NOTE: End date changed to 7/31/2021 per NSSC information (Ed., 9/9/2020)

NOTE: End date changed to 7/31/2020 per NSSC information (Ed., 5/4/2020)

Surface curvature and crystal-melt anisotropy strongly influence bias fields. Motivated by our recent detection of perturbation fields on grain boundary grooves (GBGs), which also appear to explain the anomaly reported in the microgravity data, the underlying hypotheses which we intend to test are: (a) weak capillary fields that are resident on solid-liquid interfaces modulate the shapes of melting crystalline fragments, and (b) shape perturbations from capillary fields amplify on unstable interfaces, and instigate instabilities on interfacial regions of equilibrated GBGs. Our 3D phase-field simulations on grooving will provide unprecedented insights into this fascinating autogenous mechanism of pattern formation and might also enable us to develop novel processing methods to improve microstructure-level control in alloy castings. The associated issue of comparing the efficacy of noise amplitude to the bias field intensity-- fundamental issue in understanding pattern formation--will also be investigated theoretically and via the phase-field techniques.

NOTE: End date changed to 7/31/2021 per NSSC information (Ed., 9/9/2020)

NOTE: End date changed to 7/31/2020 per NSSC information (Ed., 5/4/2020)

Surface curvature and crystal-melt anisotropy strongly influence bias fields. Motivated by our recent detection of perturbation fields on grain boundary grooves (GBGs), which also appear to explain the anomaly reported in the microgravity data, the underlying hypotheses which we intend to test are: (a) weak capillary fields that are resident on solid-liquid interfaces modulate the shapes of melting crystalline fragments, and (b) shape perturbations from capillary fields amplify on unstable interfaces, and instigate instabilities on interfacial regions of equilibrated GBGs. Our 3D phase-field simulations on grooving will provide unprecedented insights into this fascinating autogenous mechanism of pattern formation and might also enable us to develop novel processing methods to improve microstructure-level control in alloy castings. The associated issue of comparing the efficacy of noise amplitude to the bias field intensity-- fundamental issue in understanding pattern formation--will also be investigated theoretically and via the phase-field techniques.

NOTE: End date changed to 7/31/2020 per NSSC information (Ed., 5/4/2020)

Surface curvature and crystal-melt anisotropy strongly influence bias fields. Motivated by our recent detection of perturbation fields on grain boundary grooves (GBGs), which also appear to explain the anomaly reported in the microgravity data, the underlying hypotheses which we intend to test are: (a) weak capillary fields that are resident on solid-liquid interfaces modulate the shapes of melting crystalline fragments, and (b) shape perturbations from capillary fields amplify on unstable interfaces, and instigate instabilities on interfacial regions of equilibrated GBGs. Our 3D phase-field simulations on grooving will provide unprecedented insights into this fascinating autogenous mechanism of pattern formation and might also enable us to develop novel processing methods to improve microstructure-level control in alloy castings. The associated issue of comparing the efficacy of noise amplitude to the bias field intensity-- fundamental issue in understanding pattern formation--will also be investigated theoretically and via the phase-field techniques.

- Analysis of periodic grain boundary grooves was performed, which is a critical step for generalizing the idea of bias-fields. These findings will be compared with phase-field simulations to validate the underlying hypotheses.

- It is discovered that melt convection can induce growth competition in seaweed-like solidifying microstructures that have nearly isotropic or weakly-anisotropic surface energies.

Surface curvature and crystal-melt anisotropy strongly influence bias fields. Motivated by our recent detection of perturbation fields on grain boundary grooves (GBGs), which also appear to explain the anomaly reported in the microgravity data, the underlying hypotheses which we intend to test are: (a) weak capillary fields that are resident on solid-liquid interfaces modulate the shapes of melting crystalline fragments, and (b) shape perturbations from capillary fields amplify on unstable interfaces, and instigate instabilities on interfacial regions of equilibrated GBGs. Our 3D phase-field simulations on grooving will provide unprecedented insights into this fascinating autogenous mechanism of pattern formation and might also enable us to develop novel processing methods to improve microstructure-level control in alloy castings. The associated issue of comparing the efficacy of noise amplitude to the bias field intensity-- fundamental issue in understanding pattern formation--will also be investigated theoretically and via the phase-field techniques.

Our research addresses both issues for crystal-melt interfaces in unary systems, by exploring the presence of interfacial energy fields that provide pattern-forming stimuli in 2D. We detected and measured the presence of such stimuli on solid-liquid interfaces through novel measurements extracted from phase-field simulations. Capillary fields in the form of interfacial energy distributions are exposed and measured on simulated microstructures in the form of equilibrated solid-liquid grain boundary grooves (GBGs). Simulated interfacial data also allow quantifiable comparison with analytic predictions of interfacial energy fields derived from sharp-interface thermodynamics. Simulations and measurements that we report also confirm that equivalent pattern-forming fields arise within standard phase-field physics that manifest themselves as deterministic perturbations.

Numerical simulations are compared with predictions based on interface energy conservation and classical field theory. The comparison reveals the existence of persistent capillary-mediated energy fields that influence the dynamics of interfacial shape changes during phase transformation. Such fields stimulate complex pattern formation on unstable interfaces with, or without, the benefit of noise. As melt convection can interact with capillary-mediated bias-fields, a Navier-Stokes coupled phase-field solver was also developed to analyze the influence of this interaction on the evolution of directionally-solidified patterns.

To verify our findings, in future, we will compare the morphological evolution as predicted by the bias-field theory and the phase-field simulations during dendritic growth and shrinkage with the IDGE (Isothermal Dendritic Growth Experiment) data that is currently archived in the NASA-PSI.

Surface curvature and crystal-melt anisotropy strongly influence bias fields. Motivated by our recent detection of perturbation fields on Grain Boundary Grooves (GBGs), which also appear to explain the anomaly reported in the USMP-4 data, the underlying hypotheses that we intend to test are: (a) weak capillary fields that are resident on solid-liquid interfaces, modulate the shapes of melting crystalline fragments, and (b) shape perturbations from capillary fields amplify on unstable interfaces and instigate instabilities on interfacial regions of equilibrated GBGs. Our 3D phase-field simulations on grooving will provide unprecedented insights into this fascinating autogenous mechanism of pattern formation and might also enable us to develop novel processing methods to improve microstructure-level control in alloy castings. The associated issue of comparing the efficacy of noise amplitude to the bias field intensity-- fundamental issue in understanding pattern formation-- will also be investigated theoretically and via the phase-field techniques.