Refractory high-entropy alloys(RHEAs)are considered to be a promising candidate for elevated temper-ature applications.Nanocrystalline(NC)RHEAs are supposed to exhibit many different high-temperature mechanical behavi...Refractory high-entropy alloys(RHEAs)are considered to be a promising candidate for elevated temper-ature applications.Nanocrystalline(NC)RHEAs are supposed to exhibit many different high-temperature mechanical behaviors in comparison with their coarse-grained(CG)and ultrafine-grained(UFG)counter-parts.However,the creep behaviors of NC RHEAs,which must be well evaluated for high-temperature applications,are largely unknown because it is difficult to produce bulk quantities of NC RHEAs for creep tests.In the present work,an equiatomic bulk NC VNbMoTaW RHEA with an average grain size of 67±17 nm was synthesized by mechanical alloying(MA)and the subsequent high-pressure/high-temperature sintering.The creep tests were performed on bulk specimens by compression at high tem-peratures(973 and 1073 K)under different stresses(70-1100 MPa).The creep resistance of the bulk NC VNbMoTaW is slightly lower than that of the bulk CG VNbMoTaW,but much higher than that of previ-ously reported CG and UFG HEAs.The derived activation volume,stress exponent,and activation energy of bulk NC VNbMoTaW indicate that the creep deformation is dominated by grain boundary diffusion.The creep deformation is controlled by the diffusion of Mo and Nb elements,which have the two slowest grain boundary diffusivities among the five alloying elements.The present work provides a fundamental understanding of the creep behavior and deformation mechanism of NC RHEAs,which should help design advanced creep-resistant RHEAs.展开更多
With the development of agricultural technology to meet the growing demands of a rapidly increasing population and economic development,intensive agriculture practices have been widely adopted globally. However,this i...With the development of agricultural technology to meet the growing demands of a rapidly increasing population and economic development,intensive agriculture practices have been widely adopted globally. However,this intensification has resulted in adverse consequences for soil structure due to intensified farming activities and increased usage of heavy farm machinery.Of particular concern is soil compaction, which leads to the degradation of physical, chemical and biological properties of the soil. Soil compaction negatively impacts crop growth, reduces yields and poses a significant threat to food security and the overall sustainability of agricultural systems.Recognizing these challenges, this review aims to deepen understanding of the factors contributing to soil compaction and to develop effective mitigation strategies. By doing so, it is intended to attenuate the adverse impacts of soil compaction, improve soil structure, increase crop yield and ultimately enhance the sustainability of agricultural practices.展开更多
基金This work was supported by the National Natural Science Foun-dation of China(Nos.11935004 and 51971195)the High-Level Tal-ents Research Program of the Yanshan University(No.606001101)+1 种基金the Youth Fund Project of Science and Technology Research of Hebei Province(No.QN2020210)the Natural Science Founda-tion of Hebei Province(Nos.E2019203465 and B2020203037).
文摘Refractory high-entropy alloys(RHEAs)are considered to be a promising candidate for elevated temper-ature applications.Nanocrystalline(NC)RHEAs are supposed to exhibit many different high-temperature mechanical behaviors in comparison with their coarse-grained(CG)and ultrafine-grained(UFG)counter-parts.However,the creep behaviors of NC RHEAs,which must be well evaluated for high-temperature applications,are largely unknown because it is difficult to produce bulk quantities of NC RHEAs for creep tests.In the present work,an equiatomic bulk NC VNbMoTaW RHEA with an average grain size of 67±17 nm was synthesized by mechanical alloying(MA)and the subsequent high-pressure/high-temperature sintering.The creep tests were performed on bulk specimens by compression at high tem-peratures(973 and 1073 K)under different stresses(70-1100 MPa).The creep resistance of the bulk NC VNbMoTaW is slightly lower than that of the bulk CG VNbMoTaW,but much higher than that of previ-ously reported CG and UFG HEAs.The derived activation volume,stress exponent,and activation energy of bulk NC VNbMoTaW indicate that the creep deformation is dominated by grain boundary diffusion.The creep deformation is controlled by the diffusion of Mo and Nb elements,which have the two slowest grain boundary diffusivities among the five alloying elements.The present work provides a fundamental understanding of the creep behavior and deformation mechanism of NC RHEAs,which should help design advanced creep-resistant RHEAs.
基金supported by the Yunnan Science and Technology Program (202202AE090034)the National Key R&D Program of China (2021YFD1901002-5, 2022YFD1901504-2) to Kemo Jin+2 种基金supported by the Sichuan Science and Technology Program (2022YFQ0091) to Xiaoyan Tangsupported by the National Natural Science Foundation of China (31800378)the National Science and Technology Basic Resources Survey Program of China (2019FY101304) to Baoru Sun。
文摘With the development of agricultural technology to meet the growing demands of a rapidly increasing population and economic development,intensive agriculture practices have been widely adopted globally. However,this intensification has resulted in adverse consequences for soil structure due to intensified farming activities and increased usage of heavy farm machinery.Of particular concern is soil compaction, which leads to the degradation of physical, chemical and biological properties of the soil. Soil compaction negatively impacts crop growth, reduces yields and poses a significant threat to food security and the overall sustainability of agricultural systems.Recognizing these challenges, this review aims to deepen understanding of the factors contributing to soil compaction and to develop effective mitigation strategies. By doing so, it is intended to attenuate the adverse impacts of soil compaction, improve soil structure, increase crop yield and ultimately enhance the sustainability of agricultural practices.
