Ceramic matrix composites have been produced via the directed oxidation of molten A1 alloys.* The oxidation reaction product can be grown directly into the atmosphere, yielding an unreinforced composite, or through a preform of reinforcement material, such as particulates, platelets, or fibres, yielding a reinforced composite. The fabrication of both A1203 matrix composites [1-3] and A1N matrix composites [4-61 has been previously discussed, and the microstructures [7], properties [8], and failure mechanisms [9] of A1203 matrix composites have been presented. The present paper describes the microstructure and properties of three A1N matrix composites, namely (i) an unreinforced composite, (ii) an A1N particle-reinforced composite, and (iii) a TiB2 platelet-reinforced composite. The three composites were produced (grown) by the directed nitridation of AI-Sr-Si-Ni alloys in nominally pure nitrogen at 1000 °C. The unreinforced composite was produced by the growth of the nitridation reaction product directly from the alloy surface. The A1N particle and TiB2 plateletreinforced composites were produced by placing preforms that contained nominally 50 vol % reinforcement material above the alloy surface prior to the nitridation reaction. Since the nitridation reaction product grows outward at the interface of the oxidant and the reaction product (i.e. not at the interface of the alloy and reaction product) [10], the matrix is able to incorporate the reinforcement material without disturbance or rearrangement. The A1N reinforcement that was used is a commercially available powder (Advanced Refractory Technologies, grade A-200) with an average particle size of 3.3/zm, and a maximum particle size of about 10/zin. Similarly, the TiB2 platelets that were employed are commercially available (Union Carbide, grade HCT-30), and have dimensions nominally 10 ~m in diameter by 2.5/zm thick. Typical microstructures of the unreinforced composite, the A1N particle-reinforced composite, and the TiB 2 platelet-reinforced composite are shown in Fig. 1. The unreinforced composite has a very fine microstructure. It consists predominantly of A1N with some metal phase. The metal phase, which is made up of the constituents in the parent alloy, appears in regions on the order of i /xm in size. The reinforced composites contain the respective filler phases, and possess matrices that appear identical to the unreinforced composite.