Investigation of the Thermal Fatigue Behaviour of Single-Crystal Nickel-Based Superalloys SRR 99 and CMSX-4

Abstract

Thermal fatigue (TF) behaviour in the low-modulus cool> direction of a new generation nickel-based single-crystal superalloy containing rhenium, CMSX-4 and a highly strengthened first generation one, SRR 99 is investigated. Both superalloys are subjected to comparative thermal fatigue testing. Thermal fatigue tests are performed on self-constraint single-edge wedge specimens. The transient mechanical strains within the thin edge tip of the TF specimens are measured and the anisothermal Manson-Coffin life curves are established. The effect of the maximum temperature, Tmax, in the thermal cycles is evaluated from 1100 to 1175°C. Under identical test conditions a comparable crack propagation rate is observed for both single-crystal alloys. CMSX-4 has a good resistance to oxide-scale spalling. In CMSX-4 cracks initiate from small pores which have formed during solidification in interdendritic regions. In SRR 99, crater-like regions from where the crack can initiate, are formed by a mechanism of successive oxide-scale spalling and re-oxidation of the base alloy. The higher resistance of the oxide-scale in CMSX-4 to spalling combined with the higher strength of the corresponding y depleted zone improves its TF crack initiation resistance in comparison with SRR 99.

Thermal fatigue behaviour of Al–Si coated Inconel 713 LC

“…During the initiation stage in the uncoated specimen, many small cracks are nucleated at the surface, especially in the notch region where small pores were induced by high temperature oxidation, as reported by other researchers. 15,16 Therefore, with continuing thermal cycle and stress concentration on the notch region, these small cracks act as preferential places for crack initiation. This was not observed in the coated specimens.…”

A Study of the Internal Deformation Fields and the Related Microstructure Evolution during Thermal Fatigue Tests of a Single-Crystal Ni-Base Superalloy

“…Nickel-base superalloys have been widely used in gas turbines due to their superior mechanical properties at high temperatures. The turbine blades are subjected to cyclic mechanical and thermal loading during operations, and thermal gradients build up in the airfoils and from cooling channels [ 1 ]. Due to the fact that temperature and mechanical loadings usually operate simultaneously on turbine blades, many studies have been conducted on the mechanical and thermal–mechanical responses of superalloys [ 2 , 3 , 4 ], while the effect of temperature alone has attracted less attention.…”