Influencing mechanism of phosphorous on intragranular M23C6 of a Ni-base superalloy studied by atom probe tomography

Moderate addition of phosphorous (P) could remarkably improve the stress rupture properties of some super-alloys by optimizing M23C6 carbide at grain boundary, but the influencing mechanism of P on M23C6 carbide is still unclear. Using atom probe tomography, the distribution of P across M23C6/gamma interface and grain boundary were determined quantitatively. P segregation at gamma/M23C6 interface was observed for the first time. A P-rich layer enveloped M23C6 carbide forms. It is expected to inhibit the coarsening and coalescence of M23C6 carbide. The improvement of intragranular M23C6 carbide should be attributed to the formation of P-rich layer around M23C6 carbide and P segregation at grain boundary.

Automated summary

The addition of moderate phosphorous has been found to improve the stress rupture properties of super-alloys by forming a phosphorous-rich layer around carbides. Atom probe tomography revealed the segregation of phosphorous at the carbide and grain boundaries, which inhibits the coarsening and coalescence of carbides.