Gilberto Bejarano Gaitan

Metal cutting tools having wear resistant and chemically stable ceramic coatings are in many applications superior in performance to uncoated tools. Titanium boron carbon nitride (TiBCN) is a hard material particularly suitable as a protective coating for cutting tools due to its excellent properties, such as a high hardness and high wear and corrosion resistance, among other. TiBCN films were grown on Si (100) and high speed steel substrates by means of reactively pulsed DC magnetron sputtering technique. Two B₄C‐ and two Ti‐targets, to which a pulsed DC voltage of middle frequency was applied, were used for the deposition of TiBCN. A chromium layer was first deposited to obtain a better adhesion of TiBCN to the substrates. The mechanical properties of these coatings deposited under different N₂ contents were investigated. The substrates were biased through a medium frequency power supply. The bias voltage value was −90 V for all coatings. The total film thickness was maintained at approximately 2 µm. The hardness of the coatings increased with reduced nitrogen content, while the adhesion decreased from 40.8 to 24.2 N, and the wear rate increased from 0.154 to 0.744 × 10⁻¹⁶ m³/N.m, the latter probably caused by the low content of the self‐lubricating amorphous matrix of our coatings. However, the sample deposited by a nitrogen gas flow of 60 sccm presented a wear rate of four orders of magnitude smaller than the uncoated sample. The deposition method presented in this work seems very promising for the manufacture of TiBCN coatings.

In the present work wear resistance of 4 μm uncoated tungsten carbide inserts (WC) and coated with [TiN/TiAlN]n multinanolayered or with commercial TiCN-Al2O3-TiN monolayers (TINAL) are examined. Life tests, cutting area temperature analysis, surface roughness measurements on work pieces, roughness measurements on the attacked surface, contact track analysis between chip-insert and chemical composition analysis (EDS) were carried out. Mechanical tests were conducted on AISI 4340 steel parts using cutting regime and applying high speed cutting (HSC). Machining results showed that for a distance of 8,000 m the inserts coated with 300 bilayers exhibited wear values of 0.117 mm, inserts coated with 200 bilayers showed values of 0.138 mm and those coated with TINAL presented wear values of 0.174 mm. Moreover, the temperature values for cutting speed at 176.6 m/mim for 300 bilayers was 522.6 oC, for 200 bilayers was 721.4 oC and 1,327.6 oC for inserts coated with TINAL. Lower temperatures, caused by a lower friction coeffi cient and cutting force, contribute to life-time increasing at WC inserts.