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.
Formability, microstructure and mechanical properties of Ti-6Al-4V deposited by wire and arc additive manufacturing with different deposition paths
Abstract By means of wire and arc additive manufacturing (WAAM) in an inert environment, the Ti-6Al-4V thin-wall parts were fabricated. To explore the effect of different deposition paths of WAAM on formability, microstructure and mechanical properties, the samples were analyzed by surface profiler, optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers hardness and universal testing machine. The results indicate that the side surface waviness (SW) of the samples from samples by reciprocating deposition path in both ends are higher than those in the middle, but SW of the samples by co-directional deposition path gradually rise from arc starting to arc stopping. Prior-β grains from the samples by co-directional deposition path are inclined relative to the building direction, and there are many winding prior-β grains in the samples by reciprocating deposition path. In the vertical direction, the strength of samples by co-directional deposition path is higher than those by reciprocating deposition path. Furthermore, the microstructure around the white band structure consists of fine basket-weave, colony α and coarse basket-weave in sequence from top to bottom. The white band region is a slight hardness drop (~20 HV0.2), but it has almost no effect on tensile strength.
Studies on root enamel (2). Enamel pearls. A review of their morphology, localization, nomenclature, occurrence, classification, histogenesis and incidence.
Enamel pearls are one of a number of different enamel structures that can be found on the roots of deciduous and permanent teeth. They have a distinct predilection for the furcation areas of molar teeth, particularly the maxillary third and second molars. They can consist primarily of enamel, but in most instances, a core of dentin is contained within them. On rare occasions, even pulpal tissues can be found. Enamel pearls usually occur singularly, but up to 4 enamel pearls have been observed on the same tooth. Depending on the study, enamel pearls on permanent molar teeth have an incidence rate of between 1.1%-9.7% with distinct differences among racial and national groups. The incidence of enamel pearls increases greatly in histological studies, suggesting that they are often obscured by a covering of cementum.