Mechanical Properties of Aluminum Nitride Layer Formed by Duplex Coating of Barrel Nitriding and Plasma Nitriding

Aluminum nitride layers on aluminum are formed by the barrel nitriding in nitrogen gas, and duplex coatings are performed with the plasma nitriding in nitrogen and argon gas after the barrel nitriding. Aluminum nitride films with high thickness, high surface hardness, and good adhesion can be obtained on aluminum surfaces by using the above process. Hardness and Young's modulus of the AlN formed by the barrel nitriding is estimated by means of the rules of mixture. The microstructure of the AlN is proved to be composed of Al and AlN. it is suggested that the AlN formed by the barrel nitriding can play a role as the adhesion improvement of the AlN formed by the plasma nitriding. Furthermore, a microindentation test, which can obtain indentation load-penetration displacement curves, is performed in order to investigate the film fracture of the AlN.