ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-syn...ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.展开更多
Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good abla...Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good ablation resistance and low neutron absorption cross-section.Nevertheless,low sinterability of ZrC powders and poor fracture toughness and reliability of bulk ceramics limit their wide applications in extreme environments.This paper reviews the state of the art of preparation and properties of ZrC composites.Optimizing the sintering process and tailoring the chemical constituents of raw powders and sintering aids could improve sinterability to produce dense bulk ceramics.Different additives such as refractory metals,carbides,silicides,oxides,or carbon fibers are introduced into the ZrC matrix in order to improve fracture toughness,oxidation resistance or thermal shock resistance,etc.Further studies are needed to explore the effects of intrinsic defects（vacancies,dislocations,and grain or phase boundaries,etc.） and additives on microstructure and properties at elevated temperatures.展开更多
大数据和人工智能应用在数据处理过程中面临数据安全和隐私保护的问题,而MindSpore框架的MindArmour模块包含的安全技术提供了相关解决方案。首先,对MindArmour模块的对抗样本、隐私泄漏风险评估、AI Fuzzer技术和模型加密保护等功能进...大数据和人工智能应用在数据处理过程中面临数据安全和隐私保护的问题,而MindSpore框架的MindArmour模块包含的安全技术提供了相关解决方案。首先,对MindArmour模块的对抗样本、隐私泄漏风险评估、AI Fuzzer技术和模型加密保护等功能进行解构。其次,分析对抗攻防和成员推理相关算法。最后,使用fuzz_testing测试LeNet模型,采用Accuracy、Accuracy after attacking和Neural_coverage_KMNC三种评价指标以及生成图的变异效果,检验了MindArmour模块的可靠性。展开更多
基金Funded by the National Natural Science Foundation of China(Nos.52002003 and 52002098)Natural Science Foundation of Anhui Province,China(No.2008085QE196)Open Fund of Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials(Anhui University of Technology),Ministry of Education(No.GFST2020KF09)。
文摘ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.
基金Financial supports from the National Natural Science Foundation of China ( Nos. 51172052 and 51321061 )Program for New Century Excellent Talents in University ( No. NCET 13 - 0177)
文摘Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good ablation resistance and low neutron absorption cross-section.Nevertheless,low sinterability of ZrC powders and poor fracture toughness and reliability of bulk ceramics limit their wide applications in extreme environments.This paper reviews the state of the art of preparation and properties of ZrC composites.Optimizing the sintering process and tailoring the chemical constituents of raw powders and sintering aids could improve sinterability to produce dense bulk ceramics.Different additives such as refractory metals,carbides,silicides,oxides,or carbon fibers are introduced into the ZrC matrix in order to improve fracture toughness,oxidation resistance or thermal shock resistance,etc.Further studies are needed to explore the effects of intrinsic defects（vacancies,dislocations,and grain or phase boundaries,etc.） and additives on microstructure and properties at elevated temperatures.
文摘大数据和人工智能应用在数据处理过程中面临数据安全和隐私保护的问题,而MindSpore框架的MindArmour模块包含的安全技术提供了相关解决方案。首先,对MindArmour模块的对抗样本、隐私泄漏风险评估、AI Fuzzer技术和模型加密保护等功能进行解构。其次,分析对抗攻防和成员推理相关算法。最后,使用fuzz_testing测试LeNet模型,采用Accuracy、Accuracy after attacking和Neural_coverage_KMNC三种评价指标以及生成图的变异效果,检验了MindArmour模块的可靠性。
