The effect of platinum-aluminide coating features on high-temperature fatigue life of nickel-based superalloy Rene®80

Abstract

Low cycle fatigue is the most important failure mode in Aviation/Industrial engine rotary turbine parts. In this paper, the influence of Pt-aluminide coating parameters on high temperature low cycle fatigue behavior of superalloy Rene?80 which is used to manufacture turbine blades, has been investigated. For this purpose, initial platinum layers of different thicknesses (2?m and 8?m) were coated on fatigue specimens. Then the aluminizing process was performed with two conditions of low temperature-high activity and high temperature-low activity. The results of microstructure investigations performed by scanning electron microscope and X-ray diffraction phase analysis indicated a three-layer structure for the coating (bi-phase (Ni,Pt)Al+PtAl2, single-phase (Ni,Pt)Al and interdiffusion zone) with different chemical compositions at both thicknesses of the platinum layer and using both aluminizing methods. Also, the results of low cycle fatigue tests at 871?C, R=0 and strain rate of 2?10 -3 s-1 showed a decline in fatigue properties in coated specimens as compared to uncoated sample, at total strains of 0.4, 0.8, and 1.2%. This reduction was lower in the low temperature-high activity with platinum layer thickness of 2?m, while it was more significant in the high temperature-low activity with the platinum layer thickness of 8?m. The fractography studies on coated and uncoated specimens indicated a mixed mode of ductile and brittle fracture.

Comportamiento a fatiga de baja frecuencia del compuesto Rene®80 recubierto de aluminuro de platino cerca y por encima del DBTT

“…Results of fatigue test on the uncoated Rene ® 80 specimens at 871 °C and total strain range of 0.8% have been reported by us in the previous study (Barjesteh et al, 2019a). The results of the previous study are shown in Table 3.…”

“…Diffusion coatings exhibit low ductility below the DBTT, whereas above this temperature ductility increases (Bose, 2007). Decreased low cycle fatigue (LCF) properties of Rene ® 80 alloy following the application of CODEP-B, a plain aluminide coating, at the total strain range 1.2%, and an increase in this property at total strains below 0.8% at 871 °C have been reported by Rahmani and Nategh (2008b), while applying of Pt-Al coating on this superalloy reduced low cycle fatigue property at the same total strain and temperature conditions (Barjesteh et al, 2019a).…”

“…Table 3. Results of low-cycle fatigue test on uncoated Rene ® 80 specimens (ΔƐ t (%) =0.8, R =0, Ɛ̇ = 2 × 10 -3 s -1 ) (Barjesteh et al, 2019a)…”

“…Results of low-cycle fatigue test on uncoated Rene ® 80 specimens (ΔƐ t (%) = 0.8, R = 0, Ɛ̇ = 2×10 -3 s -1 ) Stress-strain hysteresis loop at Δεt= 0.8% for uncoated specimens at (a) 871 °C(Barjesteh et al, 2019a) and (b) 982 °C.Low cycle fatigue behavior of Platinum-Aluminide coated Rene ® 80 near and above the DBTT • 9Revista de Metalurgia 56(4), October-December 2020, e179, ISSN-L: 0034-8570. https://doi.org/10.3989/revmetalm.179…”

“…Maximum and minimum stresses vs time at Δε t = 0.8% for uncoated specimens at (a) 871 °C(Barjesteh et al, 2019a) and (b) 982 °C.…”