Effect of precipitates on high-temperature tensile strength of a high W-content cast Ni-based superalloy

Abstract

Tensile tests for a high W-content (13–15.5 wt%) cast Ni-based superalloy were carried out at temperatures ranging from 20 °C to 1100 °C. Temperature was varied in increments of 100 °C after reaching 500 °C. The tensile strength of the superalloy used in this study was 150–200 MPa higher than that of other low W-content (<10 wt%) cast Ni-based superalloys at 1100 °C. Microstructural observations revealed that the tensile behavior of the alloy was controlled by the cross-slip mechanism which optionally operated in most of the γ′ precipitates and a large number of isolated stacking faults (with high densities) with two different orientations were formed as temperature reached 1000 °C. At temperatures higher than 1000 °C, the applied stress facilitated the strain-induced precipitation of tungsten-rich MC type carbide particles in the matrix and along the γ/γ′ interface. On the other hand, the low lattice misfit reduced the nucleation barrier, which resulted in the formation of nanosized γ′ phases in the matrix. The strong solid solution effect along with the formation of the tungsten-rich MC precipitates and nanosized γ′ phases improved the high-temperature (temperatures higher than 1000 °C) strength of the superalloy.