RESUMEN
Film-type thermoelectric generator (TEG) utilizing Bi-Te based paste has been highly considered as advanced power sources for the wearable electronic devices due to its light, thin and flexible characteristics when producing electricity from certain thermal resources such as human body heat. However, the application of the film-typed TEG has been often limited due to its low TE conversion efficiency caused by low electrical conductivity resulting from severe porosity. Thus, it is crucial to increase electrical properties via densification of the TE film. Here, we synthesized silver nanoparticle (AgNP)-dispersed (Bi,Sb)2Te3 (BSbT) powders to fabricate AgNP-BSbT pastes by adding organic binder. The synthesized AgNP-BSbT pastes were printed through a hand-painting process and were consolidated into Ag-doped BSbT (Ag-BSbT) thick film with a few hundreds µm with controlled 2-step heat treatment. The microstructures of Ag-BSbT films show abnormally elongated grains but also the amount of porosities in the film significantly decreased by addition of AgNP. As a result, it is confirmed that the 0.072 at% Ag-BSbT thick film exhibits power factor of 2.93 × 10-3 W/mK² at room temperature, which is comparable to that of practically utilized bulk materials. It is elucidated that the increase in power factor originates from the modulation between electrical conductivity and Seebeck coefficients due to increased hole carrier density at room temperature.
RESUMEN
The triboelectric nanogenerator (TENG) has been attracting attention for electronic devices and sensors consuming low power. Among the few operating modes of the TENG, the rotation-based TENG provides a more continuous and smoother output than the linear-motion-based TENG. To evaluate the output performance of the rotation-based TENG precisely and quantitatively, a test bed that adjusts the eccentricity error, tilt angle error, contact force, and rotational speed is proposed. The test bed includes a motor, torque sensor, 2-axis planar stage, 2-axis tilting stage, 1-axis vertical stage, 3-degree-of-freedom force/torque (3-DOF F/T) sensor, and voice coil actuator. With the proposed test bed, the effects of the eccentricity error, tilt angle error, contact force, and rotational speed on the electrical output performance of the rotation-based TENG are analyzed. The test bed is expected to be used for quantitative performance analysis and comparative study of various rotation-based TENGs, and it can help improve the performance and reliability of rotation-based TENGs.
RESUMEN
The correlation between microstructure and tensile properties of selective laser melting (SLM) processed STS 316L and Inconel 718 were investigated at various heights (top, middle and bottom) and planes (YZ, ZX and XY). Columnar grains and dendrites were formed by directional growth during solidification. The average melt pool width and depth, and scan track width were similar in both specimens due to fixed processing parameters. SLM Inconel 718 has moderate tensile strength (1165 MPa) and tensile elongation (11.5%), whereas SLM STS 316L has outstanding tensile strength (656 MPa) and tensile elongation (75%) compared to other SLM processed STS 316L. Fine columnar diameter (0.5 µm) and dense microstructures (porosity: 0.35%) in SLM STS 316L promoted the enhancement of tensile elongation by suitable processing condition. Fractographic analysis suggested that the lack of fusion pore with unmelted powder should be avoided to increase tensile properties by controlling processing parameters.
RESUMEN
Small objects of an alloy tool steel were built by selective laser melting at different scan speeds, and their microstructures were analyzed using electron backscatter diffraction (EBSD). To present an explicit correlation with the local thermal cycles in the objects, prior austenite grains were reconstructed using the EBSD mapping data. Extensive growth of austenitic grains after solidification could be detected by the disagreement between the networks of carbides and austenite grain boundaries. A rapid laser scan at 2000 mm/s led to less growth, but retained a larger amount of austenite than a slow one at 50 mm/s. The rapid scan also exhibited definite evolution of Goss-type textures in austenite, which could be attributed to the growth of austenitic grains under a steep temperature gradient. The local variations in the microstructures and the textures enabled us to speculate the locally different thermal cycles determined by the different process conditions, that is, scan speeds.