Effect of thermomechanical processing on the creep behaviour of Udimet alloy 188

Boehlert, C. J.; Longanbach, S. C.; Bieler, T. R.

doi:10.1080/14786430801944836

Cited by 29 publications

(33 citation statements)

References 37 publications

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“…Figure 7a and b illustrate BSE SEM micrographs of the gage section for Sheet D. Intergranular cracking was exhibited for each of the specimens indicating that this alloy is susceptible to grain boundary deformation. Grain boundary cracking tends to develop on the GHAB for this alloy [33,34]. This may help explain why the material with the lowest fraction of GHAB exhibited the greatest creep resistance.…”

Section: Creep Behavior Creep Behaviormentioning

confidence: 96%

“…This may help explain why the material with the lowest fraction of GHAB exhibited the greatest creep resistance. Previous observations have indicated that environmental effects were not the cause of grain boundary cracking [33]. Figure 4 illustrates a log minimum strain rate versus log stress plot used to calculate the creep exponent n. The experimentallydetermined creep exponents fell in the range of 5.7-6.4.…”

Section: Creep Behavior Creep Behaviormentioning

confidence: 99%

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The Effect of Thermomechanical Processing on the Microstructure and Creep Behavior of Udimet Alloy 188

Longanbach

Boehlert²

2008

Superalloys 2008 (Eleventh International Symposium)

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Udimet 188 alloy was subjected to thermomechanical processing in attempt to understand the effects of cold-rolling deformation on the microstructure and tensile-creep behavior. Commercially available sheet was cold rolled to varying amounts of deformation (between 5%-35% reduction in sheet thickness) followed by a solution treatment at 1191ºC for one hour followed by air cooling. This sequence was repeated four times to induce a favorable grain boundary character distribution containing a high volume fraction of low-energy grain boundaries. The resultant microstructure was characterized using electron backscattered diffraction. The effect of the thermomechanical processing treatment on the hightemperature (760-815ºC) creep behavior was evaluated. Conventional lever-arm creep experiments were performed in an open air environment. The measured creep stress exponents (5.7-6.4) suggested that dislocation creep was dominant at 760ºC for stresses ranging between 100-220MPa. The material exhibited a significant extent of grain boundary cracking. The thermomechanical processing treatments which resulted in the greatest fractions (~0.8) of special grain boundaries (low-angle boundaries + coincident site lattice boundaries) also exhibited the lowest creep rates. Thus a correlation was exhibited between the grain boundary character distribution and the minimum creep rates. Creep rupture experiments were performed at T=815ºC and σ=165MPa and the thermomechanical processing treatment which resulted in the greatest special boundary fraction also resulted in the greatest average time-to-rupture.

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Section: Creep Behavior Creep Behaviormentioning

confidence: 96%

Section: Creep Behavior Creep Behaviormentioning

confidence: 99%

The Effect of Thermomechanical Processing on the Microstructure and Creep Behavior of Udimet Alloy 188

Longanbach

Boehlert²

2008

Superalloys 2008 (Eleventh International Symposium)

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“…Additional details of this apparatus and testing technique can be found elsewhere. [21][22][23][24] The fracture surfaces of failed samples were examined using SEM.…”

Section: Methodsmentioning

confidence: 99%

“…In situ characterization techniques involving electron microscopy have been developed over the past decade to the point where high-resolution scanning electron microscope (SEM) images can be obtained in situ during elevated-temperature deformation involving tension, fatigue, and creep. [21][22][23][24] This type of characterization of the deformation behavior and deformation evolution of TiAl intermetallics would be beneficial to address the issue of when interlamellar, translamellar, and colony boundary fracture are prevalent.…”

