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Metallurgical Transactions A

, Volume 19, Issue 7, pp 1739–1750 | Cite as

Chemical and metallurgical aspects of environmentally assisted fatigue crack growth in 7075-T651 aluminum alloy

  • Ming Gao
  • R. P. Wei
  • P. S. Pao
Article

Abstract

A comprehensive study has been carried out on a 7075-T651 alloy to examine the influence of water vapor on fatigue crack growth. The kinetics of fatigue crack growth were determined as a function of water vapor pressure at room temperature and at 353 K. Detailed fractographic analyses and surface chemistry studies were carried out to identify the micromechanisms and to quantify the chemical interactions for corrosion fatigue crack growth in this alloy. Experiments were also carried out in ultra-high vacuum and in oxygen to provide for comparisons. Two regions of fatigue crack growth response were identified. In the low pressure region (below 67 Pa at 5 Hz), crack growth is controlled by the rate of transport of water vapor to the crack tip, and the response can be described by a model for transport controlled crack growth. At pressures above 67 Pa, additional increases in crack growth rate occurred, which are attributed to the further reactions of water vapor with segregated magnesium in this alloy. Different micromechanisms for crack growth have been identified for vacuum, oxygen, and water vapor. These micromechanisms are considered in relation to the environmental parameters through a modified superposition model for corrosion fatigue.

Keywords

Metallurgical Transaction Crack Growth Rate Fatigue Crack Growth Fatigue Crack Growth Rate Water Vapor Pressure 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© The Metallurgical of Society of AIME 1988

Authors and Affiliations

  • Ming Gao
    • 1
  • R. P. Wei
    • 1
  • P. S. Pao
    • 2
  1. 1.Department of Mechanical Engineering and MechanicsLehigh UniversityBethlehem
  2. 2.Mechanics of Materials BranchNaval Research LaboratoryWashington, DC

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