Magnesium-calcium alloy-based composites reinforced with vapor grown carbon fibers (VGCFs) are supposed to possess satisfactory high-temperature applications. However, poor wettability of magnesium with carbon fiber is a technical problem encountered in fabrication of the composites. In order to cover the wetting problem, wetting behavior of magnesium alloys on graphite sheet, pure nickel, and nickel coated graphite sheet were investigated using sessile drop method. The graphite was non-wetting by both Mg-5Al alloy and Mg-5Al-3Ca alloy with contact angles about 120°. The droplet of magnesium alloys on nickel plate spread rapidly. Contact angle of Mg-5Al-3Ca alloy decreased from about 94°to 43°. Wettability of magnesium alloys on nickel coated graphite sheet was improved through the dissolution of nickel into the liquid magnesium alloy. Calcium addition showed negative effect on contact angle of nickel substrate, and also slightly hindered the spread of magnesium alloy droplet on nickel coated graphite sheet.
The effect of the addition of bismuth on the dynamic recrystallization (DRX) behavior of the matrix has been investigated by comparing coarse grain pure Mg with the addition of 3 wt.% Bi, using a uniaxial compression test in the temperature range of 473–623 K and the strain rate of 0.01–10 s−1. The constitutive equation, processing map, microstructure, and texture evolution of the Mg-3Bi alloy were systematically investigated. The results showed that the Bi addition could refine the grain size and accelerate the DRX process. The DRX kinetics is discussed in detail, accompanied by extensive characterization employing EBSD analysis. The DRX of the Mg-3Bi alloy depended on the deformation temperature rather than the strain rate. The {10–12} tensile twin appeared at 573 K/0.01–0.1 s−1, and discontinuous DRX (DDRX), continuous DRX (CDRX) as the main mechanism in the case of 573 K/0.01 s−1, while the dominant mechanism was DDRX when deformation temperature and strain rate increased. Particle-stimulated nucleation (PSN) was also involved in the DRX of this new RE-free Mg alloy.
In this study, we investigated the high strain rate response of Mg-6wt%Er alloys with 1wt%Zn addition by split Hopkinson pressure bar (SHPB) tests in a range of 900–2500 s−1. Their related microstructures were also characterized by optical microscopy (OM), scanning electron microscopy (SEM), electron back-scattering diffraction (EBSD), and transmission electron microscopy (TEM). In particular, the twinning and stacking faults (SFs) in Mg-6Er and Mg-6Er-1Zn alloys are characterized, and the interactions between twin/SFs and dislocations are analyzed in detail. Compared with twins, the dispersed and dense SFs seem to more readily interact with dislocations, resulting in the enhancement of the strength of alloys. Especially at a high strain rate of 1450 s−1, dislocations are prone to tangle around the twins and SFs, forming low-angle grain boundaries (LAGBs). The addition of Zn in Mg-6Er can make LAGBs more easily transform into high-angle grain boundaries (HAGBs) due to the existence of SFs.
FeB-Ni hard materials were consolidated by both electroless plating and spark sintering processes for the development of ubiquitous hard materials. Uniform nickel layers were formed quantitatively on as-received FeB powder surfaces. The amorphous Ni layers transformed to poly-crystalline during spark sintering. Sintering curves of FeB-Ni compacts showed the similar behaviors regardless of Ni contents, although their apparent relative densities were increased with the increment of Ni contents. Moreover, the sintering mechanism of FeB-Ni and pure Ni compacts consisting of both the plastic deformation and power law creep deformation occurred during spark sintering. Their maximum points of Ḋ were shown in the D of approximately 0.78. The plastic and power law creep deformation were predominantly consolidation mechanisms before and after maximum Ḋ, respectively. Values in H R A of FeB-Ni compacts were decreased with increment of the Ni contents. The compressive stress of FeB-Ni compacts was decreased with the increment of the Ni contents in contrast to the compressive strain.
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