Thermal plasma CVD and wear resistance of double layered Ti–Si–B–C/Ti–B–C coatings on WC–Co cutting tools with various roughness

The double-layer deposition of composite SiC–TiBC (Ti–Si–B–C) films with various Si contents (0, 40, 55, 60 and 100 mol%) on Ti–B–C was achieved from mixtures of titanium tetra-ethoxide, boron tri-ethoxide, and/or hexa-methyl-disiloxane solutions at about 700 °C on WC–Co cutting tools by Ar/H2 thermal plasma CVD. The crystalline phases of TiB2, TiC, and SiC were identified in the coatings by thin film grazing incidence X-ray diffraction. The surfaces and cross-sections of the double-layer coatings were observed by scanning electron microscopy to reveal their microstructure. Cutting tests of the double-layer Ti–Si–B–C/Ti–B–C were carried out by determining the flank and crater wear. The wear rate of the double-layer formed with the Ti–Si–B–C composite over-layer with 55 mol% Si was the slowest of the five samples. In addition, the effect of surface roughnesses (Ra (μm) = 0.03, 0.20 and 0.55) on the coating and wear resistance of the double-layer Ti–Si–B–C/Ti–B–C with 55 mol% Si was investigated by cross-sectional SEM observation and cutting tests.