Finish turning of Fe17Cr2Ni0.2C iron based sprayed coatings - influences of substrate preparation and cutting speed on the coating and surface properties

Cylindrical specimens are machined by turning with different cutting speeds (100 m/min – 400 m/min). Due to the high shearing load during turning, high adhesion between substrate and thermal spray coating is required. To ensure this, a helical dovetail microstructure is generated on the substrate surface before Fe17Cr2Ni0.2C coating application by APS. The geometrical properties of the machined surfaces are analysed by tactile measurements, SEM and 3D laser scanning microscopy. Residual stresses, spray particle flattening behaviour and grain size distribution of the spray coating with respect to the underlying dove-tail structural feature are described by XRD and EBSD analyses. Regarding coating finish by turning, results show that the surface roughness values (Ra, Rz, Rk, Rpk) decrease with increasing cutting speed in the range up to 300 m/min. Furthermore, the pit void volume decrease with higher cutting speeds, which is also a result of less pulled out particles. The residual stresses resulting from the machining process are independent of the cutting speed in the analysed range.

Detailed knowledge of the effects in turning of such coatings can contribute to a substitution of the honing process and hence to realise a material and energy efficient production.