Microstructural evolution and wear performance of Tantalum (Ta) treated by ultrasonic nanocrystalline surface modification (UNSM) at 25 and 1000 °C were reported. The UNSM treatment modified a surface along with subsurface layer with a thickness in the range of 20 to 150 µm, which depends on the UNSM treatment temperature, via the surface severe plastic deformation (S2PD) method. The cross-sectional microstructure of the specimens was observed by electron backscattered diffraction (EBSD) in order to confirm the microstructural alteration in terms of effective depth and refined grain size. The surface hardness measurement results, including depth profile, revealed that the hardness of the UNSM-treated specimens at both temperatures was increased in comparison with those of the untreated ones. The increase in UNSM treatment temperature led to a further increase in hardness. Moreover, both the UNSM-treated specimens with an increased hardness resulted in a higher resistance to wear in comparison with those of the untreated ones under dry conditions. The increase in hardness and induced compressive residual stress that depend on the formation of severe plastically deformed layer with the refined nano-grains are responsible for the enhancement in wear resistance. The findings of this study may be implemented in response to various industries that are related to strength improvement and wear enhancement issues of Ta.
A membrane humidifier is a device to provide water vapor into the proton exchange membrane fuel cell stack that is used for transportation application due to global warming. Since inadequate humidification severely affects the performance and durability of a fuel cell stack, it is necessary to equip the humidifier for delivery humidification into the fuel cell vehicle.
In this study, the performance of humidification in hollow fiber membrane is investigated. While the test section is exposed to external humidity condition, dry air is provided through hollow fiber membrane so that the water transport is facilitated. Since various parameters can change the performance, the performance investigation has to be carried out with parameters. In this study the water transport of hollow fiber membrane is investigated in terms of principle operating conditions such as temperature, pressure, and flow rate.
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