PHASE TRANSFORMATIONS OF Co66Cr28Mo6 POWDER ALLOY IN SELECTIVE LASER MELTING AND HIGH TEMPERATURE ANNEALING.
Abstract
The paper investigates the phase composition of a Co66Cr28Mo6 powder alloy and its changes due to temperature annealing and a dental crown obtained from the same powder created by 3D printing using the selective laser melting (SLM) method. SLM is a technology for the direct production of three-dimensional objects with certain mechanical properties using three-dimensional powders, in which a sequential layer-by-layer melting of the powder by laser radiation takes place. This technology allows you to create unique products based on three-dimensional models in one technological cycle and is the complete opposite to traditional methods of mechanical production, such as cutting and milling.
The dental crown was made from a Co66Cr28Mo6 powder alloy in a selective laser melting plant in the "Additive Technologies Centre". Structural studies of the Co66Cr28Mo6 alloy and the finished product (dental crown) were carried out at the Department of Solid State Physics and Nanostructures of Voronezh State University using a DRON 4-07 diffractometer.
X-ray diffraction studies of the original Co66Cr28Mo6 powder and the non-annealed crown showed that the laser printing completely converts the two-phase powder (90 % fcc + 10 % hex) into a single-phase fcc solid solution based on the high-temperature face-centred cubic modification of the b-Со with a noticeable increase in the interplanar distances in comparison to the b-Со.
After high-temperature annealing at a temperature of 500 °С for 11 hours, the traces of the hexagonal phase appear on the diffractogram of the crown. This is the only phase in the subsequent 8-hour high-temperature annealing at 800 °С in an argon atmosphere. An increase in the interplanar distances d in the initial powder of the Co66Cr28Mo6 alloy in comparison to the values of the interplanar distances in metallic b-Co and a-Со indicates the existence of a cobalt-based solid solution in the powder. The results obtained in the course of the study show that successive annealing leads first to an increase in the fraction of the hexagonal phase as compared to the original Co66Cr28Mo6 powder, and then to the actual complete transition to the hexagonal phase during high-temperature annealing in argon at 800 °С.
ACKNOWLEDGMENTS
The work was supported by the Ministry of Education and Science of the Russian Federation in the framework of the state order to higher education institutions in the sphere of scientific research for years 2017 - -2019. Projects No 3.6263.2017/VU and No 16.8158.2017/8.9.
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