GaN powder of nanometer scale was prepared by metal organic chemical vapor deposition using diethylgallium azide as precursor. The resulting powder was characterized by XRD and TEM. It has been found that the particle...GaN powder of nanometer scale was prepared by metal organic chemical vapor deposition using diethylgallium azide as precursor. The resulting powder was characterized by XRD and TEM. It has been found that the particle size of the powder obtained is affected by the deposition temperature, and the fine crystals formed in temperature range 500 similar to 650 degrees C were hexagonal.展开更多
Electron beam selective melting （EBSM） is a promising additive manufacturing （AM） technology. The EBSM process consists of three major procedures：（1） spreading a powder layer, （2） preheating to slightly sinte...Electron beam selective melting （EBSM） is a promising additive manufacturing （AM） technology. The EBSM process consists of three major procedures：（1） spreading a powder layer, （2） preheating to slightly sinter the powder, and （3） selectively melting the powder bed. The highly transient multi-physics phenomena involved in these procedures pose a significant challenge for in situ experimental observation and measurement. To advance the understanding of the physical mechanisms in each procedure, we leverage high- fidelity modeling and post-process experiments. The models resemble the actual fabrication procedures, including （1） a powder-spreading model using the discrete element method （DEM）, （2） a phase field （PF） model of powder sintering （solid-state sintering）, and （3） a powder-melting （liquid-state sintering） model using the finite volume method （FVM）. Comprehensive insights into all the major procedures are provided, which have rarely been reported. Preliminary simulation results （including powder particle packing within the powder bed, sintering neck formation between particles, and single-track defects） agree qualitatively with experiments, demonstrating the ability to understand the mechanisms and to guide the design and optimization of the experimental setup and manufacturing process.展开更多
文摘GaN powder of nanometer scale was prepared by metal organic chemical vapor deposition using diethylgallium azide as precursor. The resulting powder was characterized by XRD and TEM. It has been found that the particle size of the powder obtained is affected by the deposition temperature, and the fine crystals formed in temperature range 500 similar to 650 degrees C were hexagonal.
文摘Electron beam selective melting （EBSM） is a promising additive manufacturing （AM） technology. The EBSM process consists of three major procedures：（1） spreading a powder layer, （2） preheating to slightly sinter the powder, and （3） selectively melting the powder bed. The highly transient multi-physics phenomena involved in these procedures pose a significant challenge for in situ experimental observation and measurement. To advance the understanding of the physical mechanisms in each procedure, we leverage high- fidelity modeling and post-process experiments. The models resemble the actual fabrication procedures, including （1） a powder-spreading model using the discrete element method （DEM）, （2） a phase field （PF） model of powder sintering （solid-state sintering）, and （3） a powder-melting （liquid-state sintering） model using the finite volume method （FVM）. Comprehensive insights into all the major procedures are provided, which have rarely been reported. Preliminary simulation results （including powder particle packing within the powder bed, sintering neck formation between particles, and single-track defects） agree qualitatively with experiments, demonstrating the ability to understand the mechanisms and to guide the design and optimization of the experimental setup and manufacturing process.
