The Effects of Heat Treatment and Microstructure Variations on Disk Superalloy Properties at High Temperature

Gabb, Timothy P.; Gayda, John; Telesman, Jack; Garg, A.

doi:10.7449/2008/superalloys_2008_121_130

Cited by 29 publications

(20 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As a consequence, all the supersolvus HT lead to higher creep strengths. The beneficial effect of high cooling rates on the creep resistance has been reported in many studies [2,3,6,7]. This trend is confirmed when comparing the creep behaviour of the SUPER and the SUPER-FC HT specimens.…”

Section: Creep-rupture Behavioursupporting

confidence: 71%

Metallurgical optimisation of PM superalloy N19

Locq

Nazé

Franchet³

et al. 2014

MATEC Web of Conferences

View full text Add to dashboard Cite

Abstract. Microstructures of the new PM superalloy N19 have been investigated for various heat treatments in order to reach the best compromise between static strength and cyclic resistance. One subsolvus and several supersolvus heat treatments were applied to produce fine (7 µm) and medium (25 µm) grain sizes, respectively. The alloy is shown to be quite sensitive to the cooling conditions after solutioning as the γ hardening precipitates, both secondary and tertiary, have a direct influence on mechanical properties. Two cooling conditions after solutioning produce a high crack propagation resistance at 650• C with dwell time cycles, which is one of the basic requirements. The low cycle fatigue behaviour appears to be correlated to the grain size, which determines the origin of crack initiation (from ceramic inclusions or not). The other mechanical properties (tensile, creep) remain above target levels. Despite the medium size grain microstructure in the supersolvus condition, a high level of mechanical strength is observed in N19 at elevated temperature. It is understood that further improvement in properties can be achieved by developing coarse grain microstructures.

show abstract

Section: Creep-rupture Behavioursupporting

confidence: 71%

Metallurgical optimisation of PM superalloy N19

Locq

Nazé

Franchet³

et al. 2014

MATEC Web of Conferences

View full text Add to dashboard Cite

show abstract

“…Fatigue is one of the most critical properties for turbine disk alloys, and because superalloy disk materials are mostly free of any extrinsic defects, the grain structure has a significant influence on fatigue properties. [1][2][3][4][5][6][7][8] However, there is a lack of understanding of how the grain structure evolves throughout the complicated thermomechanical processing of superalloys. Powder metallurgy (P/M) processing of superalloys requires consolidation, usually by extrusion, followed by subsequent isothermal forging.…”

Section: Introductionmentioning

confidence: 99%

Deformation and Strain Storage Mechanisms during High-Temperature Compression of a Powder Metallurgy Nickel-Base Superalloy

Pollock

2010

Metall Mater Trans A

View full text Add to dashboard Cite

High-temperature compression testing combined with high-resolution electron backscatter diffraction (EBSD) analysis has been used to study microstructural-scale straining processes that occur during high-temperature deformation of a powder-consolidated nickel-base superalloy, Rene´88DT (GE Aviation, Evendale, OH). Orientation imaging has been employed to study grain-level straining and strain storage at temperatures between 1323 K (1050°C) and 1241 K (968°C) for strain rates between 0.1/s and 0.00032/s at nominal strain levels between 0.1 and 0.7. Two distinct deformation mechanisms were observed. At strain rates below 0.01/s, superplastic deformation dominates, while power-law creep occurs during high rate compression. Stored strain and evolution of the grain structure during deformation are dependent on strain rate during compression. At low strain rates in the superplastic regime, low levels of stored strain and some grain growth are observed. At high strain rates, dynamic recrystallization occurs along with higher levels of stored strain within selected grains, particularly those at the high end of the grain size distribution. A constitutive model for superplastic deformation was employed to predict the temperature and strain rate dependence of the transition from superplastic to power law deformation. The transition in rate sensitivity was consistent with the transition in stored strain measured by EBSD. Superplasticity-enhanced grain growth is observed and the implications for the transition in deformation mechanisms are discussed.

show abstract

“…[41] It has been reported that the dwell fatigue performance of Ni-base superalloys can be improved by increasing Cr content, [89,90] volume fraction of c¢, [89] and the size of tertiary c¢ precipitates. [41,91,92] The improvements by increasing Cr content and tertiary c¢ size are qualitatively illustrated in Figure 10(a). One possible explanation for these microstructural and alloying effects may be the increase in transformation toughening and the K th value by increasing Cr contents on the basis that increasing the Cr content of the Ni-base alloy is likely to promote the formation of Cr 2 O 3 .…”

Section: ½20mentioning

confidence: 69%

“…One possible explanation for these microstructural and alloying effects may be the increase in transformation toughening and the K th value by increasing Cr contents on the basis that increasing the Cr content of the Ni-base alloy is likely to promote the formation of Cr 2 O 3 . Similarly, increasing the tertiary c¢ size is likely to promote stress relaxation at the cracktip, [91,92] which would delay fracture of the oxide and increase the apparent K th . In addition, the larger tertiary c¢ size may also promote the formation of Al 2 O 3 by Al from tertiary Ni 3 Al at or near grain boundaries.…”

Section: ½20mentioning

confidence: 99%

Time-Dependent Crack Growth Thresholds of Ni-Base Superalloys

Chan

2014

Metall Mater Trans A

View full text Add to dashboard Cite

A micromechanical model has been developed for predicting the time-dependent crack growth threshold and its variability by considering oxide formation or cavity formation ahead of an elastic crack subjected to a sustained load at a stress intensity factor, K, at elevated temperatures in air. It is demonstrated that stress relaxation associated with a volume-expansion process such as the formation of creep cavities or oxides with a positive transformation strain can induce residual stresses at the tip of the elastic crack. The near-tip residual stresses must be overcome by the external load, thereby instigating a growth threshold, K th , for the onset of time-dependent crack growth. This micromechanical framework provides the basis for developing appropriate predictive models for the time-dependent crack growth thresholds associated with several damage processes, including (1) oxidation-assisted intergranular crack growth, (2) K-controlled creep crack growth along an intergranular path, and (3) stress corrosion cracking. The micromechanical threshold models have been utilized to predict the time-dependent crack growth thresholds of a variety of Ni-base superalloys. The material parameters that contribute to the variability of the time-dependent crack growth thresholds have been identified and related to variations of mixed oxides or creep cavities formed near the crack tip. A size scale effect is also predicted for the transformation toughening phenomenon, which is largest at or below K th but diminishes at increasing K levels above the threshold. Finally, the micromechanical models are utilized to identify means for suppressing time-dependent crack growth in Ni-base alloys.

show abstract

The Effects of Heat Treatment and Microstructure Variations on Disk Superalloy Properties at High Temperature

Cited by 29 publications

References 17 publications

Metallurgical optimisation of PM superalloy N19

Metallurgical optimisation of PM superalloy N19

Deformation and Strain Storage Mechanisms during High-Temperature Compression of a Powder Metallurgy Nickel-Base Superalloy

Time-Dependent Crack Growth Thresholds of Ni-Base Superalloys

Contact Info

Product

Resources

About