On the importance of interface stability in cellular automata models: Planar and dendritic solidification in laser melted YSZ

Laser-processing technologies are often applied to enhance the properties of ceramics, such as laser glazing of Yttria Stabilised Zirconia (YSZ). However, very limited attention was paid to the solidification phenomena and mechanisms of YSZ. In this paper, two coexisting solidification behaviours of laser-melted YSZ have been identified, namely grain bending (crystals with curved grain boundary geometry under the surface) and grain surface sealing (in-plane surficial crystals cover vertical columnar grains). Although these phenomena have been reported, this is the first time the two phenomena coexist in the same material. A new cellular automata (CA) approach has been proposed to explain the formation mechanisms of these two phenomena. This new CA method consists of the separation of growth modes into dendritic and planar growth, whose critical transition value is calculated based on the supercooling theory. Besides, the proposed model for planar growth is far less computationally expensive than the widely used decentred octahedron algorithm. A good agreement with the EBSD data of longitudinal cross-sections and the top surface has been observed which proves that the proposed method can become a more realistic and efficient way to predict the grain microstructure in laser processing, allowing to capture dendritic and planar growth simultaneously

Surface integrity in metal machining - Part I: Fundamentals of surface characteristics and formation mechanisms

The surface integrity of machined metal components is critical to their in-service functionality, longevity and overall performance. Surface defects induced by machining operations vary from the nano to macro scale, which cause microstructural, mechanical and chemical effects. Hence, they require advanced evaluation and post processing techniques. While surface integrity varies significantly across the range of machining processes, this paper explores the state-of-the-art of surface integrity research with an emphasis on their governing mechanisms and emerging evaluation approaches. In this review, removal mechanisms are grouped by their primary energy transfer mechanisms; mechanical, thermal and chemical based. Accordingly, the resultant multi-scale phenomena associated with metal machining are analyzed. The contribution of these material removal mechanisms to the workpiece surfaces/subsurface characteristics is reviewed. Post-processing options for the mitigation of induced surface defects are also discussed