Dynamic strain aging

Although sometimes dynamic strain aging is used interchangeably with the Portevin–Le Chatelier effect (or serrated yielding), dynamic strain aging refers specifically to the microscopic mechanism that induces the Portevin–Le Chatelier effect. This strengthening mechanism is related to solid-solution strengthening and has been observed in a variety of fcc and bcc substitutional and interstitial alloys, metalloids like silicon, and ordered intermetallics within specific ranges of temperature and strain rate.[1]

Description of mechanism

In materials, the motion of dislocations is a discontinuous process. When dislocation meets obstacles (like forest dislocations) they are temporary arrested for a certain time. During this time solutes (such as interstitial particles) diffuse around the dislocations further strengthening the obstacles held on the dislocations. Eventually these dislocations will overcome these obstacles with sufficient stress and will quickly move to the next obstacle where they are stopped and the process can repeat.[2] This process's most well-known manifestations are Lüders bands and the Portevin–Le Chatelier effect. Though the mechanism is known to affect materials without these physical observations.[3]

Material property effects

Although serrations in the stress–strain curve caused by the Portevin–Le Chatelier effect are the most visible effect of dynamic strain aging, other effects may be present when this effect is not seen.[3] Often when serrated flow is not seen, dynamic strain aging is marked by a lower strain rate sensitivity. That becomes negative in the Portevin–Le Chatelier regime.[4] Dynamic strain aging also causes a plateau in the strength, a peak in flow stress[5] a peak in work hardening, a peak in the Hall–Petch constant, and minimum variation of ductility with temperature.[6] Since dynamic strain aging is a hardening phenomenon it increases the strength of the material.[6]

Material specific example of dynamic strain aging

Dynamic strain aging has been shown to be linked to these specific material problems:

  • Decrease the fracture resistance of Al–Li alloys.[7]
  • Decrease low cycle fatigue life of austenitic stainless steels and super-alloys under test conditions which are similar to the service conditions in liquid-metal-cooled fast breeder reactors in which the material is used.[8]
  • Reduce fracture toughness by 30–40% and shorten the air fatigue life of RPC steels and may worsen the cracking resistance of steels in aggressive environments. The susceptibility of RPC steels to environment assisted creating in high temperature water coincides with DSA behavior[9]
  • PLC specific problems like blue brittleness in steel, loss of ductility and bad surface finishes for formed Aluminum Magnesium alloys.[10]

See also

References

  1. ↑ Mesarovic, Sinisa (1995)"Dynamic Strain Aging and Plastic Instabilities." J. Mech. Phys. Solids 43:671–701 No. 5
  2. ↑ Van Den Beukel, A. (1975)"Theory of the Effect of Dynamic Strain Aging on Mechanical Properties". Phys. Stat. Sol. (a) 30 197:
  3. 1 2 Atkinson, JD and Yu, J.(1997) "The Role of Dynamic Strain-Aging in the Environment Assisted Cracking observed in Pressure Vessel Steels". Fatigue Fracture Eng. Mater. Struct. Vol.20 No. 1:1–12
  4. ↑ Hahner, Peter (1996)"On the physics of the Portevin- Le Chatelier effect part 1: the Statistics of dynamic strain aging" Materials Science and Engineering A207:
  5. ↑ Mannan, S.L.(1993) "Role of dynamic stain aging on low cycle fatigue". Material Science vol 16 no 5:561–582
  6. 1 2 Samuel, K.G, Mannan, S.L, Rodriguez, P (1996) "Another Manifestation of Dynamic Strain Ageing" Journal of Material Science Letters 15:1697-1699
  7. ↑ 1
  8. ↑ 2) Mannan, S.L., "Role of dynamic stain aging on low cycle fatigue" Material Science vol 16 no 5 December 1993 p561-582
  9. ↑ Atkinson, JD and Yu, J. "the Role of Dynamic Strain-Aging in the environmental assisted cracking observed in Pressure Vessel Steels" Fatigue Fractur Engeg. Materis Struct. Vol. 20 No. 1 pp1-12 1997
  10. ↑ Abbadi, M., Hahner, P., Zeghloul, A., "On the characteristic of Portevin-Le Chatelier band in aluminum alloy 5182 under stress controlled and strain-controlled tensile testing" Materials Science and Engineering A337, 2002, p 194-201
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