Section: Introductionmentioning

confidence: 99%

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn + 0.8 vol pct TiB2

Muñoz‐Moreno

Boehlert

Pérez‐Prado

et al. 2011

Metall Mater Trans A

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The deformation and fracture mechanisms of a nearly lamellar Ti-45Al-2Nb-2Mn (at. pct) + 0.8 vol pct TiB 2 intermetallic, processed into an actual low-pressure turbine blade, were examined by means of in situ tensile and tensile-creep experiments performed inside a scanning electron microscope (SEM). Low elongation-to-failure and brittle fracture were observed at room temperature, while the larger elongations-to-failure at high temperature facilitated the observation of the onset and propagation of damage. It was found that the dominant damage mechanisms at high temperature depended on the applied stress level. Interlamellar cracking was observed only above 390 MPa, which suggests that there is a threshold below which this mechanism is inhibited. Failure during creep tests at 250 MPa was controlled by intercolony cracking. The in situ observations demonstrated that the colony boundaries are damage nucleation and propagation sites during tensile creep, and they seem to be the weakest link in the microstructure for the tertiary creep stage. Therefore, it is proposed that interlamellar areas are critical zones for fracture at higher stresses, whereas lower stress, high-temperature creep conditions lead to intercolony cracking and fracture.

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“…Further details of this apparatus and testing technique can be found elsewhere. 25,[32][33][34] 3. Results Table 1 lists the composition of each of the studied alloys.…”

Section: In-situ Creep Experimentsmentioning

confidence: 99%

The Elevated-Temperature Creep Behavior of Boron-Modified Ti-6Al-4V Alloys

Boehlert

Chen

2009

Mater. Trans.

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This work investigated the effect of nominal boron (B) additions of 0.1 mass% and 1 mass% on the elevated-temperature (673-728 K) tensile-creep deformation behavior of a Ti-6Al-4V(mass%) alloy for applied stresses between 400-600 MPa. The alloys were evaluated in the as-cast and cast-then-extruded conditions. Boron additions resulted in a dramatic refinement of the as-cast grain size and TiB whisker volume percents of approximately 0.6 and 6.0 for the Ti-6Al-4V-0.1B and Ti-6Al-4V-1B alloys, respectively. The extrusions were performed in thephase field and resulted in the TiB-phase whiskers aligning in the extrusion direction. The creep resistance of the as-cast alloys significantly improved with increased B concentration, where around an order of magnitude decrease in the secondary creep rate was observed between the Ti-6Al-4V-1B and Ti-6Al-4V as-cast alloys. Grain refinement due to the B addition did not deleteriously affect the creep resistance in the temperature and stress ranges considered, where dislocation creep was suggested to be the dominant secondary-creep mechanism. The enhanced creep resistance was attributed to load sharing by the TiB whiskers. For the same nominal B contents, the cast-then-extruded alloys exhibited significantly greater creep resistance and tensile strength than the as-cast alloys. This was explained to be an effect of the -phase texture and the decreased lath spacing in the cast-then-extruded alloys compared with the as-cast alloys. The cast-then-extruded alloys exhibited four times lower lath widths than the as-cast alloys, and the -phase was strongly textured such that the basal plane was predominately oriented perpendicular to the extrusion axis. Comparing the cast-then-extruded alloys, the Ti-6Al-4V alloy exhibited the greatest creep resistance. Overall the -phase consisted of approximately 80% of the microstructure, and the -phase texture appeared to be more dominant to the creep resistance and tensile strength than the small volume percent of TiB-phase in the microstructure. Although B is not necessary to optimize the elevated-temperature creep performance of the Ti-6Al-4V alloy, when boron was present, greater boron additions increased the creep resistance. In-situ creep observations of the surface indicated that the TiB whisker cracking occurred prior to slip and void formation in the þ phases. This was followed by = interface cracking and ductile failure of the þ microstructure.

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Effect of thermomechanical processing on the creep behaviour of Udimet alloy 188

Cited by 29 publications

References 37 publications

The Effect of Thermomechanical Processing on the Microstructure and Creep Behavior of Udimet Alloy 188

The Effect of Thermomechanical Processing on the Microstructure and Creep Behavior of Udimet Alloy 188

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn + 0.8 vol pct TiB2

The Elevated-Temperature Creep Behavior of Boron-Modified Ti-6Al-4V Alloys

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