Abstract Scope |
Additively manufactured Mar-M 509, a cobalt-based superalloy, was evaluated for its microstructure and tensile behavior (at room temperature and 650 °C) after short cycle heat treatments, along the two orientations, longitudinal (L) and transverse (T) to the build direction. The microstructural evolution after single step heat treatments at 950 °C, 1150 °C and 1250 °C for 3 h was characterized using transmission electron microscopy. The alloy comprises a columnar-cellular dendritic microstructure strengthened by MC carbides forming a network along the cell boundaries in the as-printed condition. On heat treatment, the microstructure was characterized by the precipitation of M23C6 along with MC carbides. The T orientation showed higher yield strength and lower elongation than L for all the conditions. Amongst these, the 1150 °C heat treatment showed the optimum combination of yield strength and elongation (850 MPa, 20 %), attributed to the presence of fine MC carbides along the cell boundaries and coarse M23C6 carbides at the grain boundaries, with a carbide fraction of nearly 18%. At the test temperature of 650 °C, the optimum yield strength of ~740 MPa and elongation of 21 % was seen in the 950 °C HT condition. This understanding of microstructure-mechanical property correlation for a palette of short cycle ageing treatments thus allows for choosing the right combination for the desired application. |