This study investigated microstructure and high temperature mechanical properties of Metals(pure metal, alloy) manufactured by 3D printing process. In the present study, we applied selective laser melting technique using laser source and kinetic metallization technique using spray source to 3D printing process
First, we investigated the effect of heat-treatment on the microstructure changes and high temperature properties of Ti-6Al-4V manufactured by selective laser melting process. Initial microstructure observation revealed that prior-β grains were elongated along the building direction and had fully martensite structure. Meanwhile, some martensite phases were decomposed to a’, a and β by heat treatment(stress relieving condition). A compression test results confirmed that room temperature yield strength of as-fabricated and heat-treated materials measured 1365 MPa and 1138 MPa, respectively. At higher temperatures, as-fabricated materials showed good mechanical properties than heat-treated materials to about 500°C. Meanwhile, there is no differences between the two materials after 700°C, which was attributed to microstructure evolution at high temperatures. The average charpy impact energy measured as 6.0 J before heat treatment, and after heat treatment, the average impact energy increased by approximately 20% to 7.3 J. Such an increase in impact energy is the result of complex factors including the formation of β phases, decrease of dislocation density, and residual stress relief according to heat treatment. After the formation of widmanstatten structure using only heat treatment, we compared the high temperature creep properties with as-fabricated materials consisting of martensite structure. As a result, the materials with widmanstatten structure showed relatively good creep resistance than as-fabricated materials in all the stress ranges.
With this we investigated the microstructure and high temperature properties of high melting point refractory metals(Nb, Ta) manufactured by kinetic metallization process. Initial microstructural observation confirmed that odd-shaped powder elongated in a direction vertical to the spraying direction. In addition, microstructural evolution was confirmed in the process of accepting severe plastic deformation along the powder interface area. A compression test confirmed that room temperature yield strength measured as 660 MPa in Nb, and 901 MPa in Ta bulk materials. This value is four to six times greater than materials produced using conventional processes such as P/M and E-Beam melting. The material also featured outstanding strength compared to materials formed through the severe plastic deformation process. Also these high strength characteristics were maintained even at high temperature. The reason is that rapidly increasing dislocation density in the process of severe plastic deformation of each powder.