Microstructure evolution and superior high temperature strength of cold spray additive manufactured Nb

초록

Pure Nb bulk material was fabricated by using cold spray additive manufacturing, and the high temperature compressive mechanical properties and deformation behavior were investigated at various temperatures (room temperature, 650 degrees C, 800 degrees C, and 950 degrees C). The powder, which was composed almost entirely of one crystal grain, was transformed into a severely plastic deformed interior and ultra fine grains along particle boundary by the cold spray additive manufacturing process. The results of compression tests showed that the yield strength at room temperature of approximately 660 MPa is about 2-3 times higher than those of conventional bulk Nb materials reported to date. In addition, the cold spray additive manufactured Nb material had excellent strength at high temperatures. Examination of the surfaces after compressive deformation revealed that cracks were formed in the 45 degrees direction at room temperature, and that the surface was oxidized at high temperatures. Dynamic recovery and recrystallization started to occur near 800 degrees C compression. The surface oxidation and microstructural evolution severely affected the high temperature deformation-fracture behavior of the cold spray Nb material. The relationships between the microstructure, mechanical properties, and fracture mechanism were also discussed based on these findings.

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