原料处理工艺及气孔演化对AZO靶材烧结致密化的影响

以ZnO和Al_2O_3粉体为原料,按照98∶2(质量比)球磨混合制备氧化锌铝(aluminum zinc oxide,AZO)粉体,通过扫描电镜和透射电镜观察粉体形貌及均匀性,确立最佳混合工艺;将混合均匀的粉体进行煅烧预处理后进行热压烧结致密化试验,通过差热法分析原料性能,阿基米德法分析靶材密度以及压汞实验分析气孔演化对AZO靶材烧结致密化的影响。结果表明:微纳米粉体在球磨4 hr时Al元素分布均匀性最好,煅烧前的混合粉体在差热分析过程中失重0.43%并伴随放热效应;煅烧处理后粉体形貌类球形,在差热分析实验0℃-1000℃无失重,表明挥发组分排除干净且无异常放热效应,烧结性能得到优化。采用预处理的AZO粉体在不同热压温度和保温时间下制备AZO靶材,分析热压致密过程中平均孔径和闭孔率的变化规律。由此发现:在热压致密化初级阶段(温度900℃~1100℃时),连通气孔发生合并与生长,平均孔径先稍有收缩随后迅速增大为158 nm,同时闭孔率维持在0.5%以下,靶材密度不断上升;当温度升高至1150℃时,连通孔径逐渐缩小至108 nm,大量连通气孔转为闭合状态导致闭孔率迅速上升至7.2%以上,表明体系已经进入到热压深度致密化阶段。在1150℃、18 MPa下,保温时间延长到70 min时,连通气孔合并生长同时闭孔率异常增加至7%,孔径分布范围变宽导致出现反致密化现象;当保温保压时间延长至90 min时,气孔尺寸减小到136 nm,闭孔率下降至3.7%,靶材相对密度上升到96.2%,在较低压力和较短保温时间下实现了AZO靶材的深度致密化。

Effect of raw material processing technology and pore evolution on hot-pressing densification of AZO target

Aluminum zinc oxide (AZO) are prepared by ball mill mixing with ZnO (98wt％) and Al2O3 (2wt％) powders. The morphology and uniformity of the powders are observed by SEM and TEM. The optimum mixing parameters is established. The mixed powders are calcined and hot pressing densification experiment is carried out. The density of target is measured by Archimedes method. The effect of raw material properties and pore evolution on hot-pressing densification of AZO target arestudied by differential thermal analysis and mercury intrusion porosimetry. The results are as follows: The uniformity of Al element distribution is best at 4hr ball mill mixing using the micro-nano powder. Before calcination, The powder (micro-nano mixed powder) loss 0.43％ weight accompanied by exothermic effect in the differential thermal analysis process. After the calcination treatment, the powdery morphology of the mixed powder is spherical and has no weight loss behavior, no exothermic effect during differential thermal analysis (0℃-1000℃). The results indicate that the volatile components are cleared during calcination. So the sintering performance of mixed powder are optimized. AZO targets are prepared using calcined powder at different hot pressing temperature and holding time. The change of average pore size and closed porosity are analyzed. It is found that pore size is slightly contracted and then increased rapidly to 158 nm with the increasing of temperature at the initial stage of hot pressing densification process (temperature 900℃ ～ 1100℃). At the same time, closed porosity remains below 0.5％ and target density continue to rise. When the temperature increase to 1150℃, the size of connected pore gradually reduced to 108 nm, a large number of connected pores close resulting in rapid increase of closed porosity (up to 7.2％) which indicate that the system has entered the deep densification stage of hot-pressing. When the holding time increase from 30min to 70min(temperature/1150℃, pressure/18 MPa), the size of connected pores merge to 230 nm and the closed porosity increase to 7％ abnormally while the pore size distribution is widened. This all lead to the phenomenon of anti -densification. When the holding time is extended to 90 min, the connected pore size is reduced to 136 nm while the closed porosity decrease to 3.7％.The relative density of this target increases to 96.2％, The deep densification of AZO target is achieved at lower pressure and shorter holding time using the calcined powder.