Design Strategy for Synergistic Strengthening of W and Al in High-W Superalloys

Abstract

To investigate the influence of W and Al on the microstructure and mechanical properties of a high-W superalloy, the Thermo-Calc calculation was utilized to simulate the microstructure with various W and Al contents. The results indicated that the concentration of W and Al exceeded 15.7 wt% and 5.9 wt%, respectively, the abnormal tungsten-rich α-W phase would precipitate. Compared with the results of orthogonal experiment, the precipitation of α-W phase is consistent with thermodynamic calculation results. The presence of Al not only influenced the precipitation of α-W phase but also impacted the eutectic content and the γʹ-size, both of which showed an increase with higher Al concentrations. Excessive W and Al contents promoted the precipitation of α-W phase, escalating the site of crack nucleation, and ultimately decreasing the plasticity. In the process of creep deformation (975 °C / 235 MPa), the rafted γ' phases were more continuous with increasing W contents, which increased the difficulty of dislocation climbing. As Al content increased, the density of interfacial dislocation network increased. The dislocations were entangled with each other, and the hindrance of dislocation movement was enhanced, which improved the stress rupture life. However, the precipitation of the hard and brittle α-W phase was attributed to the excessive W and Al, which increased the tendency of crack formation and significantly diminished the stress rupture life. The alloy exhibited the highest stress rupture life of 110.46 h when the W and Al contents were 15.7 wt% and 5.9 wt%, respectively.