N18, Powder metallurgy superalloy for disks: Development and applications

Influence of oxidation on fatigue crack initiation and propagation in turbine disc alloy N18

“…Powder metallurgy (PM) Ni-based superalloys have been widely used for aeroengine turbine disc application due to their exceptional combined mechanical properties at elevated temperatures in combination with good oxidation/corrosion resistance [1][2][3]. However, oxidation accelerated fatigue failure (shorter fatigue life or faster crack growth rate) is usually observed when assessing the fatigue performance of disc alloys at elevated temperatures, especially when a dwell period is applied at the peak load [4][5][6][7][8][9][10].…”

“…N18 is a PM disc superalloy, developed for the SNECMA M88 engine used in the RAFALE aircraft [1]. It is designed for long-term use at 650 o C and limited use at 700 o C. A trade-off between good fatigue crack growth and oxidation resistance as well as excellent creep and strength retention at high temperature was made during alloy design, along with some modification of grain size to optimise this balance, principally adopting sub-solvus heat treatments due to its high γʹ solvus temperatures (~1190°C) [1,[25][26][27][28].…”

“…It is designed for long-term use at 650 o C and limited use at 700 o C. A trade-off between good fatigue crack growth and oxidation resistance as well as excellent creep and strength retention at high temperature was made during alloy design, along with some modification of grain size to optimise this balance, principally adopting sub-solvus heat treatments due to its high γʹ solvus temperatures (~1190°C) [1,[25][26][27][28]. A great deal of research has illustrated that N18 has good phase stability up to 700 o C and possesses high strength and creep resistance associated with a good damage tolerance capability up to 650 o C [1,25]. It is also reported that N18 has better fatigue crack growth resistance compared with fine grained Inconel 718 and Astroloy under the same testing conditions [1].…”

“…A great deal of research has illustrated that N18 has good phase stability up to 700 o C and possesses high strength and creep resistance associated with a good damage tolerance capability up to 650 o C [1,25]. It is also reported that N18 has better fatigue crack growth resistance compared with fine grained Inconel 718 and Astroloy under the same testing conditions [1]. However, most of these studies have been conducted at 650 o C or even lower temperature, where the role of oxidation may be less significant in assisting fatigue failure processes.…”

Effects of microstructures on fatigue crack initiation and short crack propagation at room temperature in an advanced disc superalloy

“…disc application due to their exceptional combined mechanical properties at elevated temperatures in combination with good oxidation/corrosion resistance [1][2][3]. Currently however, most of the disc alloys are designed for use at operating temperatures lower than 700 o C, beyond which severe environmental attack accelerated fatigue/creep failure may happen and thereby significantly reduces the service lifetime of the disc alloys [4].…”