Investigation of faceted crack initiation and propagation in near-alpha titanium alloys

Adam L. Pilchak, Matt C. Brandes, Robert E A Williams, James C. Williams

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearchpeer-review

4 Citations (Scopus)

Abstract

It is widely recognized that titanium alloys can fail by internal crack initiation at room temperature when loaded under fatigue and creep conditions. Frequently, initiation sites show evidence of extensive faceting that has been associated with marked decrease in life.especially when induced by the application of a sustained load hold at peak stress. Despite the prevalence of faceted cracking, the mechanisms by which cracks nucleate and propagate have not been thoroughly investigated. In this work, we apply an array of microscopy techniques to the examination of initiation and propagation facets on the primary fracture surface of a titanium alloy that failed under dwell loading conditions. Quantitative fractography and EBSD revealed the gross spatial and crystallographic orientations of the facet planes, site-specific thin foil extraction techniques coupled with transmission electron microscopy (TEM) experiments have allowed for the characterization of deformation structures beneath facets at two dwell fatigue crack initiation sites. The experimental observations demonstrate that the crack initiation sites each contained a glassy facet with a very near-basal orientation that was substantially inclined to the loading direction surrounded by rougher facets oriented nearly orthogonal to the loading direction. TEM analysis of the latter facets revealed extensive basal slip.yet crack propagation occurred on irrational {hkil} planes that were inclined to (0001) and not along slip bands as previously suggested. The dislocation activities beneath the facets clearly demonstrate that planar slip and extended pile-up structures at grain boundaries play a prominent role in faceted crack initiation and growth.

Original languageEnglish
Title of host publicationTi 2011 - Proceedings of the 12th World Conference on Titanium
Pages993-997
Number of pages5
Volume2
Publication statusPublished - 2012
Externally publishedYes
EventThe World Conference on Titanium 2011 - China National Convention Center, Beijing, China
Duration: 19 Jun 201124 Jun 2011
Conference number: 12th
https://books.google.com.au/books/about/Ti_2011_Proceedings_of_the_12th_World_Co.html?id=NrJwMwEACAAJ&redir_esc=y

Conference

ConferenceThe World Conference on Titanium 2011
Abbreviated titleTi 2011
CountryChina
CityBeijing
Period19/06/1124/06/11
Internet address

Keywords

  • Crack growth
  • Crack initiation
  • Dwell fatigue
  • EBSD
  • Facets
  • Fractography

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