Enhanced Compressive Property of Al Composite Foams at Elevated Temperatures via Plasma Electrolytic Oxidation

The present work investigates the compressive property of Al matrix composite foams at different temperatures between room temperature and 200 °C. Elevated temperature results in a decreased compressive strength and energy absorption capacity of as-received Al foams. Therefore, to maintain the compressive property, the Al2O3 ceramic coating was deposited on the Al struts of the foams by the plasma electrolytic oxidation (PEO) process to form Al2O3/Al composite foams. As a consequence, the composite foams exhibit a higher compressive strength and energy absorption capacity as compared with the as-received Al foams at both room temperature and elevated temperatures because of the reinforced effect of the Al2O3 ceramic on the foam strut. The related mechanisms were explained by fractography, microstructure observation and phase composition analysis using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD)

Compressive Properties of Open-Cell Al Hybrid Foams at Different Temperatures

Hybrid Ni/Al foams were fabricated by depositing electroless Ni–P (EN) coatings on open-cell Al foam substrate to obtain enhanced mechanical properties. The microstructure, chemical components and phases of the hybrid foams were observed and analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The mechanical properties of the foams were studied by compressive tests at different temperatures. The experiment results show that the coating is mainly composed of Ni and P elements. There was neither defect at the interface nor crack in the coatings, indicating that the EN coatings had fine adhesion to the Al substrate. The compressive strengths and energy absorption capacities of the as-received foam and hybrid foams decrease with the increasing testing temperatures, but the hybrid foams exhibit a lower decrement rate than the as-received foam. This might be attributed to the different failure mechanisms at different testing temperatures, which is conformed by fractography observation

Blue-violet Lasing of Optically Pumped GaN-Based Vertical Cavity Surface-Emitting Laser With Dielectric Distributed Bragg Reflectors

Optically pumped GaN-based vertical cavity surface-emitting laser (VCSEL) with two Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs) was fabricated via a simplifled procedure direct deposition of the top DBR onto the GaN surface exposed after substrate removal and no use of etching and polishing processes. Blue-violet lasing action was observed at a wavelength of 397.3 ran under optical pumping at room temperature with a threshold pumping energy density of about 71.5 mJ/cm(2). The laser action was further confirmed by a narrow emission linewidth of 0.13 nm and a degree of polarization of about 65%. The result suggests that practical blue-violet GaN-bsaed VCSEL can be realized by optimizing the laser lift-off technique for substrate removal