Aiming to achieve silicon nitride( Si_(3)N_(4))ceramics with high hardness and high toughness,the relationships among phase composition,microstructure,and mechanical properties of Si_(3)N_(4) ceramics prepared by spar...Aiming to achieve silicon nitride( Si_(3)N_(4))ceramics with high hardness and high toughness,the relationships among phase composition,microstructure,and mechanical properties of Si_(3)N_(4) ceramics prepared by spark plasma sintering(SPS)at temperatures ranging from 1500 to 1800℃were investigated in this study.Two stages with different phase and microstructure features were observed and summarized.Theα-βphase transformation occurs first,and the development and growth of grains lag behind.During the first stage,the average grain size remains basically unchanged,and the hardness maintains at a value of~20.18±0.26 GPa,despite theβ- Si_(3)N_(4) phase fraction increases from 7.67 to 57.34 wt%.Subsequently,the equiaxed grains transform into rod-like grains with a high aspect ratio via the reprecipitation process,resulting in a significant increase in the fracture toughness from 3.36±0.62 to 7.11±0.15 MPa·m^(1/2).In the second stage of sintering process,the fraction ofβ- Si_(3)N_(4) phase increases to 100.00 wt%,and the grain growth also rapidly occurs.Thus,the fracture toughness increases slightly to 7.61±0.42 MPa·m^(1/2),but the hardness reduces to 16.80±0.20 GPa.The current results demonstrate that the phase contents ofβ- Si_(3)N_(4) and the microstructure shall be carefully tailored to achieve high-performance Si_(3)N_(4) ceramics. Si_(3)N_(4) ceramics with a finegrained bimodal microstructure,consisting of the mainα-andβ-phases,can exhibit the optimized combination of hardness and toughness.展开更多
Chromosomes, the longest molecular fiber that stores genetic information in eukaryotic cells, must be orderly packaged during mitosis for their proper segregation into daughter cells. Although the morphological change...Chromosomes, the longest molecular fiber that stores genetic information in eukaryotic cells, must be orderly packaged during mitosis for their proper segregation into daughter cells. Although the morphological changes of chromosomes during mitosis have been described in detail, how mitosis progression programs the transformation of seemingly amorphous and loose interphase .展开更多
基金supported by the Shandong Provincial Key Research and Development Program (2019JZZY010330)the National Natural Science Foundation of China (52172066 and 52172064)+3 种基金the Key Research and Development Project of Gansu Province (21YF5WA140)the Science and Technology Program of Guangzhou (201704030095)Shi-Kuan Sun acknowledges the Guangdong Key Platform&Programs of the Education Department of Guangdong Province (2021ZDZX1003)the Opening Project of State Key Laboratory of High Performance Ceramics and Superfine Microstructure (SKL202104SIC).
文摘Aiming to achieve silicon nitride( Si_(3)N_(4))ceramics with high hardness and high toughness,the relationships among phase composition,microstructure,and mechanical properties of Si_(3)N_(4) ceramics prepared by spark plasma sintering(SPS)at temperatures ranging from 1500 to 1800℃were investigated in this study.Two stages with different phase and microstructure features were observed and summarized.Theα-βphase transformation occurs first,and the development and growth of grains lag behind.During the first stage,the average grain size remains basically unchanged,and the hardness maintains at a value of~20.18±0.26 GPa,despite theβ- Si_(3)N_(4) phase fraction increases from 7.67 to 57.34 wt%.Subsequently,the equiaxed grains transform into rod-like grains with a high aspect ratio via the reprecipitation process,resulting in a significant increase in the fracture toughness from 3.36±0.62 to 7.11±0.15 MPa·m^(1/2).In the second stage of sintering process,the fraction ofβ- Si_(3)N_(4) phase increases to 100.00 wt%,and the grain growth also rapidly occurs.Thus,the fracture toughness increases slightly to 7.61±0.42 MPa·m^(1/2),but the hardness reduces to 16.80±0.20 GPa.The current results demonstrate that the phase contents ofβ- Si_(3)N_(4) and the microstructure shall be carefully tailored to achieve high-performance Si_(3)N_(4) ceramics. Si_(3)N_(4) ceramics with a finegrained bimodal microstructure,consisting of the mainα-andβ-phases,can exhibit the optimized combination of hardness and toughness.
文摘Chromosomes, the longest molecular fiber that stores genetic information in eukaryotic cells, must be orderly packaged during mitosis for their proper segregation into daughter cells. Although the morphological changes of chromosomes during mitosis have been described in detail, how mitosis progression programs the transformation of seemingly amorphous and loose interphase .
