YF3/氧化物烧结助剂对碳化硅陶瓷热导率的影响

利用YF3/氧化物体系作为烧结助剂热压烧结碳化硅陶瓷,研究了此体系中氧化物的种类、含量对样品的致密度、导热性能、物相成分、微观形貌的影响.实验结果表明,在烧结温度1900 ℃、压力50 MPa条件下,YF3/氧化物体系烧结助剂对碳化硅陶瓷热导率有所提升,其中同时添加5wt;YF3+3wt;MgO双相烧结助剂的SiC陶瓷性能最优,其致密度为98.93;,热扩散系数为71.40 mm2/s,热导率为154.29 W/(m· K).     

Abnormal breakdown of Stokes–Einstein relation in liquid aluminium

We present the results of systematic molecular dynamics simulations of pure aluminium melt with a well-accepted embedded atom potential. The structure and dynamics were calculated over a wide temperature range, and the calculated results(including the pair correlation function, self-diffusion coefficient, and viscosity) agree well with the available experimental observations. The calculated data were used to examine the Stokes–Einstein relation(SER). The results indicate that the SER begins to break down at a temperature T_x(~1090 K) which is well above the equilibrium melting point(912.5 K).This high-temperature breakdown is confirmed by the evolution of dynamics heterogeneity, which is characterised by the non-Gaussian parameter α_2(t). The maximum value of α 2(t), α_(2,max), increases at an accelerating rate as the temperature falls below Tx. The development of α_(2,max) was found to be related to the liquid structure change evidenced by local fivefold symmetry. Accordingly, we suggest that this high-temperature breakdown of SER has a structural origin. The results of this study are expected to make researchers reconsider the applicability of SER and promote greater understanding of the relationship between dynamics and structure.     

Cr8型模具钢耐磨性能研究

在环/块对摩型磨损试验机上对比测试了不同载荷下4种Cr8型模具钢的干滑动磨损性能,测量磨痕宽度,观察磨损形貌,分析磨损机制.结果表明:不同载荷下均有磨粒磨损,随载荷增大氧化加剧并伴有粘附磨损,高载荷下氧化磨损的作用变大;磨损损失体积随载荷增加而增大,磨损损失体积总量与M7C3共晶碳化物量呈正线性关系:摩擦系数随载荷增加先升高后下降.