Monolayer graphene was deposited on a Si wafer substrate decorated with SiO2 nanoparticles (NPs) and then exposed to aryl radicals that were generated in situ from their diazonium precursors. Using micro-Raman mapping...
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Mg-Al bonded composite materials expand Mg and Al alloys' applications by combining their unique performances together. However, the formation of Mg-Al intermetallic compounds in interface zone of Mg/Al directly-b...
Mg-Al bonded composite materials expand Mg and Al alloys' applications by combining their unique performances together. However, the formation of Mg-Al intermetallic compounds in interface zone of Mg/Al directly-bonded joint seriously obstructs its further development. To solve this problem, Mg-Ag-Al multilayer composite materials have been successfully prepared by diffusion bonding technology. The effect of key process parameter (bonding temperature) on microstructure of this material has been mainly investigated. The results show that Mg and Al were well bonded by using silver interlayer when the bonding temperature exceeded 370°C. But Mg17Al12 and Mg2Al3 compounds were formed in the interface zone at temperatures higher than 420°C. By means of controlling the bonding temperature (380 °C–420 °C), silver interlayer effectively restrained the generation of Mg-Al intermetallic compounds, and Mg-Ag intermetallic compounds (Mg3Ag, MgAg) were formed in the interface zone instead.
Microstructure evolution during ART-annealing （austenite reverted transformation annealing） of 0.2C-5Mn steel processed by austenitation at different temperatures was examined by SEM, TEM and XRD. It was demonstrate...
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Microstructure evolution during ART-annealing （austenite reverted transformation annealing） of 0.2C-5Mn steel processed by austenitation at different temperatures was examined by SEM, TEM and XRD. It was demonstrated that the initial mi- crostructures resulted from austenization at different temperatures strongly affect the microstructure evolution during followed ART-annealing, even the ultrafine grained ferrite/austenite duplex structure with about 30% austenite could be obtained af- ter long time ART-annealing in all cases. Austenization in the intercritical region （between Ad and At3） gave a duplex structure after quenching, which was nearly not affected by followed annealing process. However, high temperature austenization （above A^3） resulted in a full martensite structure after quenching, which gradually transformed into a ferrite/austenite duplex structure during the following anneal- ing process. Based on the analysis of austenite fraction and carbon concentrate, it was found that not only carbon partitioning but also manganese paxtitioning in the austenite affected the stability of austenite and even dominated the development of lamellar ferrite and austenite duplex structure during intercritical annealing with different times. At last an austenite lath nucleation and thickening model was pro- posed to describe the microstructure evolution of medium mangenese steel during ART-annealing.
The microstructure deformation and fracture mechanisms of particulate-filled polymer composites were studied based on microstructure observations in this paper. By using in-situ tensile test system under scanning elec...
The microstructure deformation and fracture mechanisms of particulate-filled polymer composites were studied based on microstructure observations in this paper. By using in-situ tensile test system under scanning electron microscopy, three different composites composed of polymer binder filled by three different types of particles, namely Al particles, AP particles and HMX particles, with the same total filler content were tested. The roles of initial microstructure damage and particle type on the microstructure deformation and damage are highlighted. The results show that microstructure damage starts with the growth of the initial microvoids within the binders or along the binder/particle interfaces. With the increase of strain, the microstructure damages including debonding at the particle/binder interface and tearing of the binder lead to microvoid coalescence, and finally cause an abrupt fracture of the samples. Coarse particles lead to an increase of debonding at the particle/binder interface both in the initial state and during the loading process, and angular particles promote interface debonding during the loading process.
Supercritical carbon dioxide (ScCO2) foaming which is inexpensive and environmental friendly has been widely used to prepare polymer-based microporous materials. In this paper, PMMA graded microporous materials were f...
Supercritical carbon dioxide (ScCO2) foaming which is inexpensive and environmental friendly has been widely used to prepare polymer-based microporous materials. In this paper, PMMA graded microporous materials were foamed by PMMA matrix after an unstable saturation process which was done under supercritical condition of 28MPa and 50 °C. The scanning electron microscopy (SEM) was utilized to observe the morphology of the graded foam. A gas adsorption model was proposed to predict the graded gas concentration in the different region of the polymer matrix. The SEM results showed that the solid and foam region of the graded foam can be connected without laminated layers. With the increasing thickness position of the graded microporous foam, the cell size increased from 3.4 to 27.5 μm, while the cell density decreased from 1.04 × 109 to 1.96 × 107 cells/cm3. It also found that the gradient microporous structure of the foam came from graded gas concentration which was obtained in the initial saturation process.
The fabrication of polymeric foams with gradient density is a key to investigate the response of materials in quasi-isentropic loading. In this work, a non-traditional approach was proposed to fabricate the polymeric ...
The fabrication of polymeric foams with gradient density is a key to investigate the response of materials in quasi-isentropic loading. In this work, a non-traditional approach was proposed to fabricate the polymeric foam monolayer with designed density in a fixed volume by using the pre-mixture of expandable and expanded polymeric microballoons. After heating, the expandable microballoons expanded and bonded together to be integrated block with the final density from 0.1 g/cm3 to 0.5 g/cm3. The gradient density foams were fabricated by bonding with different monolayer. The microstructure and mechanical properties of each layer were investigated by SEM and compression strength tests. The results showed that the density of polymeric foams was matched with the design value very well by controlling the ratio of expandable and expanded polymeric microballoons. The uniform closed-cell structure with good bonding interface was shown from the SEM picture. And the mean cell size is less than 35μm. The polymeric foams exhibited ideal compressive behavior with the compressive strength as high as 9MPa. The Young's modulus and compressive strength nearly linear increased with the increasing of density. The extremely wide range of accessible densities should make this technology for broad application prospects.
The downgraded and upgraded BaZrxTi2−xO5 (x=0, 0.01, 0.02, 0.03 and 0.04) films normal to Pt/Ti/SiO2/Si substrates were prepared by sol-gel method. The microstructure and dielectric properties of the compositionally g...
The downgraded and upgraded BaZrxTi2−xO5 (x=0, 0.01, 0.02, 0.03 and 0.04) films normal to Pt/Ti/SiO2/Si substrates were prepared by sol-gel method. The microstructure and dielectric properties of the compositionally graded BaZrxTi2−xO5 films were investigated. The single-phase downgraded and upgraded films were obtained as the films were annealed at 900 °C for 30 min. The downgraded BaZrxTi2−xO5 film had dense surface, while there were pores in the surface of the upgraded BaZrxTi2−xO5 film. The thicknesses of both upgraded and downgraded BaZrxTi2−xO5 films were about 500 nm. The values of permittivity (r) for the downgraded and upgraded BaZrxTi2−xO5 films were 84 and 100, respectively, at 1 MHz.
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