Thick Physical Vapour Deposited TiB2 Coatings

Abstract

Direct current magnetron sputtering combined with electron assisted growth has been used to grow thick TiB2 coatings. The coatings were evaluated with respect to structure, using X-ray diffraction (XRD), and morphology, using scanning electron microscopy (SEM). Fundamental mechanical properties were examined, such as hardness (52 GPa) and Young’s modulus (590 GPa), using nanoindentation testing. The fracture toughness Kc was determined to be 4·1 MPa m1/2 based on the length of radial cracks in Vickers indentation (the Anstis method). This deposition process, which yields low stressed magnetron sputtered TiB2 coatings makes it possible to obtain 60 μm thick coatings with excellent practical adhesion to the substrate. Scratch testing revealed that no critical failure (i.e. cohesive spalling) has occurred below 70 N. The improved scratch test behaviour is attributed to the increase in load carrying capacity by depositing a thick coating. However, small cohesive cracks were generated above 35 N. This study shows that very thick, hard and stiff coatings, with good adhesion, can be grown using the physical vapour deposition (PVD) technique if the residual stress state is controlled. One technology for that is magnetron sputtering with electron assistance.