Microstructure-Mechanical Properties of Short-Cycle Heat-Treated Additively Manufactured Mar-M 509 Cobalt Superalloy

Additively manufacturedMar-M 509 Mar-M 509, a cobalt based superalloyNi- based superalloy, was evaluated for its microstructureMicrostructure and tensile behavior (at room temperature and 650 °C) after short-cycle heat treatmentsHeat treatment, along the two orientations, longitudinal (L) and transverse (T) to the build direction. The microstructural evolutionMicrostructural evolution after single step heat treatmentsHeat treatment at 950, 1150, and 1250 °C for 3 h was characterized using transmission electron microscopyTransmission electron microscopy. The alloy comprises a columnar-cellular dendritic microstructureMicrostructure strengthened by MC carbides forming a network along the cell boundaries in the as-printed condition. On heat treatmentHeat treatment, the microstructureMicrostructure was characterized by the precipitationPrecipitation 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 treatmentHeat 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 boundariesGrain boundary, 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 microstructureMicrostructure-mechanical propertyMechanical properties correlation for a palette of short-cycle ageing treatments thus allows for choosing the right combination for the desired application.