Effects of heat treatment on the properties of powder injection molded AlN ceramics

The effects of two different heat-treatment atmospheres,nitrogen atmosphere and reducing nitrogen atmosphere with carbon,on the properties of Y2O3-doped aluminum nitride（AlN） ceramics were investigated.The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis（SHS） and compacts were fabricated by employing powder injection molding technique.The polymer-wax binder consisted of 60 wt.% paraffin wax（PW）,35 wt.% polypropylene（PP）,and 5 wt.% stearic acid（SA）.After the removal of binder,specimens were sintered at 1850°С in nitrogen atmosphere under atmospheric pressure.To improve the thermal conductivity,sintered samples were reheated.The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics.The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m^-1·K^-1 and 3.28 g·cm^-3 and the secondary phase is yttrium aluminate.For the sample reheated in reducing nitrogen atmosphere with carbon,the thermal conductivity and density are 173 W·m^-1·K^-1 and 3.23 g·cm^-3,respectively,and the secondary phase is YN.

Comparison between AlN and Al2O3 ceramics applied to barrier dielectric of plasma actuator

This paper reports the material characterization and performance evaluation of an AlN ceramic based dielectric barrier discharge（DBD） plasma actuator. A conventional Al2O3 ceramic is also investigated as a control. The plasma images,thermal characteristics and electrical properties of the two actuators are compared and studied. Then, with the same electrical operating parameters（12-kV applied voltage and 11-kHz power frequency）, variations of the surface morphologies,consumed power and induced velocities are recorded and analyzed. The experimental results show that the AlN actuator can produce a more uniform discharge while the discharge of the Al2O3 actuator is easier to become filamentary. The later condition leads to higher power consumption and earlier failure due to electrode oxidation. In the plasma process,the power increment of the AlN actuator is higher than that of the Al_2O_3 actuator. The induced velocity is also influenced by this process. Prior to aging, the maximum induced velocity of the AlN actuator is 4.2 m/s, which is about 40% higher than that of the Al2O3 actuator. After 120-min plasma aging, the maximum velocity of the aged AlN actuator decreases by 27.8% while the Al_2O_3 actuator registers a decrease of 25%.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF IN-SITU FORMATION FIBROUS POLYTYPE AlN COMPOSITE-MATERIAL

In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 system.In comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are much bettered.Microstructural observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix.Y_2O_3 seems to act as a densifier for in-situ formation materials and as medium for growth of fibrous polytype.SiO_2 is the growth promoter for fibrous polytype.The occurrnce of fibrous polytype may increase the strength and toughness of AlN ceramic composite mateirals.