Optimal Design Experiment of Ageing Time and Temperature in Inconel-713C Superalloy Based on Hardness Objective

This study consists of assessing the influence of ageing heat treatments on characteristics of the microstructure and the hardness in the Inconel-713C nickel-based superalloy. The ageing process including the time and the temperature was modified based on the material hardness, by the design of experiments (DOE). For this objective, ageing treatments consisted of heating at 850, 890 and 930 °C for 8 and 16 h, after a solutioning treatment. Experimental results showed that the mean hardness reached the highest value (as 43.2 RC) in the sample that was age-hardened at 890 °C for 8 h, without requiring usual double ageing heat treatments. Besides, the DOE also predicted the highest hardness, which would be related to the specimen, hardened at 896.1 °C for 8 h and also 895.3 °C for 16 h, based on vertical and parallel lines, respectively. The highest hardness was associated with the optimum volume fraction (as 64%) of approximately fine size (as 500 nm) of (gamma ') precipitates. Besides, M₂₃C₆-type carbides plus NbC had a positive effect to enhance the hardness value. X-ray diffraction (XRD) results indicated various phases created in different ageing heat treatments that affected the hardness.