Effect of aging heat-treatment on mechanical properties of AD730™ superalloy

A. Devaux (1) , A. Helstroffer (2) , J. Cormier (2) , P. Villechaise (2) , Joël Douin (3) , Muriel Hantcherli (3) , Florence Pettinari-Sturmel (3)

1 Aubert & Duval
2 PPrime [Poitiers] - Institut Pprime [UPR 3346]
3 CEMES-PPM - Physique de la Plasticité et Métallurgie

AD730IM was designed to be a cost effective superalloy for high temperature turbine disks. This superalloy, strengthened by gamma prime precipitates, presents a good ability for cast and wrought process route and a high combination between high temperature mechanical properties and cost. A study was performed to optimize the aging sequence considering tensile, creep and dwell-fatigue crack growth rate properties. Isothermal aging in the 730-790°C range with various durations in the 4-16h range were performed after a 1080°C/4h solution heat treatment followed by air cooling on coupons to investigate the effects of temperature and time on gamma prime precipitation and on mechanical properties. The effect of a second additional aging step (700°C/8h) was also investigated and discussed. Results show that the strengthening peak during aging is close to 730°C. Above this aging temperature, tensile strength decreases due to a slight increase of secondary gamma prime diameter. Gamma prime precipitates remain however very fine for all aging sequences with a diameter in the 20-50nm range. Creep properties at 700°C were strongly decreased by aging temperatures above 760°C. A special attention was also paid to dwell-fatigue crack growth rate behavior. Relaxation tests at 650°C were performed to compare the different microstructures assuming that best behavior during crack propagation would be obtained with microstructures that promote the highest stress relaxation magnitude. Finally, mechanical properties were assessed on a forged disk heat-treated in industrial conditions with the selected aging 730°C/8h/Air and were at the expected level.

Mots clés: Superalloys; Temperature; Tensile strength; Aging heat treatment; Aging temperatures; Effects of temperature; Gamma prime; High temperature mechanical properties; Industrial conditions; Solution heat treatment; Tensile; Fatigue crack propagation; Stress relaxation; Mechanical properties; Microstructure; Aging of materials; Cost effectiveness; Crack propagation; Cracks; Creep; Heat treatment

Domaines: Physique [physics]

A. Devaux, A. Helstroffer, J. Cormier, P. Villechaise, Joël Douin, et al.. Effect of aging heat-treatment on mechanical properties of AD730™ superalloy. 8th International Symposium on Superalloy 718 and Derivatives, 2014, Unknown, Unknown Region. pp.521-535, ⟨10.1002/9781119016854.ch41⟩. ⟨hal-01727510⟩