Functionally graded calcium zirconate molds with alginate-based spray coating for titanium investment casting

Abstract Surface quality and dimensional accuracy of titanium components produced by investment casting are limited by the conventional dip-coating procedure of the lost-wax process. This study presents a novel approach with spraying and centrifugation as alternative coating technologies. Aiming at improved surface quality, calcium zirconate slips and coatings based on alginate gelation were developed. Scanning electron microscopy and computed tomography revealed a homogeneous spray coating. The alginate-based spray coating was used for producing functionally graded calcium zirconate shell molds. These molds exhibited a fine-grained microstructure with pores in the lower μ m range. Applying an intermediate layer between the fine-grained spray coating and the coarse-grained dip-coating layers as well as the alternating application of dip-coating layers prevented cracking. The characteristic microstructure showed a bridging zone and a homogeneous distribution of coarse grain across the diameter. Ti6Al4V cast parts with no presence of an alpha case layer were obtained.