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Three types of aluminum alloy powder were mixed with the Al-based metallic glasses powder in different proportions, and the Al-based metallic glasses composites were prepared by cold spraying. The microstructure of the coatings was investigated, and the compressive strength of the Al-based metallic glasses composites was tested. Numerical simulation was carried out to study the formation of the composite coatings. The porosity of the composite coatings was significantly lower than for the Al-based metallic glasses coating. The maximum compression strength was 584 MPa when adding 50% Al7075 powder, and the compressive strength of Al-based metallic glasses composites has a positive correlation with the types of added aluminum alloy powder. The grinding effect due to the relative slip between the Al-based metallic glasses particles and the soft particles was observed at the fracture surface. The Al-based metallic glasses particles were packed closely with the surrounding Al7075 particles after fracture. Simulation results showed that the soft particles behaved like a droplet when impacted onto the metallic glasses particles, and gaps between the metallic glasses particles were filled with soft particles, but some pores still existed when adding Al7075 powder due to its relatively higher strength. [ABSTRACT FROM AUTHOR]

A novel refractory CoCrMoNbTi0.4 high-entropy alloy (HEA) was prepared via vacuum arc melting. After annealing treatment at different temperatures, the microstructure evolution, phase stability, and mechanical properties of the alloy were investigated. The alloy was composed of two primary body-centered cubic structures (BCC1 and BCC2) and a small amount of (Co, Cr)2Nb-type Laves phase under different annealing conditions. The microhardness and compressive strength of the heat-treated alloy was significantly enhanced by the solid-solution strengthening of the BCC phase matrix and newborn Laves phase. Especially, the alloy annealed at 1473 K (1200 °C) achieved the maximum hardness and compressive strength values of 959 ± 2 HV0.5 and 1790 MPa, respectively, owing to the enhanced volume fraction of the dispersed Laves phase. In particular, the HEAs exhibited promising high-temperature mechanical performance, when heated to an elevated temperature of 1473 K (1200 °C), with a compressive fracture strength higher than 580 MPa without fracture at a strain of more than 20 pct. This study suggests that the present refractory HEAs have immense potential for engineering applications as a new class of high-temperature structural materials. [ABSTRACT FROM AUTHOR]

In this work, a new refractory high-entropy alloy, the Co-Cr-Mo-Nb-Ti system, was proposed as a family of candidate materials for high-temperature structural applications. CoCrMoNbTi ( x values in terms of molar ratios, x = 0, 0.2, 0.4, 0.5 and 1.0) alloys were prepared by vacuum arc melting. The effects of variations in the Ti content on the phase constituents, microstructure and mechanical properties of the alloys were investigated using x-ray diffractometry, scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy and compressive testing. The results showed that the CoCrMoNbTi alloy possessed a typical cast dendritic microstructure consisting of a single body-centered cubic (BCC) solid solution. Laves phases (CrNb and CoTi) were formed in other alloys with different Ti contents. The results were discussed in terms of the mixing enthalpy, atomic size difference, electronegativity difference and valance electron concentrations among the elements within alloys. The alloy hardness exhibited a slightly decreasing trend as the Ti content increased, resulting from the coarser microstructure and reduced amount of Laves phases. Augmented Ti content increased the compressive strength, but decreased the ductility. Particularly, for the CoCrMoNbTi alloy, the hardness, compressive strength and fracture strain were as high as 916.46 HV, 1906 MPa and 5.07%, respectively. The solid solution strengthening of the BCC matrix and the formation of hard Laves phases were two main factors contributing to alloy strengthening. [ABSTRACT FROM AUTHOR]

In this paper, an analysis on the residual stress evolution of cold-sprayed copper coatings on Cu and Al substrates was performed. To investigate the influences of particle velocity, temperature and material combination on the final residual stresses, an integrated frame of calculation was proposed based on the simulation results obtained from the developed thermo-mechanically coupled Eulerian model. In a single Cu splat, generally speaking, the maximum residual stress and plastic deformation are concentrated at the outside contact zone rather than at the center point of initial impact. The action of friction shear between the particle and substrate during impacting should be considered as one of the essential factors on the final residual stress. And the states of residual stresses can vary significantly depending on the material combination, particle velocity, and temperature. In a single pass Cu coating, the residual stress fluctuates across the coating and there exists both compressive stress and tensile stress within the coating. At a certain range of impacting velocities, the resultant residual stresses increase with the increase of particle velocity. The present simulated results are related to the reported experiments by others, showing that the residual stress states and stress change trend are different from some of the reported results. [ABSTRACT FROM AUTHOR]

Cold spray technology, originated from the Institute of Theoretical and Applied Mechanics Siberian branch of the Russian Academy of Sciences, is a rapidly emerging industrial coating technology. Cold sprayed particles with high-velocity impact onto a substrate so as to induce severe plastic deformation and then create a deposit. For its low temperature and high velocity compared with thermal spraying, the cold spraying process is increasingly used in the industries for protective coating. The deposition characteristics of the particles, coating formation and bonding mechanism of the cold spraying process are different from thermal spraying. Many theory investigations of the cold spraying process contribute to the development of the high performance coatings, which makes the cold spraying process as a popular research field. Presently, the deposition characteristics, bonding mechanism, process optimization as well as classical applications of the cold spraying technology in the past are reviewed, and the interesting points for the further development, optimization and applications of this technology are also recommended. [ABSTRACT FROM AUTHOR]

Copper powder was cryomilled for 12 hours to achieve particle size in the range of 2 μm to 25 μm, which powder was subsequently used as feedstock for the deposition of nanocrystalline (nc) Cu coating via cold spraying. The as-milled copper powder was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The particle size of the cryomilled Cu powder was detected by laser scattering. The microstructure of the coating was analyzed using SEM and scanning transmission electron microscopy (STEM). The XRD and HRTEM analysis showed that the grain size of the cryomilled Cu powder was about 5 to 40 nm. This nanoscale structure was retained after the cold spraying. The nanoindentation analysis showed that the nc Cu coating hardness value reached 3.3 GPa, which was higher than that of its coarse grained counterpart. [ABSTRACT FROM AUTHOR]

States that the nucleus of nodular graphite is Bucky-Ball. Information on some of the hypotheses associated with nodular graphite; Reference to the inference drawn from the morphology features of Bucky-Ball.