Success Story

Hard Metal Tools With Multi-Layer Hard Coating for the Turning of Steel

The newly developed MT-TiCN coating (MT-TiCN = medium temperature titanium carbonitride) with fine grained columnar structure is a key component of hard metal coatings for the turning of steel. A coating with maximum hardness and minimum residual stress was achieved by targeted adjustment of process parameters and oxide integration.

The newly developed MT-TiCN coating (MT-TiCN = medium temperature titanium carbonitride) with fine grained columnar structure is a key component of hard metal coatings for the turning of steel. A coating with maximum hardness and minimum residual stress was achieved by targeted adjustment of process parameters and oxide integration.

The newly developed TiCN layer forms an integral part of multi-layer wear coatings on hard metal for the turning of steel. These coating systems comprise a sequence of titanium nitride (TiN), titanium carbonitride (TiCN) and aluminium oxide and are produced by chemical vapour deposition (CVD) at temperatures of 900 to 1000 °C and pressures between 50 and 300 mbar. Typical coating thicknesses are in the range of 10-25 μm, with 10 μm TiCN and 5 μm Al2O3 for ISO P25 applications. While the aluminium oxide is characterised by low thermal conductivity, high-temperature hardness and oxidation resistance, TiCN is designed as a bonding layer between the hard metal and the ceramic Al2O3 and reduces flank and crater wear due to its high abrasion resistance. The wear resistance and toughness of the tools is above all infuenced by the layer architecture.

The combination of high deposition temperatures and different expansion coefficients leads to thermal mismatch in the tool interior, which can by minimised by an appropriate layer architecture and targeted process parameter setting. The project team succeeded in achieving a fine-grained columnar TiCN structure with maximum hardness and minimum residual stresses by optimal adjustment of the coating parameters and targeted integration of oxygen. The approach led to an increase in indentation hardness and a reduction in tensile stresses determined with the XRD-sinÇΨ method.

Combined with the optimised aluminium oxide this resulted in enhanced tool life and improved process reliability in service. The optimisation of the TiCN layer extends the application of the insert, enhances tool life through increased hardness, improves process stability and reduces the probability of failure during machining operations. This layer has already been integrated in commercially available grades for the turning of steel.

The project was carried out in close cooperation with Ceratizit Austria and the Chair of Functional Materials and Materials Systems of the University of Leoben.