Formation of Aluminum Nitrides by Precipitate-Accommodated Plasma Nitriding

Abstract

AbstractPrecipitate accommodated nitriding is proposed as a new, non-traditional surface treatment of aluminum alloys. In the case of nitriding the aluminum-copper alloys, Al2Cu plays an important role as a nucleation site to form AlN by the two step reactions of Al2Cu + 2N → 2AlN + Cu and Cu + 2Al → Al2Cu and as a helper to preserve the fast nitrogen diffusion path. In this precipitate accommodation, AlN islands form on Al2Cu in coherent, and, gradually cover the matrix surface by the AlN layer. This Al2Cu accommodation in nucleation reduces the pre-sputtering time and shortens the incubation time prior to formation of AlN layer. Furthermore, the interface between Al2Cu and AlN plays a nitrogen diffusion path across the nitrided layer. This Al2Cu accommodation in growth of AlN accelerates the growth rate of AlN layer in practice. The formation rate of AlN approaches to 7 μm/ks in the present nitriding. This reduction of processing time is much favored for industrial manufacturing of automotive parts and electrical components in practice. Low friction and wear is also attained in dry sliding condition by this AlN-layered specimen: μ = 0.13 and Ws = 1.5 × 10−5 mm3N−1m−1. Since Al2Cu is common precipitate to most of aluminum alloys, this AlN-layer formation is also favored to protective coating for automotive parts and electric components.