Enhanced creep resistance induced by minor Ti additions to a second generation nickel-based single crystal superalloy

Abstract

Over the past decades, the evolution of high-performance nickel-based single crystal (SX) superalloys has advanced along the pathway of continuous increment in the Re content, which leads to microstructure instability, as well as increased density and cost. This paper proposes an alternative approach to enhance the creep resistance by slight composition modification instead of increasing the Re content. We systematically investigated the effects of minor Ti additions on the microstructure, lattice misfit, and elemental partitioning behavior of a novel second generation nickel-based SX superalloy, whose creep performance exceeded that of René N5. The addition of 0.5 wt.% Ti resulted in more and finer γ′ precipitates, narrower γ channels, and a higher magnitude of the γ/γ′ lattice misfit. In addition, all partitioning coefficients of Re, Mo, W, and Cr elements in the γ matrix were increased. Thicker γ′ and thinner γ lamellae were formed in the raft structure. The creep stain rate decreased significantly, and the creep life extended twice that of the base alloy at 1030 °C and 230 MPa. The temperature capacity of the Ti-containing alloy was superior to that of some commercial second generation SX superalloys and similar to that of René N6. Denser dislocation networks accumulated at the γ/γ′ interface, confirming the dislocation strengthening mechanism during the creep process. Stronger solid solution strengthening, impeded cross-slip, and more sluggish diffusion dynamics were considered to contribute to the enhanced creep resistance of the Ti-containing superalloy.