以YbH_(2)-MgO体系为烧结助剂制备高热导率高强度氮化硅陶瓷

Preparation of Silicon Nitride with High Thermal Conductivity and High Flexural Strength Using YbH_(2)-MgO as Sintering Additive

以YbH_(2)-MgO体系为烧结助剂,采用两步法烧结制备了高热导率高强度氮化硅陶瓷,研究了YbH_(2)-MgO对氮化硅致密化行为、相组成、微观形貌、热导率和抗弯强度的影响。在预烧结阶段,YbH_(2)在还原SiO_(2)的同时原位生成了Yb_(2)O_(3),进而形成“缺氧–富氮”液相。该液相不仅有利于晶粒的生长,更有利于阻碍晶格氧的生成,相较于Yb_(2)O_(3)-MgO助剂体系,β-Si_(3)N_(4)晶粒尺寸更大,晶格缺陷更少,低热导晶间相更少,在1900℃保温24 h后,热导率最优可达131.15 W·m^(–1)·K^(–1),较Yb_(2)O_(3)-MgO体系提升13.7%。用YbH_(2)代替Yb_(2)O_(3),在低温条件下烧结制备得到的氮化硅抗弯强度有所改善,在1800℃保温4 h的抗弯强度可达(1008±35)MPa;但在高温烧结时强度略有下降,这与微观结构的变化密切相关。研究表明,YbH_(2)-MgO体系是制备高热导率高强度氮化硅陶瓷的有效烧结助剂。

Silicon nitride with high thermal conductivity was obtained by two-step sintering method using YbH_(2)-MgO as sintering additive.The effect of YbH_(2)-MgO on shrinkage behavior,phase composition,microstruc-ture,thermal conductivity,and flexural strength was investigated.The nitrogen-riched and oxygen-lacked oxyni-tride liquid phase was generated owing to the elimination of SiO_(2) by YbH_(2).Both the removal of lattice oxygen and the growth of β-Si_(3)N_(4) were stimulated by the liquid phase.Therefore,compared to Yb_(2)O_(3)-MgO doped sample,silicon nitride with enlarged grains,purified lattice and reduced intergranular phase was obtained.Ultimately,its thermal conductivity increased by 13.7%from 115.32 to 131.15 W·m^(–1)·K^(–1) after sintering at 1900℃for 24 h by substituting Yb_(2)O_(3) with YbH_(2).Although the replacement of Yb_(2)O_(3) by YbH_(2) leads to enhanced flexural strength at low temperature,it tends to reduce the flexural strength at high temperature.The optimal flexural strength of(1008±35)MPa was achieved after sintering at 1800℃for 4 h.This variation related mainly to the exaggerated bimodal microstructure.This work signifies that YbH_(2)-MgO is effective for obtaining Si3N4 ceramics with both high flexural strength and high thermal conductivity.