| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Biomaterial Surfaces & Interfaces | Tuesday Sessions |
| Session BI-TuP |
| Session: | Biomaterial Interfaces Poster Session |
| Presenter: | Yuka Kajima, Tohoku University, Japan |
| Authors: | Y. Kajima, Tohoku University, Japan A. Takaichi, Tokyo Medical and Dental University, Japan T. Oishi, Tokyo Medical and Dental University, Japan N. Kittikundecha, Tokyo Medical and Dental University, Japan Y. Tsutsumi, Tokyo Medical and Dental University, Japan N. Nomura, Tohoku University, Japan N. Wakabayashi, Tokyo Medical and Dental University, Japan T. Hanawa, Tokyo Medical and Dental University, Japan A. Kawasaki, Tohoku University, Japan |
| Correspondent: | Click to Email |
[Objective] Selective laser melting (SLM) has attracted significant attention as an advanced method for fabricating biomedical devices. SLM-manufactured parts easily accumulate large amounts of residual stress due to rapid heating and cooling. Thus, they require a post-fabrication heat treatment to relieve the residual stress. However, the heating process inevitably changes the microstructure of the alloys, which may affect their corrosion behavior. The objective of this study was to assess the morphological characteristics and corrosion properties of SLMed CoCrMo alloys following various heat treatments.
[Methods] Block specimens were prepared using an SLM machine equipped with a fiber laser (EOSINT M280) and commercially available CoCrMo alloy powders (MP1). Specimens were heated to 750 or 1150 °C and held at this temperature for 1 or 6 h in a furnace in an Ar atmosphere. Specific section cuts of XY and YZ planes were used for analyzing microstructures and corrosion resistance. Microstructures were investigated via scanning electron microscopy (SEM), field-emission transmission electron microscopy (FE-TEM), field-emission electron probe microanalysis (FE-EPMA), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD). Additionally, anodic polarization was performed with a potentiostat (HABF-501A) with a function generator (HB-111).
[Results and Discussion] The SEM images showed that fine precipitates were formed within the grains and at the grain boundaries in the specimens heated to 750 °C. On the other hand, after heating to 1150 °C, coarse precipitates, identified as M23C6 by TEM and EPMA analysis, grew along the grain boundaries. Both γ and ε phases formed in all heat-treated specimens, and the volume fraction of the ε phase decreased with increasing heat-treatment temperature and time. In the samples heated to 750 °C, the microstructures exhibit the epitaxial growth of columnar grains with a < 001 > fiber texture along the build direction as well as the as-built state. In samples heated to 1150 °C, defect-free equiaxed grains with random orientations were found, indicating that recrystallization occurred. Considering the anodic polarization curves, the heat treatment process did not greatly affect the corrosion resistance of the SLMed specimens; resistances of all heated samples were comparable to traditional cast samples, with those heated to 750 °C exhibiting the highest corrosion potential. The enhanced corrosion resistance of SLMed CoCrMo alloys provides further support for their use in medical applications.