Summary
A micromechanical method was developed for predicting the precipitation hardening response of particle strengthened alloys hardened by ordered precipitates based on the microstructure, composition, and heat treatment, and utilizing a minimum number of experimental tests to evaluate the microstructural constants of the overall model. The overall approach was based on incorporating the dislocation particle interaction mechanics, particle growth and coarsening theory, thermodynamics, and particle strengthening mechanisms applicable to precipitation hardened alloys as part of the overall micromechanical method. The method/model evaluates, from a minimum number of experimental tensile tests, microstructural constants necessary in determining the precipitation srengthening response of a particle strengthened alloy. The materials that were used as vehicles to demonstrate and evaluate the model were precipitation hardenable aluminium-lithium-zirconium and nickel-aluminum alloys. Utilizing these demonstration alloys, the method used a total of four tensile tests to evaluate the necessary microstructural constants and thus predict the variation in strength as a function of aging time, aging temperature, and composition, for the underaged, the peak-aged, and the overaged conditions. Predictions of the precipitation strengthening response were made incorporating the Wagner particle distribution model to evaluate the size distributions of particles in the microstructures. The predicted variation of strength with aging practice and composition using the Wagner distribution model compared well with the corresponding experimental yield strength results.
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Abbreviations
- b :
-
Burgers vector
- \(\bar d\) :
-
average particle size diameter for a particle distribution
- d loop :
-
particle looping diameter for dislocation bypassing by Orowan looping
- f v :
-
volume fraction of precipitates
- h(ϱ):
-
Wagner particle size distribution function
- n total :
-
total number of precipitate particles per unit area on a given microstructural plane
- \(\bar r\) :
-
average particle size radius for a particle distribution
- \(\bar r_{pl} \) :
-
average planar particle size radius on a given microstructural plane
- t :
-
aging time, in hours
- \(\bar A_{pl} \) :
-
average planar particle cross sectional area
- G t :
-
total shear modulus of the material
- K c :
-
particle growth rate constant
- \(\bar M\) :
-
texture or Taylor grain orientation factor
- N v :
-
total number of precipitate particles per unit volume
- Q A :
-
activation energy for diffusion
- R :
-
universal gas constant
- T :
-
aging temperature
- λ:
-
the interparticle separation or spacing
- σ y :
-
yield strength
- σ q :
-
as-quenched strength
- Δσ i :
-
intrinsic lattice strength
- τ c :
-
critical resolved shear strength
- Δ τ loop :
-
critical resolved shear strength for dislocation particle bypassing via. Orowan looping
- Δ τ particle :
-
total critical resolved shear strength for particle strengthening
- Δ τ shear :
-
critical resolved shear strength for dislocation particle shearing, in underaged state
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Fragomeni, J.M., Hillberry, B.M. A micromechanical method for predicting the precipitation hardening response of particle strengthened alloys hardened by ordered precipitates. Acta Mechanica 138, 185–210 (1999). https://doi.org/10.1007/BF01291844
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DOI: https://doi.org/10.1007/BF01291844