Continuous and varied depth-of-cut turning of gray cast iron by using uncoated and TiN/Al2O3 coated silicon nitride-based ceramic tools

Silicon nitride-based (Si3N4) ceramic cutting tools are particularly good for high speed machining of gray cast iron due to their high red hardness, wear resistance and chemical stability with gray cast iron. However, the intrinsic brittleness of Si3N4 ceramics makes the cutting tools easy to be damaged when subjected to impact force. In the present work, turning tests on gray cast iron were carried out by using uncoated and CVD TiN/Al2O3 coated Si3N4 cutting tools under continuous turning and varied depth-of-cut turning. Tool wear, tool life, chemical composition on worn flank faces and failure mechanism of the cutting tools after turning tests were studied. The results show that the improved cutting performance of the coated cutting tools can be attributed to the increasing wear resistance and toughness of the cutting tools with the covering of TiN/Al2O3 coatings, both in continuous and varied depth-of-cut turning. The dominant failure mechanism of the cutting tools was abrasive wear in continuous turning and a combination of abrasive wear and chipping in varied depth-of-cut turning. In addition, adhesive wear also found to play a role in the tools failure to some extent for both uncoated and coated Si3N4 cutting tools in continuous and varied depth-of cut turning.