Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstruc...Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstructure using optical microscope, SEM, including EDS microanalysis, TEM and XRD. The results show that some equilibrium or non-equilibrium phases, such as γ-Co, Cr_(23)C_6, Y_2O_3 and ε-Co exist in the coatings. Fine and short dendritic microstructure and columnar to equiaxed transition (CET) occurred by adding nano-Y_2O_3 particles. With the increasing amount of nano-Y_2O_3 (1%, mass fraction), fully equiaxed crystallization appeared. These are caused by nano-Y_2O_3 particles acting as new nucleation site and rapid solidification of the melt. The results also show that inhomogeneous dispersion of nano-Y_2O_3 results in the formation of ε-Co phase in the coatings. The sub-microstructure of the clad is stacking fault. The mechanism of the formation of equiaxed grains is also analyzed.展开更多
Two different flow channel configurations on thermal resistances associated with the behavior of cooling of power device were studied in this paper. ANSYS Icepak 14.0 has been adopted as a numerical simulation tool. T...Two different flow channel configurations on thermal resistances associated with the behavior of cooling of power device were studied in this paper. ANSYS Icepak 14.0 has been adopted as a numerical simulation tool. The simulation results from this study showed that the shapes of channels in cooling radiator play an important role in the thermal management of water cooling radiation system. The optimal channel design could improve the heat- dissipating efficiency by 80% in water cooling radiation system. The result also indicated that the thermal resistance of heat sinks decreased with the volumetric flow rate and the number of cylindrical columns in the flow channel. Experimental results were obtained under certain channel configurations and volume rates. Moreover, the results of numerical simulation can be explained well by the experimental results.展开更多
A new computational fluid dynamics （CFD） method for the simulation of fast-axial-flow CO2 laser is developed. The model which is solved by CFD software uses a set of dynamic differential equations to describe the dy...A new computational fluid dynamics （CFD） method for the simulation of fast-axial-flow CO2 laser is developed. The model which is solved by CFD software uses a set of dynamic differential equations to describe the dynamic process in one discharge tube. The velocity, temperature, pressure and turbulence energy distributions in discharge passage are presented. There is a good agreement between the theoretical prediction and the experimental results. This result indicates that the parameters of the laser have significant effect on the flow distribution in the discharge passage. It is helpful to optimize the output of high power CO2 laser by mastering its kinetic characteristics.展开更多
We present a 2 μm Tm:YAG disk laser multi-pass pumped by a 1 μm laser. The transitions in competition of up conversion(UC) and excited state absorption(ESA) are analyzed in detail based on a numerical model that con...We present a 2 μm Tm:YAG disk laser multi-pass pumped by a 1 μm laser. The transitions in competition of up conversion(UC) and excited state absorption(ESA) are analyzed in detail based on a numerical model that considers stimulated emission, fluorescence, non-radiative decay, UC, and ESA, showing good agreement with experiments. The proportions and fractional thermal loads of all transitions are derived quantitatively. The results show that UC and ESA are critical in Tm:YAG disk lasers, resulting in a decrease in the absorbed pump power and temperature after lasing for two different disk thicknesses. In addition, although the absorbed pump power of the 0.5 mm disk is lower than in the1 mm case, its relatively weak UC and ESA and low total fractional thermal load can improve laser performance. A0.5 mm Tm:YAG disk laser thus delivered the maximum output power of 1.05 W with beam quality of M_(x)^(2)= 2.02 and M_(y)^(2)= 2.03.展开更多
文摘Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstructure using optical microscope, SEM, including EDS microanalysis, TEM and XRD. The results show that some equilibrium or non-equilibrium phases, such as γ-Co, Cr_(23)C_6, Y_2O_3 and ε-Co exist in the coatings. Fine and short dendritic microstructure and columnar to equiaxed transition (CET) occurred by adding nano-Y_2O_3 particles. With the increasing amount of nano-Y_2O_3 (1%, mass fraction), fully equiaxed crystallization appeared. These are caused by nano-Y_2O_3 particles acting as new nucleation site and rapid solidification of the melt. The results also show that inhomogeneous dispersion of nano-Y_2O_3 results in the formation of ε-Co phase in the coatings. The sub-microstructure of the clad is stacking fault. The mechanism of the formation of equiaxed grains is also analyzed.
文摘Two different flow channel configurations on thermal resistances associated with the behavior of cooling of power device were studied in this paper. ANSYS Icepak 14.0 has been adopted as a numerical simulation tool. The simulation results from this study showed that the shapes of channels in cooling radiator play an important role in the thermal management of water cooling radiation system. The optimal channel design could improve the heat- dissipating efficiency by 80% in water cooling radiation system. The result also indicated that the thermal resistance of heat sinks decreased with the volumetric flow rate and the number of cylindrical columns in the flow channel. Experimental results were obtained under certain channel configurations and volume rates. Moreover, the results of numerical simulation can be explained well by the experimental results.
文摘A new computational fluid dynamics （CFD） method for the simulation of fast-axial-flow CO2 laser is developed. The model which is solved by CFD software uses a set of dynamic differential equations to describe the dynamic process in one discharge tube. The velocity, temperature, pressure and turbulence energy distributions in discharge passage are presented. There is a good agreement between the theoretical prediction and the experimental results. This result indicates that the parameters of the laser have significant effect on the flow distribution in the discharge passage. It is helpful to optimize the output of high power CO2 laser by mastering its kinetic characteristics.
基金supported by the National Natural Science Foundation of China(NSFC,No.61975060)the Fundamental Research Funds for the Central University(HUST,No.2016YXMS213)。
文摘We present a 2 μm Tm:YAG disk laser multi-pass pumped by a 1 μm laser. The transitions in competition of up conversion(UC) and excited state absorption(ESA) are analyzed in detail based on a numerical model that considers stimulated emission, fluorescence, non-radiative decay, UC, and ESA, showing good agreement with experiments. The proportions and fractional thermal loads of all transitions are derived quantitatively. The results show that UC and ESA are critical in Tm:YAG disk lasers, resulting in a decrease in the absorbed pump power and temperature after lasing for two different disk thicknesses. In addition, although the absorbed pump power of the 0.5 mm disk is lower than in the1 mm case, its relatively weak UC and ESA and low total fractional thermal load can improve laser performance. A0.5 mm Tm:YAG disk laser thus delivered the maximum output power of 1.05 W with beam quality of M_(x)^(2)= 2.02 and M_(y)^(2)= 2.03.
