A Quantitative and Statistical Method of ' Precipitates in Superalloy Based on the High-Throughput Field Emission Scanning Eelectron Microscope

Superalloys are used widely in national defense, energy, maritime, aviation, and other vital areas requiring stable and reliable materials owing to their excellent oxidation and heat corrosion resistance, high-temperature strength, good fatigue performance, and fracture toughness. The presence of a coherent gamma prime (gamma') precipitate is the main factor affecting the high-temperature mechanical properties. Therefore, obtaining the quantitative and statistical gamma' precipitate data is indispensable for examining and developing new superalloys. On the other hand, conventional instruments and methods barely achieve this goal. In this study, high-throughput field emission scanning electron microscope (high-throughput SEM) was introduced because of its high-speed imaging and original position visualization. Based on the high-throughput SEM, an innovative deformation GH4096 superalloy prepared at five different solution cooling rates were used as an object to establish a quantitative and statistical method for characterizing the primary, secondary, and tertiary gamma' precipitates. Many images of gamma' precipitates with magnifications of x57000 and x3000 were obtained rapidly, and methodologies for recognizing the gamma' precipitates were developed using MIPAR software. Matrices of images of different amounts were formed. Through these methodologies, information on these matrices was obtained, including the ratio of the primary gamma' precipitates area fractions between images with magnifications of x57000 and x3000. The ratio between the amounts of secondary and tertiary gamma' precipitates and the area fraction of the secondary and tertiary gamma' precipitates varied with the number of images investigated, respectively. By comparing the tendencies of these three results, the minimum field of view that could represent the actual distribution of gamma' precipitates was set to a matrix of 13 x 13 images with a magnification of x57000 and a pixels square of 2048 x 2048. Considering the consistency between the results of the standardized small-angle X-ray scattering (SAXS) and gamma' precipitates in the 13 x 13 images, the established method was quantitative in characterizing the primary, secondary, and tertiary gamma' precipitates of GH4096 superalloy. The results of the samples with five different solution cooling rates showed that the solution cooling rates strongly influenced the morphology and quantitative results of the gamma' precipitates. Moreover, the behavior of the precipitates corresponded to the classical nucleation growth mechanism and Ostwald Ripening. The solution cooling rates influenced the tensile strength of the samples. The samples exhibited excellent tensile strengths at relatively faster cooling rates, more secondary gamma' precipitates, and a higher total area fraction of secondary and tertiary gamma' precipitates. Overall, a GH4096 superalloy was prepared using the established method. The statistical and quantitative results of the gamma' precipitates highlight a novel way of studying the impact of the solution cooling process on gamma' precipitates that can predict the performance of GH4096 superalloys.