Phase-field study of spacing evolution during transient growth.

Area of Science:

• Materials Science
• Physics of Materials
• Solidification Science

Background:

• Dendritic growth is crucial in materials processing and solidification.
• Understanding primary spacing evolution is key to controlling microstructure.
• Transient growth conditions introduce complexities not seen in steady-state growth.

Purpose of the Study:

• To investigate the primary spacing evolution of dendritic arrays under transient growth conditions.
• To analyze the influence of growth speed changes on spacing distribution.
• To compare experimental and numerical findings on dendritic array spacing.

Main Methods:

• Experimental observation of dendritic array growth under controlled transient conditions.
• Numerical simulations using phase-field models of directional solidification.
• Ramping of pulling speed at various rates to study transition dynamics.

Main Results:

• Primary spacing exhibits a distribution of wavelengths that evolves over time.
• Average primary spacing shows stable incubation periods followed by gradual transitions.
• The rate of change in growth speed dictates the nature and duration of transition periods.
• High ramp rates lead to transiently stable configurations, while low rates blur incubation and transition phases.

Conclusions:

• The transition in primary spacing is a gradual process, not abrupt, affecting different wavelengths at different times.
• Growth speed ramp rate is a critical parameter controlling the dynamics of dendritic array evolution.
• Phase-field simulations accurately capture the complex interplay between transient conditions and dendritic spacing.