Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality ...Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality between these 2 laser beam modes.The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample,despite 0.046%porosity generated.Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks.And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation.And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode,while pores were less detrimental to the mechanical properties than cracks.Therefore,the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.展开更多
In the field of power systems,insulating polymers have been found to have extensive applications due to their outstanding properties.However,these materials are susceptible to defects arising from various factors duri...In the field of power systems,insulating polymers have been found to have extensive applications due to their outstanding properties.However,these materials are susceptible to defects arising from various factors during production and operation,which may progress and potentially lead to safety incidents.This paper comprehensively reviews non-destructive testing(NDT)techniques for insulating polymers.Based on the physical principles underlying these methods,they are categorized into electrical testing methods,non-electrical passive testing methods,and non-electrical active testing methods.The paper offers a retrospective assessment of the applications of these methods in insulating polymers.Finally,evaluation of the applicability,advantages,and limitations of these diverse methods is systematically conducted,aiming to facilitate the targeted selection of the optimal NDT method in engineering applications.展开更多
Surge current(SC)capability is one of the main aspects of reliability for silicon carbide(SiC)power devices.In this work,the influences of neutron radiation‐induced defects on the SC capability and reliability of Si...Surge current(SC)capability is one of the main aspects of reliability for silicon carbide(SiC)power devices.In this work,the influences of neutron radiation‐induced defects on the SC capability and reliability of SiC P‐intrinsic‐N(PiN)diodes were comprehensively investigated.It was found that the surge capability of the diodes can be deteriorated even under the slightly enhanced formation of carbon‐vacancy‐related Z_(1/2) and EH_(6/7 )defects introduced by neutron irradiation.Surprisingly,it was found that the forward voltage(V_(F))decreases with the increased SC and the stress cycles in the irradiated diodes,which is usually found to in-crease under the SC tests and attributed to the bipolar degradation(BPD).By using technology computer‐aided design simulation and deep‐level transient spectroscopy characterization,it was found that the sig-nificant self‐heating during surge stress leads to the annealing effect on the Z_(1/2) defects through the promoted recombination with the nearest and second neighbor carbon interstitials injected by irradiation,which thus plays a dominant role in the decrease of VF over the BPD.展开更多
Damage points induced by 355 nm laser irradiation increase more quickly on the surface of fused silica in vacuum of about 10^-3 Pa than in atmospheric air at the same fluence. The larger concentration of point defects...Damage points induced by 355 nm laser irradiation increase more quickly on the surface of fused silica in vacuum of about 10^-3 Pa than in atmospheric air at the same fluence. The larger concentration of point defects in vacuum is confirmed by photoluminescence intensity. X-ray photoelectron spectroscopy and infrared absorption indicate the formation of sub-stoichiometric silica on the surface. The degradation mechanism of fused silica in vacuum is discussed.展开更多
基金financially supported by National Natural Science Foundation of China(No.91860131 and No.52074157)National Key Research and Development Program of China(No.2017YFB0702901)+1 种基金Shenzhen Science and Technology Innovation Commission under the Projects(No.JCYJ20170817111811303,No.KQTD20170328154443162 and ZDSYS201703031748354)joint Ph.D.program between SUSTech and UoB(No.FEFE/GAS1792)。
文摘Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality between these 2 laser beam modes.The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample,despite 0.046%porosity generated.Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks.And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation.And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode,while pores were less detrimental to the mechanical properties than cracks.Therefore,the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.
基金supported in part by the National Natural Science Foundation of China under Grant 51977117 and 51977118.
文摘In the field of power systems,insulating polymers have been found to have extensive applications due to their outstanding properties.However,these materials are susceptible to defects arising from various factors during production and operation,which may progress and potentially lead to safety incidents.This paper comprehensively reviews non-destructive testing(NDT)techniques for insulating polymers.Based on the physical principles underlying these methods,they are categorized into electrical testing methods,non-electrical passive testing methods,and non-electrical active testing methods.The paper offers a retrospective assessment of the applications of these methods in insulating polymers.Finally,evaluation of the applicability,advantages,and limitations of these diverse methods is systematically conducted,aiming to facilitate the targeted selection of the optimal NDT method in engineering applications.
基金National Natural Science Foundation of China,Grant/Award Number:12275244。
文摘Surge current(SC)capability is one of the main aspects of reliability for silicon carbide(SiC)power devices.In this work,the influences of neutron radiation‐induced defects on the SC capability and reliability of SiC P‐intrinsic‐N(PiN)diodes were comprehensively investigated.It was found that the surge capability of the diodes can be deteriorated even under the slightly enhanced formation of carbon‐vacancy‐related Z_(1/2) and EH_(6/7 )defects introduced by neutron irradiation.Surprisingly,it was found that the forward voltage(V_(F))decreases with the increased SC and the stress cycles in the irradiated diodes,which is usually found to in-crease under the SC tests and attributed to the bipolar degradation(BPD).By using technology computer‐aided design simulation and deep‐level transient spectroscopy characterization,it was found that the sig-nificant self‐heating during surge stress leads to the annealing effect on the Z_(1/2) defects through the promoted recombination with the nearest and second neighbor carbon interstitials injected by irradiation,which thus plays a dominant role in the decrease of VF over the BPD.
文摘Damage points induced by 355 nm laser irradiation increase more quickly on the surface of fused silica in vacuum of about 10^-3 Pa than in atmospheric air at the same fluence. The larger concentration of point defects in vacuum is confirmed by photoluminescence intensity. X-ray photoelectron spectroscopy and infrared absorption indicate the formation of sub-stoichiometric silica on the surface. The degradation mechanism of fused silica in vacuum is discussed.
