Papers by Keyword: AlN Ceramic

Abstract: Heat treatment is an effective means of structural adjustment and performance improvement of AlN ceramics. AlN ceramics prepared at high pressure with Y2O3 as a sintering aids were heat treated in a nitrogen flow atmosphere. The effects of heat treatment on microstructure and thermal conductivity of AlN ceramics were studied. The results show that the grain size of the AlN ceramics heat-treated at 970 °C for 2 h is significantly increased, the actual crystal morphology is realistic and the second phases are almost present at the grain boundaries or triple pockets compared with the samples without heat treatment, which thermal conductivity has reached 156.7 W/(m·K) from 77.3 W/(m·K). However, the pore size of AlN ceramics is increased and there is the phenomenon of anti-densification while the heat treatment time is extended to 4 h. The thermal conductivity of AlN ceramics heat-treated at 970 °C for 4 h is reduced to 92.6 W/(m·K).

Abstract: AlN ceramics were prepared by hot-pressing process with Y(NO3)3·6H2O as a sintering additive. Microstructure and mechanical properties of sintered AlN ceramics were measured and compared with that of monolithic AlN ceramic prepared by the same process. The results showed that the density and mechanical properties of monolithic AlN ceramics were drastically enhanced by adding Y(NO3)3·6H2O. Especially, the AlN ceramic with 3.24 wt% Y(NO3)3·6H2O (2 wt% Y2O3) displayed striking enhancement in mechanical propertie. However, such enhancement did not follow a consistent behavior with the increase of Y(NO3)3·6H2O content. A significant drop present at contents over inflection point (3.24 wt% Y(NO3)3·6H2O).

Abstract: Effect of adding up to 5wt% CaF2 on the densification and microstructural development of hot pressed aluminum nitride (AlN) was investigated. SEM investigation showed that the grain size of the sintered sample decreases with the increasing content of CaF2. Secondary-phase evolution paths converge from CA6 to CA phase above 1650°C. TEM micrographs showed that formed secondary phases could evaporate from sintered bodies at higher temperatures in the carbon-containing nitrogen atmosphere and the residuals were mainly distributed at triple grain junctions, keeping direct connections of AlN grains. Translucnet AlN ceramics were prepared using CaF2 additive sintered at 1850°C for 5 h.

Abstract: AlN ceramics doped with yttrium oxide (Y2O3) as the sintering additive were prepared via the spark plasma sintering (SPS) technique. The sintering behaviors and densification mechanism were mainly investigated. The results showed that Y2O3 addition could promote the AlN densification. Y2O3-doped AlN samples could be densified at low temperatures of 1600-1700oC in 20-25 minutes. The AlN samples were characterized with homogeneous microstructure. The Y-Al-O compounds were created on the grain boundaries due to the reactions between Y2O3 and Al2O3 on AlN particle surface. With increasing the sintering temperature, AlN grains grew up, and the location of grain boundaries as well as the phase compositions changed. The Y/Al ratio in the aluminates increased, from Y3Al5O12 to YAlO3 and to Y4Al2O9. High-density, the growth of AlN grains and the homogenous dispersion of boundary phase were helpful to improve the thermal conductivity of AlN ceramics. The thermal conductivity of 122Wm-1K-1 for the 4.0 mass%Y2O3-doped AlN sample was reached.

Abstract: In the present work the influence of two different thermal debinding atmosphere, vacuum and air, on the properties of 5wt% Y2O3-doped aluminum nitride (AlN) ceramics was investigated. The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compact was fabricated by employing powder injection molding technique. The polymer-wax binder consists of 60wt% paraffin wax (PW), 35wt% polypropylene (PP) and 5wt% stearic acid (SA). The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. After the removal of binder, specimens were sintered at 1850˚С in nitrogen atmosphere at atmospheric pressure. The result reveals that debinding atmosphere has significant effect on the thermal conductivity and densification of AlN ceramics. The microstructure and secondary phase identification was determined by scanning electron microscopy and X-ray diffraction. The thermal conductivity and density of injection molded AlN ceramics are 177.3W·m-1·K-1 and 3.31g·cm-3 in the air and 200.8W·m-1·K-1 and 3.28g·cm-3 in the vacuum.

Abstract: The paper presents the results concerning the formation of a ‘barrier’ layer on AlN ceramic during its joining with copper by the Copper Direct Bonding (CDB) technique. Prior to the joining, the AlN surface was modified by isothermal oxidation or by titanium ion implantation. The effects of the oxidation process temperature were examined within the temperature range from 673 to 1473K. The surface of the ceramic was modified by titanium ion implantation at various ion doses and various accelerating voltages. The modified ceramic was joined with oxidized copper in a nitrogen atmosphere with about 1.5ppm of oxygen, using a belt-type furnace at a temperature of 1323K. The microstructure and phase changes induced on the surfaces of the joints were examined. The modification yielded a ‘barrier’ layer (TiN), which ensured a continuous pore-less contact between the materials being joined. The results obtained under all the experimental conditions indicate that the implantation gives better effects than thermal oxidation. Ion implantation seems to be ideally suited for these purposes. The preferential dose appears to be 5*E16ions/cm2 and the preferential accelerating voltage – 15kV.