Deformation behavior of as-cast Ni-based superalloy under wide temperature range with low strain rates

The mechanical behavior of superalloys during cooling is crucial for understanding crack formation in casting. Tensile tests with different strain rates were conducted on as-cast nickel-based superalloy Mar-M247LC across 25 °C to 1,250 °C. Results show that yield strength increases with strain rates at constant temperature but decreases with temperatures at constant strain rate. Ultimate tensile strength (UTS) peaks at about 1,400 MPa between 600 °C and 800 °C before declining, and it is notable that UTS shows small differences across three strain rates below 950 °C. Strain rate sensitivity coefficient generally increases with temperature, reaching 0.2472 at 1,250 °C. The fracture morphology is jointly governed by temperature and strain rate. Intergranular fracture is dominated by brittle phases, prevailed at 25 °C and 600 °C. A transition to dimple rupture occurs between 800 °C and 950 °C, with dimple density increasing as the strain rate decreases. At 1,100 °C, an intergranular fracture mode is presented. At the extreme temperature of 1,250 °C, γ′ phase melting exacerbates brittleness under high strain rates, while promoting lamellar intergranular fracture via grain boundary segregation under low strain rates. During directional solidification above 1,100 °C, uniform cooling of the casting is essential, and it mitigates thermal shrinkage stress by narrowing temperature gradients, thus preventing stress concentrations arising from uneven cooling rates. Below 1,100 °C, the alloy shows relatively high strength under different strain rates, with small differences. Thus, the cooling rate can be increased appropriately, which improves production efficiency.