Cutting performances and wear characteristics of WC inserts coated with TiAlSiN and CrTiAlSiN by filtered cathodic arc in dry face milling of cast iron

Abstract

The aim of this work was to study the cutting performances and wear characteristics of Co-WC inserts coated with TiAlSiN and CrTiAlSiN by a filtered cathodic arc process in dry face milling of cast iron. Face milling experiments were conducted on turbine cast iron workpieces with TiAlSiN-coated, CrTiAlSiN-coated and uncoated inserts at various cutting speeds and numbers of inserts. The results showed that Ti-based coatings offered substantially better cutting performances for Co-WC inserts and could effectively protect the inserts over longer cutting lengths than uncoated ones. Specifically, the CrTiAlSiN coating offered the best cutting performances with the lowest workpiece surface roughness, the lowest flank wear rate and the longest maximum cutting length of 10 m, which was about 2.5 times as high as that of uncoated one owing to superior hardness relative to yielding and chemical properties. In addition, the workpiece quality in term of surface roughness was found to improve with increasing cutting speed in the range of 140–300 m/min and decreasing number of inserts ranging from 1 to 3. Microstructural analyses suggested that the CrTiAlSiN-coated inserts exhibited wear due to thermal cracking and partial delamination under high temperature ploughing abrasion while the TiAlSiN-coated ones displayed mainly ploughing abrasive flank wear behaviour, which resulted in a substantially lower flank wear rate than uncoated WC inserts that suffered from the combination of direct cutting and ploughing abrasive wear.