Experimental research on micro-cutting wear of 38CrSi steel caused by TiAlN- and TiCrAlN-coated tools

A comparative study was carried out on the wear of 38CrSi high-alloy steel using TiCrAlN- and TiAlN-coated tools. The presence of elemental Cr in the TiCrAlN coating resulted in formation of a Cr–O film on the tool, which provided a lower friction coefficient. This also mitigated transfer of cutting heat to the tool substrate and inhibited elemental diffusion between the tool and the workpiece. Simultaneously, the hard Cr–O film, which formed outside the Al–O film, provided excellent wear resistance and protected the Al–O film. Thus, elemental Cr played an active role in enhancing the wear resistance of the tool, prolonging its life. A workpiece cut using a TiCrAlN-coated tool had a surface roughness of 0.79 µm, which was about 62% lower than that obtained using a TiAlN-coated tool. Although wear of the TiCrAlN-coated tool was reduced, reaching 0.2 mm over the standard test time of 8 min, this time was 300% longer than that observed with the TiAlN-coated tool. Furthermore, the cutting force components were smaller, at up to 8 N, and the cutting force was 50% lower than with the TiAlN-coated tool. The wear and failure mechanisms of micro-milling 38CrSi alloy were the product of a combination of forms of wear and followed the wear law in terms of tool tip breakage, coating damage, abrasive wear, and adhesive wear; coating damage had the most important effect on tool life.