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Abstract Traditional laminated metal matrix composites are confined to two-component system of pure metal matrix and its reinforcement. To achieve further improvement of the applied mechanical properties, in this work, the soft phase of laminated composites was enhanced by alloying with Cu. The synergistic effect of Cu on phases of both soft and hard including in-situ catalyzing and precipitation hardening was firstly explored. The laminated graphene nanosheets (GNSs) /AlCu composites of 2 vol% GNSs, were fabricated by ball milling and hot-rolling processes with much higher mechanical properties. The multi-pass hot rolling provided the solution-precipitation process of Cu transforming into Al 2 Cu and significantly increased the dislocation density of the original soft Al matrix. In addition, the fracture mechanism and fracture model of the laminated GNSs/AlCu composites were also investigated. [ABSTRACT FROM AUTHOR]

Graphene nanosheets (GNS) have attracted lots of attention as an ideal reinforcement in Al matrix composites. However, there are still challenges limiting the performance of the composites, such as the homogenous distribution of GNS in Al matrices, the structural integrity of GNS after ball-milling, and the interfacial bonding between GNS and Al matrices. This work presents a new approach to grow GNS on Al powders at 600 °C by in-situ chemical vapor deposition (CVD) process, using methane as the carbon source, and Cu as the catalyst. The GNS coated Cu reinforced Al matrix bulk composites (Cu@GNS/Al) from the composite powders was fabricated by powder metallurgy (PM) technique. It was found that Cu 2+ from CuCl 2 can easily anchor onto the surfaces of Al particles uniformly though a nanoscale-disperse-method in alcohol, enabling the homogenously dispersion of Cu particles in Al matrices after being reduced from Cu 2+ in hydrogen. With the assistance of Cu particles, network-liked GNS was successfully synthesized in-situ and strongly bonded with Al, resulting in a good mechanical performance of the composites. It is indicated that the tensile strength of the composites was improved by ~ 200% compared to the unreinforced pure Al. The strengthening mechanism was mainly ascribed to the load transfer of GNS, precipitation strengthening of Al 2 Cu compounds after 400 °C annealing and dislocation strengthening. [ABSTRACT FROM AUTHOR]

Doping second phase particles tends to improve the strength of additively manufactured nickel-based superalloys fabricated via laser powder bed fusion (LPBF). However, the stress concentration caused by the second phase particles inevitably deteriorates their ductility. In this study, Hastelloy X (HX) composites with single (1 wt% Y 2 O 3) and multiple (0.5 wt% Y 2 O 3 and 0.5 wt% La 2 O 3) oxide particles are successfully prepared via in-situ chemical doping method together with LPBF. The results show that co-doping Y 2 O 3 and La 2 O 3 refines oxide particles from 35 nm to 26 nm in the LPBF fabricated HX. The finer oxide particles can more effectively increase the Zener force and block the grain boundary migration, thus weakening the preferred (001) texture and inhibiting the grain growth. As a result, the Y-HX and Y–La-HX samples possess an ultimate tensile strength of 1091 ± 10 MPa and 975 ± 6 MPa, respectively, representing an increase of 26.8% and 13.3% compared to the HX sample (860 ± 5 MPa). The strengthening mechanisms are mainly attributed to Orowan strengthening, dislocation strengthening and grain refinement. Moreover, the Y–La-HX sample exhibits the highest elongation, increasing by 9% compared to the HX sample. The high elongation is associated with excellent strain hardening behavior caused by finer oxide particles within grains. Our work can provide guidance for the preparation of additively manufactured nickel-based superalloys with superior mechanical properties. [ABSTRACT FROM AUTHOR]

The interface doping with rare earth elements is a novel strategy to enhance the weak interface bonding of copper-graphene system (Cu-G). In this work, taking Sc, Y, La as representatives, we investigated the structural, electronic and mechanical properties of clean and doped Cu-G systems using first principles calculations. By the comparison of interface spacing and work of separation with clean system, the significantly improved interface interaction in rare earth elements doped systems has been verified. Besides, difference charge density, Bader charge and density of states were employed to reveal the microscopic modifying mechanism on the atomic scale. Then, the tensile stress-strain curves were obtained using a fitting function related with the element electronegativity, and thus the quantitative relationship between the interface bonding and mechanical properties was determined, which could provide theoretical guidance for the interface modification of Cu-G composites through doping rare earth elements. The introduction of rare earth elements could significantly enhance the interface bonding of copper-graphene system by promoting charge transfer and electron interaction at the interface, which could be demonstrated by the analysis of electronic properties. Then, the rigid stretching was implemented, and a fitting function containing electronegativity was employed to determine the quantitative relationship between interface bonding and tensile properties. [Display omitted] • Rare earth elements doping effects on copper-graphene system are studied. • The structural and electronic characteristic of doped systems are analyzed. • The rigid stretching is used to study the related mechanical properties. • Quantitative relationship between interface binding and mechanical property is explored. [ABSTRACT FROM AUTHOR]

The rare earth scandium (Sc) as a microalloying element has attracted an increasing interest in aluminum alloys for achieving excellent mechanical properties. Combining with zirconium, high strength and low price Al–Sc alloys are expected. The effects of Sc and Zr on the grain refinement, recrystallization resistance and precipitation hardening were investigated in new type of Al–Zn–Mg–Sc–Zr alloys by rolling, annealing and aging processes. Scandium addition into the Al–Zn–Mg alloys can efficiently refine the grain size and increase recrystallization resistance, especially together with zirconium addition. The maximum value of the yield-to-tensile strength (627 MPa/667 MPa) was obtained with 0.2Sc/0.4Zr ratio of the alloy after solution-aging treatment. The additional strengthening of the alloys is attributed to the grain refinement and the precipitation-strengthening effect of Al 3 Sc, Al 3 Zr or Al 3 (Sc, Zr) in the proper ratio of Sc/Zr during aging. [ABSTRACT FROM AUTHOR]

The interface bonding was found to be related with the element electronegativity. And the first-principles tensile experiments including the rigid stretching and the relaxed stretching were implemented to simulate the stretching process, then a fitting function was applied to determine the quantitative relationship between the interface bonding and mechanical properties. [Display omitted] • Transition metal (TM) elements doping effects on Gr/Cu interface binding are studied. • Work of separation of the doped interfaces relates to the TM electronegativity. • The rigid and relaxed stretching are used to study the related mechanical properties. • Quantitative relationship between interface binding and mechanical property is explored. The interface doping with transition metal elements (TM = Ti, Cr, Co, Ni) has been experimentally proved to be an effective pathway to improve the weak interface bonding of graphene/copper (Gr/Cu) composites. In this paper, the microscopic influencing mechanism of TM doping on the interface interaction and mechanical properties of Gr/Cu was investigated by the first-principles calculations. The sandwich model with graphene embedded in Cu matrix was adopted here to simulate the TM-doped interfaces. It is revealed that the introduction of TM doping elements can significantly improve the work of separation, which relates to the electronegativity difference between TM and Cu elements based on the analysis of the interface electronic structure. Then, the mechanical properties of the clean and TM-doped interfaces were studied by the rigid stretching and the relaxed stretching. We found that, in rigid case, the theoretical tensile strengths of different interfaces are positively correlated with the work of separation, and the electronegativity is also a main factor affecting the mechanical properties. Furthermore, a fitting function containing the element electronegativity was applied to get the stress–strain relationship curve, and the quantitative relationship between the interface bonding and mechanical properties determined in this work can be served as a favorable support for the experimental design of Gr/Cu composites. [ABSTRACT FROM AUTHOR]