Influence of aluminide diffusion coating on low cycle fatigue properties of René 80

Mechanical Properties of Uncoated and Aluminide-Coated René 80

“…Considering the fact that the turbine blades of the aircrafts even in their worst stress-strain case (taking off) should never experience the coating fracture strain (the strains higher than 1 pct), the coated specimens were loaded to reach a maximum 1 pct of plastic strain at 871°C and 982°C. [30,31] In this strain condition, i.e., max 1 pct, no crack is observed in the specimens at both temperatures of 871°C and 982°C, even in the r phase. Figure 9 shows the longitudinal section of coated specimens that have undergone tensile strain of 1 pct at 871°C and 982°C during which no crack was observed.…”

“…This internal stress is the result of the difference between the thermal expansion coefficient of the coating and the base metal. [30,35] In view of the preceding observations, failure does not occur as a result of changes in either the c¢ morphology nor does it reach a critical dislocation density and arrangement. Instead, the most failure events appeared to be the development of oxide spikes along grain boundaries and the c¢ depleted zone.…”

“…Experimental results show that, in coated specimens, while the total cyclic strain is lower than 1 pct, the presence of coating increases the fatigue life, but in strains more than 1 pct, fatigue lifetime of the coated specimens is lower than that of uncoated specimens. [30,31] Figure 10 presents the stress-strain hysteresis loop for coated and uncoated specimens according to the test conditions previously described for De t = 0.8 pct, at 871°C and 982°C. In all of them, the tensile stress and compressive stress required to enforce the strain decrease with the increasing number of cycles.…”

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

“…Depending on the testing temperature which is above or below the DBTT of the coatings, the positive or negative effects of the coatings on the mechanical properties of the alloys are reported. A reduction in Low Cycle Fatigue (LCF) properties of Rene ® 80 after applying CODEP-B, a plain aluminide coating, at total strains exceeding 1%, and an increase in this property at total strains below 0.8% at 871 °C have been reported by Rahmani and Nategh [4]. Julis et al [5] investigated LCF properties of Al-Si-coated IN713LC superalloy and reported no effect of the coating on the Basquin curve and its positive effect on the Coffin-Manson curve at 800 °C.…”

“…According to this relationship (T DBTT = 698 + 10t Pt ) [24], where T DBTT is ductile-to-brittle temperature (ºC) and t Pt represents platinum layer thickness, an increase in platinum thickness directly affects the increase in this parameter. At temperatures lower than DBTT, the properties of the coating are highly different from the base alloy, whereas, in the temperature range above DBTT, the differences between the properties of the metal coatings and the base are lower [4]. Therefore, the working temperature of coated Rene ® 80 should be chosen in a way that the properties of its coating remain in the ductile range [25].…”