The microstructure and creep behavior of cold rolled Udimet 188 sheet

C. J. Boehlert, S. C. Longanbach

Research output: Contribution to journalArticle

Abstract

Udimet 188 was subjected to thermomechanical processing (TMP) in an 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 1,464 K (1,191°C) for 1 h and subsequent air cooling. This sequence was repeated four times to induce a high-volume fraction of low-energy grain boundaries. The resultant microstructure was characterized using electron backscattered diffraction. The effect of the TMP treatment on the high-temperature [1,033-1,088 K (760-815°C)] creep behavior was evaluated. The measured creep stress exponents (6.0-6.8) suggested that dislocation creep was dominant at 1,033 K (760°C) for stresses ranging between 100-220 MPa. For stresses ranging between 25-100 MPa at 1,033 K (760°C), the stress exponents (2.3-2.8) suggested grain boundary sliding was dominant. A significant amount of grain boundary cracking was observed both on the surface and subsurface of deformed samples. To assess the mechanisms of crack nucleation, in situ scanning electron microscopy was performed during the elevated-temperature tensile-creep deformation. Cracking occurred preferentially along general high-angle grain boundaries (GHAB) and less than 25% of the cracks were found on low-angle grain boundaries (LAB) and coincident site lattice boundaries (CSLB). Creep rupture experiments were performed at T = 1,088 K (815°C) and σ = 165 MPa and the greatest average time-to-rupture was exhibited by the TMP sheet with the greatest fraction of LAB+CSLB. However, a clear correlation was not exhibited between the grain boundary character distribution and the minimum creep rates. The findings of this work suggest that although grain boundary engineering may be possible for this alloy, simply relating the fraction of grain boundary types to the creep resistance is not sufficient.

LanguageEnglish (US)
Pages350-361
Number of pages12
JournalMicroscopy and Microanalysis
Volume17
Issue number3
DOIs
StatePublished - Jun 2011

Profile

Creep
Grain boundaries
grain boundaries
microstructure
Microstructure
tensile creep
Crystal lattices
Processing
cracks
Cracks
exponents
Grain boundary sliding
Creep resistance
air cooling
creep strength
Cold rolling
cold rolling
Electron diffraction
Volume fraction
Nucleation

Keywords

  • creep
  • electron backscattered diffraction
  • microstructure
  • superalloy

ASJC Scopus subject areas

  • Instrumentation

Cite this

The microstructure and creep behavior of cold rolled Udimet 188 sheet. / Boehlert, C. J.; Longanbach, S. C.

In: Microscopy and Microanalysis, Vol. 17, No. 3, 06.2011, p. 350-361.

Research output: Contribution to journalArticle

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