Microstructural refinement of Ni-Cr-W superalloy by isothermal treatment near the liquidus

• The effect of isothermal treatment on undercooling, liquid fraction and the grain growth was studied.
• Microstructural refinement by isothermal treatment near the liquidus was explained.
• The effect of different average grain sizes on mechanical properties was also analyzed.

The solidification process of Ni-Cr-W superalloy was investigated by confocal scanning laser microscope (CSLM). The liquid fraction during solidification was obtained as a function of real time and temperature in reference with the in-situ observation. In this work, the effect of isothermal treatment near the liquidus on undercooling, grain initiation and the grain growth was studied, and an analytical model is developed to account for the effect of solute field on grain refinement. This study revealed that isothermal treatment near the liquidus restricted the growth of crystal and increased the number density of active particles for nucleation, giving rise to a finer grain size. The tensile results of Ni-Cr-W superalloy tested at different temperatures indicated fine grain microstructure can improve the mechanical properties at different temperatures.

Cooling curves of Ni-Cr-W superalloy either isothermal treatment or not isothermal treatment near the liquidus temperature and solidification process in-situ observed by CSLM at different temperatures: (a) to (d) isothermal treatment near the liquidus temperature; (e) to (h) non-isothermal treatment near the liquidus temperature.Figure optionsDownload as PowerPoint slide