultant composites displayed outstanding damage tolerance and anisotropic electrical conductivities. Specifically, for an ∼31 vol% TiC–Cu composite containing 24 wt% Ni in the ceramic lamellae (based on the TiC content), a fracture toughness (K Jc) of 72.5 ± 1.0 MPa·m1/2, work of fracture of 53.4 ± 3.5 kJ/m2, bending strength of 725 ± 11 MPa and longitudinal electrical conductivity of 22.7 MS/m (∼60% of the Cu matrix) were achieved, which were approx. 81%, 536%, 122% and 97% higher than those of the Ni-free composite, respectively. Noticeable toughening was demonstrated to be a consequence of multiple cracking, plastic deformation and uncracked-ligament bridging of the metal layers, as well as crack deflection and blunting. On the other hand, significant strengthening resulted from tailoring the microstructures in the ceramic layers and at the Cu/TiC interface as a result of Ni doping. We believe that the facile strategy adopted herein provides an effective way to solve the problems of wetting and bonding related to metal infiltration and can be readily extended to the preparation of other nacre-inspired metal−ceramic composites. [ABSTRACT FROM AUTHOR]

Directionally aligned prismatic and lamellar porous alumina scaffolds with a high strength-to-density ratio were fabricated from submicron Al2O3 powders and a tiny quantity of nanoscale TiO2 sintering aids by freeze casting using TBA and water as solvents. Both freezing temperature (− 10 °C, − 50 °C, − 90 °C) and sintering temperature (1300 °C, 1350 °C, 1400 °C) were varied to adjust pore parameters while a low solid loading (15 vol%) was maintained to ensure high porosity. This paper describes and compares the microstructures, porosity, pore size, wall thickness and compressive behavior of the scaffolds with two typical pore morphologies (lamella and honeycomb), which help to identify their scope of application and to unveil the relationship between pore morphology and mechanical property to optimize the material performance. The failure modes of these two types of scaffolds under compression were simulated. The TBA-based 1 wt% TiO2-containing alumina scaffolds with dense ceramic walls that were freeze-cast at − 90 °C and sintered at 1400 °C exhibited a compressive strength of 160 MPa with a porosity of 59%, indicating lightweight and high-strength characteristics. [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]

It is well known that the development of lightweight alloys with improved comprehensive performance and application value are the future development directions for the ultra-high-strength 7xxx series Al-Zn-Mg-Cu alloys used in the aircraft field. As the lightest metal element in nature, lithium (Li) has outstanding advantages in reducing the density and increasing the elastic modulus in aluminum alloys, so Al-Zn-Mg-Cu alloys containing Li have gained widespread attention. Furthermore, since the Al-Zn-Mg-Cu alloy is usually strengthened by aging treatment, it is crucial to understand how Li addition affects its aging precipitation process. As such, in this article, the effects and mechanism of Li on the aging precipitation behavior and the impact of Li content on the aging precipitation phase of Al-Zn-Mg-Cu alloys are briefly reviewed, and the influence of Li on the service properties, including mechanical properties, wear resistance, and fatigue resistance, of Al-Zn-Mg-Cu alloys are explained. In addition, the corresponding development prospects and challenges of the Al-Zn-Mg-Cu-Li alloy are also proposed. This review is helpful to further understand the role of Li in Al-Zn-Mg-Cu alloys and provides a reference for the development of high-strength aluminum alloys containing Li with good comprehensive properties. [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]

TiC/Al–Cu nanocomposites were fabricated in Al–Ti–C powder systems using carbon black, a mixture of C and carbon nanotubes (C + CNTs), and CNTs via an in-situ method involving combustion synthesis and hot pressing. As the carbon source changed from pure carbon black to the C + CNT mixture and pure CNTs, the size of the TiC nanoparticles decreased gradually. The nanocomposites synthesized based on the C + CNT mixture exhibited the most uniform dispersion of TiC nanoparticles. The 30 vol% TiC/Al–Cu nanocomposite prepared from the C + CNT mixture had the best comprehensive mechanical properties (yield strength (411 MPa), compressive strength (712 MPa), fracture strain (17.2%), hardness (206.8 HV), and wear resistance under the experimental conditions due to having the most uniformly dispersed TiC nanoparticles. The wear mechanism was a combination of plastic deformation, abrasion, and adhesion. This method may be a low-cost and convenient means to control the sizes of in-situ TiC nanoparticles and prepare high-performance TiC/Al–Cu nanocomposites. [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]