CrAlYN/CrN superlattice coatings deposited by the combined high power impulse magnetron sputtering/unbalanced magnetron sputtering technique

Abstract

CrAlYN/CrN coatings represent a new generation Ti-free PVD coatings tailored to serve high temperature applications such as dry high speed machining and protection of special grades aerospace and automotive alloys against environmental attack. The novel High Power Impulse Magnetron Sputtering (HIPIMS) technique was used for substrate pre-treatment (etching) followed by coating deposition utilising Unbalanced Magnetron Sputtering (UBM). The employment of HIPIMS resulted in smooth ( R a = 0.036 μm) and well adherent films with typical scratch adhesion critical load values on M2 high speed steel of L C = 65 N. Low-angle XRD analysis showed that the coating has a nanoscale multilayer (superlattice) structure with a typical bi-layer thickness of 4 nm. XTEM observations confirmed this result and further revealed the dense, growth defect free structure of the coating due to the HIPIMS etching. CrAlYN/CrN combines high hardness of HK 0.025 = 3320 with a low coefficient of friction of 0.5 and an exceptionally low sliding wear coefficient of 3.7 × 10 − 17 m 3 N − 1 m − 2 , which is comparable to that of TiAlN/VN and Me-Carbon films. In dry high speed milling ( V cutting = 385 m min − 1 ) of hardened A2 tool steel (HRC = 58), 8 mm cemented carbide ball nosed end mills coated with CrAlYN/CrN outperformed TiAlCrYN, which is one of the market leading coatings dedicated to this application. When the test is carried out at the higher end of the cutting speed range of 500 m min − 1 this difference in performance becomes even more pronounced (factor of 8 longer life time), which demonstrates the excellent quality of CrAlYN/CrN.