In situ cutting analysis of CrAlON coatings with varying oxygen content

Incorporating oxygen into CrAlN leads to the oxynitride system CrAlON, thereby changing its coating properties and influencing its cutting behavior. Recent studies show that steel exhibits a reduced tendency to adhere to CrAlON coatings compared to CrAlN coatings when these are deposited using physical vapor deposition (PVD) and employed as part of a coating/tool system during machining. This influences chip formation and reduces friction. This study investigates the influence of oxygen content on the cutting behavior in terms of steel adhesion considering the contact length, chip thickness, and coefficient of friction. Moreover, the coatings' crack resistance affect the wear behavior and are therefore analyzed. (Cr 40 ,Al 60 )O 10 N 90 , (Cr 40 ,Al 60 )O 30 N 70 , and (Cr 40 ,Al 60 )O 40 N 60 coatings were deposited on cemented carbide tools by High Power Pulsed Magnetron Sputtering (HPPMS). The cracking behavior was analyzed with nanoscratch tests. To in situ measure the contact length at the rake face, chip thickness, and coefficient of friction (CoF), a high-speed camera was used during planing of a 42CrMo4+QT workpiece. The tests were conducted with cutting speeds of v c = 150 m/min and v c = 200 m/min. The wear of the coated tools was analyzed afterwards. Increasing the O content from x O:N ≈ 10:90 to x O:N ≈ 30:70 resulted in reduced plastic deformation and a higher likelihood of crack formation. With a further oxygen increase to x O:N ≈ 40:60, the opposite behavior was observed. Furthermore, CrAlON coated tools with higher oxygen content showed a reduced contact length and lower adhesion tendency towards steel workpieces at both cutting speeds. This could be why coated tools with higher O content have lower adhesive wear. All tools showed comparable CoF during planing independent of the coating, whereas CoF reduces with increasing cutting speed. By adjusting the O-content for CrAlON, the adhesion tendency of steel and therefore the adhesive wear can be controlled during cutting.