Effects of elemental vaporization and condensation during heat treatment of single crystal superalloys

Discontinuous Precipitation in Ni-Base Superalloys During Solution Heat Treatment

“…Since the latter arises from vaporization, this can be achieved by solutioning in an environment saturated with Ni vapor, such as the use of ''sacrificial'' Ni-foils interspersed within the furnace to minimize Ni vaporization losses from the test bar. [32] Figure 16 is a BEI that shows the DP cells growing from the surface into the substrate, where the microstructure is similar to that observed in Figures 3(a) and 4(b) although there is also some evidence of clamellae within the cells at the grain boundary. However, there exists one fundamental difference-there is the nucleation and growth of two re-crystallized grains ahead of the DP cell interface (grain boundary) and which subsequently grow into the substrate.…”

Study into the Role of Nickel Vapor on Surface Modification of a Third-Generation Single-Crystal Superalloy

“…BEI depicted that after a 24-hour heat treatment in the presence of the Ni source at 1350°C, there was no evidence of surface melting or TCP formation as found in previous work. [5] On close inspection using BEI and EBSD mapping, different layers were distinguished near the surface of the sample ( Figure 1). The most obvious one was a thin layer of pores, which marked the original surface of the sample.…”

“…[10] In a previous study, it was suggested that these elements sublime during heat treatments. [5] The vapor above the sample is rich in Ni, due to the presence of a Ni source, but poor in Al, Cr, and Co. The latter elements, therefore, experience a driving force to sublimate and increase their partial pressure in the vapor.…”

“…[1][2][3][4] Industrial processing involves casting followed by solution heat treatment, during which pronounced surface modification has been reported for the Re-rich third-generation Ni-based superalloys. [5] It was suggested that this could be the result of sublimation-the direct transition from solid into the gas state-of alloying elements at high temperature and high vacuum. The idea that a Ni source can act as an inhibitor to the reaction of sublimation was first suggested by Wang et al [5] The current work aims to explore this idea further and study the effect on the microstructure beneath the surface of a third-generation SX superalloy after it has been exposed to Ni vapor at high temperature.…”

“…[5] It was suggested that this could be the result of sublimation-the direct transition from solid into the gas state-of alloying elements at high temperature and high vacuum. The idea that a Ni source can act as an inhibitor to the reaction of sublimation was first suggested by Wang et al [5] The current work aims to explore this idea further and study the effect on the microstructure beneath the surface of a third-generation SX superalloy after it has been exposed to Ni vapor at high temperature. Simulations are used to rationalize the observations.…”