Abstract
This study evaluates the suitability of as-hot isostatically pressed (HIP) RR1000 for non-critical applications in aero-engine components. RR1000, an advanced powder nickel-based superalloy, was developed for disc rotor components in aero-engines. For these critical applications, the consolidated alloy powder particles are extruded to break down carbide and oxide networks, known as prior particle boundaries (PPBs), and to refine the structure into a fine grain size for isothermal forging. In this study, hot isostatically pressed compacts, made from two different powder particle size fractions have been assessed following heat treatments below and above the gamma prime solvus temperature. A microstructural evaluation shows a greater degree of PPB decoration occurs in the finer powder particle size fraction. Following a super-solvus heat treatment these PPBs pin grain boundaries of the fine powder particle size compacts, whilst the reduction of PPB decoration in coarse powder particle compacts allows significant grain growth. Tensile test results of as-HIP RR1000 show, good yield strengths, ultimate tensile strengths and ductility, which are comparable with extruded and isothermal forged RR1000 disc material. Dwell crack propagation tests show that finer powder particle size compacts, which have received a sub-solvus heat treatment, give the highest crack growth rates; whilst the remaining material conditions show markedly improved crack growth resistance. In conclusion, as-HIP RR1000 demonstrates clear potential for use in non-critical applications, employing either powder particle size fraction used in this study subject to the appropriate solution heat treatment.
Highlights
RR1000 is a third generation γ’ strengthened gas turbine nickel disc alloy, [1,2] designed to achieve the high levels of creep resistance and damage tolerance at the elevated temperatures required for modern civil jet engine discs
The microstructure, tensile and crack propagation properties of RR1000 have been evaluated in the as-hot isostatically pressed (HIP) form for sub- and supersolvus heat treatment conditions, using two different powder fractions
prior particle boundaries (PPBs) density is greater in the finer powder compact material (PSD A) due to the higher surface area of the powder, resulting in higher bulk oxygen content, and an increase in PPB density
Summary
RR1000 is a third generation γ’ strengthened gas turbine nickel disc alloy, [1,2] designed to achieve the high levels of creep resistance and damage tolerance at the elevated temperatures required for modern civil jet engine discs. The complex chemistry of RR1000, requires that the alloy be manufactured by powder metallurgy to avoid macro segregation, which can occur in billet manufactured via cast and wrought processes It is well reported [3,4,5,6] that superalloys produced via a powder metallurgy production route can suffer from PPB precipitate networks. Using powder metal alloys in the HIP form can provide cost reductions for superalloy components presently manufactured from the more traditional cast and wrought techniques. This is due to the fewer processing steps required for as-HIP manufacture and reductions in material input from use of net or near net shape manufacture. The powder used in this study was a blend of several heats and sieved to two different powder size distributions (PSD) shown in Fig
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