Effect of Salt-Deposit Hot Corrosion on Creep Rupture Behaviors of DZ466 Superalloy

Abstract

Since gas turbine blades in engines suffer centrifugal stress and gas corrosion during service, a good creep resistance in hot corrosion environment is one of the important considerations to evaluate service performance of the blade materials. In this work, the creep rupture behaviors of the directionally solidified superalloy DZ466 with and without salt deposition at 760°C/765MPa, 850°C/500MPa and 950°C/220MPa are preliminarily investigated based on the creep properties measurement and microstructure observations. The effects of hot corrosion on the creep properties and fracture mode are examined. The results show that the creep-rupture life in salt-deposit environment is lower than that in air-exposure environment at different temperatures. The creep-rupture life reduction caused by hot corrosion is increased with increase of the creep temperature. The fracture mode is exhibited by transgranular fracture in all crepted specimens. The propagation directions of all the secondary cracks are almost perpendicular to the crept specimen surface or the stress axis. The surface cracks are mainly produced in air-exposure environment at low temperature or in salt-deposited environment at high temperature. Induced by the stress concentration, the internal cracks are initiated surrounding the carbides in both air-exposure and salt-deposit environments. The creep-rupture life is dependent on the crack initiation at low temperature but on the crack propagation at high temperature. The reduction of the active load bearing area in transversal direction is the main reason why the creep-rupture life is decreased at 950°C.