Phase Diagram Simulation and Investigation of Microstructure of Ni-Based Alloys

To develop proper Ni-based alloys for high-temperature vitriol pump which is submitted the corrosion of vitriol and rush of liquid with solid particles, the equilibrium phase diagrams of some Ni-Cr-Fe-C-Mo-Si-Cu alloys were calculated by software Thermo-Calc. Based on the simulation results and the mechanism of sigma phase precipitation strengthening, the chemical composition of a new Ni-based alloy was proposed. The alloy was casted and treated by solid solution at 1373K+2h, followed cooling to 1323K and quenching in water at room temperature, then strengthened by ageing respectively at 973K, 1023K, 1073K, 1123K for 4h. It was investigated the phases by XRD, the microstructures by OM and SEM. The proposed alloy consists of g, s and M23C6 from 1073K to 1273K. The most amount of s phase is up to 12.45 % (mass) at 1023K, it decreases with the augment of equilibrium temperature. s phase disappears above 1323K. The amount of s phase is enough in alloy to supply good precipitation hardening at a large temperature range. Experimental results were compared with the results of phase diagram simulation by Thermo-Calc. The alloy can be effectively strengthened by sigma phase precipitation at the temperature from 1023K to 1073K. Experimental results verified the validity of phase diagram simulation.