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Structure and Mechanical Properties of Cr(Al)N/Al2O3 Nanocomposite Hard Coatings Fabricated by Differential Pumping Cosputtering
M. Kawasaaki, I. Onishi, K. Matsuda, M. Nose, M. Shiojiri
JEOL USA Inc., US
Keywords: nanocomposite film, Cr(Al)N/Al2O3, sputtering, analytical electron microscopy, hardness, Young’s modulus
Summary:
Analytical electron microscopy revealed the structure of Cr(Al)N/Al2O3 nanocomposite coatings prepared on the Si substrate rotated at a speed as high as 12 rpm in a differential pumping cosputtering system(DPCS). The main layer that sputter-deposited with flows of Ar (10 sccm)+N2 (20 sccm) and Ar (20 sccm) from the CrAl and Al2O3 targets, respectively, grew in a columnar structure normal to the substrate plane. Each column comprised NaCl-type Cr(Al)N crystallites and amorphous Al2O3.particles. The indentation hardness (HIT) and Young’s modulus (E*) of the Cr(Al)N/Al2O3 layers were measured. HIT and E* increased with increasing substrate rotational speed within a measured range of 1~12 rpm. With increasing oxide fraction, HIT and E* increased to reach maximum values and then decreased. This shows that the hardness of nitride coatings is improved by fabricating the nanocomposite layer. The maximum HIT and E* were obtained at 17 vol. % oxide for Cr(Al)N/Al2O3 and also for Cr(Al)N/SiOx and AlN/SiOx. The Cr(Al)/17 vol. %Al2O3 and Cr(Al)/17 vol. %SiOx layers prepared at 12 rpm are superhard with HIT = ~43 GPa and E*＝~350 GPa. The mechanical property of these layers was interpreted on the basis of structural analysis.
