A high-entropy(Ti Zr Nb Ta Mo)C ceramic has been successfully fabricated by hot pressing the newlysynthesized quinary carbide powder to investigate its microstructure and mechanical properties.The carbothermal reducti...A high-entropy(Ti Zr Nb Ta Mo)C ceramic has been successfully fabricated by hot pressing the newlysynthesized quinary carbide powder to investigate its microstructure and mechanical properties.The carbothermal reduction process of equimolar quinary metallic oxides at 1500℃for 1 h generates a carbide powder mixture,which consists mainly of Ta C-and Zr C-based solid solutions.The as-synthesized powder was then sintered to form a single-phase high-entropy ceramic by a two-step hot pressing at 1850℃for1 h and 2100℃for 0.5 h,respectively.The high-entropy ceramic exhibits a fine grain size of about 8.8μm,a high compositional uniformity and a high relative density of 98.6%by adding Mo as the strategic main component.The measured nanohardness values of(TiZrNbTaMo)C ceramic are 25.3 GPa at 9.8 N and 31.3 GPa at 100 m N,respectively,which are clearly higher than those of other available high-entropy carbide ceramics.展开更多
The article reviews the present state of the art in the magnetron sputtering of hart and superhard nanocomposite coatings. It is shown that there are (1) two gr oups of hard and superhard nanocomposites: (i) nc-MN/har...The article reviews the present state of the art in the magnetron sputtering of hart and superhard nanocomposite coatings. It is shown that there are (1) two gr oups of hard and superhard nanocomposites: (i) nc-MN/hard phase and (ii) nc-MN/s oft phase, (2) three possible origins of the enhanced hardness: (i) dislocation- dominated plastic deformation, (ii) cohesive forces between atoms and (iii) nano structure of materials, and (3) huge differences in the microstructure of single - and two-phase films. A main attention is devoted to the formation of nanocryst alline and/or X-ray amorphous films. Such films are created in a vicinity of tra nsitions between (i) crystalline and amorphous phases, (ii) two crystalline phas es of different chemical composition or (iii) two different preferred orientatio ns of grains of the same material from which the coating is composed. The existe nce of the last transition makes it possible to explain the enhanced hardness in single-phase films. The thermal stability and oxidation resistance of hard nano composite films is also shortly discussed.展开更多
基金supported financially by the National Natural Science Foundation of China(Nos.51602074,51872061,51532006 and 51621091)the Natural Science Foundation of Heilongjiang Province(No.E2016026)+1 种基金the China Postdoctoral Science Foundation(No.2016 M600246)the Heilongjiang Postdoctoral Foundation(No.LBH-Z16084).
文摘A high-entropy(Ti Zr Nb Ta Mo)C ceramic has been successfully fabricated by hot pressing the newlysynthesized quinary carbide powder to investigate its microstructure and mechanical properties.The carbothermal reduction process of equimolar quinary metallic oxides at 1500℃for 1 h generates a carbide powder mixture,which consists mainly of Ta C-and Zr C-based solid solutions.The as-synthesized powder was then sintered to form a single-phase high-entropy ceramic by a two-step hot pressing at 1850℃for1 h and 2100℃for 0.5 h,respectively.The high-entropy ceramic exhibits a fine grain size of about 8.8μm,a high compositional uniformity and a high relative density of 98.6%by adding Mo as the strategic main component.The measured nanohardness values of(TiZrNbTaMo)C ceramic are 25.3 GPa at 9.8 N and 31.3 GPa at 100 m N,respectively,which are clearly higher than those of other available high-entropy carbide ceramics.
基金This work was supported in part by the Ministryof the Education of the Czech Republic(No.MSM#234200002)and in part by the goverment of the Czech Republic and Japan under Intermational Projects KONTAKT Czech Republic-Japan ME#173 and ME#529.
文摘The article reviews the present state of the art in the magnetron sputtering of hart and superhard nanocomposite coatings. It is shown that there are (1) two gr oups of hard and superhard nanocomposites: (i) nc-MN/hard phase and (ii) nc-MN/s oft phase, (2) three possible origins of the enhanced hardness: (i) dislocation- dominated plastic deformation, (ii) cohesive forces between atoms and (iii) nano structure of materials, and (3) huge differences in the microstructure of single - and two-phase films. A main attention is devoted to the formation of nanocryst alline and/or X-ray amorphous films. Such films are created in a vicinity of tra nsitions between (i) crystalline and amorphous phases, (ii) two crystalline phas es of different chemical composition or (iii) two different preferred orientatio ns of grains of the same material from which the coating is composed. The existe nce of the last transition makes it possible to explain the enhanced hardness in single-phase films. The thermal stability and oxidation resistance of hard nano composite films is also shortly discussed.
