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The structure of the Guinier-Preston (GP) zone in an Al-1.6 mass pct Mg 2 Si alloy aged at 343 and 423 K was investigated by high-resolution transmission electron microscopy (HRTEM). The morphology of the GP zone is that of a fine plate having the dimensions of a monolayer in thickness, 2.5 nm in width, and less than 30 nm in length. Its elongated direction is parallel to the ͗100͘ m direction. The chemical composition of the GP zone in an Al-Mg 2 Si alloy indicated a ratio of Mg/Si ϭ 1.0. The zones aggregate with increasing aging time and exhibit a more complicated morphology because of the transformation to the metastable phase that takes place inside the GP zones.K. MATSUDA, Research Associate, and S. IKENO, Professor, are with

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TiAlN/a-C nano-composite coatings were synthesized by a reactive co-sputtering process to investigate the effects of sputtering conditions on the microstructure and mechanical properties. Coating films were deposited on square plates of Si and high speed steel (ANSI M2) by the cosputtering of TiAl (pulsed-d.c. sputtering) and C (d.c. sputtering) targets using a ''Facing Target-type Sputtering'' system at an atmosphere with a mixture of Ar and N 2 but without hydrocarbon gas. The structure of the coatings was investigated by means of XRD, XPS and HRTEM with GIF (Gatan Imaging Filter). Mechanical properties of coating films were measured by a submicron indentation system. Though TiAlN and a-C coatings showed hardness of about 32 and about 10 GPa, respectively, TiAlN/a-C coatings containing 4.6 at% of C showed higher hardness of 43 GPa. The energy filter images depicted that a change of contrast in the zero-loss image corresponded to nanometer-size of Ti agglomerates in Ti map. C1s spectrum in XPS analysis revealed that carbon in the coatings was bounded as C-C and C-N without bonding of Ti-C or Al-C. These results indicated that the TiAlN/a-C nano-composite coatings consisted of complicated mixture of nanocrystalline Ti-Al-N phase and a-C phase (including C-N bonding).

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