INVESTIGATION OF WEAR PROCESSES ON WORN TOOLS USING RAMAN MICROSCOPY

Abstract

In order to address the industry driven interest in wear and associated mechanisms of coated tools during dry high speed machining applications, two commercially available physical vapour deposited (PVD) coatings were studied. These were TiAlN based and had multilayered architectures deposited on to cemented carbide 8 mm ball-nosed two flute end mills. Raman microscopy and SEM-EDX analysis were used to characterise the molecular and elemental species, respectively, present on the worn surfaces of tools after controlled lifetime tests milling into A2 HRC58 die steel. This was performed to gain a better understanding of tribochemical reactions that occur in the highly complex wear environment during milling. Cutting temperatures were estimated as ≥950°C, indicated by oxide phase transformations and corroborated by static oxidation studies. In addition, transfer layers of iron/steel and iron oxide species (FeO, Fe₃O₄, and Fe₂O₃), oxidation products of the coating (TiO₂ and α-Al₂O₃), and spectral changes owing to deformation and stress state were observed as a consequence of wear. The high spatial resolution (2 μm), sensitivity to structural/chemical changes, and the non-destructive nature of the technique make Raman microscopy ideal for the study of wear on tools with complex geometry that cannot be readily studied by other techniques without difficult sample preparation.