Metallurgical Transactions A

, Volume 23, Issue 10, pp 2849–2857 | Cite as

Processing map for controlling microstructure in hot working of hot isostatically pressed powder metallurgy NIMONIC AP-1 superalloy

  • M. C. Somani
  • E. S. Bhagiradha Rao
  • N. C. Birla
  • M. L. Bhatia
  • Vakil Singh
  • Y. V. R. K. Prasad
Mechanical Behavior


The hot deformation behavior of hot isostatically pressed (HIP) NIMONIC AP-1 superalloy is characterized using processing maps in the temperature range 950 °C to 1200 °C and strain rate range 0.001 to 100 s•1. The dynamic materials model has been used for developing the pro-cessing maps which show the variation of the efficiency of power dissipation given by [2m/ (m + 1)] with temperature and strain rate, withm being the strain rate sensitivity of flow stress. The processing map revealed a domain of dynamic recrystallization with a peak efficiency of 40 pct at 1125 °C and 0.3 s•1, and these are the optimum parameters for hot working. The microstructure developed under these conditions is free from prior particle boundary (PPB) de-fects, cracks, or localized shear bands. At 100 s•1 and 1200 °C, the material exhibits inter-crystalline cracking, while at 0.001 s•1, the material shows wedge cracks at 1200 °C and PPB cracking at 1000 °C. Also at strain rates higher than 10 s•1, adiabatic shear bands occur; the limiting conditions for this flow instability are accurately predicted by a continuum criterion based on the principles of irreversible thermodynamics of large plastic flow.


Metallurgical Transaction Power Dissipation Strain Rate Sensitivity Adiabatic Shear Band Strain Rate Range 
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Copyright information

© The Minerals, Metals and Materials Society, and ASM International 1992

Authors and Affiliations

  • M. C. Somani
    • 1
  • E. S. Bhagiradha Rao
    • 1
  • N. C. Birla
    • 1
  • M. L. Bhatia
    • 1
  • Vakil Singh
    • 2
  • Y. V. R. K. Prasad
    • 3
  1. 1.Defence Metallurgical Research LaboratoryHyderabadIndia
  2. 2.Department of Metallurgical EngineeringBanaras Hindu UniversityVaranasiIndia
  3. 3.Department of MetallurgyIndian Institute of ScienceBangaloreIndia

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