Microstructure, mechanical properties, and cutting performance of TiCxN1 − x coatings with various x values fabricated by moderate temperature chemical vapor deposition

Abstract

TiCxN1−x composite coatings on carbide substrate are important modern coating systems for cutting tools. The hardness, adhesion, and wear resistance of these coatings are determined by their structure and chemical composition. Therefore, TiCxN1−x coatings with varied x values were deposited on carbide tools via moderate temperature low pressure chemical vapor deposition using a mixed TiCl4–CH3CN–C2H4–H2 precursor system at 840°C and 9kPa. Furthermore, the effect of the x value on their mechanical properties and cutting performance was investigated. Deposition of the TiCxN1−x coatings with various x values was achieved by changing the molar ratio of C2H4 relative to CH3CN from 0 to 30. The x value of the TiCxN1−x coatings, defined as the atomic concentration ratio C/(C+N), was determined using X-ray photoelectron spectroscopy and observed to increase as the C2H4/CH3CN molar ratio increased until saturation at x=0.75. The crystallite sizes of the TiCxN1−x coatings were determined from X-ray diffraction analyses, and the microstructures were observed using a scanning electron microscope and an optical microscope. Additionally, the hardness and adhesion of the TiCxN1−x coatings were evaluated by indentation and scratch tests. Indentation hardness increased with the x value because of a decrease in the crystallite size and reached a maximum of 28.6GPa at x=0.69. Contrarily, the adhesion of the TiCxN1−x coatings to carbide substrates decreased as the x value increased because of a change in the morphology and formation of a discontinuous bonding interphase. Longitude turning operation test using ductile cast iron (AISI:100-70-03) was also performed on TiCxN1−x (10μm)/Al2O3 (5μm)-coated carbide inserts with different x values (x=0.59–0.74). It was observed that the TiC0.69N0.31/Al2O3-coated carbide insert exhibited a significant increase in tool life of 30%–50% compared with that of a commercially available TiC0.59N0.41/Al2O3-coated carbide tool.