Reduction in anisotropic response of corrosion properties of selective laser melted Co–Cr–Mo alloys by post-heat treatment

• Published in: Dental materials 2021-03, Vol.37 (3), p.e98-e108
• Main Authors: Kajima, Yuka, Takaichi, Atsushi, Kittikundecha, Nuttaphon, Htat, Hein Linn, Cho, Hla Htoot Wai, Tsutsumi, Yusuke, Hanawa, Takao, Wakabayashi, Noriyuki, Yoneyama, Takayuki
• Format: Article
• Language: English
• Subjects: Alloys; Anisotropy; Anodic polarization; Chromium; Chromium Alloys; Cobalt base alloys; Corrosion; Corrosion resistance; Corrosion tests; Co–Cr alloys; Dental Alloys; Dental restorative materials; Dentistry; Heat treating; Heat treatment; Heat treatments; High temperature; Hot Temperature; Immersion; Immersion test; Immersion tests (corrosion); Laser beam melting; Lasers; Metal ions; Microstructures; Molten pool boundaries; Molybdenum; Polarization; Precipitates; Properties (attributes); Prostheses; Prosthetics; Reliability analysis; Reproducibility of Results; Selective laser melting; Surface Properties
• ISSN: 0109-5641; 1879-0097
• DOI: 10.1016/j.dental.2020.10.020

•Anisotropic corrosion resistance was found in SLM-processed Co-Cr alloys.•Selective corrosion occurred along the molten pool boundaries (MPBs).•The MPB area was dependent on the building plane, resulting in the anisotropy.•Post-fabrication heat treatment effectively reduced anisotropy by eliminating MPBs.•Excessive heat treatment at high temperature produced less-protective passive films. The application of selective laser melting (SLM) to dentistry has been rapidly expanding; however, SLM-processed parts possess orientation-dependent properties (i.e., anisotropy) that can affect the long-term reliability of the dental prostheses. This study aimed to evaluate the anisotropic corrosion response of SLM-processed Co–Cr–Mo alloys under various heat treatments. Samples fabricated via SLM along the horizontal plane (x-y plane) and vertical plane (x-z plane), with respect to the build direction, were subjected to various heat treatments. The resulting microstructures of the samples were characterized, and their corrosion properties were evaluated using anodic polarization and immersion tests. All samples showed similar transpassive behavior of the polarization curves. However, the immersion tests showed that the as-built x-z plane samples released significantly more metal ions than those fabricated on the x-y plane because of the larger area of preferentially corroded molten pool boundaries (MPBs) in the x-z plane samples. Our results further demonstrated that the heat treatments eliminated the MPBs, resulting in isotropic corrosion properties. However, excessive heat treatment at high temperatures induces the formation of coarse precipitates, resulting in a less-protective passive film. The post-build heat treatments at temperatures that eliminate the MPBs are effective in reducing anisotropic corrosion behavior, and the lowest possible temperature is suitable for reducing the amount of released metal ions. These findings are expected to facilitate the application of SLM in dentistry to allow fast and precise production of prosthetic devices.