Metallurgical Transactions A

, Volume 8, Issue 10, pp 1621–1627 | Cite as

Fatigue crack propagation in a cobalt base aligned eutectic

  • C. M. Austin
  • N. S. Stoloff
  • D. J. Duquette
Mechanical Behavior
Received:

Abstract

Fatigue crack propagation rates were determined for directionally solidified Co-10Ni-10Cr-14Ta-1.0C (CoTaC) at room temperature in laboratory air. Single edge crack specimens, 0.25 cm thick, tested in tension-tension at a stress ratio of less than 0.1 produced a relationship between crack growth rates,da/dN, and stress intensity range,AK, as follows:da/dN = 8 × HF △K(m and MN/m).

A stress ratio ofR = 0.5 increasedda/dN by a factor of six. A prestrain sufficient to break fibers into 5 to 10 μm long segments had no effect upon subsequent crack growth rate. Compact tension specimens, tested with the stress axis normal to the fiber axis, exhibited more rapid cracking for equivalent △K and a steeper slope, obeying the relationshipda/dN = 1.2 × lO △K.

Fractographic examination showed Stage I cracking for △K less than 10 MN/m, mixed Stage I and Stage II cracking for 10 MN/m <AK < 20 MN/m and only Stage II cracking for larger △K. The extent of fiber failure was measured and found to be proportional toK max. The plastic zone size was shown to be three times greater at the surface than at the interior.

Keywords

Metallurgical Transaction Fatigue Crack Propagation Plastic Zone Size Compact Tension Specimen Fiber Failure 
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 1977

Authors and Affiliations

  • C. M. Austin
    • 1
  • N. S. Stoloff
    • 1
  • D. J. Duquette
    • 1
  1. 1.Materials Engineering DepartmentRensselaer Polytechnic InstituteTroy

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