Prediction of Phase Stability with Minor Amounts of P in Ni‑base Superalloys

These examples using the TCS Ni-based Superalloys Database (TCNI) include the use of the recently added element, phosphorus (P).

For other examples using P, seeIsothermal Solidification During Brazing: A Diffusion Simulation and Predicting Phase Stability: Applications Involving P.

Ni-Cr-Fe-C-P Alloy

In Figure 1 the plot shows the volume fraction of phases versus temperature, for a Ni-Cr-Fe-C alloy with 0.09 wt% P added. Experimental studies have found M3P and M23C6 precipitates in such alloys, water‑quenched after solutioning at 1100 °C [2019Lia], both of which are predicted to be stable at lower temperature in the calculation.

$Volume fraction of phases as a function of temperature for a Ni-Cr-Fe-C-P alloy, showing M3P and M23C6 phases$

Figure 1: Volume fraction of phases as a function of temperature for a Ni-Cr-Fe-C-P alloy, showing M3P and M23C6 phases found in the literature [2019Lia].

IN706 Alloy

A similar calculation is shown in Figure 2 for alloy 706 with 0.025 wt% P added. Here we see a predicted presence of M2P C37-type phosphide phase, which is found in the literature in samples quenched from high temperature and then soaked at 980 °C, as a result of segregation of P in grain boundaries. The calculation is metastable; the stable sluggish phases are suspended to promote the typical gamma prime/double prime phases.

$Mole fraction of phases as a function of temperature for a IN706 alloy with 0.025 wt% P, showing the prediction of the C37 phosphide, as found in the literature$

Figure 2: Mole fraction of phases as a function of temperature for an IN706 alloy with 0.025 wt% P, showing the prediction of the C37 phosphide, as found in the literature [2017Zha].

Reference

[2017Zha] S. Zhang, L. Huang, A. Zhang, L. Yu, X. Xin, W. Sun, X. Sun, Segregation of Phosphorus and Precipitation of MNP-Type Phosphide at the Grain Boundary of IN706 Superalloy. J. Mater. Sci. Technol. 33, 187–191 (2017).

[2019Lia] X.-T. Lian, W.-R. Sun, F. Liu, D.-D. Zheng, X. Xin, Effects of Phosphorus and Iron on Microstructures and Mechanical Properties in NiCrFe-Based Alloys. Acta Metall. Sin. (English Lett. 32, 659–667 (2019).