Tribological properties of multilayer CVD coatings deposited on SiAlON ceramic milling inserts

This work characterises the structure and mechanical properties, such as adhesion, of two different chemical vapour deposition (CVD) coatings deposited onto silicon aluminium oxynitride (Si3N4 + Al2O3 + Y2O3) round (RNGN) milling cutter tooling inserts. These inserts are often known by the trade abbreviation “SiAlON”. Wear was produced on the inserts using unidirectional sliding (pin-on-disc type) and scratch testing. Two coatings were investigated: a multilayer CVD coating (Coating A) with a composition of TiN + TiCN + Al2O3 and a bilayer coating (Coating B) with a composition of Al2O3 + TiN. Microstructural analysis was conducted after wear testing and Coating B demonstrated high stability when subjected to high alternating shear and tensile stresses, high abrasion resistance and very high adhesion to the SiAlON ceramic insert substrate when compared to Coating A. Coating A demonstrated a low capacity to distribute alternating shear and tensile stresses during the pin-on-disc and scratch testing, which led to failure. The scratch and pin-on-disc results from this study correlate highly with completed machining insert wear analysis that has used Coating A and Coating B SiAlON inserts to machine aged Inconel 718.