Topography of high-speed steel substrates sputter cleaned by an Ar/Ti cathodic arc plasma

Hard coated high-speed steels are often used for tooling applications and consist of three different microstruc-tural constituents: a martensitic matrix, M6C and MC carbides. The behavior of these three during the various tool manufacturing steps has a detrimental effect on the final tool performance. The focus of the current work is the surface topography change due to variation of the substrate bias voltage applied during the Ar/Ti arc plasma sputter cleaning process which changed the sputtering behavior of the high-speed steel's microstructural con-stituents and the appearance of droplets on the sputtered surface. The surface topography was characterized by laser confocal and scanning electron microscopy. Furthermore, microstructural analysis was carried out on cross-section lamellae prepared by a focus ion beam technique and analyzed by transmission electron microscopy. At each of the three investigated substrate bias voltages (Ub) of-600,-800 and-1000 V during the Ar/Ti arc plasma sputter cleaning process, the mentioned microstructural constituents behaved differently. At an Ub threshold of-600 V, sputter erosion starts at M6C carbides in an inhomogeneous material erosion pattern. At-800 V, a homogeneous sputter behavior was established for the entire sample. M6C carbides showed the highest sputter erosion rate, on MC carbides Ti deposition occurred instead of sputter erosion, and the martensitic matrix was smoothened, as peaks and exposed features were sputtered preferentially. As of Ub =-1000 V, the sputter erosion behavior of the martensitic matrix changed and exposed features were preserved. The reason for this change was identified to be Ti+ ion implantation indicated by Monte Carlo simulations and the associated in-crease of the matrix' cohesive strength, calculated using Density Functional Theory. The published results in this study will help to further utilize Ar/Ti arc plasma sputter cleaning processes for intentional surface topography design.