Introduction
Material and Methods
Element | Al | V | Fe | H | N | O | Ti |
---|---|---|---|---|---|---|---|
Weight Percent | 5.75 | 3.96 | 0.07 | 0.00445 | 0.013 | 0.11 | bal. |
Results
Microstructure Observations
Mathematical Modelling Framework
Field and Flux Balance
Spherical Particles
Growth
Shrinkage
Lamellar α-Phase Particles
Growth
Shrinkage
Diffusion
Model Validation
Spherical Precipitate Growth
Lamellar Precipitate Dissolution
Predictions for the β-Transus Temperature
E (J/mol) | K0 (1/s) |
J
|
n
|
---|---|---|---|
494,830 | 488,160,301 | − 0.466 | 0.633 |
Conclusions
-
For equiaxed grains, the model predicts the phase fraction evolution during cooling reasonably when considering vanadium as the single diffusing element, and better than with aluminum as the diffusing element. For lower heating rates, this difference is exacerbated, whereas at higher cooling rates both vanadium and aluminum diffusion results converge. The predictions are relatively insensitive to small measurement errors of initial particle size.
-
For lamellar structures, the model predicts the correct trends for lamellae thickness and volume fraction values, with some error in the thickness calculations being more noticeable for the fastest heating rate. The latter could be due to the high internal energy of the material, allowing a switch to the more stable BCC crystallographic structure even though the dissolution of the alpha phase is incomplete.
-
In order to determine the beta-transus as a function of the heating rate, a JMA approach was adopted and applied to the diffusion-based model to establish when a complete transition from alpha to beta phase was obtained; this was independent of the state of the alpha-phase dissolution.