Novel aluminum-rich Ti1-xAlxN coatings by LPCVD

Today, Ti1-xAlxN coatings represent a standard PVD coating for cutting tools. Fcc-Ti1-xAlxN is a metastable homogeneous phase with excellent properties such as high hardness, high oxidation resistance and high cutting performance. An important aim is the preparation of coatings with maximum aluminum content and oxidation resistance. But PVD processes are limited to the deposition of monophase Ti1-xAlxN coatings with a maximum x=0.65. In this work the preparation of monophase fcc-Ti1-xAlxN coatings with x-values of up to 0.9 is described. A low pressure chemical vapordeposition process (LPCVD) using TiCl4, AlCl31, NH3, H-2, N-2 and Ar was applied. At deposition temperatures between 800 degrees C and 900 degrees C very hard Ti1-xAlxN layers with 0.8 < x < 0.9 were prepared. The layers possess a high hardness of approx. 3000 HV and a Young's modulus of up to 540 GPa. A strong adherence on hardmetal inserts was achieved by the deposition of a thin TiN coating followed by a special bonding layer. Scratch test measurements showed critical loads of more than 80 N. In the coatings compressive stress was determined that depends on the deposition temperatures and varies between -450 MPa and -920 MPa. In different wear tests a high performance of the CVD-Ti1-xAlxN was observed. Coated inserts showed a reduced wear by 30% in comparison with a state-of-the-art PVD coating in reaming of steel and cast iron. In milling of 42 CrMo4 V or GGG60 the new CVD-Ti1-xAlxN significantly exceeds the best PVD coatings available on the market today. (C) 2008 Elsevier B.V. All rights reserved.