Li_2O对SPS烧结AlN陶瓷致密化、显微结构和导热性的影响

Effects of Li_2O on Densification,Microstructure and Thermal Property of Spark Plasma Sintered AlN Ceramics

研究了低温烧结助剂Li2O对SPS烧结AlN陶瓷烧结致密化过程、烧结体显微结构和导热性的影响.研究表明:在SPS烧结过程中,烧结助剂Li2O和Sm2O3(或Y2O3)的加入使AlN试样开始收缩并进入烧结初期阶段的温度从1550℃左右下降到1200℃以下;同时Li2O使AlN试样的烧结温度显著降低,完全致密化温度降低到1650℃左右.烧结体的显微结构表明:Li2O的加入有助于形成润湿性良好的液相,促进AlN陶瓷的液相烧结;但不利于快速烧结坯体中气体的扩散与逸出,使试样的致密度受到影响.同时,Li2O影响AlN晶粒的发育,使液相润湿性提高,晶界相均匀分布,增加了晶粒界面上的声子散射,对AlN材料的热导率产生不利影响.同时,添加1.0wt%Li2O和1.5wt%Sm2O3的AlN试样的热导率低于仅添加1.5wt%Sm2O3的试样.

A newly developed rapid densify technique,spark plasma sintering（SPS）,is used to prepare full-densified aluminum nitride（AlN） ceramics which are poorly sinterable.Some sintering aids are also used to promote the AlN ceramics’ densification and improve its thermal conductivity.In this work,effects of sintering aid Li2O on densifica-tion,microstructure and thermal property of SPS sintered AlN ceramics were investigated.Results suggest that the ini-tial sintering temperature of AlN samples reduce from 1550℃ to lower than 1200℃ with 1.0wt% Li2O and 1.5wt% Sm2O3（or Y2O3） adding as sintering aids.With Li2O addition,AlN compacts can be fully densified at 1650℃.The microstructure of AlN compacts indicates that Li2O is beneficial to generate aluminate liquid phase with better wet-tability and promote the densification of AlN ceramics,but it is unable to obtain higher relative density of AlN com-pacts because the escapement of gas phase though out liquid phase is very difficult in a rapid sintering process.Meanwhile,Li2O addition affects the growth of AlN grains,and the better wettability of aluminate with AlN grain in-duces the homogeneous distribution of grain boundary phase.The deterioration of thermal conductivity of AlN ceram-ics is caused by the fact that the scattering of phonon is enhanced by small grain size and the secondary phase spreading adequately along the AlN grain boundaries.The thermal conductivity of AlN samples with 1.0wt% Li2O and 1.5wt%Sm2O3 as sintering aids is lower than that of sample only with Sm2O3 as sintering aids.