Cylinder linings of lightweight combustion engine blocks made from aluminium cast alloys are typically coated with thermally sprayed layers to enhance the chemical resistance. Finish machining of the cylinder linings is currently done by honing. A substitution of this process by machining with geometrically defined cutting edges would have significant advantages, especially concerning ecological aspects. For the investigations Fe17Cr2Ni0.2C iron based coatings applicated by atmospheric plasma spraying on substrates, prepared with a dovetail microstructure are machined by turning. In the experiments the feed is varied in the range of 0.025 mm to 0.15 mm. The tools used comprise CBN tips involving a rake angle of 0°. Tool wear and machining forces are determined. The geometrical properties of the machined surfaces are detected by tactile measurements, 3D laser scanning microscopy and SEM. The residual stresses are characterised by XRD. An increase of the feed results in increasing components of the resultant machining force and higher values for Ra, Rz, Rpk, Rk and Rvk. Additionally, the amount of opened pores and pulled out coating material is reduced for high feeds. By increasing the feed the absolute values of the compressive principle stresses decrease. The increase of the knowledge in machining of thermally sprayed coatings by tools with defined cutting edges contributes to a substitution of the honing process and hence enables a more material and energy efficient production.
High-entropy alloys (HEAs) provide advanced properties like a high resistance to corrosion and wear. Concerning this and the elevated material costs wear protection layers are a possible field of application. Finish machining of these layers is necessary to achieve adequate surface properties. In the experimental investigations face turning of high-entropy alloy CoCrFeNi layers generated by spark plasma sintering is regarded. In this context, the influence of the cutting material and the cutting speed is analysed. For this, CBN tipped (two types), PCD tipped, CVD diamond tipped, and solid cemented carbide indexable inserts are used. Additionally, the influence of four different cutting speeds in the range between 100 m/min and 400 m/min is analysed. The feed and the depth of cut are kept constant with 0.05 mm and 0.1 mm, respectively. The geometrical surface properties are determined by tactile measurements and 3D laser scanning microscopy. The tool wear is analysed microscopically. Regarding the surface roughness, CBN tipped tools with a high content of boron nitride lead to the best results with the lowest roughness values irrespective of the cutting speed. The tool wear is also significantly reduced compared to the other cutting materials tested. The investigations represent the first results analysing the influence of the cutting material in machining of high-entropy alloys. Hence, this contributes to the enhancement of the field of application of HEAs.
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