A comprehensive study of the influence of post-processing on the microstructure evolution and high-temperature performance of Haynes 230 superalloy manufactured by laser-powder bed fusion

This study evaluates the effects of various post-processing treatments on the nickel-based HA230 superalloy processed by Laser Powder Bed Fusion. The study focuses on microstructural features, deformation, and fracture behavior at room temperature and at an elevated temperature of 850 °C. Post-processing consists of a series of heat treatment regimes, including solution annealing (SA) and hot isostatic pressing (HIP) at 1160 and 1200 °C, as well as a combination of these treatments. A parametric study revealed that, in the as-built state, a higher number of solid-state cracks and various types of defects were present in the microstructure. There was found significant reduction of both cracks and defects after implementing HIP in combination with SA, which achieved nearly complete densification. Combining HIP at 1200 °C also induces an extensive static recrystallization, resulting in a significant reduction in dislocation density and the GOSS texture component, as well as the formation of coarse columnar grains. The SA state exhibits the highest mechanical properties at room temperature, while the combined treatment of HIP and SA reaches the highest values at elevated temperatures. The sustained high strain hardening ability at elevated temperatures is associated with a combination of carbides, low-angle grain boundaries, and nano-twins. Regardless of the heat treatment, the fracture behavior at room temperature exhibits a transcrystalline ductile fracture with checkerboard morphological features. The morphology transforms into an array of voids at 850 °C, accompanied by the formation of intercrystalline fracture features. This phenomenon is further amplified by both HIP regimes. • HIP application achieves a fully dense structure with optimal mechanical properties. • Post-treatment results in stress relief and formation of large columnar grains. • Heat treatment affects the fraction and intensity of existing texture components. • Fracture behavior is transforming from near ductile at RT to mixed mode at 850 °C. • Carbides, nanotwins and LAGBs promotes strengthening at elevated temperatures.