Phase Equilibria and Phase Transformation in the Aluminum Nitride‐Aluminum Oxycarbide Pseudobinary System

Abstract

Samples in the pseudobinary AIN-A120C were fabricated by hot-pressing mixtures of AIN, A14C3, and Al2O3 powders in graphite dies in an atmosphere of nitrogen. The resulting dense samples were subjected to thermal treatments over a range of temperatures from 1550" to 1950°C. The hot-pressed as well as annealed samples were examined using optical microscopy, scanning transmission electron microscopy, and X-ray diffraction. An electron microprobe was used to determine composition. X-ray diffraction showed that AlzOC dissolved in AIN up to 44 mol% at 1800°C. Thermal treatment at lower temperatures led to the decomposition of the solid solution into two isostructural phases. In samples containing -14 to 60 mol% AlN, the morphology of the precipitates was lenticular. Diffraction contrast analysis showed that the precipitates were rich in AIN. Lattice images showed that the (001) planes of the 2H structure were continuous between the matrix and the precipitates. These precipitates appear to be similar to Guinier-Preston zones observed in metallic alloys. When annealed for long periods of time, interface dislocations formed, signifying partial loss of coherency. In some compositions (-61 to 64 mol% AIN), a lamellar microstructure developed similar to that observed in cellular phase separation. Also, in some of the compositions, an additional phase was observed whose composition and structure were not determined. [

Phase Relations in the Aluminum Carbide–Aluminum Nitride–Aluminum Oxide System

“…10,11,14 In the Al 4 C 3 -AlN system, Stackelberg and coworkers 15,16 found the intermediate phase Al 5 C 3 N with a layer structure of Al 4 C 3 and AlN. Later, Jeffrey and Wu 17,18 reported three new compounds (Al 6 C 3 N 2 , Al 7 C 3 N 3 , and Al 8 C 3 N 4 ) in this system.…”

“…Recently, Groen and coworkers [2][3][4] explored new ceramics with high thermal conductivity in the system and identified three new quaternary compounds. Other experimental works [5][6][7] also have been conducted to study the phase equilibria and phase transformation in the aluminum nitride-aluminum oxycarbide (AlN-Al 2 OC) system, and a homogeneous solid solution that forms between AlN and Al 2 OC has been observed at high temperatures (>1900°C). However, this solution phase undergoes phase segregation when annealing at lower temperatures.…”

Formation of (Al2OC)1−x(AlN)x solid solution starting from Al–Si–Al2O3 powder matrix at 1300°C in flowing nitrogen

“…The initial investigation of the Al 2 O 3 –Al 4 C 3 –AlN system was made by Henry et al to search for the composition that may exhibit desirable high‐temperature properties, and different phases in the system were classified. Other related work has been done in the flowing time . Encouragingly, a homogeneous solid solution with excellent properties that forms between AlN and Al 2 OC has been observed at elevated temperature above 1900°C .…”

“…Other related work has been done in the flowing time . Encouragingly, a homogeneous solid solution with excellent properties that forms between AlN and Al 2 OC has been observed at elevated temperature above 1900°C . Lihrmann et al investigated a series of samples along the join from Al 2 OC to AlN, and 2AlN·Al 2 OC–SiC composites with excellent properties were successfully prepared by hot‐pressing at 1950°C.…”

“…[6][7][8][9] Encouragingly, a homogeneous solid solution with excellent properties that forms between AlN and Al 2 OC has been observed at elevated temperature above 1900°C. [7][8][9] Lihrmann et al 10 investigated a series of samples along the join from Al 2 OC to AlN, and 2AlN·Al 2 OC-SiC composites with excellent properties were successfully prepared by hot-pressing at 1950°C. In which, the stabilized wurtzite-type 2AlN·Al 2 OC solid solution is formed in-situ as the second phase in SiCbased composites.…”