Microstructure of Haynes® 282® Superalloy after Vacuum Induction Melting and Investment Casting of Thin-Walled Components

The aim of this work was to characterize the microstructure of the as-cast Haynes (R) 282 (R) alloy. Observations and analyses were carried out using techniques such as X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray spectroscopy (EDS), wave length dispersive X-ray spectroscopy (WDS), auger electron spectroscopy (AES) and electron energy-loss spectrometry (EELS). The phases identified in the as-cast alloy include: gamma (gamma matrix), gamma' (matrix strengthening phase), (TiMoCr)C (primary carbide), TiN (primary nitride), sigma (sigma-TCP phase), (TiMo)(2)SC (carbosulphide) and a lamellar constituent consisting of molybdenum and chromium rich secondary carbide phase together with gamma phase. Within the dendrites the gamma' appears mostly in the form of spherical, nanometric precipitates (74 nm), while coarser (113 nm) cubic gamma' precipitates are present in the interdendritic areas. Volume fraction content of the gamma' precipitates in the dendrites and interdendritic areas are 9.6% and 8.5%, respectively. Primary nitrides metallic nitrides (MN), are homogeneously dispersed in the as-cast microstructure, while primary carbides metallic carbides (MC), preferentially precipitate in interdendritic areas. Such preference is also observed in the case of globular s phase. Lamellar constituents characterized as secondary carbides/gamma phases were together with (TiMo)(2)SC phase always observed adjacent to sigma phase precipitates. Crystallographic relations were established in-between the MC, sigma, secondary carbides and gamma/gamma' matrix.