The Flexural Strength and Fracture Toughness of TC4-Based Laminated Composites Reinforced with Ti Aluminide and Carbide
TiC–Ti–Al mixed powders and TC4 titanium alloy foils were overlapped layer-by-layer in the graphite die. The TC4-based laminated composite sheets reinforced by Ti aluminide and carbide were successfully fabricated via spark plasma sintering (SPS) at 1100 °C with a well-bonded interface. The composite layers were mainly composed of TiAl, Ti3Al, Ti2AlC, and Ti3AlC2 phases. The carbides particles distributed in the matrix played an important role in the deflection of cracks and the passivation of microcracks. TC4 titanium alloy layers had an obvious effect on the stress distribution during the loading process, and provided an energy dissipation mechanism, which could improve the mechanical properties of the laminated composite sheets obviously. When the theoretical amount of Ti2AlC was 20 wt %, the flexural strength and fracture toughness of the laminated composite sheets reached the maximum value in the arrester direction, which were 1428.79 MPa and 64.08 MPa·m1/2, respectively.
Nature-inspired nacre-like Ti6Al4V-(Ti2AlC/TiAl) laminate composites combining appropriate strength and toughness with synergy effects
Abstract Nacre, a biomimetic model system with multiscale architectures and adjustable components, has always inspired researchers to create novel materials with advantages such as light-weight, exceptional strength and toughness. Inspired by nature, nacre-like bionic Ti2AlC/TiAl–Ti6Al4V laminated composite sheets had been designed and fabricated by spark plasma sintering technology using commercial Ti6Al4V as the toughening layers and Ti–Al–TiC reaction system as the composite layers. The phase compositions and structural characteristics of the composite sheets were characterized by XRD, SEM and EDS. In addition, the mechanical properties at room temperature were also measured. The results indicated that a Ti3Al interfacial layer was formed between the composite layer and the toughening layer, meanwhile the compositions of the composite layer were composed of TiAl, Ti3Al, Ti2AlC and a small amount of TiC. It's noteworthy that the Ti2AlC/TiAl–Ti6Al4V laminated composite sheets showed a significant increase in toughness while maintaining or improving strength even with holes in the sheets, in comparison with monolithic TiAl. When the loading direction was perpendicular to the laminated structure, the flexural strength and fracture toughness of the composite sheet with 20 wt% Ti2AlC reached good comprehensive values, which were up to 564.86 MPa and 39.15 MPa m1/2, respectively. The particles-reinforced composite layers and laminated structure design not only affected the crack propagation, but also cooperated with each other leading to a complex deflection and expansion behavior, which consumed the fracture energy and improved the overall mechanical properties of the composite sheets.
The peculiar thermo-structural behavior of the anionic lipid DMPG.
Aqueous dispersions of the anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG), around 100 mM ionic strength, are known to exhibit a thermal behavior similar to that of the largely studied lipid dimyristoyl phosphatidylcholine (DMPC), which undergoes a gel to liquid crystalline phase transition at 23 degrees C, well characterized by differential scanning calorimetry (DSC), and other methods. However, at low ionic strength, DMPG has been shown to present a large gel-fluid transition region, ranging from 18 to 35 degrees C. This intermediate phase is optically transparent and characterized by a continuous change in membrane packing. Structural properties of the DMPG gel-fluid transition region will be discussed, based on results obtained by several techniques: electron spin resonance (ESR) of spin labels at the membrane surface and intercalated at different depths in the bilayer; light scattering; DSC; small angle X-ray scattering (SAXS); and fluorescence spectroscopy of probes in the bilayer.