Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950°C

Tung, Hsiao Ming; Mo, Kun; Stubbins, James F.

doi:10.1016/j.jnucmat.2013.12.016

Cited by 28 publications

(20 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These results are in qualitative agreement with results for thin walled hot drawn tubes examined at University of Illinois under a Nuclear Energy University Program (NEUP) project. 41 Those experiments also indicated more rapid failure and greater formation of porosity in pressurized tubes compared to uniaxial creep tests. It should be noted that one of the motivations of the current work was to directly compare the same material for both types of creep testing by machining tubes from plate, since the NEUP project used material that had grain size differences and inhomogeneity result from the hot working to achieve thin wall tube.…”

Section: Discussionmentioning

confidence: 92%

See 1 more Smart Citation

Creep Rupture of Pressurized Alloy 617 Tubes

Wright¹,

Wright²

2013

View full text Add to dashboard Cite

Creep behavior of Alloy 617 under multi-axial loading has been characterized at 950°C using thin walled tubes with internal gas pressure. Tubes were machined from Alloy 617 plate material to ensure comparability of material properties with extensive testing carried out in the VHTR Research and Development program. Properties of this alloy under multi-axial loading are of interest for elevated temperature design in advanced nuclear heat transfer systems. A constitutive model in the form of a Norton relationship was developed for Alloy 617 plate to allow development of a suitable creep specimen using finite element simulation. It was determined that proper description of the minimum creep rate at 750°C required a threshold stress formalism. The magnitude of the threshold stress was determined to be 75MPa for creep tests using the conditions examined. This threshold stress arises from strengthening by the γ'(Ni 3 Al,Ti) intermetallic phase; above this temperature this phase is unstable and Alloy 617 behaves as a solid solution. Comparison of strengthening models to detailed TME analysis of dislocation-particle interaction in crept specimens indicated that strengthening arises from localized climb, or a combination of climb and Orowan bowing depending on the creep time and stress. Quantification of the strengthening from γ' is an important result to confirm the region over which it is acceptable to extrapolate creep rupture times on a Larson-Miller plot. This result will also help inform the activities underway in the US and Europe to develop a γ' strengthened version of Alloy 617 for application in ultra-supercritical fossil power plants. Failure of the pressurized tubes initiates at low strain by cracking of the majority of grain boundaries that intersect the exterior surface. For radial strains of about 5% or less the total creep damage fraction is equivalent to uniaxial test specimens with similar tertiary creep strain. Above this value the surface nucleated cracks begin to open rapidly with increasing strain and the volume fraction of creep damage exceeds that for comparable uniaxial tests. Final failure, defined for the pressurized tubes as loss of the ability to maintain pressure, occurs by linking of damage ahead of one of the cracks that nucleate on the surface on a 45° angle to the tube radius. Although the time to tube rupture was comparable to uniaxial creep rupture on the Larson-Miller diagram, cavitation was more extensive and the creep strain was considerably reduced to plate. The minimum creep rate determined from pressurized tube results appears to fit a different Monkman-Grant relationship compared to uniaxial creep data.

show abstract

Section: Discussionmentioning

confidence: 92%

“…Time to rupture is less than for uniaxial creep, as reported previously. 5,41 A photo of a tube that was tested to a failure strain of about 8% is shown in Figure 23. The fracture that resulted in gas leakage is shown in a low magnification macrograph in Figure 24.…”

Section: Experimental Results On Creep Of Tubesmentioning

confidence: 99%

Creep Rupture of Pressurized Alloy 617 Tubes

Wright¹,

Wright²

2013

View full text Add to dashboard Cite

show abstract

“…Plot of experimental Mises equivalent stress versus rupture time data for alloy 617 at 850°C in both uniaxial and biaxial stress states. The uniaxial and biaxial results are not parallel, inconsistent with the classical Hayhurst relation[140].…”

mentioning

confidence: 67%

“…In an effort to understand the reason for this difference between uniaxial and biaxial results, we have implemented a mechanism based model to reproduce experimental data for pressurized tubes made of alloys 230 and 617. Micrographs of these tubes indicated that failure was caused by the nucleation, growth, and coalescence of voids along grain boundaries within the tube walls [140] (see Fig. 4.57).…”

Section: Modeling Of Creep Rupture Behaviorsmentioning

confidence: 99%