Microstructure and wear mechanisms of texture-controlled CVD α-Al2O3 coatings

- The wear mechanisms of texture-controlled CVD α-Al2O3 layers are investigated in steel turning.
- A correlation between growth texture of α-Al2O3 and cutting performance is clearly established.
- The occurrence of plastic flow in the near surface of the α-Al2O3 layers is observed.
- α-Al2O3 wear resistance is enhanced when the (001) planes are oriented parallel to the tool surface.

In the present study, the microstructure and wear mechanisms of texture controlled CVD α-Al2O3 layers with (001), (012) and (100) growth textures were investigated in single point turning of C45 carbon steel at low and high cutting speeds. The experimental coatings were investigated by FEG-SEM, EBSD and a combination of FIB and analytical TEM techniques prior to and after machining. Significant texture effects on wear performance of the α-Al2O3 coating layers were observed, confirming results from previous wear studies in the context of machining AISI 4140 carbon steel. The wear mechanisms of the coating layers were further interpreted in the light of thermal, mechanical and frictional conditions occurring at the tool-chip contact interface. Possible deformation mechanisms of the α-Al2O3 layers under the conditions of high pressure and temperatures acting on the tool surface are discussed. The high dislocation density revealed by the TEM observations in the subsurface α-Al2O3 layers was attributed to the activation of a basal slip deformation mechanism resulting from the combined action of the shear stress field and high temperature acting on the tool surface. It is suggested that the enhanced and more uniform near surface deformation capability of (001) α-Al2O3 is responsible for the improved machining performance.